Biosolids Applied to Land Advancing Standards and Practices (2002) / Chapter Skim
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5 Evaluation of EPA's Approach to Setting Chemical Standards
5 Evaluation of EPA's Approach to Setting Chemical Standards
Pages 164-256
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From page 164... ...
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 .
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From page 165... ...
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)
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From page 166... ...
. 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)
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From page 167... ...
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.
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From page 168... ...
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.
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From page 169... ...
The detection limits are difficult to discern
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From page 170... ...
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.
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From page 171... ...
.0 ~ s y c o .m c ,. O OSO.1 0~5 x ~ ~ ~, - - ~ - - - -1= 0.l , , 05 1 , S 10 Percent Solids X Minimum Level ~ Above Minimum Level B A B A FIGURE 5-1 Detected concentrations ~—~ and detection limits (x)
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From page 172... ...
compared with soil screening levels (A, ingestion and dermal) for indeno(1,2,3-cd)
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From page 173... ...
compared with soil screening levels (A, ingestion and der~l~al) for toxaphene and pentachlorophenol.
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From page 174... ...
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.
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From page 175... ...
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.
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From page 176... ...
It should be noted that the tracked metals are not the same as the inorganic chemicals regulated under the Part 503 rule.
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From page 177... ...
. 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-specif~c calculations or when toxicity data were insufficient for a given pollutant.
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From page 178... ...
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)
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From page 179... ...
179 own ~ ~ , Q · :: .-: · o° · o o .:° ~5 .° ' 8 ;E ,., ~ ,;.
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From page 180... ...
Although these pathways may include the primary exposure pathways for a resident near biosolids-amended herds, 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.
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From page 182... ...
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.
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From page 183... ...
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 herds or fed forage from the fields, and in other media identified in the various exposure pathways.
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From page 185... ...
185 o Cal C
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From page 186... ...
Current practice ts to use a reasonable maximum exposure <~E) receptor.
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From page 187... ...
, 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.
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From page 188... ...
. Soil Concenirations 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)
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From page 189... ...
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.
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From page 190... ...
Plant Cor~centrailons Plant uptake of metals from biosolids-amended soils is another important factor in several of the exposure pathways. To determine plant uptake, EPA (1992a)
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From page 191... ...
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.
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From page 192... ...
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.
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From page 193... ...
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.
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From page 194... ...
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: Tissue Concentration (microgram of pollutant / gram of plant tissue, dry weight)
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From page 195... ...
56 300 170 2. For studies in which multiple application rates and tissue concentrations were given, the slope was determined by least-squares linear regression.
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From page 196... ...
That variation highlights the importance of considering regional variations in environmental conditions and crop types when assessing plant uptake assumptions for national applicat~ons.
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From page 197... ...
Livestock Co'~cenirations EPA used assumptions about transfer of pollutants from biosolids to livestock and resulting human exposures to contaminants in meat, organ meat, poultry, Davy products, and eggs inn's screeningprocess foridentify~ngpollutants 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)
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From page 198... ...
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)
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From page 199... ...
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)
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From page 200... ...
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.
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From page 201... ...
1999) should be considered prior to using biased distributions or upper percentile values in risk assessments.
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From page 202... ...
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.
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From page 203... ...
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~.
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From page 204... ...
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.
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From page 205... ...
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.
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From page 206... ...
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.
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From page 207... ...
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
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From page 208... ...
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.
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From page 209... ...
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)
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From page 210... ...
210 in ~ ^ o ~ ~ o o o c,)
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From page 211... ...
211 .= o em o A At o en m o CD o en o · _ .= cn .= ~ 3 o ~ o o o I, 1 ~ t>.o .
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From page 212... ...
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)
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From page 213... ...
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)
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From page 214... ...
. Metals primarily form strong inner-sphere chemical bonds with metal oxides, clay minerals, and humic substances that substantially restrict their mobility in natural environments.
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From page 215... ...
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)
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From page 216... ...
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; I(elley et al.
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From page 217... ...
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~.
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From page 218... ...
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.
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From page 219... ...
1993; Safe 2000~. As discussed previously in the section Hazard Assessment and Chemical Selection, all organic chemicals considered by EPA were originally exempted
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From page 220... ...
/ 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 was tewater and biosolids, the method of biosolids application, the physicochemical properties of the chemical, and environmental conditions.
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From page 221... ...
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.
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From page 222... ...
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)
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From page 223... ...
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.
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From page 224... ...
. 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.
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From page 225... ...
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 weighs without a change in bodyweight.
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From page 226... ...
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.
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From page 227... ...
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~.
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From page 228... ...
Herren and Berset (20003 reported concentrations of nitro musks, their amino metabolites, and polycyclic musks in sewage sludge from 12 Swiss W=ll's. Nitro-musk concentrations in sewