National Academies Press: OpenBook

Biosolids Applied to Land: Advancing Standards and Practices (2002)

Chapter: 5 Evaluation of EPA's Approach to Setting Chemical Standards

« Previous: 4 Advances in Risk Assessment since the Establishment of the Part 503 Rule
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

5
Evaluation of EPA’s Approach to Setting Chemical Standards

The U.S. Environmental Protection Agency used risk-assessment methods to set biosolids chemical standards (termed “pollutant limits” under the Part 503 rule) to be protective of human health and the environment. Risk-based standards are generally maximum levels that should not be exceeded. Risks experienced by a typical receptor population are likely to be lower, and in most cases, much lower than target risk levels used to derive risk-based standards. However, the protectiveness of the risk-based standards is dependent on the data and methods used to establish the standards, as well as on compliance with specified conditions of use.

The risk-assessment methods for establishing the Part 503 rule were developed in the mid-1980s. Since that time, EPA has refined risk-assessment methods and approaches and has issued a number of guidance documents to support standardized approaches to risk assessment (see Chapter 4). In this chapter, the methods used for the Part 503 rule risk assessments are reevaluated in light of the current practice of risk assessment. Specific assumptions made in the risk assessments are also reevaluated on the basis of available scientific information.

Risk assessments typically include four steps: hazard identification, exposure assessment, toxicity (dose-response) assessment, and risk characterization (NRC 1994). Elements of all four steps are considered in the following sections. The first section considers the hazard-identification approach used to select chemicals for inclusion in the risk assessment (EPA 1985, 1992a,b). Subsequent sections address general issues for exposure assessment and risk

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

characterization. These sections are followed by a discussion of issues relevant to specific inorganic and organic chemicals, including toxicity assessment.

HAZARD ASSESSMENT AND CHEMICAL SELECTION

To date, EPA has conducted two rounds of assessments to identify chemicals to regulate in the Part 503 rule. Round 1 was conducted to identify an initial set of chemical pollutants to regulate, and Round 2 was conducted to identify additional pollutants for regulation. Standards for the Round 2 pollutants have not been established, but EPA is considering regulation of dioxins (a category of compounds that has 29 specific congeners of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls) for land application. Therefore, although evaluation of EPA’s dioxin risk assessments for biosolids is outside the scope of the committee’s charge, the committee believes that evaluating the selection of dioxins for regulation is within the charge.

Round 1 Pollutant Selection

EPA used a two-stage process to select its initial set of contaminants to regulate under the Part 503 rule. First, a list of chemicals was subjected to a hazard screening. Second, chemicals found to represent a potentially significant risk were subject to formal risk assessment.

In 1984, using available data on effects in humans, plants, domestic animals, wildlife, and aquatic organisms and frequency of chemical occurrence in biosolids, EPA identified 200 potential chemicals of concern in biosolids. A panel of scientific experts selected 50 chemicals of potential concern for evaluation by EPA. A screening process was then used to select 22 pollutants for potential regulation (Table 5–1). The process involved developing environmental profiles for each pollutant for which data were readily available on toxicity, occurrence, fate, and pathway-specific hazards. When relevant, aggregate cancer risks from exposure via several pathways were assessed. Risks posed by some of the pathways subsequently analyzed in the risk assessment were not used in the screening process (pathways 11–14, see Table 5–4 in summary of exposure pathways).

To determine whether a full risk assessment was warranted for a particular chemical via a specific exposure pathway, a hazard index was calculated for each contaminant and pathway that had sufficient data (EPA 1985). This index is the ratio of the estimated concentration of the pollutant in the envi-

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–1 Pollutants Selected for Potential Regulation

Inorganic Chemicals

Organic Chemicals

Arsenic

Aldrin and dieldrin

Cadmium

Benzo[a]pyrene

Chromium

Chlordane

Copper

DDT, DDD, DDE

Lead

Heptachlor

Mercury

Hexachlorobenzene

Molybdenum

Hexachlorobutadiene

Nickel

Lindane

Selenium

N-Nitrosodimethylamine

Zinc

Polychlorinated biphenyls

 

Toxaphene

 

Trichloroethylene

Abbreviations: DDT, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane; DDE, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene; DDD, 1,1-dichloro-2,2-bis(p-chlorophenyl)-ethane.

Source: EPA 1992a.

ronment (soil, plant or animal tissue, water, or air) to the established human health or other regulatory criteria (e.g., acceptable daily intake for noncarcinogens or a cancer risk-specific intake). The calculated soil concentrations were based on “typical” and “worst” concentrations of the contaminant found in biosolids and were evaluated at application rates of 5 and 50 metric tons per hectare (mt/ha) and a cumulative application of 500 mt/ha based on the assumption of 5 mt/ha per year for 100 years. Data on concentrations of pollutants in sewage sludge were obtained primarily from survey data collected in a 40-city study (EPA 1982). Median values were used to represent typical concentrations, and the 95th percentile was used to represent the worst-case concentrations. It is not clear how calculations on typical concentrations and low application rates were used in the screening process, because the hazard index was reportedly derived using worst-case conditions.

After the screening process, pollutants with a hazard index equal to or greater than 1 were evaluated further. The hazard index for each of these pollutants was adjusted so that it reflected the hazard attributable only to

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

biosolids for the specific pathway of exposure being evaluated. This adjustment was done by excluding background exposure to the pollutant from sources other than biosolids. When adjusted values exceeded 1, the pollutant was evaluated for that particular pathway in a detailed risk assessment. Thus, background exposure was eliminated, and only pollutants for which the hazard index was greater than 1 for the increment contributed by biosolids were subjected to further analysis through risk assessment. This analysis assessed exposure via each pathway to each chemical. For human-health-related pathways, this procedure resulted in the elimination of fluoride and lindane from consideration in several pathways.

After the proposed Part 503 rule was issued in 1989, EPA completed a National Sewage Sludge Survey (NSSS) (EPA 1990). The NSSS collected data on more than 400 pollutants from approximately 180 sewage treatment plants throughout the country to produce national estimates of concentrations of pollutants in sewage sludge. Using the NSSS data and information from the risk assessments, EPA conducted a further screening analysis to eliminate from regulation any pollutant that was not present at concentrations deemed to pose a significant public health or environmental risk. On the basis of this screening analysis, the 12 organic chemicals were exempted, leaving only inorganic chemicals for regulation by the Part 503 rule. The following criteria for exempting organic pollutants were used:

  1. The pollutant has been banned from use, has restricted use, or is no longer manufactured for use in the United States.

  2. The pollutant has a low frequency of detection in sewage sludge (less than 5%) based on data from the NSSS.

  3. The concentration of the pollutant in sewage sludge is already low enough that the estimated annual loading to cropland soil would result in an annual pollutant-loading rate within allowable risk-based levels.

Aldrin and dieldrin; chlordane; 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene, 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDT, DDE, DDD); heptachlor; lindane; N-nitrosodimethylamine; polychlorinated biphenyls (PCBs); and toxaphene were eliminated on the basis of criterion 1. All the organics except aldrin and dieldrin, bis(2-ethylhexyl)phthalate, and PCBs met criterion 2. On the basis of agricultural application assumptions, all the organics except benzo[a]pyrene, hexachlorobenzene, N-nitrosodimethylamine, and PCBs met criterion 3. Under different application scenarios, some of these same organics might not meet criterion

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

3. For example, EPA (1992b) noted that under scenarios for applications to forests and public contact sites, toxaphene and the organics eliminated under the agricultural scenario do not meet criterion 3.

Round 2 Pollutant Selection

Subsequent to the promulgation of biosolids regulations in 1993, another evaluation was conducted to develop a list of Round 2 pollutants to consider for regulation (EPA 1996a). As with the Round 1 pollutants, EPA conducted a preliminary hazard identification followed by a risk assessment for those contaminants and pathways identified as potential hazards. In this evaluation, degradation products of organic contaminants were assumed to be nontoxic. The list of 411 pollutants analyzed in the NSSS (EPA 1990) was the starting point of the Round 2 assessments. Pollutants were eliminated from consideration if they were not detected (254 pollutants) or were detected in less than 10% of sewage sludge (69 pollutants). Pollutants present in more than 10% of sewage sludge but with insufficient toxicity data were also eliminated from Round 2 consideration (see Table 5–2). Some of these chemicals lack toxicity values due to a relative lack of toxicity. Several pollutants were grouped into classes of congeners (e.g., PCBs, chlorinated dioxins, and furans).

The screening process identified 30 pollutants that had a frequency of detection of 10% or greater in the NSSS and that had data on human health and/or ecological toxicity (Table 5–3). Asbestos, which was not analyzed in the NSSS, was added as another potential candidate for regulation because it is toxic, persistent, and can be in biosolids. These 31 pollutants were subject to further analysis in a comprehensive hazard identification study. The study used a mix of conservative and average value assumptions similar to those used in the Round 1 risk assessments. The aggregate exposure through more than one pathway was not assessed. Analysis of a particular pathway of exposure for certain candidate chemicals was not conducted when EPA determined that chemical-specific data were insufficient for that pathway. The result of the evaluation was that only dioxins, furans, and coplanar PCBs (considered as a group) were subject to further risk assessment (EPA 1996a). That risk assessment led to a proposed standard in December 1999 (EPA 1999a). EPA sponsored a peer review of that risk assessment and proposed standard (Versar 2000). On the basis of review comments and the agency’s reassessment of dioxin risks, EPA decided to revise the risk assessment. A peer-review draft was released November 30, 2001 (EPA 2001a), and a notice of data availability was subsequently issued for public comment on June 12, 2002 (EPA 2002).

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–2 Chemicals Eliminated from Consideration in the Round 2 Assessments Because of Lack of Toxicity Data

Calcium

Magnesium

Decane, n-

Octacosane, n-

Dodecane, n-

Sodium

Eicosane, n-

Tetracosane, n-

Hexacosane, n-

Tetradecane, n-

Hexadecane, n-

Triacontane, n-

Hexanoic acid

Yttrium

Iron

 

 

Source: EPA 1996a.

Limitations of the Assessment and Selection Process

Survey Data

Accurate data on pollutant concentrations in biosolids are crucial to the selection of chemicals to regulate under the Part 503 rule. Many of the decisions made in the chemical selection process were based on concentration data from the NSSS (EPA 1990). The NSSS was an ambitious undertaking and provides the most comprehensive data on the content of sewage sludge in the United States to date. However, the survey was conducted over a decade ago, and there is a need to conduct a new survey to characterize the concentrations and distribution of chemicals now present in biosolids. For example, state survey data presented in Chapter 2 show that concentrations of some of the regulated inorganic elements have generally decreased over the past decade. Furthermore, the accuracy of the NSSS data was called into question by an earlier NRC committee that was asked to evaluate the use of biosolids on croplands (NRC 1996). That committee found inconsistencies in the survey’s sampling analyses and data-reporting methods that undermined the reliability of the data. Therefore, it recommended that another comprehensive survey be conducted to rectify the NSSS’s sampling and analytical limitations. To date, no such survey has been done.

Some chemicals that were undetected because of analytical problems or detection limits that exceeded risk-based concentrations were likely eliminated mistakenly. Each of the chemicals in the NSSS was assigned a “detection limit,” which was equivalent to the minimum concentration of pollutant that could be quantitated (EPA 1990). The detection limits are difficult to discern

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–3 Candidate Pollutants for Round 2 Regulationsa

Acetic acid (2,4-dichlorophenoxy)

Methylene chloride

Aluminumb

Nitrate

Antimony

Nitrite

Asbestosc

Pentachloronitrobenzene

Barium

Phenol

Beryllium

Polychlorinated biphenyls-coplanar

Bis(2-ethylhexyl)phthalate

Propanone, 2-

Boron

Propionic acid, 2-(2,4,5-trichlorophenoxy)

Butanone, 2-

Silver

Carbon disulfide

Thallium

Cresol, p-

Tin

Cyanides (soluble salts and complexes)

Titanium

Dioxins and dibenzofurans

Toluene

Endosulfan-II

Trichlorophenoxyacetic acid, 2,4,5-

Fluoride

Vanadium

Manganese

aPollutants detected at a frequency of at least 10% with human health and/or ecological toxicity data available.

bAluminum does not have human health or ecological toxicity data available but is included because of its potential for phytotoxicity.

cAsbestos was not tested in the NSSS but is toxic, persistent, and can be in sewage sludge.

Source: EPA 1996a.

from the NSSS data, and actual detection limits for a given chemical varied over a wide range of concentrations among samples (Figures 5–1 through 5–4). Data presented in the technical support document for the Round 2 assessment (EPA 1996a) indicated that some detection limits exceeded several hundred parts per million for some of the organic chemicals. At the request of the committee, detection limits of NSSS samples for eight chemicals, four of which were not detected in the NSSS (ideno[1,2,3-cd]pyrene, N-nitrosodimethylamine, pentachlorophenol, and toxaphene), were provided by EPA (Charles White, EPA, personal communication, February 2001). Before conducting a risk assessment, the adequacy of the available chemical concentration data to support the risk assessment is typically evaluated (EPA 1991). It is

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

FIGURE 5–1 Detected concentrations (▲) and detection limits (×) for nondetects (as a function of solids content of sewage sludge) compared with siol screening levels (A, ingestion and dermal; B, inhalation) for hexachlorobenzene and mercury. Source: NSSS data from EPA 1990.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

FIGURE 5–2 Detected concentrations (▲) and detection limits (×) for nondetects (as a function of solids content of sewage sludge) compared with soil screening levels (A, ingestion and dermal) for indeno(1,2,3-cd)pyrene and PCB-1254. Source: NSSS data from EPA 1990.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

FIGURE 5–3 Detected concentrations (▲) and detection limits (×) for nondetects (as a function of solids content of sewage sludge) compared with soil screening levels (A, ingestion and dermal) for toxaphene and pentachlorophenol. Source: NSSS data from EPA 1990.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

FIGURE 5–4 Detected concentrations (▲) and detection limits (×) for nondetects (as a function of solids content of sewage sludge) compared with the soil screening levels for dieldrin and the EPA Region 9 preliminary remediation goal (A, ingestion and dermal) and for N-nitrosodimethylamine (B, ingestion) (EPA 2002b). Note: The PRG for N-nitrosodimethylamine is approximately 1 µg/kg, and could not be shown grapically on the figure. Source: NSSS data from EPA 1990.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

current risk-assessment practice to evaluate the adequacy of analytical detection limits by comparing them with conservative risk-based screening concentrations (RBCs). For example, EPA (2001b) has developed soil screening levels (SSLs), which are based either on incidental ingestion of and dermal contact with soil or on inhalation of vapors or resuspended soil particulates. Figures 5–1 through 5–4 show chemical concentrations and detection limits for selected chemicals in sewage sludge as a function of the percent solids in the sample (elevated detection limits were sometimes associated with low percent solids). These values compared with the SSLs1 show that for some of those chemicals, most sample detection limits exceed the lowest SSL. Thus, the NSSS failed to achieve sufficient detection for four of the eight chemicals, selected as examples, to determine whether they were present at concentrations requiring further evaluation in a risk assessment.

Data regarding detection frequency were used to make critical decisions in Rounds 1 and 2. For example, chemicals were eliminated from consideration in Round 1 if they were detected at a frequency of less than 5% in the NSSS (EPA 1992a) and in Round 2 if detected at a frequency of less than 10% (EPA 1996a). On a national scale a 10% elimination criterion might seem reasonable; however, because of the local use of most biosolids, that criterion could overlook potentially significant site-specific risk.

NSSS data were also used in calculating the hazard screening indexes that determined whether a chemical would be evaluated in a risk assessment. For example, some organic chemicals were excluded from regulation because their concentrations in biosolids were already low enough, and their estimated annual loading to cropland soil would result in an annual pollutant loading rate within allowable risk-based levels. EPA compared the annual pollutant loading rate (APLR) of a specific chemical, based on its 99th percentile concentration in the NSSS, with the annual pollutant loading concentrations calculated by the Part 503 exposure assessment If the 99th percentile concentration of a pollutant resulted in an APLR less than the loading rate calculated through the risk-based exposure assessment, EPA did not regulate the pollutant. However, as noted by the 1996 NRC committee, the 99th percentile concentrations of four pollutants (PCBs, benzo[a]pyrene, hexachlorobenzene, and N-nitrosodimethylamine) resulted in calculated APLRs higher than those calculated by the exposure assessment (NRC 1996). The four compounds were eliminated from regulation because they were either no longer manufactured

1  

When an SSL was unavailable, the EPA Region 9 preliminary remediation goal was used.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

(PCBs and N-nitrosodimethylamine) or had a low frequency of detection in the NSSS (benzo[a]pyrene and hexachlorobenzene). If these pollutants are present in biosolids at concentrations approaching the 99th percentile, they can pose more of a risk than would be considered acceptable in the exposure assessment.

Additional Chemicals of Potential Concern

A number of contaminants not included in the NSSS have since been identified as biosolids pollutants. Some of these chemicals enter wastewater from industrial releases, but analyses for them are not routinely conducted, whereas other chemicals entering wastewater primarily from domestic releases are not typically included in environmental analyses, which usually focus on industrial chemicals found at hazardous waste sites.

Some categories of chemicals, such as pharmaceuticals, personal-care products, and chemicals added to condition and dewater sewage sludge, that are especially likely to be present in domestic sewage, remain unstudied in biosolids. Only a few studies have been conducted on the wide variety of odorants present in sewage sludge. New data described below and other considerations demonstrate the need for a new hazard assessment of biosolids to expand the suite of chemicals evaluated. Some categories of pollutants in addition to those mentioned above that should be considered in future assessment are discussed later in this chapter in the section Organic Chemicals.

The Toxics Release Inventory, which tracks the release of over 600 pollutants that are discharged by businesses meeting certain thresholds, documents that pollutants continue to be released to sewer systems from industrial and commercial sources. Although data on a core set of chemicals tracked consistently between 1988 and 1999 show that transfers to publicly owned treatment works (POTWs) substantially decreased (for example, transfer of metals decreased by 65%), trend data between 1995 and 1999 indicate a transfer increase for all tracked chemicals of about 7.6% to POTWs, with greater increases for tracked metals2 (EPA 2001c). Over the same period, wastewater flows into sewage treatment plants and sewage sludge volumes increased approximately 8.5% (calculated based on data in Appendix A of EPA [1999b]).

2  

Transfers of tracked TRI metals increased 31% during this four-year period. It should be noted that the tracked metals are not the same as the inorganic chemicals regulated under the Part 503 rule.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

This suggests that overall industrial discharges to POTWs are increasing at a similar rate as sewage sludge volumes.

Under the Clean Water Act, EPA is required to review the regulations in Part 503 at least every 2 years to identify additional toxic pollutants and promulgate regulations for such pollutants (33 USC Section 1345(d)(2)(C)). A new hazard assessment should include review of new studies from the United States, Canada, Europe, and elsewhere to identify additional pollutants to be evaluated. In addition to evaluating more industrially used chemicals, consideration must be given to identifying and characterizing nonindustrial chemicals that are released into sewer systems (e.g., pharmaceuticals and personal-care products) or added to wastewaters during treatment processes (e.g., dewatering agents).

Data Gaps

Some pollutants and exposure pathways were eliminated in the screening processes and risk assessments when chemical-specific data were insufficient to perform pathway-specific calculations or when toxicity data were insufficient for a given pollutant. For example, a plant uptake factor for lindane was not available, so no assessments were conducted for any pathway that relied on that factor. Thus, the potential risks from lindane via those particular pathways were not assessed. The technical support documents for EPA’s Round 1 and Round 2 assessments do not provide a list of data gaps, nor do they specify the chemicals and pathways that were eliminated from consideration because of data gaps. The lack of that information makes it impossible to identify the implications of the data gaps. Lack of information does not equate to lack of risk. Therefore, data gaps should not be used as a criterion for eliminating chemicals from consideration but should be used to identify important areas for future research.

In conclusion, new studies of the contaminant concentrations in biosolids should include evaluation of pollutants, such as surfactants, flame retardants, and pharmaceuticals, not included in previous surveys. Biosolids should be monitored periodically as new pollutants are identified and analytical methods improved. As analytical methods are identified, risk-based screening concentrations should be used to ensure that detection limits are adequate to support risk assessment. Use of a lower frequency of detection to eliminate contaminants from regulation should be considered. Data gaps that result in the inability to assess risks need to be identified so that research can be conducted to fill those gaps.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

EXPOSURE ASSESSMENT

As described in Chapter 4, exposure assessment is the identification and quantification of potential exposures. For exposure to chemicals to occur, a complete exposure pathway must exist. A complete pathway requires the following elements (EPA 1989):

  • A source and mechanism for release of chemicals.

  • A transport or retention medium.

  • A point of potential human contact (exposure point) with the affected medium.

  • An exposure route at the exposure point.

These elements are typically identified in a conceptual site model. If any one of these elements is missing, the pathway is not considered complete. For example, if human activity patterns and the location of human populations relative to the location of an affected medium prevent human contact, then that exposure pathway is not complete. One of the primary differences between the Part 503 rule risk assessment and current risk-assessment practice is that the Part 503 rule risk assessment derived separate risk-based levels for each individual exposure pathway evaluated, whereas current practice is to perform aggregate risk assessments, in which risk-based standards are derived after aggregation of exposures by all pathways to which a single individual is likely to be exposed.

EPA has used a conceptual site model in a new analysis of risks associated with dioxins in biosolids (EPA 2001a). The conceptual site model used by EPA for agricultural application is shown in Figure 5–5. A number of important assumptions that may be questioned are embedded in such a model (e.g., the notion of the buffer zone). However, this figure provides an example of how a conceptual site model illustrates the mechanisms by which contaminants in biosolids are transported from the site of application to a point of contact with a human receptor. For each category of receptor identified, exposures from all identified pathways are summed to provide an estimate of total exposures.

This section reviews the approach used by EPA to select exposure pathways for the Round 1 Part 503 rule risk assessment, describes current EPA exposure-assessment procedures (focusing on multipathway risk assessment), and then attempts to assess the implications of the differences in current versus historical approaches. The final section reviews and compares the historical and current exposure assumptions for pathway-specific parameters and examines methodological issues for derivation of some chemical-specific parameters.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

FIGURE 5–5. Agricultural application conceptual site model. Source: EPA 2001a

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Summary of Approach Used to Select Exposure Pathways

The Part 503 risk assessment evaluated 14 exposure pathways, 9 of which included human pathways (Table 5–4). The human exposure pathways consider direct ingestion of biosolids by a child, ingestion of produce grown on biosolids-amended soil by either a home gardener or consumers buying the produce in stores, ingestion of animal products derived from livestock exposed via food or soil ingestion, inhalation by a farmer of dust or inhalation of vapors containing chemicals released from biosolids-amended soils, and ingestion of fish and water affected by release of chemicals from amended soils. Although these pathways may include the primary exposure pathways for a resident near biosolids-amended fields, EPA did not identify a single common receptor and calculate exposures in such a way that exposure via multiple pathways could be added. The conservatism in the exposure assumptions varies widely in the Part 503 rule risk assessment. The variability in the conservatism of the assumptions for the various pathways results in the highest risks being associated with the pathway with the most conservative assumptions—that is, the child ingesting undiluted biosolids—rather than the pathways most likely to contribute to exposures. A more robust assessment of potential exposures to contaminants in biosolids would be provided by an aggregate assessment of total exposures from all pathways that a single receptor is likely to encounter. Although it is likely that one or two pathways will be the dominant contributors to exposure for any one chemical, the dominant pathways may vary with chemicals and are not always correctly predicted before conducting the risk assessment.

Description of Conceptual Model and Exposure Scenario Approach

For each biosolids-application scenario being evaluated, a conceptual model should be developed to describe the scenarios under which exposures could occur. Agricultural, forestry, and land-reclamation applications may all result in somewhat different conceptual models. A conceptual site model should identify the biosolids source (e.g., biosolids tilled into soil or applied to the surface for agricultural soils), the pathways by which biosolids constituents may be released and transported, and the nature of human contacts with the constituents. The limitations of the assessment should be clearly articulated (e.g., whether exposures are evaluated only after land application), and any exclusion of exposures associated with processing and transporting biosolids should be reported.

The conceptual site model developed for the risk assessment for dioxins in biosolids (EPA 2001a) provides an illustration of this approach for the

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–4 Exposure Assessment Pathways Use in Risk Assessment for Land Application of Biosolids

Pathway Number

Receptor

Pathway

1

Human

Biosolids-soil-plant-human

2

Human

Biosolids-soil-plant-home gardener

3

Human

Biosolids-soil-child

4

Human

Biosolids-soil-plant-animal-human

5

Human

Biosolids-soil-animal-human

6

Ecological and agricultural

Biosolids-soil-plant-animal

7

Ecological and agricultural

Biosolids-soil-animal

8

Ecological and agricultural

Biosolids-soil-plant

9

Ecological

Biosolids-soil-soil biota

10

Ecological

Biosolids-soil-soil biota-predator of soil biota

11

Human

Biosolids-soil-airborne dust-human

12

Human

Biosolids-soil-surface water-fish-human

13

Human

Biosolids-soil-air-human

14

Human

Biosolids-soil-groundwater-human

 

Source: EPA 1995.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

agricultural application scenario. Although some of the assumptions of the site model are open to question, the model is clearly laid out. The dioxin risk assessment examines exposures of two primary kinds of human receptors: a farm family living adjacent to and downhill from the land-application site (in an area termed a buffer) and a recreational fisher catching fish from a stream downhill from the land-application site. For the farm family, aggregate exposures by the following pathways are assessed:

  • Incidental ingestion of soil in the buffer.

  • Ingestion of above- and below-ground produce grown on cropland.

  • Ingestion of beef and dairy products from a pasture.

  • Ingestion of home-produced poultry and eggs from the buffer.

  • Inhalation of ambient air (particulates and vapor).

  • Ingestion of mother’s milk by an infant.

Only chronic exposures to dioxins are evaluated, and one pathway (groundwater ingestion) considered in setting the Part 503 standards is excluded. The inclusion of some pathways and exclusion of others in this focused risk assessment reflects both assumptions about the exposure, such as the absence of a farm pond used for fishing, and the expected behavior of the chemicals being evaluated. Dioxins, dibenzofurans, and coplanar PCBs are persistent lipophilic chemicals that are expected to partition into meat, eggs, and milk but are not expected to leach to groundwater. Similarly, the focus on chronic exposures is appropriate for persistent chemicals present in biosolids in low concentrations.

In developing a conceptual site model that could form the foundation for a multipathway risk assessment for a great variety of chemicals, it is necessary to think more broadly about the exposure pathways and exposure durations to be evaluated. Consequently, groundwater ingestion and short-term exposures to volatile chemicals should be included in a biosolids risk assessment. Similarly, different application practices, such as forestry, land reclamation, or direct application of biosolids to home gardens by consumers, would require separate conceptual site models.

Evaluation of Exposure Models and Parameters

Estimation of potential exposures to chemicals for the purpose of deriving risk-based concentrations requires theoretical calculations based on understanding how people come into contact with chemicals in environmental media and how chemicals move among various environmental media. These calculations include assumptions for many parameters, beginning with fate and

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

transport models for predicting chemical concentrations in the exposure media. Some of the assumptions for each of the pathways evaluated in the Part 503 rule risk assessment are presented in Table 5–5. Working backward from land application of biosolids, it is necessary to predict chemical concentrations in soil, in plants grown in the soil, in livestock grazed in the fields or fed forage from the fields, and in other media identified in the various exposure pathways. Once chemical concentrations in the exposure media are estimated, assumptions must be made about the values of other parameters that control the degree of exposure to the media. Some of these parameters are specific to the exposure pathway being evaluated. For example, to evaluate incidental ingestion of chemicals in soil, an assumption must be made about the amount of soil a person will ingest. Other parameters are chemical specific, such as the relative bioavailability of a chemical in soil.

In addition, several management requirements in the Part 503 rule could affect predicted chemical concentrations in exposure media. The risk assessments assume compliance with those requirements. Management requirements and compliance with them are discussed in more detail in Chapter 2. The committee found that EPA does not have an adequate program for ensuring compliance with those requirements. Some of the critical management practices and assumptions are discussed in Box 5–1.

As discussed in Chapter 4, there have been several important advances in risk assessment since the Part 503 rule was promulgated. One of the most significant advances in exposure assessment has been the development of probabilistic risk assessment methods that provide a quantitative description of variability and uncertainties in exposure estimates (EPA 2001d). EPA’s most recent risk assessment for dioxins in biosolids (EPA 2001a) includes both deterministic and probabilistic risk assessments. In the following sections, the methods and assumptions used to identify exposure parameters in the Part 503 rule risk assessment are reviewed in light of those advances. The assumptions make use of scientific data and knowledge, but policy decisions are inherent in making choices about what estimates to use. While general issues related to exposure parameters are addressed, specific values are not recommended because such values must be identified in the context of the risk assessment being conducted. Similarly, no recommendation is made regarding using deterministic or probabilistic approaches because the relative utility of these approaches varies (EPA 2001d).

HEI Receptor Versus RME Receptor

One of the most critical policy decisions in conducting the biosolids risk assessments was the decision to use the highly exposed individual (HEI) as the

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–5 Exposure Assumptions for the Human Exposure Pathways

Pathway

Assumptions in the Part 503 Rule Risk Assessment

1. Biosolids → Soil → Plant → Human (except home gardener) lifetime ingestion of plants grown on biosolids-amended soil

-

2% of vegetables biosolids-amended

-

Average U.S. diet circa 1980

-

Plant uptake coefficient was geometric mean

2. Biosolids → Soil → Plant → Human (home gardener) lifetime ingestion of plants grown in biosolids-amended soil

-

59% of most vegetables biosolids-amended

-

Average nonmetropolitan diet circa 1980

-

Biosolids mixed into 15 cm of soil

-

Plant uptake coefficient was geometric mean

-

70 kg of body weight

3. Biosolids → Human (child) ingesting biosolids

-

Child ingests 200 mg/d for 5 yr

-

Soil ingested is undiluted biosolids

-

Contaminants are 100% bioavailable

4. Biosolids → Soil → Plant → Animal → Human lifetime ingestion of animal products (animals raised on forage grown on biosolids-amended soil)

-

Average nonmetropolitan diet circa 1980

-

Biosolids mixed into 15 cm of soil

-

Average nonmetropolitan percent of animals raised at home and thus exposed to biosolids

-

Uptake coefficient into animals is geometric mean of data

-

100% of forage grown on biosolids-amended soil

-

70 kg of body weight

5. Biosolids → Soil → Animal → Human lifetime ingestion of animals products (animals ingest biosolids directly)

-

1.5% animal diet is soil

-

Soil is undiluted biosolids

-

Uptake coefficient into animals is geometric mean

-

Animal exposed 1 yr out of 3

-

70 kg of body weight

11. Biosolids → Soil → Airborne Dust → Human

-

Tractor operator (did not assess mine reclamation land applicators or residents)

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

lifetime inhalation of particles (dust) (e.g., tractor driver tilling a field)

-

Dust level representing NIOSH occupational standard is acceptable

-

Dust is biosolids diluted with soil

-

Receptor will not be exposed to >10 mg/m3 (the OSHA standard at which it is assumed farmer will be in an enclosed cab)

12. Biosolids → Soil → Surface Water → Human lifetime drinking surface water and ingesting fish containing pollutants in biosolids

-

Person drinking 2 L/d

-

Person eating 40 g/d of fish

-

0.24% of watershed is biosolids-amended soil

-

Average erosion rates

-

Eroded materials are diluted with soil

-

Contaminant concentrations in eroded materials are reduced through leaching and volatilization

-

70 kg of body weight

13. Biosolids → Soil → Air → Human lifetime inhalation of pollutants in biosolids that volatilized to air

-

Receptor lives 1.6 km downwind

-

20 m3/d inhalation rate

-

Biosolids diluted with soil

-

4.5 m/s wind speed

-

15°C temp

14. Biosolids → Soil → Groundwater → Human lifetime drinking well water containing pollutants from biosolids that leached from soil to groundwater

-

Well immediately down gradient

-

High dilution and attenuation (chemical-specific values)

-

1m depth to groundwater

-

Partition coefficients from lab experiment with sandy loam, pH 8, aerobically digested biosolids

-

0.5 m/yr recharge

-

70 yr of exposure

-

70 kg of body weight

Abbreviations: NIOSH, National Institute for Occupational Safety and Health; OSHA, Occupational Safety and Health Administration.

Source: EPA 1992a.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

BOX 5–1 Management Practices and Assumptions

Management Practices

  • Biosolids shall not be applied to land if it is likely to adversely affect a threatened or endangered species or its designated critical habitat.

  • Biosolids cannot be applied to flooded, frozen, or snow-covered land in such a way that bulk biosolids enter a wetland or other waters of the United States unless allowed in a permit. The implementation of this requirement is unclear.

  • A 10-meter setback from watercourses is required for biosolids not meeting Class A and vector attraction reduction requirements and pollutant-concentration limits.

  • Regulations require that bulk biosolids be applied to agricultural fields, forests, and public contact sites at a rate equal to or less than the nitrogen-based agronomic rate. This requirement also applies to reclamation sites unless otherwise approved by the permit authority. It is not applicable to bagged products or bulk application of Class A biosolids meeting pollutant-concentration limits.

Management Assumptions

  • EPA (1992a) states that surface application is normally limited to slopes of 6% or less to reduce surface runoff. That is not a requirement, and how or whether that slope limitation was used in the biosolids risk assessments is unclear.

  • Field storage of biosolids at the site of land application is a common practice that is allowed under the Part 503 rules. Recognizing the potential for stockpiling and field storage to cause problems, including odors, EPA developed nonregulatory guidance (EPA 2000a). The Part 503 risk assessments and rules do not address stockpiling.

  • Tile drains (drainage pipes installed at shallow depths in agricultural fields) are common in some portions of the United States. Designed to dry out soils, these drains provide conduits for the rapid movement of contaminants from land-applied biosolids into surface waters. The Part 503 risk assessments and rules did not consider the potential for this type of exposure.

  • Different methods of biosolids application are not addressed and may have different implications for risks, particularly those associated with airborne emissions.

receptor of concern (EPA 1992a). The HEI is an individual who remains for an extended period at or adjacent to the site where maximum exposure occurs. Current practice is to use a reasonable maximum exposure (RME) receptor. EPA (1989) specifies that calculation of the RME in a deterministic risk assessment requires a combination of average and upper-bound values for vari-

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

ous exposure parameters so that the final exposure estimate will be an upper-bound exposure with a reasonable expectation of occurrence. This calculation is commonly interpreted to be a 90th to 95th percentile of exposures for each pathway. For some exposure pathways, the use of more than one or two upper-bound exposure parameters might result in exposure estimates with no reasonable expectation of occurrence. Thus, the impact of multiple conservative assumptions must be evaluated carefully. For probabilistic risk assessment, risks corresponding to the 90th to 99.9th percentiles of the risk distribution are considered plausible high-end risks for selection of the RME (EPA 2001d). However, EPA notes that very high percentiles may be numerically unstable and should only be used if reproducible.

The goal of the Part 503 rule is to establish pollutant limits that are protective of reasonably anticipated adverse effects. But this standard should be applied to all settings, to all biosolids, and to all land-application practices that are reasonably anticipated to occur. That goal necessitates assessing risks under the most sensitive exposure setting that is likely to occur. For example, a farm family living near a land-application site may produce much of their own food and have exposures via multiple pathways. In addition, parameters that are linked should be identified, and those links should be maintained throughout the risk assessment. For example, in the revised risk assessment for dioxins in biosolids (EPA 2001a), dioxin and PCB congener data were linked within samples, and those links were maintained throughout the probabilistic risk assessment.

Determination of Chemical Concentrations in Exposure Media

Most of the exposure pathways evaluated by EPA require that chemical concentrations be estimated in one or more exposure media. The exposure media for which concentrations were estimated in the Part 503 rule risk assessment are soil, plants, livestock, airborne dust, vapors, surface water, fish, and groundwater. Estimates of chemical concentrations in those media are based on a number of assumptions, such as assumptions about chemical fate and transport. This section reviews one of the more important assumptions about chemical fate (mass balance and distribution of contaminants) and evaluates EPA’s approach to estimating concentrations in environmental media. Special emphasis is given to the determination of soil and plant concentrations. This section is followed by a brief assessment of assumptions about human intake parameters.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Mass Balance and Distribution of Contaminants

For pathways involving exposure via surface water, air, or groundwater (Pathways 12–14, Table 5–5), losses of pollutant mass from soil due to partitioning to other media are assumed by EPA. For example, pollutant mass losses from soil are assumed to occur to surface water through erosion, to air through volatilization, and to groundwater through leaching. For organic chemicals, it is assumed that degradation occurs and that degradation products are nontoxic, an assumption that is not universally true. In assessing risk via these pathways, the assumption is made that pollutant mass is conserved. Thus, for example, the amount of a pollutant in sediment eroded from a site is adjusted to account for the amount that is predicted to be removed because of leaching, degradation, and volatilization. Many of these estimates are based on models that make a number of assumptions on scant data, resulting in a high degree of uncertainty. For example, data on partition coefficients for specific chemicals were based on a single study of only one type of biosolids (see discussion below).

Soil Concentrations

Most of EPA’s exposure pathways begin with estimated soil concentrations resulting from the mixing of biosolids into soil, the exceptions being Pathway 3 (inadvertent direct ingestion of biosolids) and Pathway 5 (biosolids applied to pastures and not mixed with soil). Consequently, the accuracy of the exposure assessment is highly dependent on the accuracy of the predicted soil concentrations. These predictions are based on assumptions regarding the incorporation of biosolids into soil and the depth of the incorporation; chemical retention in soils; and the frequency, duration, and loading rates of application.

Incorporation. In exposure scenarios in which biosolids are incorporated into soil, EPA’s risk assessment assumed a tillage depth of 15 centimeters (cm). The revised dioxin risk assessment assumes 20 cm (EPA 2001a). However, 10 cm has been proposed as a more realistic figure when biosolids are incorporated by disking rather than plowing (Versar, Inc. 2000), and for home gardens, hand tillage could be shallower than 15 cm. Surface application without incorporation is typical in some scenarios, such as pasture-land application or conservation tillage.

Retention. Inorganic chemicals in biosolids were assumed to stay in soil for all pathways except Pathways 12–14, where a mass-balance approach was

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

used to predict soil concentrations. Retention or release of metals and organic contaminants in soils is highly dependent on the characteristics of the contaminants; the mineralogical composition of the biosolids and the soil to which it is applied; and the pH, wetting and drying, and ionic strength of the soil solution.

Soils that are sandy and that contain low amounts of clay and organic matter (e.g., those in the Atlantic Coastal Plain Region) will have less capacity to retain metals and organic chemicals than those that have high amounts of clay and organic matter. The latter soils are often accompanied by metal oxide coatings electrostatically bound to the clay minerals and organic matter, enhancing the soil’s ability to retain contaminants. In higher clay and organic-matter soils, metals and organic chemicals can be strongly bound and resistant to release into groundwaters. Organic matter is especially important in the retention of organic contaminants.

In many instances, an “aging” effect is observed with metals, oxyanions, and organic chemicals in soils—that is, the longer the time of contact between the contaminant and the soil, the more sequestered the contaminant. It is well documented that with many organic chemicals, the release of the chemical and its bioavailability is greatly diminished as time in soil increases (Alexander 2000; Pignatello 1999; Young et al. 2001). The aging effect with organic chemicals has been largely ascribed to interparticle diffusion into the organic matter of the soil. The aging effect has also been observed with such metals as cadmium, zinc, cobalt, and nickel (Barrow 1998; McLaren et al. 1998; Scheckel et al. 2000). This effect has been attributed to diffusion into the inorganic components of the soils, inner-sphere complex interactions, and surface precipitation. It should not be assumed that the aging effect precludes release of chemicals from soil. For example, certain metals, including cadmium, molybdenum, and zinc, show continued availability for plant uptake from biosolids-amended sites despite aging (McBride et al. 1997; McGrath et al. 2000; Broos et al. 2001).

The aging effect must be considered when predicting the fate of contaminants in biosolids in soils and waters. Traditionally, partition coefficients (Kps) are based on a 24-h reaction time; however, if the rates of retention and release are slow and a residence time effect is pronounced, the Kp values can be greatly underestimated when a 24-h reaction time is assumed in the calculation. Consequently, the mobility of the contaminant would be overpredicted.

Application Rates and Duration. The Part 503 rule addresses several application scenarios, including agricultural use, silvicultural use, and land reclamation. Different biosolids-application techniques are used in these scenarios and can affect the resulting contaminant concentrations in soils. For example, the rate of application at reclamation sites is usually much higher

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–6 Estimated Biosolids Application Rates for Different Scenarios

Scenario

Number of Observations

Mean Application Rate (metric tons/ha/y of DW)

Standard Deviation

75th Percentile (metric tons/ ha/y of DW)

Agricultural

87

6.8

105

16

Forest

2

26

26

34

Public contact

11

19

122

125

Reclamation

7

74

148

101

Abbreviation: DW, dry weight.

Source: EPA 1992b.

than that at agricultural sites, although reclamation applications typically involve one-time or limited-time applications rather than repeated applications. Estimates of application rates were based on data from the NSSS (EPA 1990) and are presented in Table 5–6. The number of applications before regulatory cumulative pollutant loading rates are reached at these application rates is approximately 13, 32, 55, and 100 years for reclamation, public contact, forest, and agricultural uses, respectively (EPA 1992a). EPA based its chemical standards on the scenario of biosolids application to agricultural land for 100 years, which was considered applicable to the other types of land applications that would not occur as routinely or for as long a duration.

Plant Concentrations

Plant uptake of metals from biosolids-amended soils is another important factor in several of the exposure pathways. To determine plant uptake, EPA (1992a) derived plant uptake coefficients (UCs) for each pollutant. A UC is the uptake-response slope of a pollutant in plant tissue for each food group and is estimated by the increase in pollutant in plant tissue for each kilogram of pollutant added to the soil from biosolids. Five main steps were used to estimate UCs: (1) the primary literature was reviewed and evaluated; (2) the relevant data were compiled in a database; (3) the uptake slope for each study was calculated by linear regression of the concentration of the pollutant in plant tissue against the application rate of the pollutant; (4) the plants were placed in categories (e.g., leafy vegetables and garden fruits); and (5) the uptake slope of each plant group was calculated for each pollutant by using the geometric mean of the uptake slopes from relevant studies.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

The likely concentrations of the pollutant in food groups were then calculated for the risk assessment by using information on the amount of soil contamination and the UC. Data for those calculations were derived from three categories of studies: (1) field studies of biosolids, (2) non-field studies of biosolids (greenhouse or potted) or field studies with biosolids spiked with additional metals, and (3) studies of metal salts, metal-contaminated soils, or mine tailings. Obviously, the first category of studies was the most relevant to the risk assessments. Studies have unequivocally demonstrated that greenhouse or potted plants and added inorganic metal salts do not mimic the characteristics of metals within biosolids. Such studies are irrelevant to real land application of biosolids. For the metals regulated on the basis of human health, the UCs were based on field studies for cadmium, field and nonfield studies for selenium and mercury, and primarily studies of metal salts, metal-contaminated soils, or mine tailings for arsenic.

Factors affecting the estimates of UCs and limitations in the UCs selected due to the variation in bioavailability of metals to plants in different situations are discussed below.

Plant Response to Metals. Some field-plot experiments with biosolids show that plant concentrations of some metals do not increase with high rates of biosolids application (Corey et al. 1987; Mahler et al. 1987; Chancy and Ryan 1994). EPA (1992a, 1995) attributes that observation to the binding of metals by biosolids and uses it to support the concept of a plateau response in plant uptake. (The rate of pollutant uptake by plants in the biosolids-soil mixture decreases with increasing biosolids loadings, because adsorptive materials in the biosolids become as important as or more important than the adsorptive materials initially in the soil.) One of the main limitations of the available database is that the data are insufficient to separately characterize the changes in uptake with the metal concentration at a constant biosolids loading rate as compared with the changes in uptake with increasing biosolids loading. Accurate prediction of plant concentrations requires both characterizations.

EPA used a linear-response, rather than a plateau-response, assumption for the low biosolids loading linear portion of the uptake curve in its risk assessments, because it was a conservative approach and assumed that the linear response would overestimate pollutant uptake by plants. EPA’s assertion that metals bind to biosolids and are thus less available for plant uptake should be validated using the latest direct molecular scale techniques. That assumption does not consider the extent to which the proposed binding is reversible (Bell et al. 1991). If soil conditions and land use change, such as the soil acidifying when organic matter decays, uptake could increase (Heckman et al. 1987; Mulchi et al. 1987a,b; Bell et al. 1988; Adamu et al. 1989; Chaney

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

1990), although this was not the case for cadmium uptake by lettuce after 13– 15 years in one experiment (Brown et al. 1998). Other researchers believe that the plateau effect could be due to plant physiological factors rather than attenuation due to biosolids chemistry (Hamon et al. 1999). If that is the case, the conservatism of the linear assumption will depend on the metal concentration at the plateau as compared with the concentration used in the biosolids standards. For example, Sloan et al. (1997) show some evidence of curve linearity in uptake of cadmium by lettuce above about 8 mg/kg of cadmium in soil.

EPA pointed out that the linear approach underestimates the UC at low concentrations. As the metal concentrations in biosolids have been reduced and result in low-end concentrations in soil, EPA’s approach may underestimate uptake. Thus, any further risk assessment should focus on plant uptake over the likely loading rates and range of soil concentrations resulting from biosolids applications in practice. In addition, other explanations for a plateau effect should be investigated. For example, higher rates of biosolids application might have other effects, such as increasing soil pH or enhancing plant growth, which results in the “growth dilution” effect on metal concentrations.

Many studies on plant uptake of metals have been published since the risk assessments were conducted for the Part 503 rule. Some of the most relevant studies to review are those of Sauerbeck and Lübben (1991), McGrath et al. (2000), Chang et al. (1997), Logan et al. (1997), Sloan et al. (1997), Brown et al. (1996, 1998), and Chaudri et al. (2001).

Older data on trace elements in soils and plants must be carefully evaluated, as most of those data were derived using analytical methods that had higher detection limits than those that are characteristic of methods used today. Error in crop analyses of low-concentration cadmium, mercury, and lead is well documented (Tahvonen 1996). Those errors may be associated with the high values observed in crops grown on some control plots used for UC calculations in the EPA database. Erroneously high values for controls have the effect of decreasing the slope of the UC. Real UCs may be higher if accurate measurements on control plots are used (McBride 1998).

Finally, the observed concentration in plant materials used as food, including both above-and below-ground produce, is assumed in the above studies to be derived from actual uptake into the tissues. However, dust and soil particles can be deposited on plant surfaces by wind, harvesting, and soil “splash” after rain. In the case of metals, especially those that are relatively insoluble in soil, these particles may become included in the plant tissue (Preer et al. 1984). This “entrapment” can be a substantial proportion of the concentration of leafy or root vegetables (e.g., up to 5% of dry weight of leafy greens may be soil particles) (Cary et al. 1994). Although these particles may not be

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

strictly taken up into the tissues, they strongly adhere and are not efficiently washed off during food preparation. Consequently, the metals in soil embedded in plant tissue will be included in estimated plant metal concentrations.

Exposure to Plants. In the database used by EPA (1992a,b) to derive UCs, some experiments have concentrations measured in the topsoil of each experimental rate, whereas others were not measured and only the loading of metal added to the soil was recorded. EPA used metal loading rates to calculate plant uptake of metals for all studies, necessitating conversion to loadings for those with concentrations given by multiplying the concentration by the weight of topsoil. The studies that gave loading rates rather than soil concentrations have several problems associated with their use. First, loading assumes that all the metals remain on the plot for the duration of the experiment. That assumption ignores two factors: leaching losses (McBride et al. 1997, 1999; Barbarick et al 1998; Richards et al. 1998) and physical movement of soil laterally due to cultivation. Both factors have the effect of decreasing the actual concentrations of metals that plants are exposed to and make the plant uptake slopes less steep. Only those studies in the database for which actual soil concentrations were recorded avoid this underestimation. Second, in the mainly short-term experiments that constitute the majority of the evidence, plant roots respond to the concentration of metals in their environment and not to loading rates. That factor is important for assessing exposure. For example, in the short-term studies typical of the experiments used for the risk assessment, if biosolids were surface applied and not incorporated into the soil, the roots might not have been exposed to the full metal concentration. Alternatively, if the biosolids were ploughed deeper than the assumed 15 cm, crop roots would be exposed to a smaller concentration than anticipated.

Soil concentrations of metals are therefore better estimates of exposure to plants than loading rates. However, several additional factors must be taken into consideration when using soil concentrations or loadings. The rate at which metal concentrations in experimental field plots decrease due to cultivation and dispersion is proportional to the plot size, the repetition of application, the number of cultivations, and the amount of control soil surrounding each plot and the difference in concentration (Sibbesen and Andersen 1985; Sibbesen et al. 1985; Sibbesen 1986; McGrath and Lane 1989; Berti and Jacobs 1998; Sloan et al. 1998). If a metal is added once or only on a few occasions, the concentration within the original treated area declines particularly rapidly with increasing number of cultivations on small experimental plots (McGrath and Lane 1989; Berti and Jacobs 1998). Decreasing metal concentrations in soils have the effect of making the dose-response curve for plant uptake steeper, as illustrated in Figure 5–6. The data in Table 5–7 show

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

FIGURE 5–6 Effect of dilution of soil zinc concentration by cultivation. Data from Table 5–7.

that 50:50 mixing of a biosolids-treated soil results in a plant uptake slope that is twice that when cultivation effects are ignored.

Another effect of mixing due to cultivation is the increase in metal concentrations in nearby control plots. That effect might be another explanation for the unusually high concentrations of metals in plants from some of the control treatments in the database. Lack of proper controls may have made some of the reported UC curves shallower and underestimated the real UC values (McBride 1998). This may not be as important in the few experiments that used large treatment plots (e.g., 30×73 meter plots used by Sloan et al. [1998]).

Calculations. Two basic methods were used for calculating plant uptake slopes:

  1. For studies in which one metal application rate and one plant tissue concentration were given, the following algorithm was used:

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–7 Effect of Soil Mixing on Actual Soil Concentrations Due to Cultivation of Field Experimental Plots

 

Biosolids rate 1

Biosolids rate 2

Metal in plant (mg/kg of dry weight)

44

56

Soil (mg/kg), calculated from the loadinga

75

300

Soil (mg/kg) actualb

57.5

170

aLoadings 150 and 600 kg/ha, both divided by 2 to account for mixing to 15 cm in soil of 1.33 density (EPA 1992a). UC=12/(300−75)=0.05.

bLoadings assumed to be 50:50 mixed with surrounding control soil with 40 mg/kg background concentration, so actual concentrations (75+40)/2=57.5 and (300+ 40)/2=170. UC=12/(170−57.5)=0.11.

  1. For studies in which multiple application rates and tissue concentrations were given, the slope was determined by least-squares linear regression.

The first method is not an accurate method of measuring an uptake slope, as a full response curve is not used. The second method also has problems. For example, using data on cadmium in spinach, EPA fitted a linear function for five data points. The “best-fit” line for those data points resulted in an intercept for cadmium at nearly 10 mg/kg in spinach. The control (no biosolids added) was in fact only 5 mg/kg. The effect of that difference is to make the UC slope 0.40 (less steep than if the four data points had been treated separately in the same way as the single-point UC calculations), resulting in UCs of 1.75, 1.75, 0.75, and 0.45.

EPA grouped crop species into seven categories and used the geometric mean of all available UC data on metals from field experiments for each of those crop groups. There are a number of reasons why the geometric mean may not be the appropriate statistic to use to represent these data. In many cases, an arithmetic mean will best approximate exposure for use in risk assessment. EPA should reexamine the statistic used to represent the UC after considering the risk assessment goals (i.e., identifying a reasonable maximum exposure [RME]) and the causes of variation in the data set. The number of data points used by EPA to determine the geometric mean UC value varies significantly for each pollutant, with only four points available for arsenic and 167 available for cadmium. Data included a range of study conditions, including varied pH. Obviously, if the data set is very small, the causes of variation will be difficult to elucidate. However, for the large data sets, such as the one for cadmium, a more sophisticated evaluation of the causes of variation should

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

be possible, and should be used to derive the most appropriate statistic for the risk assessment.

Within a category, such as leafy vegetables, results were not weighted according to the fraction of diet. Thus, for example, cadmium uptake into leafy vegetables constitutes a major component of the potential dietary dose of cadmium. Data on crucifers compose a high proportion of the available data, yet most diets contain a lower fraction of crucifers than lettuce. The UC for cadmium into crucifers is generally much lower than the UC for lettuce. Thus, taking the geometric mean of available data gives greater weight to the lower-UC crucifers than lettuce. Weighting the UCs by the fraction of diet would give a more representative UC for dietary exposures.

Environmental and Crop Considerations. A variety of environmental factors affect contaminant bioavailability, including soil organic matter, buffering capacity, oxide content, pH, temperature, and rainfall. In addition, different crops and even different cultivars of the same crop type vary greatly in their tendency to take up pollutants from the soil. That variation highlights the importance of considering regional variations in environmental conditions and crop types when assessing plant uptake assumptions for national applications.

EPA recognized that soil pH has a significant influence, the uptake of metal cations generally being higher at lower pH and the uptake of such anions as arsenate and molybdate being higher at higher pH. EPA also indicated that the data set considered included studies with pH as low as 4.5. However, pH differences between untreated controls and biosolids-treated plots might also be another contributory reason for the apparent plateau effect in the relationship between loading and crop uptake. Compared with control soil pH, biosolids soil pH frequently increases after initial application of biosolids, especially when lime is part of the treatment process. However, that effect does not persist, and pH can fall by 1–1.5 units because of leaching of cations and the mineralization of the added organic matter (Chaney et al. 1977). In the database, the duration of many of the experiments is restricted to a few years after biosolids are applied, and that might also underestimate the UC slopes for many metals.

EPA stated that agricultural biosolids-applied soils rarely have a pH below 5.5. That is true, but taking the median calculated UC from the data collected tends to have the effect of biasing the effective UC to the near-neutral pH range (Stern 1993). Because the risk assessment does not take into account pH and instead sets allowable loading for all soils, this approach relies on the practice of maintaining pH at near neutral values for crop production reasons.

Cadmium, zinc, and chloride in soil have important effects on crop uptake and consequences for human or animal nutrition (Chaney et al. 1998; Reeves and Chaney 2001). Zinc in soil has a competitive effect on cadmium uptake

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

by crops, thus reducing cadmium uptake, whereas chloride ions (present in saline soils or derived from irrigation water) preferentially increase cadmium mobility and crop uptake compared with zinc (McLaughlin et al. 1994; Chaney et al. 1998). In earlier experiments that were used in the original risk assessment database, zinc was, of course, present when cadmium uptake was studied.

Livestock Concentrations

EPA used assumptions about transfer of pollutants from biosolids to livestock and resulting human exposures to contaminants in meat, organ meat, poultry, dairy products, and eggs in its screening process for identifying pollutants to regulate and in its risk assessments for Pathways 4 and 5 (human consumption of animal products affected by chemicals taken up into forage from biosolids or by direct ingestion of biosolids). It is not clear why these two pathways were not combined to estimate chemical concentrations in livestock because of both soil ingestion and plant ingestion. A much more appropriate integrated approach was used by EPA in the revised risk assessment for dioxins in biosolids (EPA 2001a) and in the dioxin reassessment (EPA 2000b). This approach, developed by Fries and Paustenbach (1990), involves the prediction of chemical concentrations in livestock based on the proportions of soil, grass, and feed in dry-matter intake.

In the initial screening process to select contaminants for detailed risk assessment, biosolids intake by livestock was assumed to be 5% of diet (presumably dry matter), even though intake could be 10% from a combination of adherence to forage crops and direct ingestion of treated soil (EPA 1985). In the pathway-specific risk assessments used to develop the Part 503 rule, EPA (1992a) assumed that 1.5% of a grazing animal’s diet is biosolids. That value was based on the assumption that biosolids are applied to pasture once every 3 years and that biosolids intake is 2.5% of diet in the year of application and 1% in the other 2 years.

Assumptions about pollutant intake due to biosolids should be based on estimated pollutant concentrations in soil, pollutant uptake into crops, soil intake by livestock, and the relative bioavailability of the pollutant in soil relative to the bioavailability in forage. The proportion of biosolids in ingested soil is variable, depending on the type and form of biosolids application, climate, grazing habits, percent of time spent in pasture, percent of diet obtained from pasture, season, and management conditions. Soil ingestion by cattle feeding on pasture can range from 1% to 18% of the diet, depending on the growing season and climate (Fries 1995), and sheep might ingest as much as 30%, depending on the seasonal supply of grass and grazing management

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

(Thornton and Abrahams 1983). On average, soil is estimated to comprise about 6% of the total dry matter intake of most grazing stock (Fries 1995; Wild et al. 1994). In risk-assessment documents, EPA (1998, 2000b, 2001a) assumed that soil ingested by cattle averages 4% of diet dry matter, and soil ingested by dairy cattle averages 2–3% of diet, because dairy cows spend less time in pasture. For uptake of pollutants from soil into animal tissue, a relative bioavailability factor is needed to adjust for differences in the relative bioavailability of a chemical in soil as compared with that in forage. In 1998, EPA suggested using a default assumption of 1 (no difference in bioavailability) in the absence of more specific supporting data. In risk assessments for dioxins (EPA 2000b, 2001a), default values of less than 1 were used (e.g., 0.65 for the relative bioavailability of dioxins in soil to cattle). In the Part 503 rule risk assessment, bioavailability was calculated as the geometric mean of values obtained from research literature. The appropriate statistic to use should be selected in the context of characterizing RME exposures.

In addition to direct ingestion of biosolids applied to soil, biosolids sprayed onto forage adhere to plant surfaces. It is important that pollutants in biosolids sprayed onto and adhering to crops be included in the forage chemical concentrations.

Air Concentrations

Exposure to biosolids pollutants in air is considered in Pathway 11 (airborne dusts) and Pathway 13 (volatilization from soil). Critical parameters that influence air concentrations of pollutants, such as wind velocity and temperature, should be reconsidered. EPA (1992a) used a “typical” windspeed of 4.5 m/s in its risk assessments, but data from the National Oceanic and Atmospheric Administration (NOAA 2000a) show that at 115 of 275 locations in the United States for which long-term data are collected, average annual windspeeds exceed 4.5 m/s. For air temperature, EPA used a national annual average of 15°C, but average daily temperatures are higher than that for approximately one-third of the United States (NOAA 2000b). The revised risk assessment for dioxins in biosolids (EPA 2001a) addressed regional differences by relying on a database that divides the country into 41 distinct regions on the basis of climate and other factors. Meteorological data from each region were used in the risk assessment to predict a distribution of annual average air concentrations. Whether average values are appropriate in assessing risks is subject to question; however, the use of regional data as part of a probabilistic assessment is a useful approach.

Biosolids are generally spread during the growing season and not under winter conditions. Therefore, warmer temperatures and higher rates of volatil-

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

ization would be expected at the time biosolids are applied. This issue will be particularly important in the valuation of short-term exposures. For these exposures, risks posed under high-wind and high-temperature conditions should be assessed.

Surface-Water Concentrations

Calculations of the concentration of contaminants in surface water rest on several assumptions, including watershed ratio, contaminant load from sediments, and dilution. EPA’s risk assessment for Pathway 12 (human drinking water and ingesting fish from surface water contaminated by biosolids) assumed that the biosolids-amended area is 1,074 ha, which is based on data from the NSSS (90th percentile for the size of agricultural areas used by publicly owned treatment works). The water body for which risks were assessed was assumed to have a watershed of 440,300 ha (mean watershed size for the United States), an area greater than the size of Rhode Island and representing a fifth- to sixth-order stream. Only 0.24% of the watershed is thus assumed to receive biosolids. EPA (1998) protocol suggested that the impacts on farm ponds be assessed, because the farm family might be exposed through fishing and swimming. In the EPA (2001a) reassessment of risks for dioxins in biosolids, a much smaller, third-order stream was assumed, and chemicals were assumed to enter the stream via wet and dry deposition from air and via runoff and erosion from the local (farm with agricultural fields and a buffer zone) and regional watersheds. It is not clear, however, what proportion of the watershed was assumed to receive biosolids.

In the original assessment of exposures from surface water, EPA assumed that the entire watershed is agricultural and that soil loss is the same throughout the watershed. It is also assumed that all pollutants in the receiving stream are from biosolids and that no other pollutants enter the stream. For a watershed as large as that postulated, significant portions are likely to be forested areas that have lower erosion rates than agricultural areas, and other areas will be paved, increasing storm runoff and erosion. Thus, a higher proportion of the sediment in receiving water would be from agricultural areas, including those amended with biosolids. For a large watershed, other sources of pollutants would be expected.

The Part 503 rule risk assessment used an average soil loss estimated from agricultural lands of 8.5 metric tons (mt)/ha-y. This rate appears to be low, as the average annual soil loss has been measured to be 3.57±5.64 kg/square meters, and loss of 8.5 mt/ha-year was below the 50th percentile for measured rates (Risse et al. 1993). Sand was used as a worst-case soil type in the Part 503 risk assessment. Although sand would be a worst case for leaching, it

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

would not necessarily be that for erosion (Brady and Weil 1999). Also, no consideration was given to heavy rainfall events. Many of these issues could be appropriately addressed by using a probabilistic surface-water model.

In estimating the amount of pollutant available via surface water, the total concentration in biosolids is reduced by estimating the fractions lost through leaching, volatilization, and degradation (see earlier discussion of mass balance). The eroded material, thus adjusted, is assumed to be biosolids diluted with soil because of tilling into the top 15 cm of soil. For surface application, such as that on pastures or in conservation tillage scenarios, that assumption would not be valid. In the draft revaluation of dioxins in biosolids, EPA (2001a) assumed that over time biosolids are mixed with the top 2 cm of soil in pastures; however, it is not clear whether or how this assumption was incorporated into the runoff and erosion model.

Groundwater Concentrations

Prediction of groundwater concentrations that might result from biosolids application requires modeling and making assumptions about critical parameters, such as the partition coefficient, leaching, and dilution and attenuation. Partition coefficients are used in the Part 503 rule risk assessment to estimate the proportion of a contaminant that dissolves and is thus leachable. Partition coefficient values for the regulated contaminants were taken from the work of Gerritse et al. (1982), who studied only one type of biosolids and several soil types. Recent studies suggest that processing methods for biosolids have an influence on metal mobilities (Richards et al. 1997, 2000), as does pH and soil type. A single partition coefficient based on a single type of aerobically digested biosolids and on a sandy loam soil of pH 8 was used for each contaminant in the risk assessment. Some contaminants, such as cadmium, show much greater movement at lower pH and in sands. Thus, the partition coefficients used by EPA are not necessarily representative of the range of conditions that exist in the United States.

Leaching calculations are based on a model of contaminant movement through soil. However, there are several limitations of the model used, including failure to account for rapid transport through preferential flow paths and for facilitated transport of contaminants in association with organic constituents (McCarthy and Zachara 1989). For a number of inorganic and organic contaminants, evidence indicates that leaching might be greatest immediately after application (Beck et al. 1996; Richards et al. 2000). More accurate modeling is needed to estimate rates of leaching. Soil-screening guidance (EPA 1996b) pertaining to groundwater impacts from leaching suggests a dilution

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

and attenuation factor (DAF) of 1 or 20 in initial screening evaluations. EPA noted that those values can be used at sites with shallow water tables, fractured media, or karst topography. However, in the Part 503 rule risk assessment, much higher dilution factors appear to have been used. In the example given by EPA, a DAF of 152 was used in evaluating arsenic in groundwater.

Groundwater conditions vary greatly throughout the United States. For the Part 503 rule to be applicable nationwide, reasonable worst-case scenarios, such as areas with karst or gravel conditions, need to be evaluated. Groundwater was not evaluated in the reassessment of dioxins in biosolids (EPA 2001a), because dioxins are unlikely to leach to groundwater to an appreciable degree; however, the regional climate and soils database developed for that risk assessment could be adapted to support a more robust groundwater model.

Human Intake Parameters

Assumptions regarding the intake behavior and characteristics of the human receptor should be updated using the most recent EPA (1997) guidance on exposure factors (see Chapter 4 for more details), as well as newly published studies. One broad issue for both deterministic and probabilistic risk assessment applies to many of the intake parameters. This issue is the reliability of identified distributions and upper percentile values for many intake parameters estimated from short-term studies with observations occurring over a period of days (EPA 1997). Upper percentiles identified in such studies are values for short-term intakes only. It is not appropriate to apply these values to represent variability in chronic intakes without assessing the potential for bias due to short survey periods (Wallace et al. 1994; Buck et al. 1997). A number of factors contribute to overestimation bias in the upper percentiles of such distributions (Chaisson et al. 1999). The various approaches proposed to correct these biases (Wallace et al. 1994; Buck et al. 1997; Chaisson et al. 1999) should be considered prior to using biased distributions or upper percentile values in risk assessments. If the biases cannot be corrected, use of extreme upper percentile values should be avoided, and the impact of the biases should be examined in an uncertainty assessment. This issue is an important consideration in assessing intakes of soil, food, and water. The potential impacts are described in greater detail below for soil ingestion. The uncertainty and variability associated with many of these parameters might be characterized by using probabilistic risk-assessment approaches (Stern 1993).

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Some important parameters and special considerations that should be given to biosolids exposures are duration of exposure, bioavailability, soil ingestion, dietary intake of vegetables and animal products, water consumption, inhalation rate, and body weight.

Duration of Exposure. Default assumptions about length of residence are based on data on the amount of time people reside in one home. Data on length of residence in one location vary among different populations. Farm residents have an average residence time nearly four times that of other households (Israeli and Nelson 1992). In performing a risk assessment pertaining to land application of biosolids, the human receptor for many of the exposure pathways is a farm family member. Residence times also vary regionally, the northeastern region having residence times nearly twice those in the western United States (Israeli and Nelson 1992).

Bioavailability. The relative bioavailability of individual chemicals to human receptors can vary with exposure medium and should be accounted for in risk assessments if sufficient supporting data are available (EPA 1989). Soil-ingested chemicals typically are less bioavailable than soluble forms of drinking-water-ingested chemicals (NEPI 2000a,b). Even for a given exposure medium such as soil, many factors can affect relative bioavailability, including the characteristics of the biosolids matrix and the form of the contaminant (e.g., metal salt and organic complex). The contaminant’s form and relative bioavailability can change over time and with environmental conditions. The Part 503 rule risk assessment did not make adjustments to reflect differences in the relative bioavailability of chemicals in different exposure media. There is no EPA guidance regarding relative bioavailability, but the default assumption is typically 1.0. The reassessment of dioxins in biosolids (EPA 2001a) is silent on this issue.

Soil Ingestion. Incidental soil ingestion by children and adults is assumed to occur primarily from adherence of fine soil particles to hands or objects that are subsequently placed in the mouth (EPA 1997). In the Part 503 rule risk assessment, soil ingestion was considered only for children, who were assumed to ingest 200 mg/day of pure biosolids for 5 years. It was calculated as the most limiting pathway for four of the regulated contaminants. This pathway should be revised to use estimated soil concentrations rather than biosolids concentrations and should use the same exposure duration as other exposure pathways. Estimates of soil intakes should include intakes by teenagers and adults and particularly for home gardeners and farm family members, whose ingestion of soil might be relatively high.

The assumption that children ingest 200 mg of soil per day is consistent with current EPA guidance that describes this value as a conservative estimate of the mean (EPA 1997). More recent studies suggest that this value might

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

exceed a 95th percentile for long-term average daily exposure (Stanek and Calabrese 2000; Stanek et al. 2001). Reported upper percentiles in soil-ingestion studies typically represent the upper percentiles among the observations reported for all subjects during a short study period (e.g., among 64 children observed for 7 days). Estimates of true average 95th percentile soil ingestion over longer periods might be much lower (Table 5–8). It is critical that new, more reliable information on the distributions of soil ingestion be considered in new risk assessments.

Pica behavior for soil was considered in the screening process to select chemicals for regulation, but the child with pica was not used as a receptor in the risk assessments. There is no evidence that geophagia occurs routinely in children over long periods; however, many children might occasionally ingest 1–10 g or more of soil (EPA 1997). This finding suggests that consideration of pica behavior is most important when assessing acute exposures (EPA 1997).

The average amount of soil ingested by adults was estimated to be 10 mg/day (Stanek et al. 1997). EPA recommended that 50 mg/day be used as a “reasonable central estimate of adult soil ingestion” (EPA 1997); however, the estimate was based on an earlier study by Calabrese et al. (1990) and did not include this group’s more recent analysis (Stanek et al. 1997). Given the high degree of uncertainty in soil-ingestion data, EPA should make further research on soil ingestion among children and adults a high priority. Probabilistic assessments might also be useful for characterizing uncertainty and variability of this parameter.

Dietary Intake of Vegetables. The risk assessment of vegetable intake evaluated risks based on an average nonmetropolitan diet around 1980 (USDA 1982). A limitation of the 3-day food-consumption survey in this study is that 3 days is insufficient to ascertain typical dietary intake (Anderson 1986) and is likely to overestimate long-term average upper-percentile intake. Vegetable consumption varies greatly, and surveys suggest that vegetable intake has been increasing in the general population (EPA 1997). Biosolids exposure of the vegetarian home gardener would be a reasonable maximum exposure. Data used by EPA in its risk assessment for developing the biosolids standards show that farm households on average consume 2.5 times more vegetables than the nonmetropolitan population (EPA 1997). Consumption also varies within a particular population. Unfortunately, no data could be found that address vegetarians who would be expected to have high rates of intake. Consideration should also be given to regional differences in production and assessment of the fraction of homegrown and nonhomegrown crops that are grown on biosolids-amended soils for the RME receptor.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–8 Estimates of True Average 95th Percentile Soil Ingestion for Children Over Various Time Periods

 

95th Percentile Soil Ingestion Per Day (mg)

Time (days)

Anacondaa

Amherstb

1

141

210

7

133

177

30

112

135

90

108

127

365

106

124

aStudy of 64 children aged 1–4 years residing in Anaconda, MT; mean soil ingestion =31 mg/day.

bStudy of 64 children aged 1–4 years residing in Amherst, MA; mean soil ingestion= 57 mg/day.

Source: Data from Stanek and Calabrese 2000.

Dietary Intake of Animal Products. The risk assessment of animal-product intake (not including poultry or eggs) is based on an average nonmetropolitan diet from around 1980 (USDA 1982) and is limited by its short-term surveys that do not adequately predict long-term average upper-percentile intake. Consumption of animal products varies greatly. An RME receptor would be represented by a livestock farm family consuming home-raised products (meat, poultry, and dairy). Data show that those households consume far more animal products than the average nonmetropolitan consumer. Farm resident mean meat intake is approximately four times that of nonmetropolitan residents, and mean dairy intake is approximately nine times greater for farm residents (EPA 1997). Consideration should be given to the assumptions made for the RME receptor about the fraction of the animal products coming from animals exposed to biosolids.

Water Consumption. Water-consumption rates should reflect more recent studies and account for variations in expected activity and climate. The study that forms the basis for EPA’s default water-ingestion rates was conducted over 20 years ago. Consequently, the distribution of tap-water-ingestion rates used in the model does not reflect expected reductions in tap-water ingestion because of increases in consumption of soft drinks and bottled water. An analysis based on a 1994–1996 food consumption survey suggested as much as a 30% drop in mean tap-water consumption during the last two decades (EPA 2000c). In addition, the tap-water-intake data reported by Ershow and Cantor (1989) were collected for only a 3-day period; therefore, the extrapolation to chronic intake is uncertain, particularly for the upper percentiles (EPA 1997).

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Inhalation Rate. Assumptions about inhalation rates should be based on the specific RME receptor and likely activities by the receptor during exposure. Assessment of acute exposures should reflect the higher inhalation rates that may be sustained for shorter periods, whereas assessment of chronic exposures should reflect the variation in average population breathing rates over longer periods. Age-related variations in inhalation rate should also be part of the evaluation.

DERIVATION OF RISK-BASED STANDARDS

The risk assessment conducted to support the Part 503 rule was designed to support the development of risk-based standards—that is, to identify concentrations of specific chemicals in biosolids that could be applied to land in the manner specified by the rule without posing unacceptable risks. Four types of standards were developed: (1) cumulative pollutant loading rates, (2) annual pollutant loading rates, (3) pollutant concentration limits, and (4) ceiling pollutant concentration limits. A deterministic approach was used to calculate the various standards (see Table 5–9) for the nine regulated metals. EPA identified an allowable dose for each chemical as a starting point and then used pathway-specific algorithms that incorporate a number of exposure parameters (discussed previously in this chapter) to calculate the biosolids standards. The exposure pathway with the lowest pollutant limit was considered the “limiting” pathway, and this lowest value was used to establish the cumulative pollutant loading rates, annual pollutant loading rates, and pollutant concentration limits. The ceiling concentration limits were set at either the 99th percentile level found in the NSSS or the risk-based number, whichever was greater. The major aspects of the process are discussed below.

Toxicity Assessment

The starting point of EPA’s calculations was to identify a chemical dose that is not expected to cause unacceptable adverse effects in humans. For most of the chemicals, the starting point was an EPA-established measure of either toxicity (reference dose [RfD] or reference concentration [RfC]) or carcinogenicity (cancer potency value [q1*]). For two chemicals, copper and zinc, a recommended daily allowance (RDA) was the starting point. This was done for copper, because EPA has not established toxicity or carcinogenicity values for it. An RfD is available for zinc, but that value was considered insufficient to meet daily nutritional requirements, so the higher RDA value

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–9 Pollutant Concentration Limits and Loading Rates for Land Application in the United States, Dry Weight Basis

Contaminant

Ceiling Concentration Limit (mg/kg)

Cumulative Pollutant Loading Rate Limit (kg/ha)

Pollutant Concentration Limit (mg/kg)

Annual Pollutant Loading Rate (kg/ha-yr)

Arsenic

75

41

41

2.0

Cadmium

85

39

39

1.9

Copper

4,300

1,500

1,500

75

Lead

840

300

300

15

Mercury

57

17

17

0.85

Molybdenuma

75

Nickel

420

420

420

21

Selenium

100

100

100

5.0

Zinc

7,500

2,800

2,800

140

aStandards for molybdenum were dropped from the original regulation. Currently, only a ceiling concentration limit is available for molybdenum, and a decision about establishing new pollutant limits for this metal has not been made.

Source: 40 CFR Part 503.

was used (EPA 1992a). None of the regulated contaminants were assessed as carcinogens.

All the starting points are based on chronic exposure scenarios. EPA risk assessments typically focus on chronic exposures, because long-term exposure is generally a more sensitive end point than acute or short-term exposures. (The use of chronic toxicity data will yield a lower or more protective standard.) EPA periodically reviews the literature and updates the dose-response assessments for individual chemicals. Thus, any reassessment of risks associated with land application of biosolids should include verification that the most recent toxicity values are used. Consideration should also be given to evaluating risks from short-term episodic exposures, which may be important for volatile chemicals.

Calculations

In deriving the risk-based standards, a number of calculations and algorithms were used to determine the concentration of a specific chemical that can be present in biosolids and not result in exceedance of the acceptable dose. Because EPA’s acceptable doses include consideration of chemical

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

exposures to the evaluated inorganic contaminants from all sources, the first step was to determine the dose of the chemical from biosolids alone by subtracting total background in take (TBI) of a chemical from the EPA-established acceptable dose. The adjusted health parameter was then used in algorithms specific to each exposure pathway. The algorithms incorporated pathway-specific information and assumptions regarding chemical intake, such as plant uptake of the pollutant, to derive a pollutant limit. In most cases, calculation of the pollutant limit involved two or more algorithms.

Target Risks

Selection of target risks is a policy decision made by EPA. For carcinogens in biosolids, EPA used a target incremental cancer risk of 1 in 10,000 (1 ×10−4), the high end of the 1×10−6 to 1×10−4 risk used by EPA in establishing various regulations. For noncancer health effects, a hazard index of 1 (the ratio of the predicted exposure either to the threshold dose for toxicity or to the predicted cancer risk) was used. It was beyond the committee’s charge to assess the adequacy of target risks used to derive risk-based standards; however, actual risks might be substantially less than the target risks, because in many cases the concentrations of the regulated contaminants in biosolids are generally less than the regulatory limits.

In developing the Part 503 rule, EPA sought to develop one standard for each chemical that would be protective in all circumstances that could be reasonably anticipated to occur. Thus, a standard derived for use nationwide must provide adequate protection for all reasonably anticipated environmental conditions, biosolids types, and application practices anywhere that biosolids application might occur. This goal necessitates assessing risks for exposure conditions that might occur anywhere in the United States.

The Part 503 rule standards were derived to be protective for land application in accordance with the regulations. Exposures that might occur due to failure to comply with the regulations were not considered during the development of the biosolids standards. An assessment of risks associated with noncompliance is an enforcement issue and is not related to a determination of the adequacy of the methods used to derive risk-based standards. Noncompliance associated with risk assessment is thus beyond the scope of this report.

INORGANIC CHEMICALS

In light of the advances made in risk-assessment methods discussed in Chapter 4 and the need to update many of the exposure parameters used in

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

the risk assessment process, the existing biosolids standards for inorganic chemicals clearly need to be reevaluated. As noted in Chapter 2, average concentrations of some regulated inorganics in biosolids decreased substantially throughout the 1980s and early 1990s, and have stabilized since that time (see Tables 2–23 and 2–24). Recent survey data from Pennsylvania that includes 95th percentile values, as well as median values, suggest that in Pennsylvania, and perhaps in other states, pollutant limits will only rarely be exceeded for most inorganics (Table 5–10).

In order to assess the potential impacts of reevaluating the standards, it is instructive to compare the pollutant limits for biosolids with current risk-based soil screening levels (SSLs) for residential scenarios. Such a comparison is predicated on the assumption that inorganic chemical concentrations in soil to which biosolids are added will never exceed the pollutant limits. EPA (1995) has projected that at such time as the cumulative loading rate (kg/ha) has been achieved, the risk-based limit of acceptable soil concentration (mg/kg) will also have been reached and would be 50% of the cumulative loading rate, plus the initial background concentration of the pollutant. As can be seen from Table 5–11, most of the pollutant limits are lower (i.e., more conservative) than the EPA residential SSLs based only on dermal and direct ingestion pathways.

A limitation of such a comparison is that the residential SSLs are based on exposures via a limited number of exposure pathways, including soil ingestion, dermal contact with soil, and inhalation of resuspended particulates. The SSLs may not be adequately protective for chemicals for which other exposure pathways may be especially important. This limitation is of particular concern for cadmium, due to potential uptake into plants, and for mercury, due to the potential for mercury entering surface water via runoff from soil to be converted to methylmercury and bioaccumulated in aquatic organisms. For this reason, Table 5–11 also shows risk-based screening levels developed by the British (UK Environment Agency 2002) that include consideration of home garden exposure. The importance of differing assumptions in assessing risk is pointed out by comparing the UK and EPA values (columns 2 and 3), which for some elements are significantly different. The potential impact of including the plant uptake pathway on risk-based soil concentrations for some pollutants (e.g., cadmium) is demonstrated by comparing the values in columns 3 and 4 of Table 5–11.

In addition to SSLs based on exposure pathways involving direct contact with chemicals, EPA has also devised soil SSLs for the protection of groundwater (EPA 2001b). A comparison of selected pollutant concentration limits

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–10 Median and 95th Percentile Trace Element Concentrations in Pennsylvania Sewage Sludge Produced in 1996 and 1997 Compared with Limits Contained in the Part 503 Rule

Trace Element

Concentration in Sewage Sludge (mg/kg)

Pollutant Concentration Limit (mg/kg)

Median

95th Percentile

Arsenic

3.60

18.7

41a

Cadmium

2.26

7.39

39a

Chromium

35.1

314

1,200b,c

Copper

511

1,382

1,500c

Mercury

1.54

6.01

17a

Molybdenum

8.18

36.0

18b,d

Nickel

22.6

84.5

420c

Lead

64.9

202

300a

Selenium

4.28

8.47

100a

Zinc

705

1,985

2,800c

aBased on risks for child eating biosolids.

bThe current Part 503 rule does not include chromium, and there is no cumulative pollutant loading limit or pollutant concentration limit for molybdenum. The values given in this table were included in the original Part 503 rule.

cBased on plant phytotoxicity.

dBased on animal eating feed.

Source: Adapted from Stehouwer et al. 2000.

in biosolids with U.S. background soil concentrations and soil screening levels for groundwater are presented in Table 5–12.

A comparison of the biosolids pollutant limits with risk-based SSLs suggests that the pollutant standards are adequately protective for some exposure pathways (i.e., soil/biosolids ingestion) but may need to be reevaluated for others (i.e., ingestion of homegrown produce grown on biosolids-amended soil). In this section, two factors that are important for assessing human exposure to inorganic compounds and their toxicity—bioavailability to human receptors and metal speciation—are discussed. Other factors—plant uptake of metals and bioavailability of metals to plants—were addressed earlier in the section on exposure parameters. The general discussion is followed by a description of issues specific to several of the regulated metals.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–11 Pollutant Concentration Limits in Sewage Sludge Compared with Risk-Based Soil Concentrations (Italic numbers represent risk-based soil concentrations below the Part 503 rule pollutant concentration limits.)

Trace Element

Part 503 Pollutant Concentration Limita (mg/kg DW)

EPA Residential SSLs (ingestion and dermal) (mg/kg DW)

UK Residential SGVs (ingestion), without plant uptakeb (mg/kg DW)

UK Residential SGVs (ingestion), with plant uptakec (mg/kg DW)

Arsenic

41

0.4 (40)d

20

20

Cadmium

39

70

30

1 (pH 6)

2 (pH 7)

8 (pH 8)

Chromium

NAe

230/120,000f

200g

130g

Lead

300

400

450

450

Mercury

17

23/10h

15

8

Nickel

420

1,600

75

50

Selenium

100

390

260

35

aPollutant concentration limits for biosolids based on human health risks, except for nickel (plant phytotoxicity).

bHouse or apartment with no private garden area.

cHouse with a garden with the possibility of ingestion of homegrown vegetables.

dArsenic SSL is 0.4 mg/kg based on a 1 in 1,000,000 cancer risk. Value of 40 in parentheses reflects the cancer risk of 1 in 10,000 used for the Part 503 rule.

eChromium was deleted from the Part 503 rule because of a court suit.

fChromium SSL assumes that all chromium is Cr(VI). Value for Cr(III) is 120,000.

gThe UK SGV for chromium assumes that all chromium is CR(VI).

hMercury SSL is based on the reference dose for mercuric chloride. SSL for inhalation is 10 mg/kg.

Abbreviations: DW, dry weight; NA, not applicable; SGV, soil guideline value; SSL, soil screening level; UK, United Kingdom.

Sources: 40 CFR Part 503; EPA 2001b; UK Environment Agency 2002.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–12 Pollutant Concentration Limits in Biosolids Compared with Background Concentrations and Soil Screening Levels for Groundwater

 

Background Concentrationsb

SSL for Groundwaterc

Trace Elements

Part 503 Pollutant Concentration Limit (mg/kg DW)a

Arithmetic mean (mg/kg)

Geometric mean (mg/kg)

Geometric standard deviation (mg/kg)

Range (mg/kg)

DAF=20 (mg/kg)

DAF=1 (mg/kg)

Arsenic

41

7.2

5.2

2.23

<0.1–97

29

1

Cadmium

39

0.02–1.67d

0.175

2.70

ND-11d

8

0.4

Chromium

NAe

54

37

2.37

1–2,000

38f

2f

Lead

300

19

16

1.86

<10–700

-g

-g

Mercury

17

0.09

0.058

2.52

<0.01–4.6

2

0.1

Nickel

420

19

13

2.31

<5–700

130

7

Selenium

100

0.39

0.26

2.46

<0.1–4.3

5

0.3

aCFR 40 Part 503. Pollutant concentration limits for biosolids based on human health risks, except for nickel (plant phytotoxicity).

bData for U.S. soils, Shacklette et al. 1984.

cEPA 2001b.

dRange of means reported in Dragun and Chaisson (1991) for various states and soil types. Single U.S. mean not reported.

eChromium was deleted from the Part 503 rule because of a court suit.

fSSL for total Cr and Cr(VI). This pathway is not of concern for Cr(III).

gA screening level of 400 mg/kg has been set for lead.

Abbreviations: DAF, dilution attenuation factor; NA, not applicable; ND, not detected; SSL, soil screening level

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Bioavailability to Humans

The term “bioavailability” may have different meanings in different contexts. In the context of human exposures to chemicals in environmental media, bioavailability is the degree to which a chemical present in an environmental medium is capable of being absorbed into the systemic circulation. Bioavailability depends on the release of the chemical from the medium and the absorption efficiency of the released chemical. Oral toxicity assessments of metals are often based on studies in which a metal salt is dissolved in water or mixed with food. If the toxicity factors (reference doses and cancer slope factors) used in risk assessments in soil or other heterogeneous exposure media are based on studies using soluble forms of the metals, the impacts of soil exposures could be overestimated.

Reduced absorption of metals from biosolids-amended soils ingested by human receptors might be due to sorption and precipitation reactions of the metals with soil components, such as metal oxides and humic substances, and due to the presence of metals in compounds with limited water solubility (Ruby et al. 1999). For example, it is well established that metals, such as cobalt, manganese, nickel, and zinc, can form metal hydroxide surface precipitates on metal oxides, clay minerals, and soils. The formation of these surface precipitates significantly reduces the release of the metal, even when strong acids and complexing organic ligands are used as dissolution agents (Scheidegger et al. 1997, 1998; Ford et al. 1999; Scheckel et al. 2000). Arsenic, lead, mercury, and nickel also occur in soils in compounds exhibiting a wide range of water solubility. Thus, metal dissolution from ingested soil could be limited during movement through the gastrointestinal tract. Accordingly, absorption will be reduced, as the major mode of absorption of many metals is passage of dissolved metal species across the small intestine epithelium (Whitehead et al. 1996).

Risk-assessment guidance from EPA (1989) acknowledges the need to make adjustments in exposure assessments to account for differences in relative bioavailability between the exposure medium in toxicity studies and the exposure medium in risk assessments. These adjustments for reduced bioavailability of chemicals from such media as soils are typically termed relative absorption factors (RAF). RAFs typically take the form of a fractional adjustment in the exposure algorithms used to estimate intake or dose.

In the Part 503 risk assessment, EPA considered making such adjustments for relative bioavailability (using the term ”relative effectiveness“) but concluded that available data were inadequate to support default adjustments for the metals being evaluated. During the past decade, substantial research better characterizing the occurrence of reduced metal bioavailability in soils has been

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

published (NEPI 2000a). Reduced metal bioavailability in biosolids-amended soils is very likely, and several laboratories have active research programs on the use of biosolids amendments as a method of reducing metal bioavailability in contaminated soils (Basta and Sloan 1999; Henry and Brown 1997).

Metal Speciation and Availability

The lack of direct information on the speciation of metals and metalloids in biosolids and soil-biosolids mixtures complicates attempts to assess both toxicity and bioavailability of these chemicals. Although a great deal of information on metal contents of biosolids and soils exists, the total content is not indicative of the forms or species of the metals. For several of the regulated metals, toxicity varies with different forms of the metal, and it is important to distinguish differences in the nature of toxicity from differences in solubility and bioavailability of different metal forms.

Mercury may be present in three forms with varying toxicity (i.e., elemental mercury, inorganic mercury compounds, and methylmercury). The exposure routes of concern are different for the different mercury forms. Inhalation is the primary route of exposure to elemental mercury released from soil, and ingestion is the exposure route of concern for inorganic and methylmercury. Consequently, for evaluation in risk assessment, the forms of mercury in soil and other exposure media must be known or assumptions must be made regarding the forms present. Arsenic compounds also exhibit marked variation in toxicity. The organic forms are practically nontoxic, and inorganic forms are quite toxic. Typically, only inorganic arsenic compounds are assumed to be present in soil, but for the reasons described below, that assumption might not apply to biosolids. In contrast, the toxicity of inorganic cadmium and lead compounds expected to be present in biosolids does not vary, although solubility and bioavailability can be highly variable.

Most bioavailability studies of metals in soil have relied on animal species that have anatomical and physiological characteristics different from humans. Only a few studies have assessed metal absorption from ingested soil by humans. The relative bioavailability of metals in soil is dependent on speciation of the metal, size distribution of soil particles, and composition of the soil.

Chemical extractions (e.g., sequential extractions) can provide some information on the extraction ease, such as readily exchangeable or occluded from various phases, but the order of extractions and extractants that are used can create artifacts. Such extractions also do not mimic dissolution rates likely to occur in the human gastrointestinal tract. Sequential extractions do not provide direct speciation analyses. For example, many metals can exist as inor-

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

ganic and organic species and in multiple oxidation states and can be associated with multiple solid phases (e.g., metal oxides, phyllosilicates, and humic substances). Metals primarily form strong inner-sphere chemical bonds with metal oxides, clay minerals, and humic substances that substantially restrict their mobility in natural environments. Moreover, with time, metals can undergo transformations with soils that often render them less prone to leaching. In laboratory experiments, such metals as nickel and zinc can form surface precipitates on soils, aluminum oxides, and clay minerals that transform over time to more stable mixed metal hydroxide phyllosilicate phases. Some fraction of the metals is sequestered even with treatment with acids and organic ligands, such as ethylenediaminetetraacetate (Scheidegger et al. 1997, 1998; Ford et al. 1999; Roberts et al. 1999; Scheckel et al. 2000; Scheckel and Sparks 2001). Furthermore, metal speciation, and thus bioavailability, is not static in the natural environment. Changes may result from weathering reactions and microbiological activity in soils (Hooda and Alloway 1994; Sadovnikova et al. 1996; Basta and Sloan 1999; Kamaludeen et al. 2001).

The speciation of metals and metalloids in biosolids and biosolids-amended soils is critical in determining the mobility and bioavailability of the toxic metals (Ruby et al. 1999). In the last decade, important advances have occurred in the use of in situ molecular-scale techniques that can provide direct information on chemical speciation of metals and metalloids in model systems, such as metal oxides and clay minerals, and in soils. One major innovation has been the use of synchrotron-based spectroscopies, such as x-ray absorption fine-structure spectroscopy (XAFS), to determine oxidative states and local chemical environment of metals and metalloids at natural particle interfaces. Thus, metal species in heterogeneous materials can be determined in the presence of water without having to dry the sample and subject it to desiccation. Numerous studies have appeared in the scientific literature on the application of XAFS and other in situ spectroscopic techniques to speciate metals in natural systems. Recent changes are the use of micro-focused XAFS and micro-x-ray fluorescence spectroscopy to speciate and map metal distributions in soils (Manceau et al. 2000; Roberts 2001). With these techniques, an area of square microns can be chemically mapped and the chemical associations of various metals can be determined, certain spots can be zoomed in on, and via XAFS data analyses, the species of the metals at different locations can be determined. In addition, the quantitative associations of the metals with various components of the solid can be determined (e.g., metal oxides, clays, and humic substances). Scientists have applied micro-XAFS and micro-x-ray absorption near-edge structure (XANES) to phosphorus and arsenic speciation in poultry-litter and poultry-litter amended soils (Arai and Sparks 2001; Peak et al. 2001), both extremely heterogeneous

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

materials. Biosolids-applied soils will also be heterogeneous in regard to the distribution of biosolids-borne metals. Application of such techniques to biosolids would allow for direct speciation of the metals and metalloids and a better understanding of the mechanisms affecting bioavailability.

Regulated Metals and Metalloids

The inorganic chemicals regulated on the basis of human health (specifically risks to children from direct ingestion of biosolids) are arsenic, cadmium, lead, mercury, and selenium. Specific issues to consider in updating the risk assessments for the first four of these metals are described below.

Arsenic

The primary issue related to arsenic is EPA’s treatment of arsenic in soil as noncarcinogenic in the Part 503 rule risk assessment. However, ingestion of inorganic arsenic in drinking water is an established cause of skin cancer, and recent studies strengthen the evidence that arsenic can also cause cancers of the lung and urinary bladder (NRC 1999, 2001). In the Part 503 rule risk assessment, EPA justified using the arsenic reference dose on the grounds that there was no evidence that soil arsenic is carcinogenic. Although that assertion is true, there is no evidence that arsenic absorbed into the body from ingested soil and arsenic absorbed from drinking water behave any differently. Consequently, current EPA risk-assessment practice is to treat inorganic arsenic in all media as potentially carcinogenic.

However, if arsenic is treated as a carcinogen, it will be necessary to confirm that it is present in biosolids as inorganic arsenic rather than organic forms that are much less toxic and noncarcinogenic. As with many toxic metals and metalloids, the speciation of arsenic in biosolids is not well characterized. Although organic arsenicals are generally not present in soils in measurable quantities, the extent of their presence in biosolids is not known. Thus, the forms of arsenic present in biosolids should be assessed, and only the fraction that is inorganic should be regulated.

Total arsenic in soils has been reported to range from 0.1 to 97 ppm with an arithmetic mean concentration of 7.2 ppm and a geometic mean of 5.2 ppm for surface soils in the United States (Shacklette and Boerngen 1984). Gustavsson et al. (2001) reported that U.S. soils have a mean arsenic concentration of 5.57 ppm, and 25th and 75th percentile concentrations of 4.21 ppm and 7.06 ppm, respectively. Arsenic occurs in two major oxidative states,

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

arsenous acid (AsIII) and arsenic acid (AsV). AsIII is primarily present in anoxic environments, and AsV is found in oxic soils. Both arsenic species occur primarily as oxyanions in the natural environment and strongly complex with metal oxides, such as aluminum and iron oxides, as inner-sphere products. These oxides, and particularly manganese oxides, can affect oxidation of AsIII to AsV, which reduces the toxicity of arsenic. Arsenic can also occur as sulfide minerals, such as arsenopyrite (FeAsS) and enargite (Cu3AsS4), at mining sites.

There is reason to suspect that some of the arsenic in biosolids is in organic forms; however, no studies testing this hypothesis were found. Ingested inorganic arsenic is methylated and excreted primarily as monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) (NRC 2001). Farmer and Johnson (1990) examined the speciation of arsenic in urine excreted by workers exposed to inorganic arsenic compounds and found 1–6% AsV, 11–14% AsIII, 14–18% MMA, and 63–70% DMA. Most dietary arsenic is organic arsenic, and many of these organic forms are excreted unchanged in the urine. Thus, most arsenic from domestic sources in wastewater may be organic. Under certain environmental conditions, however, organic arsenic has the potential to mineralize. The possibility that biosolids-borne arsenic can be transformed from organic to inorganic forms should be evaluated. The greater water solubility of organic arsenic compounds makes it unlikely that these compounds will preferentially segregate to biosolids and makes it difficult to predict the predominant speciation of arsenic in biosolids.

Studies of the relative bioavailability of soil arsenic have been limited primarily to soils from mining and smelting sites and from arsenic pesticide manufacturing or application (NEPI 2000a; Kelley et al. 2002). Those studies yielded relative bioavailability estimates of soil arsenic of 10% to 50% as compared with bioavailability of soluble arsenic forms. It might not be practical to determine the relative bioavailability of arsenic in biosolids in animal experiments because of the low arsenic concentrations typically present in biosolids. However, in vitro approaches are available that may be used to estimate relative bioavailability of arsenic in biosolids. Ruby et al. (1999) noted that the particle-size distribution and the chemical composition of the arsenic species greatly affect bioavailability. Dissolution rates (and bioavailability) increase as particle size decreases. In vivo and in vitro studies show that for a constant particle size, soil-arsenic phases, such as arsenic sulfides and arsenic found in slag, have a lower bioavailability than iron, manganese, and lead-arsenic oxides (Ruby et al. 1999). Bioavailability data also suggest that bioavailable arsenic from soil occurs primarily from dissolution of surface-bound arsenic fractions or the exterior part of individual arsenic-containing grains rather than from complete dissolution of discrete arsenic mineral phases (Ruby et al. 1999).

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Cadmium

The most limiting exposure pathway for cadmium in the Part 503 rule risk assessment was exposure to a child from direct ingestion of biosolids. To derive concentration limits for cadmium in biosolids, EPA used the oral RfD and considered only a childhood exposure rate. However, the oral RfD is based on a lifetime accumulation of cadmium in the kidney to the point where the toxicity threshold, which is associated with toxicity to the kidney cortex, is reached. Consequently, it is more appropriate to average child and adult exposure rates over the course of a lifetime. Children are expected to ingest greater quantities of soil per unit of body weight than adults but do so over a shorter period. Thus, a safe average daily dose will typically be an average of the child daily dose for 6 years and an adult dose for 24 years or more.

Conducting a multiplepathway risk assessment that aggregates exposures from all pathways is particularly important for cadmium. Because plants take up cadmium more efficiently than most other metals, dietary cadmium is likely to be an important exposure pathway in a revised risk assessment.

A number of dietary factors are known to affect cadmium toxicity, most notably dietary deficiencies in iron, calcium, and zinc may be associated with increased cadmium body burden and toxicity (ATSDR 1999). There have also been studies demonstrating a protective effect of zinc at overtly toxic doses of cadmium (ATSDR 1999). More recent studies suggest that even when dietary cadmium intakes are only slightly increased, increased zinc intake may limit increases in cadmium body burden (Vahter et al. 1996; Reeves and Chaney 2001). Thus, it may be useful to consider predicted dietary zinc intake when evaluating predicted dietary intake of cadmium.

Lead

The bioavailability of lead in biosolids-amended soils is an important factor in assessing lead exposures. Absorption of lead in the gastrointestinal tract varies with age, diet, nutritional status, and the chemical species and particle size of lead that is ingested (Ruby et al. 1999). Adults absorb 7–15% of lead ingested by dietary means, and dietary absorption by infants and children ranges from 40% to 53% (Ziegler et al. 1978). In the Part 503 rule risk assessment, EPA used a version of the integrated exposure uptake biokinetic (IEUBK) model to assess lead exposures of children. EPA revised that model in 1994. The Part 503 rule limit for lead was also set more restrictively than the IEUBK-based value for policy reasons.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

The revised model includes a default assumption that children absorb 30% of lead from soil as compared with 50% of lead from diet and drinking water. Recent reviews have summarized studies of soil lead from many kinds of sites and show that soil lead bioavailability ranges from near zero to somewhat higher than the EPA default value of 30% (NEPI 2000a; Ruby et al. 1999). The great variability in soil lead bioavailability reflects the great variation in solubility of different lead compounds. For example, soil lead from mine sites with sulfidic ores exhibits low bioavailability, and soil lead from mine sites with carbonate ores exhibits much more bioavailability.

Dissolution rate-controlling processes are important in determining oral lead bioavailability, because lead must dissolve in the gastrointestinal tract to become bioaccessible (Ruby et al. 1992). Less-soluble lead minerals, such as lead in calcium phosphates, dissolve by surface-reaction controlled kinetics. The bioavailability of metals that dissolve via a transport-controlled mechanism is dependent on the mixing that occurs in the gastrointestinal tract, and dissolution via surface-controlled phenomena is sensitive to transit times (Ruby et al. 1999).

A number of studies have been conducted on the bioavailability of lead in biosolids to livestock. A study at the University of Maryland (1980) used 0%, 3.3%, and 10% sewage-sludge compost in diet that had lead at 215 mg/g of dry weight for 180 days. No significant change occurred in the indicator tissue lead concentrations despite the finding that fecal analyses show that the animals ingested greatly increased amounts of lead. In similar studies, Keinholz et al. (1979) found that tissue lead was significantly increased by ingesting 12% sewage sludge containing lead at 780 mg/g. These studies are suggestive of low bioavailability but do not provide quantitative information that can be used in a risk assessment.

Mercury

The speciation of mercury in land-applied biosolids is a critical factor in assessing its fate and transport. EPA assumed that mercury in soil from land application of biosolids was similar in toxicity and bioavailability to mercuric chloride, a highly water-soluble form of inorganic mercury. However, methylmercury has been shown to be present in biosolids-amended soils (Cappon 1981, 1984; Carpi et al. 1997).

The formation of methylmercury is much greater in aquatic systems owing to biomagnification in aquatic food chains. For this reason, the potential transport from application sites to surface water is of greater concern for mercury than for other metals. Several studies have also reported emission of

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

mercury vapors from biosolids. Sunlight and heat can cause reduction of HgII to elemental mercury (Hg0) and volatilization from surface soils (Carpi and Lindberg 1997, 1998; Carpi et al. 1997). That was observed when biosolids were applied to a soil in which the vegetative cover had been removed, and the biosolids were incorporated in the soils to a small depth (Carpi and Lindberg 1997; Carpi et al. 1997). Methylmercury was also shown to be emitted to the atmosphere (Carpi et al. 1997).

Other Regulated Inorganic Chemicals

Copper, molybdenum, nickel, selenium, and zinc are also regulated under the Part 503 rule. These metals are much less toxic when ingested as compared with the four metals described above, suggesting that it is appropriate that they are regulated on the basis of ecological or plant effects. Standards for copper, nickel, and zinc were based on effects on plants, the standard for selenium is based on human health, and the standard for molybdenum is a non-risk-based ceiling limit. Nickel is the most toxic to humans when inhaled, so it is important that inhalation of resuspended particulates be considered in any risk assessment for this metal.

ORGANIC CHEMICALS

Biosolids are likely to include many categories of chemicals that differ from the categories of chemicals of concern in industrial discharges. Although it is impossible to identify all of these pollutants, it is important that EPA continually think about the types of chemicals released into wastewaters and added during wastewater and sewage-sludge treatment processes as part of its process for updating the Part 503 rule. Because some organic chemicals, such as organochlorines, are persistent in the environment, consideration should be given to their tendency for trophic transfer and biomagnification, which is a longstanding public-health concern (Svensson et al. 1991). Particular attention should also be paid to chemicals that are lipophilic or that have lipophilic metabolites or degradation products, because those chemicals are more likely to partition to sewage sludge. Consideration should also be given to toxic end points that might not have been evaluated adequately in the earlier assessment (e.g., potential interactions of chemicals with the endocrine system) (Colborn et al. 1993; Safe 2000).

As discussed previously in the section Hazard Assessment and Chemical Selection, all organic chemicals considered by EPA were originally exempted

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

from regulation. In 1999, EPA proposed to add dioxins (a category of compounds that includes 29 specific congeners of polychlorinated dibenzo-p-dioxins, polychlorinated dibenzofurans, and coplanar polychlorinated biphenyls [PCBs]) to the regulation in response to its Round 2 assessment of additional chemicals to regulate under the Part 503 rule. No standard for dioxins has yet been finalized. This section reviews some of the important considerations that should be given to dioxins and other organic chemicals and provides examples of some of the types of chemical categories EPA should be assessing in the future.

Environmental Fate and Transport

A variety of factors jointly determine which organic pollutants will partition from wastewater to sewage sludge and how human receptors might come into contact with these chemicals in biosolids. These factors include treatment processes for wastewaters and sewage sludge, the concentration of the pollutant in the wastewater and biosolids, the method of biosolids application, the physicochemical properties of the chemical, and environmental conditions. Some factors that are particularly important for organic pollutants are their persistence in the environment, their potential for transport from soil to other environmental media, and their potential for uptake into plant and animal foods.

Degradation rates vary among chemicals, their half-lives ranging from days to years. For individual chemicals, degradation rates may also vary with environmental conditions, and measures of persistence may be substantially affected by the experimental design and analytical capabilities (Beck et al. 1996). It is also noteworthy that degradation of parent compound may not lead to loss of toxic potential if persistent, toxic breakdown products are formed. The breakdown of DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane) to DDE (1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) and DDD (1,1-dichloro-2,2-bis(p-chlorophenyl)ethane) is an example of this phenomenon.

Decreases in organic contaminant concentrations in biosolids-amended soils is usually not a linear function of time (Beck et al. 1996). Chlorobenzene concentrations initially decline rapidly from biosolids-amended soil, but about 10% of the residues become recalcitrant and remain in soil up to 30 years after application (Wang et al. 1995). Reports of persistence of polyaromatic hydrocarbons (PAHs) in biosolids-amended soil vary widely. In a review of the available literature, Beck et al. (1996) found one study reporting a decline in total soil PAHs of 80–100% 20 years after biosolids application and another reporting 60% of benzo[a]pyrene (a persistent PAH) remaining 30 years after

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

25 biosolids applications to a sandy loam soil. In a study of biosolids-associated di-(2-ethylhexyl)phthalate in a laboratory microcosm, approximately half remained after 1 year (Madsen et al. 1999). A study of flocculent polymers used as dewatering agents in wastewater treatment processes reported that the polymer is partially degradable under both aerobic and anaerobic conditions (Chang et al. 2001); however, no data were available on the persistence of these compounds in environmental media.

Half-lives for organic contaminants are also influenced by sewage sludge-treatment processes. For example, the half-life of linear alkylbenzene sulfonates can be over a year under anaerobic conditions, but they degrade with half-lives of 7–30 days under aerobic conditions (Cavalli and Valtorta 1999; Scott and Jones 2000). Climatic conditions, especially temperature and rainfall, also influence degradation, volatilization, and leaching rates for organic chemicals in mixtures of biosolids and soil.

Contaminants in biosolids are typically most available to plants and potentially to animals immediately after application and before degradation may have reduced concentrations. For both organic and inorganic contaminants in biosolids, the greatest potential for leaching, which may also be related to bioavailability, appears to occur immediately after application (Marcomini et al. 1988; Beck et al. 1996). Sorption of organic contaminants from biosolids to soil particles is another important determinant of mobility and availability. Soil composition and moisture interact to influence sorption capacity for organic contaminants (Chiou and Shoup 1985). In moist soils, organic matter is the dominant constituent to which sorption occurs. In dry soils, where water occupies little of clay particle surfaces, clay can absorb large amounts of organic contaminants. However, the ability of a soil to sorb organic contaminants generally increases with organic matter content. Sorbed organic contaminants may degrade by chemical, biochemical, or photochemical reactions. Desorption may occur from solid-to-solid, solid-to-liquid, or solid-to-gas phases.

Mobilization into air may be an important route for transport of organic contaminants to plants. The rate of degradation and bioavailability of organic contaminants in soils decreases with time (Alexander 2000). Sequestration into the solid phase or nanopores of soil may explain this phenomenon. This sequestration should be considered when evaluating data on total chemical concentration in soil and may be addressed by studies of relative bioavailability.

The relative importance of specific routes of exposure will vary with the organic contaminant of concern, climate, and soil type. For example, volatile chemicals will be released from soil to air, and hydrophobic, persistent organics are more likely to be retained in soil.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Dioxin and Dioxin-like Chemicals

The dioxins category includes seven chlorinated dibenzo-p-dioxins (CDDs), 10 chlorinated dibenzofurans (CDFs), and 12 coplanar PCB congeners. These compounds share common modes of toxic action and are considered a group for risk assessment (Van den Berg et al. 1998). Although the toxicity of these chemicals varies up to 5 orders of magnitude, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is the most potent. All the dioxins bind and activate the aryl hydrocarbon receptor (AhR). The AhR is a ligand-activated transcription factor that participates in regulating a battery of genes (Gu et al. 2000). A change in expression of AhR-regulated genes is the current explanation for much of the toxicity of TCDD and dioxin-like compounds. The CDDs, CDFs, and PCBs that activate the AhR are approximate stereoisomers of TCDD. Because the stereoisomers of TCDD are all less potent than TCDD, each is assigned a potency relative to TCDD for AhR activation (Van den Berg et al. 1998). The assigned potency is referred to as a toxic equivalency factor (TEF). By definition, the TEF for TCDD is 1. Multiplying the concentrations of each CDD, CDF, or dioxin-like PCB in biosolids by their TEFs and summing the products yields the toxic equivalents (TEQs) in that material.

EPA (1999a) has proposed application of TEQs in biosolids for setting regulatory standards. The validity of this approach is supported by reviews of recent literature that consider tissue concentrations (Van den Berg et al. 1998; Gu et al. 2000). There is at least one major limitation to application of the TEQ concept to estimating risks of dioxins in biosolids-amended soil. Bioavailability of all CDDs, CDFs, and PCBs that contribute to TEQs is not equivalent (Jones and Sewart 1997). A particular chlorination pattern distinguishes each of over 400 potential CDD (75), CDF (135), and PCB (209) congeners. Extent and pattern of chlorination markedly influences hydrophobicity and hence the tendency for sorption to and desorption from organic matter in a biosolids-amended soil. Biodegradation rates, water solubility (an inverse function of hydrophobicity), and volatility generally decrease with an increase in chlorination for aromatic hydrocarbons. Theoretically, each CDD, CDF, and PCB congener processes a specific half-life and bioavailability in a biosolids-amended soil. Complete characterization requires data on each congener. Because of the impracticality of that requirement, environmental chemistry data for the most toxic congener (TCCD) typically provide the basis for risk assessment.

EPA (1999a) has proposed a TEQ limit of 300 parts per trillion (ppt) in biosolids applied to land, which is well above the means of 32 or 48 ppt detected in recent biosolids surveys (Alvarado et al. 2001; EPA 2002a). In the

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Alvarado survey, 14 of 201 biosolids samples contained dioxin TEQs greater than 60 ppt. Thirteen of those samples were in the range of 62–256 ppt, and one sample contained dioxins at 3,590 ppt. The one unusually high dioxin level has been verified by two laboratories, the source of the dioxin has been identified, the sewage sludge is being land filled, and investigation into the high dioxin level continues (R.Dominak, AMSA Co-chair Biosolids Management Committee, personal communication with G.Kester, Wisconsin Department of Natural Resources, May 24, 2002).

Eljarrat et al. (1997) reported that soil concentrations of CDDs, CDFs, and dioxin-like PCBs in biosolids-amended soil were 1.2 to 11.6 times greater than those in control soils one year after application of biosolids containing 56–260 ppt TEQs. Biosolids were applied in four consecutive years at rates that exceeded the nitrogen-based Spanish annual application recommendations for agriculture (5–10 ton/ha) by 4- to 15-fold. In soils with low initial TEQs (0.3 ppt), concentrations remained suitable for agriculture. In soil with high initial TEQs (3.1 ppt), concentrations increased to levels (8.6 picograms [pg]/g TEQ) that would trigger German crop restrictions. Molina et al. (2000) concluded that CDD and CDF concentrations in biosolids-amended soils are directly related to loading 1 year after application.

Both atmospheric transport and biosolids application contribute to total TEQ loading in agricultural soils (Jones and Sewart 1997). Atmospheric loading was more significant in urban sites than in rural sites. The half-life of CDDs and CDFs in soils is generally accepted to be about 10 years (Jones and Sewart 1997). Therefore, the history of contamination and atmospheric loading in addition to biosolids application are worthy of consideration in site evaluation. For example, assuming (1) biosolids with dioxins at 300 ppt, (2) a biosolids application rate of 10,000 kg/ha, (3) biosolids incorporation into 15 cm of soil, (4) soil mass of 1,200 kg/m3, and (5) a dioxin half-life of 10 years with exponential decay, rough estimates of dioxin concentrations are 1.65 ppt in agricultural soil after a single application and 12.57 ppt after annual applications for 10 consecutive years. For biosolids containing dioxins at 50 ppt, the corresponding concentrations are 0.28 and 2.10 ppt.

EPA (2001a) released a peer-review draft of a revised risk assessment for dioxins in biosolids that reflects responses to comments on the earlier risk assessment supporting the proposed TEQ limit of 300 ppt. The revised risk assessment uses data from a recent biosolids survey and both deterministic and probabilistic approaches to estimate dioxin concentrations in soil and other exposure media near land-application sites. Risks were evaluated for a farm family residing in an area receiving runoff from cropland and for a recreational fisher. For the farm family, risk results were presented for specific pathways (soil ingestion; air inhalation; produce ingestion; ingestion of poultry,

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

eggs, beef, and milk; and breast-milk ingestion for an infant) and for total multiple-pathway risks. Beef and milk ingestion were the primary contributors to risks for both adults and children. The risk results did not change when survey samples exceeding 300 ppt TEQ (the proposed standard) were excluded from the database because of low frequency of occurrence of increased concentrations. A notice of data availability on EPA’s revised risk assessment was released for public comment on June 12, 2002 (EPA 2002a).

Other Organic Chemicals

Data regarding the occurrence of organic chemicals in biosolids is needed for additional chemical categories, and they should be given consideration in future risk assessments. Among these are flame retardants (e.g., brominated diphenyl ethers), surfactants, chlorinated paraffins, nitro and polycyclic musks, pharmaceuticals, odorants, and chemicals used to treat sewage sludge (e.g., dewatering agents). Evaluation of these types of chemicals in risk assessment will depend on the characteristics of the compound, their occurrence in biosolids, and the availability of toxicity data. In this section, brominated diphenyl ethers are used as an example to illustrate a specific class of chemicals identified as a potential hazard in biosolids. Other categories of compounds are reviewed briefly; special consideration is given to pharmaceuticals and odorants.

Brominated Diphenyl Ethers

Brominated diphenyl ethers (BDEs) are flame retardants used in the furniture, electrical and computer component, and housing industries. Only penta-, octa-, and deca-BDEs are of commercial interest (WHO 1994). The composition and production estimates in 1994 for these BDEs are presented in Table 5–13. Environmental concerns about BDEs have arisen because they have been detected in various environmental media, are highly persistent in the environment, and bioaccumulate in aquatic food webs (de Boer et al. 1998; Hale et al. 2001).

BDE formulations differ in their toxicological properties (WHO 1994). The acute toxicity of the deca-, octa-, and penta-BDEs is low. There are no apparent adverse effects in rats fed deca-BDE at 50 g/kg for 13 weeks. That response is largely explained by very low absorption of deca-BDE across the gastrointestinal tract (about 0.3%). There is evidence of toxic effects from exposure to the less highly brominated BDE formulations. For example, rats

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–13 Composition and Approximate Annual Use of Brominated Diphenyl Ester Formulations

Preparation

Composition

Annual Worldwide Production (ton)

Deca-BDE

97–98% deca-BDE

0.3–3% nona-BDE

30,000

Octa-BDE

43–44% hepta-BDE

31–35% octa-BDE

10–12% hexa-BDE

9–11% nona-BDE

0–1% deca-BDE

6,000

Penta-BDE

50–62% penta-BDE

24–38% tetra-BDE

4–8% hexa-BDE

0–1% tri-BDE

4,000

 

Source: Data from WHO 1994.

fed a diet containing octa-BDE at 1 or 10 g/kg for 13 weeks had reduced body weight at both doses and decreased red-blood-cell count at the high dose. An increase in liver weight and no changes in body weight or blood-cell counts were found in rats fed a diet containing octa-BDE at 0.1 g/kg for 13 weeks. Rats fed penta-BDE at 0.1 or 1 g/kg for 4 weeks had increased liver weight without a change in body weight. Histopathology analyses indicate that higher doses of octa- and penta-BDE alter liver and thyroid tissue.

More recent work focused on actions of BDEs on liver enzymes and thyroid hormones in rats. Octa- and penta-BDE formulations increased the activities of hepatic enzymes that metabolize thyroid hormone, whereas deca-BDE did not (Zhou et al. 2001). These increased enzyme activities were associated with reduced serum concentrations of thyroxin. Because thyroid-stimulating hormone was not altered by BDEs, increased elimination by the liver rather than decreased secretion by the thyroid appeared to explain the reduced serum thyroxin. The potential for BDE metabolites to interact with transthyretin (a protein that carries thyroxin in blood) was demonstrated by Meerts et al. (2001). Three hydroxylated BDEs effectively displaced thyroxin from this protein. Eriksson et al. (2001) reported neurotoxic actions of a tetra-BDE and a penta-BDE congener in mice. Neonatal exposure to both congeners altered spontaneous behavior, and the penta-BDE reduced memory.

Despite the evidence of the toxic potential of BDEs, a review of the above studies and other toxicological studies estimated that current human

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

dietary intakes of BDEs were a million times lower than the lowest-observed-adverse-effect levels in animal studies (Darnerud et al. 2001). Concentrations of BDEs in human breast milk and fish have increased over time. BDE concentrations in breast milk from Swedish women have been reported to increase exponentially over the past 25 years as commercial use of these chemicals has increased (Hooper and McDonald 2000). Preliminary data indicated that concentrations in milk from North American women were 10- to 40-fold higher than those from Swedish women (Betts 2001). Norén and Meironyté (2000) reported that BDEs in the breast milk of Swedish women ranged from 0.07 to 0.48 ng/g of lipid between 1972 and 1980 and from 0.72 to 4.01 ng/g of lipid between 1984 and 1997.

Few data are available on concentrations of BDEs in biosolids. One study reported that the sum of penta- and deca-brominated BDEs in biosolids ranged from 1 to 7 ppm in the United States (Hale et al. 2001). The extent to which BDEs in biosolids are related to current human body burdens is unclear.

Surfactants

Surfactants used in laundry detergents and other cleaning products enter wastewater in large quantities from domestic and commercial wastewater sources. Linear alkylbenzene sulfonates (LAS), alkyl phenol ethoxylates (APE), and alcohol ethoxylates (AE) are high-production surfactants that have respective U.S. annual consumptions of 415, 322, and 208 million kg in 1990 (McAvoy et al. 1998). Standards for LAS and APE established in some European countries are largely based on ecotoxicological impacts and not human health (Cavalli and Valtorta 1999). Use of nonylphenol-based surfactants is banned in Switzerland.

Studies of LAS dominate the literature on degradation of surfactants. The type of sewage-sludge treatment will have a strong impact on the presence of surfactants. LAS, for example, is readily degraded in an aerobic environment but not in an anaerobic environment (Scott and Jones 2000). The half-life of LAS in aerobic soils is 7–30 days (Cavalli and Valtorta 1999; Scott and Jones 2000) and over a year under anaerobic conditions (Cavalli and Valtorta 1999). Soil concentrations of LAS immediately after biosolids applications range from 0.5 to 66.4 ppm (Scott and Jones 2000). Differences in amounts of aerobic and anaerobic treatment before application might at least partially explain this wide range. A 2-year feeding and reproduction study in rats with a LAS preparation (hydrocarbon-chain-length distribution of 10 to 14 carbons) revealed little or no toxicity (Buehler et al. 1971). Rats fed LAS at a concentration of 5 g/kg gained body weight and consumed food at the same

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

rate as controls. Hematology and visceral organ histology were normal. Oral LAS dosing of rhesus monkeys also indicated very low toxicity (Heywood et al. 1978). Some studies reported that these anionic surfactants are rapidly degraded in soils, and risk assessments suggested that they pose little threat to the food chain (de Wolf and Feijtel 1998; Jensen 1999).

Talmage (1994) reviewed the biodegradation and toxicology of the nonionic surfactant AEs and APEs. Most AEs are mixtures of 8 to 18 carbon linear primary alcohols, but linear secondary and branched AEs are also used. About 90% of AEs undergoing activated sewage-sludge treatment degrade, indicating rapid aerobic metabolism. Feeding rats a medium-chain-length AE for 2 years at 10 g/kg reduced food consumption and body-weight gain, but these effects were not seen at 1 g/kg. A dose-dependent increase in myocarditis was the only effect observed. Direct attachment of a branched alkyl chain (usually 9 carbons) and ester linkage of a polyethoxy chain (4–40 carbons) to phenol yields APEs. Although activated sewage-sludge treatment removes up to 97% of APEs, substantial adsorption to sewage sludge occurs. APE concentrations of tens to hundreds parts per million occur in sewage sludge. The concentrations of potentially toxic metabolites, especially nonylphenol, range from an approximate equivalent to the parent compound to several times higher. Survival and growth of rats fed a long polyethoxy chain (40 carbons) APE at 14 g/kg for 2 years were the same as those of controls. No pathological lesions were associated with treatment. Reduced body weight and enlarged livers occurred in rats fed a short polyethoxy chain (4 carbons) APE at 1 g/kg/day. At lower doses (30 and 140 mg/kg/day), no growth reduction or evidence of histopathological changes were found after 2 years of feeding. APEs degrade to nonylphenols and octylphenols in aerobic environments, and that increases toxicity of the material up to 10-fold (Scott and Jones 2000). For example, the mono- and di-ethoxylates degrade to 4-nonylphenol. Studies from the United States (LaGuardia et al. 2001) and Switzerland (Giger et al. 1984) detected nonylphenol polyethoxylates in sewage sludge. A nonylphenol concentration of 4.7 ppm was reported in soil soon after biosolids application (Scott and Jones 2000). Concentrations of nonylphenols in anaerobically digested sewage sludge may be as high as 4,000 mg/kg (Bennie 1999). They may be rapidly degraded in soil, limiting the potential transfer into the food chain, but there are few field-based data. Although recent evidence suggests that nonylphenols spiked into uncontaminated biosolids are degraded over several months, a significant portion of the nonylphenols in aged biosolids is recalcitrant to biological transformation (Topp and Starratt 2000). In addition to persistence in the soil, the sorption of nonylphenol onto organic matter may give rise to the facilitated transport of these compounds into groundwater (Nelson et al. 1998). Nonylphenol and other alkylphenolics activity as endocrine disruptors is of some concern. The

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

risk from environmental exposure is most clear for fish in surface waters receiving wastewater treatment plant (WWTP) effluents (Jobling et al. 1996).

Chlorinated Paraffins

Chlorinated paraffins or polychlorinated n-alkanes (PCAs) are used as additives in lubricants, plastics, flame retardants, paints, sealants, and cutting and lubricating oils. These chemicals are actively produced in large tonnages and have numerous uses and sources. When dissolved in a polymer, they probably leak slowly into the environment, and almost half of the oils used in manufacturing might enter wastewater streams (Alcock et al. 1999). Therefore, industrial effluents are much more likely sources of chlorinated paraffins in biosolids than in domestic wastewater.

High doses of chlorinated paraffins (100–1,000 mg/kg/day for 14 days) increased liver size and peroxisomal enzyme activity in rats and mice (Wyatt et al. 1993). They also reduced plasma thyroid hormone concentrations in rats at the highest dose in that study. Chlorinated paraffins induced liver and thyroid tumors in rats and mice and are probable human carcinogens (NTP 1986). These materials deserve attention in future analytical work on biosolids.

Nitro and Polycyclic Musks

Nitro and polycyclic musks are fragrances in a variety of personal-care products, including shampoos, soaps, detergents, perfumes, and skin lotions. Feeding mice musk xylol at 1.5 g/kg for 80 weeks increased liver tumor incidence (Maekawa et al. 1990). Although sewage treatment markedly reduces nitro musk concentrations in wastewater, amino metabolites that are more toxic than parent compounds occurred in effluents at 1–250 ppt (Daughton and Ternes 1999). Herren and Berset (2000) reported concentrations of nitro musks, their amino metabolites, and polycyclic musks in sewage sludge from 12 Swiss WWTPs. Nitro-musk concentrations in sewage sludge ranged from less than 0.1 to 7 ppb dry weight. Amino metabolites ranged from less than 0.1 to 49 ppb dry weight. Much higher concentrations of polycyclic musks in sewage sludge occurred at up to 12 ppm dry weight for galaxolide and 4 ppm dry weight for tonalide. Those concentrations can be explained by the phase out of nitro musks and the increased production of polycyclic musks (reviewed in Daughton and Ternes 1999) and slow rates of degradation. One estimate of half-life for polycyclic musks in soils is 180 days (Balk and Ford 1999). Future risk assessment on biosolids should consider polycyclic musks.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Pharmaceuticals

Since the early 1980s, there have been increasingly frequent reports of pharmaceuticals detected in wastewater treatment effluent or surface water in trace concentrations (typically in nanograms per liter) (Daughton and Ternes 1999; Ayscough et al. 2000). These reports have become more frequent as analytical techniques have improved to enable identification of very low concentrations of these chemicals in complex mixtures. Many of these chemicals are produced in very high volumes, and they or their metabolites are added directly to wastewater after use. Most of the concern regarding the potential effects of these chemicals, particularly the potential endocrine-disrupting effects of hormones, has been for the impact on aquatic receptors. The majority of drugs are water soluble, and metabolism after ingestion generally increases the solubility further. Consequently, most drugs and their metabolites are unlikely to be present in significant quantities in biosolids. Nevertheless, more lipophilic compounds will have a greater tendency to partition to biosolids.

Since 1969, the National Environmental Policy Act has required the assessment of risk to the environment from use of drugs. Environmental assessments are part of the registration procedure for new human pharmaceuticals (PDA 1985; Eirkson 1987). The procedure in place since 1995 calls for estimation of an expected introductory concentration (EIC) based on dividing the expected annual production volume by the number of liters of wastewater entering publicly owned treatment works per year (U.S. Center for Drug Evaluation and Research 1995). When the predicted EIC in wastewater effluent is less than 1 mg/liter, a detailed environmental assessment is not needed.

Active pharmaceutical compounds and a wide variety of metabolites enter wastewater after personal use at home and work (Ayscough et al. 2000). A somewhat different spectrum of chemicals will enter wastewater after use in hospitals and medical centers. The parent compounds may also be disposed of directly to wastewater. These chemicals may be further degraded or biodegraded in wastewater and during treatment at wastewater treatment plants. Analytical methods to characterize the resulting complex mixtures of chemicals are useful for research but are not currently adequate for routine screening (Daughton and Ternes 1999). Standard reference materials are often not readily available, and many of these substances are not included in environmentally oriented mass spectral libraries.

The efficiency of removal of drugs in wastewater treatment plants has mainly been determined by measuring influent and effluent concentrations. Removal efficiency varies greatly among different pharmaceuticals and varies over time at any single treatment plant (Daughton and Ternes 1999). Removal of a drug could reflect either degradation and biodegradation or sequestration

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

in biosolids; no data on drug concentrations in sewage sludge or biosolids were identified for this review. Partition coefficients between organic matter and water vary up to 500-fold for different drugs (Tolls 2001). Since thousands of drugs are approved for use, any attempt to determine whether drugs are routinely present in biosolids would require a carefully focused approach, perhaps looking for the highest volume drugs that have lipophilic properties and are not predominantly metabolized to water-soluble forms.

Toxicity studies have been conducted for most drugs, but the results of such studies are often not reported in the peer-reviewed literature. If drugs are detected in biosolids, approaches for evaluating potential adverse health effects will need to be considered. Typically, effects of toxicity would be limited to doses exceeding the therapeutic doses. However, therapeutic dose effects in a non-target population might be considered adverse effects. Therefore, health-based screening could rely on toxicity values that are a specific fraction of therapeutic dose levels.

In summary, pharmaceuticals and personal care products are produced in high volumes, and they and their metabolites are excreted directly to wastewater, where they have been detected in very low (generally, nanograms per liter) concentrations. The potential for most of these chemicals to partition to biosolids is limited by their generally high water solubility; however, some drugs may be sufficiently lipophilic to partition preferentially to biosolids. At present, there is not adequate evidence that pharmaceuticals are likely to occur in biosolids at concentrations sufficient to warrant their inclusion in a biosolids risk assessment; however, EPA should continue to monitor research in this area.

Volatile Emissions and Odorants

The chemical selection process used for the Part 503 rule risk assessment included consideration of volatile organic chemicals (VOCs) that are priority pollutants. These VOCs are generally limited to chlorinated and aromatic volatiles, which might be present in biosolids as a result of industrial or other discharges to sewer systems. Because the majority of these VOCs will be released to the air during wastewater processing, VOCs were ruled out as chemicals of concern for land application of biosolids.

Sewage sludge also emits many VOCs not included in the EPA priority pollutant list. These VOCs include sulfur and nitrogen-containing chemicals that are strong odorants, as well as acids, aldehydes, and ketones that are also odorants. A review by Gostelow et al. (2001) provides an overview of odorant generation during wastewater treatment and describes measurement methods. Many of these chemicals are generated during the biodegradation of waste-

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

water and sewage-sludge components, and the protein breakdown contributes to the generation of sulfur and nitrogen-containing compounds (Gostelow et al. 2001). Sufonates from detergents are additional sources of sulfur, and urine and amino acids contribute to formation of nitrogen-containing compounds. Carbohydrate fermentation during anaerobic sewage sludge treatment contributes to the formation of volatile fatty acids, aldehydes, alcohols, and ketones.

The mixture of odorants in biosolids will differ from that in sewage sludge, and the relative concentrations will differ between the two mixtures for odorants present in both. Table 5–14 lists odorants associated with wastewater treatment, their characteristic odors, and their odor thresholds. As noted in the table, many of these odorants have been detected in biosolids.

Although hydrogen disulfide is the predominant odorant associated with wastewater treatment, it is less of a factor in the odors of biosolids (Striebig 1999). In an unpublished laboratory study, the predominant odorants varied, depending on treatment methods used to reduce pathogens in the biosolids. Overall odor increased with lime treatment and increasing temperature (Striebig 1999). Additional studies are needed to provide a more robust database of odorants released from biosolids. Potential risks associated with odorants cannot be properly assessed until such a database is developed.

Noxious odors are one of the primary causes of complaints from the public about land application of biosolids. Odor perception consists of two steps: physiological reception and psychological interpretation (Gostelow et al. 2001). Although odorants may cause toxic effects, perception of an odor as noxious is not directly linked to toxicity. Perception of sewage odors as unpleasant might be due to an association with decaying material that needs to be avoided. As noted by Schiffman et al. (2000), foul environmental odors frequently engender concerns for safety. Odor perception has been shown to affect mood, in eluding levels of tension, depression, anger, fatigue, and confusion (Schiffman et al. 1995). Mood impairments and stress can potentially lead to physiological and biochemical changes with subsequent health consequences (Shusterman et al. 1991; Cohen and Herbert 1986). In addition, conditioned responses (behavioral and physiological) can be developed to odors perceived to be associated with health symptoms (Bolla-Wilson et al. 1988; Shusterman et al. 1988).

Odors associated with biosolids are due to complex mixtures of odorous chemicals that vary greatly in toxicity and in odor thresholds. The olfactory system processes stimuli from the chemicals in these mixtures, perceiving one overall odor. There are two primary approaches to measuring odors: analytical measurements of individual odorants in a mixture and sensory studies in which human subjects provide subjective evaluations of odors (reviewed in Gostelow et al. 2001). Fully characterizing an odor requires the use of both

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–14 Odorants Generated During Sewage Treatment

Classa

Compounda

Formulaa

Charactera

Detected in Biosolidsb

Odor Threshold (ppm)

Sulfurous

Hydrogen sulfide

H2S

Rotten eggs

X

0.0081c

Dimethyl sulfide

(CH3)2S

Decayed vegetables, garlic

X

0.001d

Diethyl sulfide

(C2H5)2S

Nauseating, ether

 

0.005d

Diphenyl sulfide

(C6H5)2S

Unpleasant, burnt rubber

X

0.0001e

Diallyl sulfide

(CH2CHCH2)2S

Garlic

 

0.0001d

Carbon disulfide

CS2

Decayed vegetables

X

0.0078d

Dimethyl disulfide

(CH3)2S2

Putrification

X

0.000026d

Methyl mercaptan

CH3SH

Decayed cabbage, garlic

X

0.0016c

Ethyl mercaptan

C2H5SH

Decayed cabbage

X

0.0003e

Propyl mercaptan

C3H7SH

Unpleasant

X

0.0005e

Butyl mercaptan

C4H9SH

Unpleasant

 

0.00043d

t-Butyl mercaptan

(CH3)3CSH

Unpleasant

 

Allyl mercaptan

CH2CHCH2SH

Garlic

X

0.0001d

Crotyl mercaptan

CH3CHCHCH2SH

Skunk, rancid

 

Benzyl mercaptan

C6H5CH2SH

Unpleasant

X

0.0002e

Thiocresol

CH3C6H4SH

Skunk, rancid

X

0.0001e

Thiophenol

C6H5SH

Putrid, nauseating, decay

 

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

 

Sulfur dioxide

SO2

Sharp, pungent, irritating

 

1.1c

Nitrogenous

Ammonia

NH3

Sharp, pungent

X

5.2c

Methylamine

CH3NH2

Fishy

X

3.2c

Dimethylamine

(CH3)2NH

Fishy

X

0.34c

Trimethylamine

(CH3)3N

Fishy, ammoniacal

X

0.00044c

Ethylamine

C2H5NH2

Ammoniacal

X

0.95c

Diethylamine

(C2H5)2NH2

 

0.13c

Triethylamine

(C2H5)3N

 

X

0.48c

Diamines (cadaverine)

NH2(CH2)5NH2

Decomposing meat

 

Pyridine

C6H5N

Disagreeable, irritating

X

0.66e

Indole

C8H6NH

Fecal, nauseating

X

0.0001e

Scatole or skatole

C9H8NH

Fecal, nauseating

X

0.001e

Acids

Acetic (ethanoic)

CH3COOH

Vinegar

X

1.02d

Butyric (butanoic)

C3H7COOH

Rancid, sweaty

X

0.0003d

Valeric (pentanoic)

C4H9COOH

Sweaty

 

0.0006d

Aldehydes and ketones

Formaldehyde

HCHO

Acrid, suffocating

 

0.83c

Acetaldehyde

CH3CHO

Fruit, apple

X

0.067e

Butyraldehyde

C3H7CHO

Rancid, sweaty

 

0.0046d

Isobutyraldehyde

(CH3)2CHCHO

Fruit

 

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Classa

Compounda

Formulaa

Charactera

Detected in Biosolidsb

Odor Threshold (ppm)

 

Isovaleraldehyde

(CH3)2CHCH2CHO

Fruit, apple

 

 

Acetone

CH3COCH3

Fruit, sweet

 

13c

 

Butanone

C2H5COCH3

Green apple

 

aGostelow et al. 2001.

bUnpublished data from Striebig 1999.

cAmoore and Hautala 1983.

dRuth 1986.

eWEF/ASCE 1995.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

approaches. Although analytical measurements allow for identification of the chemicals present, sensory studies may provide assessments of the intensity, character, and hedonic tone (pleasantness or unpleasantness) of an odor. Analytical measurements are crucial for an assessment of the potential toxicity of odorous chemicals, because toxicity thresholds often do not correlate with odor thresholds.

In assessing odorants, it is important to distinguish between symptoms or health complaints due to odor perception and irritant effects and other forms of toxicity. Participants at a workshop held at Duke University in 1998 defined a set of odor levels to clarify the intensities associated with potential health impacts (Schiffman et al. 2000) (see Table 5–15). These levels begin with odor detection and progress through odor intolerance (defined as physical symptoms occurring at a nonirritant concentration), irritant effects, and chronic and acute toxicity.

Identification of these levels does not imply that consistent increases in concentrations trigger each level of response. For example, some odorants might have minimal irritant effects but produce chronic or acute toxicity. Strong odorants might be detected at concentrations far less than those that cause toxicity, whereas weak odorants might cause toxicity at concentrations close to odor detection thresholds. Table 5–16 provides a comparison of odor thresholds and thresholds for toxicity of odorants detected in biosolids. Toxicity threshold values for airborne chemicals are derived by a variety of organizations. EPA and the Agency for Toxic Substances and Disease Registry are the primary sources of toxicity values for evaluating effects of chronic exposure. EPA is also overseeing the development of acute exposure guideline levels (AEGLs) to evaluate acute exposures of the general public, and the National Institute for Occupational Safety Health, the American Conference of Governmental Industrial Hygienists, and the Occupational Safety and Health Administration derive acute exposure guidelines for occupational exposures. The divergence of odor threshold and toxicity is illustrated by comparing values for hydrogen sulfide and carbon disulfide. The odor thresholds for the two chemicals are similar, but the reference concentrations suggest that the chronic toxicity of hydrogen sulfide is more than 100 times greater than that of carbon disulfide.

As can be seen in Table 5–16, toxicity values are available for only a small number of odorants found in biosolids. Evaluation of risks of exposure to odorants will depend on the availability of appropriate toxicity values for these chemicals. Appropriate toxicity values will need to be based on the likely exposure duration (short-term vs. chronic). Consequently, initial efforts to evaluate the potential hazards of odorants identified in biosolids should focus on dose-response assessment for exposure durations likely to occur in the

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–15 Perception of Odors and Health Complaints

Level

Description

1. Odor detection

The level of odor that can first be differentiated from ambient air.

2. Odor recognition

The level of odor at which the odor quality can be characterized (e.g., the level at which a person can detect that an odor is apple or manure).

3. Odor annoyance

The level at which a person is annoyed by an odor but does not show or perceive a physical reaction.

Note: Health symptoms are not expected at these first three levels unless the odor occurs with a copollutant such as dust as in Paradigm 3 or the level of annoyance is intense or prolonged.

4. Odor intolerance (causing somatic symptoms)

The level at which an individual may show or perceive physical (somatic) symptoms to an odor.

Note: This level corresponds to Paradigm 2 in which the odor induces symptoms even thought the odorant concentration is lower than that known to cause irritation.

5. Perceived irritant

The level at which a person reports irritation or physical symptoms as a result of stimulation of nerve endings in the respiratory tract.

6. Somatic irritant

The level at which an odorant (not an odor) results in a negative physical reaction regardless of an individual’s predisposition. This can occur when an odorous compound (e.g., chlorine) damages tissue.

Note: Perceived and somatic irritation correspond to Paradigm 1.

7. Chronic toxicity

The level at which an odorant can result in long-term health impact.

8. Acute toxicity

The level at which an immediate toxic impact is experienced (e.g., a single event may evoke an acute health impact).

Note: In the case of chronic or acute toxicity, the compound should not be considered an odorant but rather a compound with toxic effects that happens to have an odor.

 

Source: Schiffman et al. 2000. Reprinted with permission from Journal of Agromedicine; copyright 2000, Haworth Press, Inc.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

TABLE 5–16 Comparison of Odor Thresholds and Thresholds for Toxicity

Class

Compound

Odor Threshold (ppm)a

Threshold Limit Values (ppm)b

Acute Exposure Guideline Levels (ppm)c

Reference Concentrations (ppm)d

Sulfurous

Hydrogen sulfide

0.0081

10

0.11

0.0007

Carbon disulfide

0.0078

10

 

0.22

Methyl mercaptan

0.0016

0.5

0.5

 

Ethyl mercaptan

0.0003

0.5

 

Nitrogenous

Ammonia

5.2

25

25

0.14

Methylamine

3.2

5

 

Dimethylamine

0.34

5

 

Trimethylamine

0.00044

5

 

0.0017

Ethylamine

0.95

5

 

Triethylamine

0.48

1

 

Pyridine

0.66

5

 

Acids

Acetic (ethanoic)

1.02

10

 

aValue taken from Table 5–11.

bEight-hour time-weighted averages for workers (ACGIH 2001a,b,c).

cAEGL-1 values for 8-h exposures (nondisabling); protection of general public from irritation (Paul Tobin, EPA, personal communication, October 2001)

dReference concentrations expected to pose no risk of adverse effects in public populations with chronic exposures (EPA 2002c, IRIS database).

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

exposed populations. Because many of these chemicals are structurally similar, quantitative structure activity analysis (QSAR) might be a useful tool to augment the limited toxicity database. In conclusion, a wide variety of odorants are present in wastewater effluents, and the chemical compositions and concentrations of odorants in biosolids vary with the treatment processes as well as the origin of the effluents. Inhalation is the only exposure pathway of concern for VOCs, and both acute and chronic exposures should be considered. Additional studies are needed to identify odorants typically released from biosolids and to determine the range of likely air concentrations near biosolids-application sites. Acute and chronic toxicity values (air concentrations determined to be safe for specified kinds of exposures) should be developed for the predominant odorants, and a hazard analysis should be conducted to determine whether air concentrations generated near application sites are high enough to warrant more detailed risk assessment for this category of chemicals. Research is also needed on the impacts of odors. Particular attention should be paid to the degree to which effective biosolids treatment reduces odorant concentrations and impacts.

FINDINGS AND RECOMMENDATIONS

In responding to the committee’s charge to evaluate the technical basis of the biosolids chemical standards, it is important to distinguish between the appropriate risk-assessment methods at the time the standards were developed versus the most appropriate methods now. The committee did not attempt to determine whether the methods used at that time were appropriate, and the committee’s findings and recommendations should not be construed as either criticism or approval of the standards when issued. Instead, the findings and recommendations focus on how current risk-assessment practices and current knowledge regarding chemicals in biosolids can be used to update and strengthen the scientific credibility of EPA’s chemical standards.

In light of the advances made in risk-assessment methods and the need to update many of the exposure parameters used in the risk assessment process, the existing biosolids standards for inorganic pollutants clearly need to be reevaluated. A comparison of the pollutant limits with risk-based soil screening levels suggests that the pollutant standards are adequately protective for some exposure pathways (i.e., soil/biosolids ingestion), but may need to be reevaluated for others (i.e., ingestion of homegrown produce grown on biosolids-amended soil, groundwater). Reevaluating the standards is not the same as saying that the standards should be lower. In fact, some standards might increase after a reevaluation. A lower standard for a particular pollutant also would not necessarily indicate the presence of a health risk. The risk

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

would depend on the actual concentrations of the pollutant in biosolids to which people were exposed. Nonetheless, the current limits cannot with confidence be stated to be adequately protective for all of the regulated pollutants. Additionally, limitations in the chemical selection process apply to inorganic, as well as organic, pollutants.

Recommendation: A revised multipathway risk assessment should be performed for the currently regulated pollutants, with particular attention paid to arsenic and to indirect exposure pathways for cadmium and mercury. In addition, new survey data should be used to identify any additional inorganic or organic pollutants that might need to be included in a risk assessment.

The science and body of knowledge underlying the practice of risk assessment have evolved substantially since the risk assessment supporting the Part 503 rule was conducted. Consequently, different approaches and supporting data would be used if the Part 503 rule risk assessment were conducted again today or in the future. One important development has been the recognition of the importance of engaging stakeholders in the risk-assessment process to help characterize potential exposures. Stakeholders are groups potentially affected by the risk, risk managers, and groups affected by efforts to manage the source of the risk. Involving stakeholders throughout the risk-assessment process provides opportunities to bridge gaps in understanding, language, values, and perspectives and to address concerns of affected communities.

Recommendation: Risk-based standards for land application of biosolids should be reevaluated on a regular basis to take into account new information regarding the identity and properties of chemicals present in these mixtures and current approaches to evaluating the risks of exposure to such mixtures. Stakeholders should be included in the process, particularly in the development of the exposure assessments.

The chemical selection process used to identify chemicals of concern for the risk assessment is now outdated. Data from the NSSS that was used in the selection process are over a decade old, and there is a need to characterize the concentrations and distribution of chemicals now present in biosolids. Additional chemicals not included in the NSSS analyses have now been identified as new concerns. Analytical methods have improved since the NSSS was conducted.

Recommendation: The committee endorses the recommendation of the previous NRC committee (NRC 1996) that a new national survey of chemicals in biosolids be conducted. It recognises that more recent survey data are available through many state programs and recommends that EPA consider those databases in the course of designing a

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

new national survey. Other elements that should be included in a new survey are the following: evaluation of the adequacy of analytical methods and detection limits to support risk assessment; consideration of categories of chemicals of current concern that were not previously evaluated (e.g., odorants, surfactants, and pharmaceutical); and assessment of the possible presence of multiple species of mercury, arsenic, and other metals that have different toxic end points.

EPA’s decision to eliminate all chemicals detected at less than 5% or 10% frequency in the NSSS is unjustified. Data gaps may now be filled for toxicity and fate and transport characteristics that were previously used to eliminate chemicals from the risk assessment. In addition, uncertainties associated with the chemical selection process have not been adequately evaluated.

Recommendation: Selected persistent, bioaccumulative, and highly toxic chemicals should be retained in the risk assessment even if they are detected relatively infrequently or if some chemical-specific fate and transport parameters are missing. An uncertainty assessment should be performed to evaluate the significance of eliminating chemicals from the risk assessment because of lack of toxicity data or other parameters.

The Part 503 rule risk assessment focused on agricultural land-application scenarios. Conceptual site models documenting the exposure pathways judged to be major and minor are not available for the scenarios evaluated. Consequently, it is difficult to determine whether all relevant pathways were identified. Although the pathways evaluated are likely to be the major exposure pathways for chronic exposures in agricultural scenarios, there might be differences in the significance of pathways for short-term exposures and for different scenarios.

Recommendation: A new risk assessment should include separate exposure scenarios that represent substantial differences in exposure potential (e.g., land reclamation and forestry applications). For each scenario, a conceptual site model approach should be used to identify major and minor exposure pathways and routes of exposure. Risks from short-term episodic exposures should also be evaluated for volatile chemicals, such as odorants.

The degree of realism varies by exposure pathway. The pathways were not evaluated in a consistent manner (i.e., it is not apparent that exposure estimates were comparably conservative for all pathways). Exposures also were not added for multiple pathways affecting a single receptor. For the indirect pathways, the use of multiple, highly conservative assumptions could result in unrealistic overestimates of risk. However, because of the diversity

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

of exposed populations, environmental conditions, and agricultural practices in the United States, exposure analyses based on a nationwide range of exposures might not be adequately protective for all cases.

Recommendation: A comparable reasonable maximum exposure (RME) should be evaluated for each exposure pathway in each exposure scenario, and where the same receptor is likely to be exposed to more than one pathway, exposures should be added across pathways. Such considerations are applicable for both deterministic and probabilistic exposure assessment approaches. Multiple highly conservative assumptions should be avoided; however, care should be taken to ensure that the risks are assessed for the high-end population and that the most sensitive conditions for biosolids application are considered. For example, for the groundwater infiltration pathway, if biosolids application is likely to occur in areas of sandy soil or karst topography with shallow groundwater, those conditions should be used in the risk assessment.

As described above and in Chapter 4, new scientific data are now available that could be used to support alternative assumptions for many of the exposure parameters used in the risk assessment. Comprehensive reviews and updated recommendations for many parameters have been compiled in several EPA guidance documents. Fate and transport models used to estimate exposure point concentrations for many pathways have also been updated.

Recommendation: The most recent EPA reviews and new studies reported in the literature should be used to identify updated assumptions for exposure parameters for use in risk assessment. Updated fate and transport models should be used to estimate exposure point concentrations. For each exposure pathway, fate and transport models and exposure parameter assumptions should be selected so that pathway exposures reflect the RME.

Biosolids are likely to include many categories of chemicals that differ from the categories of chemicals of concern in industrial discharges. Although it is impossible to identify all of these pollutants, it is important that EPA continually think about the types of chemicals released into wastewaters and added during wastewater and sewage-sludge treatment processes as part of its process for updating the Part 503 rule. EPA eliminated certain chemicals of concern from further assessment when there was an absence of data on fate, transport, and toxicity. New data on some of these chemicals might now be available for determining whether risk assessments for those chemicals are needed. Because some organic chemicals, such as organochlorines, are persistent in the environment, consideration should be given to their tendency for trophic transfer and biomagnification. EPA has already undertaken such an evaluation for dioxins. Consideration should also be given to toxic end points

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

that might not have been evaluated adequately in the earlier assessment (e.g., potential interactions of chemicals with the endocrine system). Two categories of chemicals deserving special attention are pharmaceuticals and odorants. Considering the amounts discharged to sewage systems, the presence of pharmaceuticals in biosolids has not been adequately investigated. For odorants, the need for further evaluation is driven by the high level of public concern, as well as very limited characterization of the odorants present in biosolids and their toxicity.

Recommendation: In addition to the recommendation above for a new biosolids survey and chemical selection process, it is recommended that a research program be developed for pharmaceuticals and other chemicals likely to be present in biosolids that are not currently included in routine monitoring programs. This includes chemicals eliminated from Round 1 and Round 2 evaluations because of data gaps. The research program should have the goal of identifying additional chemicals that should be included in routine biosolids surveys and in future risk assessments. For odorants, research in needed to identify the odorants present in various kinds of biosolids. For odorants commonly present in biosolids, EPA should move aggressively to develop acute toxicity values for use in assessing the risks posed by these chemicals and should support research on the interaction between these chemicals and pathogens in causing human disease.

REFERENCES

ACGIH (American Conference of Governmental Industrial Hygienists). 2001a. Documentation of the Threshold Limit Values for Chemical Substances, 7th Ed., ACGIH, Cincinnati, OH.

ACGIH (American Conference of Governmental Industrial Hygienists). 2001b. Documentation of the Physical Agents Threshold Limit Values, 7th Ed., ACGIH, Cincinnati, OH.

ACGIH (American Conference of Governmental Industrial Hygienists). 2001c. Documentation of the Threshold Limit Values and Biological Exposure Indices, 7th Ed., ACGIH, Cincinnati, OH.

Adamu, C.A., P.F.Bell, C.Mulchi, and R.Chaney. 1989. Residual metal concentrations in soils and leaf accumulations in tobacco a decade following farmland application of municipal sludge. Environ. Pollut. 56(2):113–126.

Alcock, R.E., A.Sweetman, and K.C.Jones. 1999. Assessment of organic contaminant fate in wastewater treatment plants. I. Selected compounds and physicochemical properties. Chemosphere 38(10):2247–2262.

Alexander, M. 2000. Aging, bioavailability, and overestimation of risk from environmental pollutants. Environ. Sci. Technol. 34(20):4259–4265.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Alvarado, M.J., S.Armstrong, and E.Crouch. 2001. The AMSA 2000/2001 Survey of Dioxin-Like Compounds in Biosolids: Statistical Analyses. Prepared for Association of Metropolitan Sewage Agencies (AMSA), by Cambridge Environmental Inc., Cambridge, MA. October 30, 2001. [Online]. Available: http://www.amsa-cleanwater.org/advocacy/dioxin/final_report.pdf [May 17, 2002].

Amoore, J.H., and E.Hautala. 1983. Odor as an aid to chemical safety: odor thresholds compared with threshold limit values and volatilities for 214 industrial chemicals in air and water dilution. J. Appl. Toxicol. 3(6):272–290.

Anderson, S.A. 1986. Guidelines for Use of Dietary Intake Data. Bethesda, MD: life Sciences

Research Office, Federation of American Societies for Experimental Biology. 89pp.

Arai, Y., and D.L.Sparks. 2001. Microscale Arsenic (AS) Chemical Speciation in Poultry Litter. Presentation at Soil Science of America Annual Meeting, Charlotte, NC, Oct. 21–25, 2001. [Online]. Available: http://ag.udel.edu/soilchem/publications.html [April 17, 2002].

ATSDR (Agency for Toxic Substances and Disease Registry). 1999. Toxicological Profile for Cadmium (Update). U.S. Dept of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry, Atlanta, GA.

Ayscough, N.J., J.Fawell, G.Franklin, and W.Young. 2000. Review of Human Pharmaceuticals in the Environment. R&D Tech. Report P390. WRc Report No. EA4761. WRc-NSF Ltd, Buckinghamshire. Bristol: Environment Agency.

Balk, F., and R.A.Ford. 1999. Environmental risk assessment for the polycyclic musks AHTN and HHCB in the EU. I. Fate and exposure assessment. Toxicol. Lett. 111(1–2):57–59.

Barbarick, K.A., J.A.Ippolito, and D.G.Westfall. 1998. Extractable trace elements in the soil profile after years of biosolids application. J. Environ. Qualit. 27(4):801–805.

Barrow, N.J. 1998. Effects of time and temperature on the sorption of cadmium, zinc, cobalt, and nickel by soil. Aust. J. Soil Res. 36(6):941–950.

Basta, N.T., and J.J.Sloan. 1999. Bioavailability of heavy metals in strongly acidic soils treated with exceptional quality biosolids. J. Environ. Qual. 28(2):633–638.

Beck, A.J., D.L.Johnson, and K.C.Jones. 1996. The form and bioavailability of nonionic organic chemicals in sewage sludge-amended agricultural soils. Sci. Total Environ. 185(1–3):125–149.

Bell, P.F., C.A.Adamu, C.L.Mulchi, M.McIntosh, and R.L.Chaney. 1988. Residual effects of land applied municipal sludge on tobacco. 1. Effects on heavy metal concentrations in soils and plants. Tob. Sci. 32:46–51.

Bell, P.F., B.R.James, and R.L.Chaney. 1991. Heavy metal extractability in longterm sewage sludge and metal salt-amended soils. J. Environ. Qual. 20:481–486.

Bennie, D.T. 1999. Review of the environmental occurrence of alkylphenols and alkylphenol ethoxylates. Water Qual. Res. J. Can. 34(1):79–122.

Berti, W.R., and L.W.Jacobs. 1998. Distribution of trace elements in soil from repeated sewage sludge applications. J. Environ. Qual. 27(6):1280–1286.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Betts, K. 2001. Mounting concern over brominated flame retardants. Environmental Science and Technology Online Science News. June 1, 2001. Available: http://www.acs.org [March 1, 2002].

Bolla-Wilson, K., R.J.Wilson, and M.L.Bleecker. 1988. Conditioning of physical symptoms after neurotoxic exposure. J. Occup. Med. 30(9):684–686.

Brady, N.C., and R.R.Weil. 1999. The Nature and Properties of Soils, 12th Ed. Upper Saddle River, NJ: Prentice Hall.

Broos, K., F.Degryse, and E.Smolders. 2001. Cadmium and Zinc Availability and Toxicity to Symbiotic Nitrogen Fixation in Soils Contaminated by Various Sources. GP100. Presentation at the 6th International Conference on the Biogeochemistry of Trace Elements, Guelph, Ontario, Canada, July 29-August 2, 2001. [Online]. Available: http://www.uoguelph.ca/~gparkin/ICOBTE/ICOBTEprogram.pdf [February 25, 2002].

Brown, S.L., R.L.Chaney, J.S.Angle, and J.A.Ryan. 1998. The phytoavailability of cadmium to lettuce in long-term biosolids-amended soils. J. Environ. Qual. 27(5):1071–1078.

Brown, S.L., R.L.Chaney, C.A.Lloyd, J.S.Angle, and J.A.Ryan. 1996. Relative uptake by garden vegetables and fruits grown on long-term biosolids-amended soils. Environ. Sci. Technol. 30(12):3508–3511.

Buck, R.J., K.A.Hammerstrom, and P.B.Ryan. 1997. Bias in population estimates of long-term exposure from short-term measurements of individual exposure. Risk Anal. 17(4):455–466.

Buehler, E.V., E.A.Newmann, and W.R.King. 1971. Two-year feeding and reproduction study in rats with linear alkylbenzene sulfonate (LAS). Toxicol. Appl. Pharmacol. 18(1):83–91.

Calabrese, E.J., E.J.Stanek, C.E.Gilbert, and R.M.Barnes. 1990. Preliminary adult soil ingestion estimates: results of a pilot study. Regul. Toxicol. Pharmacol. 12(1):88–95.

Cappon, C.J. 1981. Mercury and selenium content and chemical form in vegetable crops grown on sludge-amended soil. Arch. Environ. Contam. Toxicol. 10(6):673–689.

Cappon, C.J. 1984. Content and chemical form of mercury and selenium in soil, sludge, and fertilizer materials. Water Air Soil Pollut. 22:95–104.

Carpi, A., and S.E.Lindberg. 1997. Sunlight-mediated emission of elemental mercury from soil amended with municipal sewage sludge. Environ. Sci. Technol. 31(7):2085–2091.

Carpi, A., and S.E.Lindberg. 1998. Application of a Teflon dynamic flux chamber for quantifying soil mercury flux: tests and results over background soil. Atmos. Environ. 32(5):873–882.

Carpi, A., S.E.Lindberg, E.M.Prestbo, and N.S.Bloom. 1997. Methyl mercury contamination and emission to the atmosphere from soil amended with municipal sewage sludge. J. Environ. Qual. 26(Nov/Dec):1650–1654.

Cary, E.E., D.L.Grunes, S.L.Dallyn, G.A.Pearson, N.H.Peck, and R.S.Hulme. 1994. Plant Fe, Al and Cr concentration in vegetables as influenced by soil inclusion. J. Food Qual. 17:467–476.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Cavalli, L., and L.Valtorta. 1999. Surfactants in sludge-amended soil. Tenside Surf. Det. 36(1):22–28.

Chaisson, C.F., R.L.Sielken Jr, and D.K.Waylett. 1999. Overestimation bias and other pitfalls associated with the estimated 99.9th percentile in acute dietary exposure assessments. Regul. Toxicol. Pharmacol. 29(2 Pt 1):102–127.

Chaney, R.L. 1990. Twenty years of land application research. BioCycle 31 (9):54–59.

Chaney, R.L., and J.A.Ryan. 1994. Risk Based Standards for Arsenic, Lead and Cadmium in Urban Soils: Summary of Information and Methods Developed to Estimate Standards for Cd, Pd and As in Urban Soils. Frankfurt: DECHEMA.

Chaney, R.L., S.L.Brown, and J.S.Angle. 1998. Soil-root interface: ecoystem health and human food-chain protection. Pp. 279–311 in Soil Chemistry and Ecosystem Health, P.M.Huang, D.C.Adriano, T.J.Logan, and R.T.Checkai, eds. Madison, WI: Soil Science Society of America.

Chaney, R.L., S.B.Hornick, and P.W.Simon. 1977. Heavy metal relationships during land utilization of sewage sludge in the Northeast. Pp. 283–314 in Land as a Waste Management Alternative: Proceedings of the 1976 Cornell Agricultural Waste Management Conference, R.C.Loehr, ed. Ann Arbor, MI: Ann Arbor Science Pub.

Chang, A.C., H.N.Hyun, and A.L.Page. 1997. Cadmium uptake for Swiss chard grown on composed sewage sludge treated field plots: plateau or time bomb? J. Environ. Qual. 26(1):11–19.

Chang, L.L., D.L.Raudenbush, and S.K.Dentel. 2001. Aerobic and anaerobic biodegradability of a flocculant polymer. Water Sci. Technol. 44(2–3):461–468.

Chaudri, A.M., C.M.Allain, S.H.Badawy, M.L.Adams, S.P.McGrath, and B.J.Chambers. 2001. Cadmium content of wheat grain from a long-term field experiment with sewage sludge. J. Environ. Qual. 30(5):1575–1580.

Chiou, C.T., and T.D.Shoup. 1985. Soil sorption of organic vapors and effects of humidity on sorptive mechanism and capacity. Environ. Sci. Technol. 19(12):1196–1200.

Cohen, S., and T.B.Herbert. 1996. Health psychology: psychological factors and physical disease from the perspective of human psychoneuroimmunology. Annu. Rev. Psychol. 47:113–142.

Colborn, T., F.S.vom Saal, and A.M.Soto. 1993. Developmental effects of endocrine-disrupting chemicals in wildlife and humans. Environ. Health Perspect. 101(5):378–384.

Corey, R.B., L.D.King, C.Lue-Hing, D.S.Fanning, J.J.Street, and J.M.Walker. 1987. Effects of sludge properties on accumulation of trace elements by crops. Pp. 25– 51 in Land Application of Sludge, Food Chain Implications, A.L.Page, T.J. Logan, and J.A.Ryan, eds. Chelsea, MI: Lewis.

Darnerud, P.O., G.S.Eriksen, T.Johannesson, P.B.Larsen, and M.Viluksela. 2001. Polybrominated diphenyl ethers: occurrence, dietary exposure, and toxicology. Environ. Health Perspect. 109(Suppl. 1):49–68.

Daughton, C.G., and T.A.Ternes. 1999. Pharmaceuticals and personal care products in the environment: agents of subtle change? [Review]. Environ. Health Perspect. 107(Suppl. 6):907–938.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

de Boer, J., P.G.Wester, H.J.Klamer, W.E.Lewis, and J.P.Boon. 1998. Do flame retardants threaten ocean life? Nature 394(6688):28–29.

de Wolf, W., and T.Feijtel. 1998. Terrestrial risk assessment for linear alkyl benzene sulfonate (LAS) in sludge-amended soils. Chemosphere 36(6):1319–1343.

Dragun, J., and A.D.Chiasson. 1991. Elements in North American Soils. Hazardous Materials Control Resources Institute, Greenbelt, MD.

Eirkson, C. 1987. Environmental Assessment Technical Assistance Handbook. FDA/CFSA N-87/30. PB87–175345. Washington, DC: Food and Drug Administration.

Eljarrat, E., J.Caixach, and J.Rivera. 1997. Effects of sewage sludges contaminated with polychlorinated benzo-p-dioxins, dibenzofurans, and biphenyls on agricultural soils. Environ. Sci. Technol. 31(10):2765–2771.

EPA (U.S. Environmental Protection Agency). 1982. Fate of Priority Pollutants in Publicly Owned Treatment Works, Vol. 1. Final Report. EPA/440/1–82/303. Effluent Guidelines Division, Water and Waste Management, U.S. Environmental Protection Agency, Washington, DC. September.

EPA (U.S. Environmental Protection Agency). 1985. Summary of Environmental Profiles and Hazard Indices for Constituents of Municipal Sludge: Methods and Results. EPA 822/S-85–001. NTIS PB95–156436. Office of Water Regulations and Standards, Wastewater Criteria Branch, U.S. Environmental Protection Agency, Washington, DC. July.

EPA (U.S. Environmental Protection Agency). 1989. Risk Assessment Guidance for Superfund, Vol. 1. Human Health Evaluation Manual (Part A). Interim Final. EPA/540/1–89/002. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. December 1989.

EPA (U.S. Environmental Protection Agency). 1990. National sewage sludge survey: availability of information and data, and anticipated impacts on proposed regulations. Fed. Regist. 55(218):47210–47283. (November 9, 1990).

EPA (U.S. Environmental Protection Agency). 1991. Guidance for Data Useability in Risk Assessment (Part A). Final. EPA/540/R-92/003. Office of Research and Development, U.S. Environmental Protection Agency, Washington, DC. December 1991.

EPA (U.S. Environmental Protection Agency). 1992a. Technical Support Document for Land Application of Sewage Sludge, Vol. I. EPA 822/R-93–001A. Prepared for Office of Water, U.S. Environmental Protection Agency, Washington, DC, by Eastern Research Group, Lexington, MA. November 1992.

EPA (U.S. Environmental Protection Agency). 1992b. Technical Support Document for Land Application of Sewage Sludge, Vol. II. Appendices. EPA 822/R-93– 001b. Prepared for Office of Water, U.S. Environmental Protection Agency, Washington, DC, by Eastern Research Group, Lexington, MA. November 1992.

EPA (U.S. Environmental Protection Agency). 1995. A Guide to the Biosolids Risk Assessments for the EPA Part 503 Rule. EPA 832-B-93–005. Office of Wastewater Management, U.S. Environmental Protection Agency, Washington, DC. September 1995.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

EPA (U.S. Environmental Protection Agency). 1996a. Technical Support Document for the Round Two Sewage Sludge Pollutants. EPA-822-R-96–003. Office of Water, Office of Science and Technology, Health and Ecological Criteria Division, U.S. Environmental Protection Agency, Washington, DC. August 1996.

EPA (U.S. Environmental Protection Agency). 1996b. Soil Screening Guidance: Technical Background Document . EPA/540/R-95/128. PB96–963502. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. May 1996.

EPA (U.S. Environmental Protection Agency). 1997. Exposure Factors Handbook. Vol. I, II, III. EPA/600/P-95/002Fa-c. National Center for Environmental Assessment, Office of Research and Development, U.S. Environmental Protection Agency. [Online]. Available: http://www.epa.gov/ncea/exposfac.htm. [July 31, 2001].

EPA (U.S. Environmental Protection Agency). 1998. Human Health Risk Assessment Protocol for Hazardous Waste Combustion Facilities, Vol. 1. Peer Review Draft. EPA530-D-98–001A. Office of Solid Waste and Emergency Response, Washington, DC. July 1998. [Online]. Available: http://www.epa.gov/epaoswer/hazwaste/combust/riskvol.htm#volume1 [February 14, 2002].

EPA (U.S. Environmental Protection Agency). 1999a. Standards for the use or disposal of sewage sludge. Proposed rule. Fed. Regist. 64(246):72045–72062. (December 23, 1999).

EPA (U.S. Environmental Protection Agency). 1999b. Biosolids Generation, Use, and Disposal in the United States. EPA530-R-99–009. Municipal and Industrial Solid Waste Division, Office of Solid Waste, U.S. Environmental Protection Agency, Washington, DC. September 1999.

EPA (U.S. Environmental Protection Agency). 2000a. Guide to Field Storage of Biosolids. EPA/832-B-00–007. Office of Wastewater Management, U.S. Environmental Protection Agency, Washington, DC. July 2000.

EPA (U.S. Environmental Protection Agency). 2000b. Exposure and Human Health Reassessment of 2,3,7,8-Tetrachlorodibenzo-p-Dioxin (TCDD) and Related Compounds . EPA/600/P-00/001. National Center for Environmental Assessment, Office of Research and Development, Washington, DC. [Online]. Available: http://www.epa.gov/NCEA/pdfs/dioxin/index.htm [February 26, 2002].

EPA (U.S. Environmental Protection Agency). 2000c. Estimated Per Capita Water Ingestion in the United States: Based on Data Collected by the United States Department of Agriculture’s 1994–96 Continuing Survey of Food Intakes by Individuals. EPA-822-R-00–008. Office of Water, U.S. Environmental Protection Agency, Washington, DC. April 2000. [Online]. Available: http://www.epa.gov/waterscience/drinking/percapita/. [February 26, 2002].

EPA (U.S. Environmental Protection Agency). 2001a. Exposure Analysis for Dioxins, Dibenzofurans, and CoPlanar Polychlorinated Biphenyls in Sewage Sludge. RTI Project No. 92U-7600.OP3.040. Prepared by Center for Environmental Analysis, Research Triangle Institute, Research Triangle Park, NC, for Office of Water, U.S. Environmental Protection Agency, Washington, DC. November 30,

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

2001. [Online]. Available: http://www.epa.gov/waterscience/biosolids/riskasdraft.pdf [February 26, 2002].

EPA (U.S. Environmental Protection Agency). 2001b. Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites. Peer Review Draft. OSWER 9355.4–24. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. March 2001.

EPA (U.S. Environmental Protection Agency). 2001c. 1999 Public Data Release Report. Toxic Release Inventory (TRI) Program. EPA 260/R-01/001. U.S. Environmental Protection Agency. [Online]. Available: http://www.epa.gov/triinter/tridata/tri99/index.htm [May 21, 2002].

EPA (U.S. Environmental Protection Agency). 2001d. Risk Assessment Guidance for Superfund: Vol. 3.- Part A. Process for Conducting Probabilistic Risk Assessment. EPA 530-R-02–002. PB2002 963302. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. December 2001. [Online]. Available: http://www.epa.gov/oerrpage/superfund/programs/risk/rags3a/pdf/contpref.pdf [May 21, 2002].

EPA (U.S. Environmental Protection Agency). 2002a. Standards for the Use or Disposal of Sewage Sludge; Notice. Fed. Regist. 67(113):40554–40576. June 12, 2002.

EPA (U.S. Environmental Protection Agency). 2002b. PRG Tables. Preliminary Remediation Goals. Solid and Hazardous Waste Programs, Region 9, U.S. Environmental Protection Agency. [Online]. Available: http://www.epa.gov/Region9/waste/sfund/prg/s1_01.htm [May 21, 2002].

EPA (U.S. Environmental Protection Agency). 2002c. Integrated Risk Information System (IRIS). [Online]. Available: http://www.epa.gov/iris/ [February 26, 2002].

Eriksson, P., E.Jakobsson, and A.Fredriksson. 2001. Brominated flame retardants: A novel class of developmental neurotoxicants in our environment? Environ. Health Perspect. 109(9):903–908.

Ershow, A.G., and K.P.Cantor. 1989. Total Water and Tapwater Intake in the United States: Population-Based Estimates of Quantities and Sources. Bethesda, MD: Life Sciences Research Office, Federation of American Societies for Experimental Biology.

Farmer, J.G., and L.R.Johnson. 1990. Assessment of occupational exposure to inorganic arsenic based on urinary concentrations and speciation of arsenic. Br. J. Ind. Med. 47(5):342–348.

FDA (Food and Drug Administration). 1985. FDA Final rule for compliance with NEPA: Policy and Procedures. Fed. Regist. 50FR 16636, 21CFR 25. (April 26, 1985).

Ford, R.G., A.C.Scheinost, K.G.Scheckel, and D.L.Sparks. 1999. The link between clay mineral weathering and the stabilization of Ni surface precipitates. Environ. Sci. Technol. 33(18):3140–3144.

Fries, G.F. 1995. Transport of organic environmental contaminants to animal products. Rev. Environ. Contam. Toxicol. 141:71–109.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Fries, G.F., and D.J.Paustenbach. 1990. Evaluation of potential transmission 2,3,7,8-tetrachlorodibenzo-p-dioxin-contaminated incinerator emissions to humans via food. J. Toxicol. Environ. Health 29(1):1–43.

Gerritse, R.G., R.Vriesema, J.W.Dalenberg, and H.P.De Roos. 1982. Effect of sewage sludge on trace element mobility in soils. J. Environ. Qual. 11 (3):359–364.

Giger, W., P.H.Brunner, and C.Schaffner. 1984. 4-nonylphenol in sewage sludge: Accumulation of toxic metabolites from nonionic surfactants. Science 225(4662):623–625.

Gostelow, P., S.A.Parsons, and R.M.Stuetz. 2001. Odour measurements for sewage treatment works. Wat. Res. 35(3):579–597.

Gu, Y.Z., J.B.Hogenesch, and C.A.Bradfield. 2000. The PAS superfamily: Sensors of environmental and developmental signals. Annu. Rev. Pharmacol. Toxicol. 40:519–561.

Gustavsson, N.B.Bolviken, D.B.Smith, and R.C.Severson. 2001. Geochemical Landscapes of the Conterminous United States-New Map Presentations for 22 Elements. U.S. Geological Survey Professional Paper 1648. Denver, CO: U.S. Dept. of the Interior, U.S. Geological Survey. [Online]. Available: http://geology.cr.usgs.gov/pub/ppapers/pl648 [March 8, 2002].


Hale, R.C., M.J.LaGuardia, E.P.Harvey, M.O.Gaylor, T.M.Mainor, and W.H.Duff. 2001. Flame retardants. Persistent pollutants in land-applied sludges. Nature 412(6843):140–141.

Hamon, R.E., P.E.Holm, S.E.Lorenz, S.P.McGrath, and T.H.Christensen. 1999. Metal uptake by plants from sludge-amended soil: Caution is required in the plateau interpretation. Plant Soil 216(1/2):53–64.

Heckman, J.R., J.S.Angle, and R.L.Chaney. 1987. Residual effects of sewage sludge on soybean. 1. Accumulation of heavy metals. J. Environ. Qual. 16(2):113–117.

Henry, C., and S.Brown. 1997. Restoring superfund site with biosolids and fly ash. BioCycle 38:79–80.

Herren, D., and J.D.Berset. 2000. Nitro musks, nitro mush amino metabolites and polycyclic musks in sewage sludges. Quantitative determination by HRGC-iontrap-MS/MS and mass spectral characterization of the amino metabolites. Chemosphere 40(5):565–574.

Heywood, R., R.W.James, and R.J.Sortwell. 1978. Toxicology studies of linear alkylbenzene sulphonate (LAS) in rhesus monkeys. I. Simultaneous oral and subcutaneous administration for 28 days. Toxicology 11(3):245–250.

Hooda, P.S., and B.J.Alloway. 1994. The plant avaqilability and DTPA extractability of trace metals in sludge-amended soils. Sci. Total Environ. 149(1–2):39–51.

Hooper, K., and T.A.McDonald. 2000. The PBDEs: An emerging environmental challenge and another reason for breast-milk monitoring programs. [Review]. Environ. Health Perspect 108(5):387–392.


Israeli, M., and C.B.Nelson. 1992. Distribution and expected time of residence for U.S. households. Risk Anal. 12(1):65–72.


Jensen, J. 1999. Fate and effects of linear alkylbenzene sulponates (LAS) in the terrestrial environment. Sci. Total Environ. 226(2–3):93–111.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Jobling, S., D.Sheahan, J.A.Osborne, P.Matthiessen, and J.P.Sumpter. 1996. Inhibition of testicular growth in rainbow trout (Oncorhynchus mykiss) exposed to estrogenic alkylphenolic chemicals. Environ. Toxicol. Chem. 15(2):194–202.

Jones, K.C., and A.P.Sewart. 1997. Dioxins and furans in sewage sludges: A review of their occurrence and sources in sludge and of their environmental fate, behavior, and significance in sludge-amended agricultural systems. Crit. Rev. Environ. Sci. Technol. 27(1):1–86.

Kamaludeen, S.P.B., R.Naidu, M.Megharaj, A.L.Juhasz, and G.Merrinston. 2001. Do Microbial Manganese Oxides Aid Chromium (III) Oxidation in Long-term Tannery Waste Contaminated Soils? GP208. Presentation at the 6th International Conference on the Biogeochemistry of Trace Elements, Guelph, Ontario, Canada, July 29-August 2, 2001. [Online]. Available: http://www.uoguelph.ca/~gparkin/ICOBTE/ICOBTEprogram.pdf [February 25, 2002].

Keinholtz, E.W., G.M.Ward, D.E.Johnson, J.Baxter, G.Braude, and G.Stern. 1979. Metropolitan Denver sewage sludge fed to feedlot steers. J. Anim. Sci. 48(4):735–741.

Kelley, M., S.Brauning, R.Schoof, and M.Ruby. 2002. Assessing Oral Bioavailability of Metals in Soil. Columbus, OH: Battelle Press. 136 pp.


LaGuardia, M.J., R.C.Hale, E.Harvey, and T.M.Mainor. 2001. Alkylphenol ethoxylate degradation products in land-applied sewage sludge (biosolids). Environ. Sci. Techol. 35(24):4798–4804.

Logan, T.J., B.J.Lindsay, L.E.Goins, and J.A.Ryan. 1997. Assessment of sludge metal bioavailability to crops: Sludge rate response. J. Environ. Qual. 26(2):534– 550.


Madsen, P.L., J.B.Thyme, K.Henriksen, P.Moldrup, and P.Roslev. 1999. Kinetics of di-(2-ethylhexyl), phthalate mineralization in sludge-amended soil. Environ. Sci. Technol. 33(15):2601–2606.

Maekawa, A., Y.Matsushima, H.Onodera, M.Shibutani, H.Ogasawara, Y.Kodama, Y.Kurokawa, and Y.Hayashi. 1990. Long-term toxicity/carcinogenicity of musk xylol in B6C3F1 mice. Food Chem. Toxicol. 28(8):581–586.

Mahler, R.J., J.A.Ryan, and T.Reed. 1987. Cadmium sulfate application to sludge-amended soils. I. Effect on yield and cadmium availability to plants. Sci. Total Environ. 67(2–3):117–132.

Manceau, A., B.Lanson, and G.M.Lamble. 2000. Quantitative Zn speciation in smelter-contaminated soils by EXAFS spectroscopy. Am. J. Sci. 300(4):289–343.

Marcomini, A., P.D.Capel, W.Giger, and H.Haeni. 1988. Residues of detergent-derived organic pollutants and polychlorinated biphenyls in sludge-amended soil. Naturwiss. 75(9):460–462.

McAvoy, D.C., S.D.Dyer, N.J.Fendinger, W.S.Eckhoff, D.L.Lawrence, and W.M. Begley. 1998. Removal of alcohol ethoxylates, alkyl ethoxylate sulfates, and linear alkylbenzene sulfonates in wastewater treatment. Environ. Toxicol. Chem. 17(9):1705–1711.

McBride, M.B. 1998. Growing food crops on sludge-amended soils: Problems with the U.S. Environmental Protection Agency method of estimating toxic metal transfer . Environ. Toxicol. Chem. 17(11):2274–2281.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

McBride, M.B., B.K.Richards, T.Steenhuis, J.J.Russo, and S.Sauve. 1997. Mobility and solubility of toxic metals and nutrients in soil fifteen years after sludge application. Soil Sci. 162(7):487–500.

McBride, M.B., B.K.Richards, T.Steenhuis, and G.Spiers. 1999. Long term leaching of trace elements in a heavily sludge-amended silty clay loam soil. Soil Sci. 164(9):613–623.

McCarthy, J.F., and J.M.Zachara. 1989. Subsurface transport of contaminants. Environ. Sci. Technol. 23(5):496–503.

McGrath, S.P., and P.W.Lane. 1989. An explanation for the apparent losses of metals in a long-term field experiment with sewage sludge. Environ. Pollut. 60(3–4):235– 256.

McGrath, S.P., F.J.Zhao, S.J.Dunham, A.R.Crosland, and K.Coleman. 2000. Long-term changes in the extractability and bioavailability of zinc and cadmium after sludge application. J. Environ. Qual. 29(3):875–883.

McLaren, R.G., C.A.Backes, A.W.Rate, and R.S.Swift. 1998. Cadmium and cobalt desorption kinetics from soil clays: Effect of sorption period. Soil Sci. Soc. Am. J. 62(2):332–337.

McLaughlin, M.J., L.T.Palmer, K.G.Tiller, T.A.Beech, and M.K.Smart. 1994. Increased soil salinity causes elevated cadmium concentration in field-grown potato tubers. J. Environ. Qualit. 23(5):1013–1018.

Meerts, I.A., R.J.Letcher, S.Hoving, G.Marsh, A.Bergman, J.G.Lemmen, B.van der Burg, and A.Brouwer. 2001. In vitro estrogenicity of polybrominated diphenyl ethers, hydroxylated PDBEs, and polybrominated bisphenol A compounds. Environ. Health Perspect 109(4):399–407.

Molina, L., J.Diaz-Ferrero, M.Coll, R.Marti, F.Broto-Puig, L.Cornellas, and M.C. Rodriguez-Larena. 2000. Study of evolution of PCDD/F in sewage sludge-amended soils for land restoration purposes. Chemosphere 40(9–11):1173–1178.

Mulchi, C.L., P.F.Bell, C.Adamu, and R.Chaney. 1987a. Long term availability of metals in sludge amended acid soils. J. Plant Nutr. 10(9116):1149–1161.

Mulchi, C.L., P.F.Bell, C.Adamu, and J.R.Heckman. 1987b. Bioavailability of heavy metals in sludge-amended soils ten years after treatment. Recent Adv. Phytochem. 21:235–259.

Nelson, S.D., J.Letey, W.J.Farmer, C.F.Williams, and M.Ben-Hur. 1998. Facilitated transport of napropamide by dissolved organic matter in sewage sludge-amended soil. J. Environ. Qual. 27(5):1194–1200.

NEPI (National Environmental Policy Institute). 2000a. Assessing the Bioavailability of Metals in Soil for Use in Human Health Risk Assessments. Bioavailability Policy Project Phase II, Metals Task Force Report. Summer 2000. Washington, DC: National Environmental Policy Institute. [Online]. Available: http://www.nepi.org/pubs.htm#Bioavail [January 25, 2002].

NEPI (National Environmental Policy Institute). 2000b. Assessing the Bioavailability of Organic Chemicals in Soil for Use in Human Health Risk Assessments. Bioavailability Policy Project Phase II, Organic Task Force Report. Fall 2000. Washington, DC: National Environmental Policy Institute. [Online]. Available: http://www.nepi.org/pubs.htm#Bioavail [April 16, 2002].

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

NOAA (National Oceanic and Atmospheric Administration). 2000a. Wind-Average Speed. National Climatic Data Center, National Oceanic and Atmospheric Administration . [Online]. Available: http://lwf.ncdc.noaa.gov/oa/climate/online/ccd/avgwind.html [December 19, 2001].

NOAA (National Oceanic and Atmospheric Administration). 2000b. Normal Daily Mean Temperature. National Climatic Data Center, National Oceanic and Atmospheric Administration. [Online]. Available: http://lwf.ncdc.noaa.gov/oa/climate/online/ccd/meantemp.html [December 19, 2001].

Norén, K., and D.Meironyté. 2000. Certain organochlorine and organobromine contaminants in Swedish human milk in perspective of past 20–30 years. Chemosphere 40(9–11):1111–1123.

NRC (National Research Council). 1994. Science and Judgment in Risk Assessment. Washington, DC: National Academy Press.

NRC (National Research Council). 1996. Use of Reclaimed Water and Sludge in Food Crop Production. Washington, DC: National Academy Press.

NRC (National Research Council). 1999. Arsenic in Drinking Water. Washington, DC: National Academy Press.

NRC (National Research Council). 2001. Arsenic in Drinking Water: 2001 Update. Washington, DC: National Academy Press.

NTP (National Toxicology Program). 1986. NTP Technical Report on the Toxicology and Carcinogenesis Studies of Chlorinated Paraffins (C12, 60% chlorine) (CAS No. 63449–39–8) in F344/N Rats and B6C3F1 Mice (Gavage Studies). NTP TR 308. NIH Pub. No. 86–2564. National Toxicology Program, Public Health Service, Research Triangle Park, NC. May 1986.

Peak, J.D., T.J.Sims, and D.L.Sparks. 2001. Direct Determination of Phosphate Species in Alum-amended Poultry Litter. Presentation at Soil Science of America Annual Meeting, Charlotte, NC, Oct. 21–25, 2001 . [Online]. Available: http://ag.udel.edu/soilchem/publications.html [April 17, 2002].

Pignatello, J.J. 1999. The measurement and interpretation of sorption and desorption rates for organic compounds in soil media. Pp. 1–73 in Advances in Agronomy, Vol. 69, D.L.Sparks, ed. San Diego, CA: Academic Press.

Preer, J.R., J.O.Akintoye, and M.L.Martin. 1984. Metals in downtown Washington, DC gardens. Biol. Trace Elem. Res. 6(1):79–91.


Reeves, P.G., and R.L.Chaney. 2001. Mineral status of female rats affects the absorption and organ distribution of dietary cadmium derived from edible sunflower kernels (Helianthus annuus L.). Environ. Res. 85(3):215–225.

Richards, B.K., J.P.Peverly, T.S.Steenhuis, and B.N.Liebowitz. 1997. Effect of processing mode on trace elements in dewatered sludge products. J. Environ. Qual. 26(3):782–788.

Richards, B.K., T.S.Steenhuis, J.H.Peverly, and M.B.McBride. 1998. Metal mobility at an old, heavily loaded sludge application site. Environ. Pollut. 99(3):365–377.

Richards, B.K., T.S.Steenhuis, J.H.Peverly, and M.B.McBride. 2000. Effect of sludge-processing mode, soil texture and soil pH on metal mobility in undisturbed soil columns under accelerated loading. Environ. Pollut. 109(2):327–346.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Risse, L.M., M.A.Nearing, A.D.Nicks, and J.M.Laflen. 1993. Error assessment in the Universal Soil Loss Equation. Soil Sci. Soc. Am. J. 57(3):825–833.

Roberts, D.R. 2001. Speciation and Sorption Mechanisms of Metals in Soils Using Bulk and Micro-Focused and Microscopic Techniques. Ph.D. Thesis. University of Delaware.

Roberts, D.R., A.M.Scheidegger, and D.L.Sparks. 1999. Kinetics of mixed Ni-Al precipitate formation on a soil clay fraction. Environ. Sci. Technol. 33(21):3749– 3754.

Ruby, M.V., A.Davis, J.H.Kempton, J.W.Drexler, and P.D.Bergstrom. 1992. Lead bioavailability: Dissolution kinetics under simulated gastric conditions. Environ. Sci. Technol. 26(6):1242–1248.

Ruby, M.V., R.Schoof, W.Brattin, M.Goldade, G.Post, M.Harnois, D.E.Mosby, S.W.Casteel, W.Berti, M.Carpenter, D.Edwards, D.Cragin, and W.Chappel. 1999. Advances in evaluating the oral bioavailability of inorganics in soil for use in human health risk assessment. Environ. Sci. Technol. 33(21):3697–3705.

Ruth, J.H. 1986. Odor thresholds and irritation levels of several chemical substances: A review. Am. Ind. Hyg. Assoc. J. 47(3):A142–151.

Sadovnikova, L., E.Otabbong, O.Iakimenko, I.Nilsson, J.Persson, and D.Orlov. 1996. Dynamic transformation of sewage sludge and farmyard manure components. 2. Copper, lead and cadmium forms in incubated soils. Agric. Ecosyst. Environ. 58(2–3):127–132.

Safe, S.H. 2000. Endocrine disruptors and human health—is there a problem? An update. Environ. Health Perspect 108(6):487–493.

Sauerbeck, D., and S.Lübben. 1991. Auswirkungen von Siedlungsabfällen auf Böden, Bodenorganismen und Pflanzen. Berichte aus der Okologischen Forschung 6. Jülich: Forschungszentrum Jülich.

Scheckel, K.G., and D.L.Sparks. 2001. Dissolution kinetics of nickel surface precipitates on mineral clay and oxide surfaces. Soil Sci. Soc. Am. J. 65(3):685–694.

Scheckel, K.G., A.C.Scheinost, R.G.Ford, and D.L.Sparks. 2000. Stability of layered Ni hydroxide surface precipitates—a dissolution kinetics study. Geochim. Cosmochim. Acta 64(16):2727–2735.

Scheidegger, A.M., G.M.Lamble, and D.L.Sparks. 1997. Spectroscopic evidence for the formation of mixed-cation hydroxide phases upon metal sorption on clays and aluminum oxides. J. Colloid Interf. Sci. 186(1):118–128.

Scheidegger, A.M., D.G.Strawn, G.M.Lamble, and D.L.Sparks. 1998. The kinetics of mixed Ni-Al Hydroxide formation on clay and aluminum oxide minerals: A time-resolved XAFS study. Geochim. Cosmochim. Acta 62(13):2233–2245.

Schiffman, S.S., E.A.Miller, M.S.Suggs, and B.G.Graham. 1995. The effect of environmental odors emanating from commercial swine operations on the mood of nearby residents. Brain Res. Bull. 37(4):369–375.

Schiffman, S.S., J.M.Walker, P.Dalton, T.S.Lorig, J.H.Raymer, D.Shusterman, and C.M.Williams. 2000. Potential health effects of odor from animal operations, wastewater treatment, and recycling of byproducts. J. Agromed. 7(1):7–81.

Scott, M.J., and M.N.Jones. 2000. The biodegradation of surfactants in the environment. Biochem. Biophys. Acta 1508(1–2):235–251.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Shacklette, H.T., and J.G.Boerngen. 1984. Element Concentrations in Soils and Other Surficial Materials of the Conterminous United States: An Account of the Concentrations of 50 Chemical Elements in Samples of Soils and Other Regoliths. U.S. Geological Survey Professional Paper No. 1270. Washington, DC: U.S. Government Pringting Office. 105 pp.

Shusterman, D., J.Balmes, and J.Cone. 1988. Behavioral sensitization to irritants/odorants after acute overexposures. J. Occup. Med. 30(7):565–567.

Shusterman, D., J.Lipscomb, R.Neutra, and K.Satin. 1991. Symptom prevalence and odor-worry interaction near hazardous waste sites. Environ. Health Perspect 94:25–30.

Sibbesen, E. 1986. Soil movement in long term field experiments. Plant Soil 91(1):73–85.

Sibbesen, E., C.E.Andersen, S.Andersen, and M.Flensted-Jensen. 1985. Soil movement in long-term field experiments as a result of cultivations. I. A model for approximating soil movement in one horizontal dimension by repeated tillage. Exp. Agric. 21(2):101–107.

Sibbesen, E., and C.E.Andersen. 1985. Soil movement in long term field experiments as a result of cultivations. II. How to estimate the two dimensional movement of substances accumulating in the soil. Exp. Agric. 21(2):107–117.

Sloan, J.J., R.H.Dowdy, and M.S.Dolan. 1997. Long-term effects of biosolids applications on heavy metal bioavailability in agricultural soils. J. Environ. Qual. 26(July/Aug):966–974.

Sloan, J.J., R.H.Dowdy, and M.S.Dolan. 1998. Recovery of biosolids-applied heavy metals sixteen years after application. J. Environ. Qual. 27(Nov/Dec):1312–1317.

Stanek III, E.J., and E.J.Calabrese. 2000. Daily soil ingestion estimates for children at a superfund site. Risk Anal. 20(5):627–635.

Stanek III, E.J., E.J.Calabrese, and M.Zorn. 2001. Biasing factors for simple soil ingestion estimates in mass balance studies of soil ingestion. Hum. Ecol. Risk. Assess. 7(2):329–355.

Stanek III, E.J., E.J.Calabrese, R.Burnes, and P.Pekow. 1997. Soil ingestion in adults-results of a second pilot study. Ecotoxicol. Environ. Saf. 36(3):249–257.

Stehouwer, R.C., A.M.Wolf, and W.T.Doty. 2000. Chemical monitoring of sewage sludge in Pennsylvania: Variability and application uncertainty. J. Environ. Qual. 29:1686–1695.

Stern, A.H. 1993. Monte Carlo analysis of the U.S. EPA model of human exposure to cadmium in sewage sludge through consumption of garden crops. J. Exp. Anal. Environ. Epidemiol. 3(4):449–469.

Striebig, B. 1999. Quantifying the Emission Rate of Ammonia and Trimethyl Amine From Biosolids for Bioset, Inc. Draft Final Report. Bioset, Inc., Houston, TX. November 30, 1999.

Svensson, B.G., A.Nilsson, M.Hansson, C.Rappe, B.Akesson, and S.Skerfving. 1991. Exposure to dioxins and dibenzofurans through the consumption of fish. N. Engl. J. Med. 324(1):8–12.

Tahvonen, R. 1996. Contents of lead and cadmium in foods and diets. Food Rev. Int. 12(1):1–70.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

Talmage, S.S. 1994. Environmental and Human Safety of Major Surfactants: Alcohol Ethoxylates and Alkyphenol Ethoxylates. Boca Raton: Lewis. 374 pp.

Thornton, I., and P.Abrahams. 1983. Soil ingestion-a major pathway of heavy metals into livestock grazing contaminated land. Sci. Total Environ. 28:287–294.

Tolls, J. 2001. Sorption of veterinary pharmaceuticals in soils: A review. Environ. Sci. Technol. 35(17):3397–3406.

Topp, E., and A.Starratt. 2000. Rapid mineralization of the endocrine-disrupting chemical 4-nonylphenol in soil. Environ. Toxicol. Chem. 19(2):313–318.

U.K. Environment Agency. 2002. Soil Guideline Values for Chromium Contamination. R&D Publication SGV 4. U.K. Department for Environment, Food and Rural Affairs, The Environmental Agency, Bristol.

University of Maryland. 1980. Feasibility of Using Sewage Sludge for Plant and Animal Production. Final Report 1978–1979. University of Maryland, College Park, MD. 222pp.

U.S. Center for Drug Evaluation and Research. 1995. Guidance for Industry for the Submission of An Environmental Assessment in Human Drug Applications and Supplements. CMC 6. Rockville, MD: U.S. Center for Drug Evaluation and Research.

USDA (U.S. Department of Agriculture). 1982. Food Consumption: Households in the United States, Season and Year 1977–78. Nationwide Food Consumption Survey 1977–78 Report No. H-6. (as cited in EPA 1992).


Vahter, M., M.Berglund, B.Nermell, and A.Akesson. 1996. Bioavailability of cadmium from shellfish and mixed diet in women. Toxicol. Appl. Pharmacol. 136(2):332–341.

Van den Berg, M., L.Birnbaum, A.T.Bosveld, B.Brunstrom, P.Cook, M.Feeley, J.P. Giesy, A.Hanberg, R.Hasegawa, S.W.Kennedy, T.Kubiak. J.C.Larsen, F.X.van Leeuwen, A.K.Liem, C.Nolt, R.E.Peterson, L.Poellinger, S.Safe, D.Schrenk, D.Tillitt, M.Tysklind, M.Younes, F.Waern, and T.Zacharewski. 1998. Toxic equivalency factors for PCBs, PCDDs, PCDFs for humans and wildlife. Environ. Health Perspect 106(12):775–792.

Versar. 2000. Peer Review of Risk Analysis for the Round Two Biosolids Pollutants. Summary Report. Prepared for U.S. Environmental Protection Agency, Office of Water, Office of Science and Technology, Health and Ecological Criteria Division, Washington, DC, by Versar, Inc., Springfield, VA. June 2000.


Wallace, L.A., N.Duan, and R.Ziegenfus. 1994. Can long-term exposure distributions be predicted from short-term measurements? Risk Anal. 14(1):75–85.

Wang, M.J., S.P.McGrath, and K.C.Jones. 1995. Chlorobenzenes in field soil with a history of multiple sewage sludge applications. Environ. Sci. Technol. 29(2):356–362.

WEF/ASCE (Water Environmental Federation and American Society of Civil Engineers). 1995. Odor Control in Wastewater Treatment Plants. WEF Manual of Practice No. 22. Alexandria, VA: Water Environment Federation.

Whitehead, M.W., R.P.Thompson, and J.J.Powell. 1996. Regulation of metal absorption in the gastrointestinal tract. Gut 39(5):625–628.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×

WHO (World Health Organization). 1994. Brominated Diphenyl Ethers. Environmental Health Criteria 162. Geneva: World Health Organization.

Wild, S.R., M.L.Berrow, and K.C.Jones. 1994. The persistence of polynuclear aromatic hydrocarbons (PAHs) in sewage sludge amended agricultural soils . Environ. Pollut. 72(2):141–158.

Wyatt, I., C.T.Courts, and C.R.Elcombe. 1993. The effect of chlorinated paraffins on hepatic enzymes and thyroid hormones. Toxicology 77(1–2):81–90.

Young, S., A.Tye, and N.Crout. 2001. Rates of Metal Ion Fixation in Soils Determined by Isotopic Dilution. S0202. Presentation at the 6th International Conference on the Biogeochemistry of Trace Elements, Guelph, Ontario, Canada, July 29-August 2, 2001. [Online]. Available: http://www.uoguelph.ca/~gparkin/ICOBTE/ICOBTEprogram.pdf [February 25, 2002].


Zhou, T., D.G.Ross, M.J.DeVito, and K.M.Crofton. 2001. Effects of short-term in vivo exposure to polybrominated diphenyl ethers on thyroid hormones and hepatic enzyme activities in weanling rats. Toxicol. Sci. 61(1):76–82.

Ziegler, E.E., B.B.Edwards, R.L.Jensen, K.R.Mahaffey, and S.J.Fomon. 1978. Absorption and retention of lead by infants. Pediatr. Res. 12(1):29–34.

Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 164
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 165
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 166
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 167
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 168
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 169
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 170
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 171
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 172
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 173
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 174
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 175
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 176
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 177
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 178
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 179
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 180
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 181
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 182
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 183
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 184
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 185
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 186
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 187
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 188
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 189
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 190
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 191
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 192
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 193
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 194
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 195
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 196
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 197
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 198
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 199
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 200
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 201
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 202
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 203
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 204
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 205
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 206
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 207
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 208
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 209
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 210
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 211
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 212
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 213
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 214
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 215
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 216
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 217
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 218
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 219
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 220
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 221
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 222
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 223
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 224
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 225
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 226
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 227
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 228
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 229
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 230
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 231
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 232
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 233
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 234
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 235
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 236
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 237
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 238
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 239
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 240
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 241
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 242
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 243
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 244
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 245
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 246
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 247
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 248
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 249
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 250
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 251
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 252
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 253
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 254
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 255
Suggested Citation:"5 Evaluation of EPA's Approach to Setting Chemical Standards." National Research Council. 2002. Biosolids Applied to Land: Advancing Standards and Practices. Washington, DC: The National Academies Press. doi: 10.17226/10426.
×
Page 256
Next: 6 Evaluation of EPA's Approach to Setting Pathogen Standards »
Biosolids Applied to Land: Advancing Standards and Practices Get This Book
×
Buy Paperback | $60.00 Buy Ebook | $48.99
MyNAP members save 10% online.
Login or Register to save!
Download Free PDF

The 1993 regulation (Part 503 Rule) governing the land application of biosolids was established to protect public health and the environment from reasonably anticipated adverse effects. Included in the regulation are chemical pollutant limits, operational standards designed to reduce pathogens and the attraction of disease vectors, and management practices. This report from the Board on Environmental Studies and Toxicology evaluates the technical methods and approaches used by EPA to establish those standards and practices, focusing specifically on human health protection. The report examines improvements in risk-assessment practices and advances in the scientific database since promulgation of the regulation, and makes recommendations for addressing public health concerns, uncertainties, and data gaps about the technical basis of the biosolids standards.

  1. ×

    Welcome to OpenBook!

    You're looking at OpenBook, NAP.edu's online reading room since 1999. Based on feedback from you, our users, we've made some improvements that make it easier than ever to read thousands of publications on our website.

    Do you want to take a quick tour of the OpenBook's features?

    No Thanks Take a Tour »
  2. ×

    Show this book's table of contents, where you can jump to any chapter by name.

    « Back Next »
  3. ×

    ...or use these buttons to go back to the previous chapter or skip to the next one.

    « Back Next »
  4. ×

    Jump up to the previous page or down to the next one. Also, you can type in a page number and press Enter to go directly to that page in the book.

    « Back Next »
  5. ×

    Switch between the Original Pages, where you can read the report as it appeared in print, and Text Pages for the web version, where you can highlight and search the text.

    « Back Next »
  6. ×

    To search the entire text of this book, type in your search term here and press Enter.

    « Back Next »
  7. ×

    Share a link to this book page on your preferred social network or via email.

    « Back Next »
  8. ×

    View our suggested citation for this chapter.

    « Back Next »
  9. ×

    Ready to take your reading offline? Click here to buy this book in print or download it as a free PDF, if available.

    « Back Next »
Stay Connected!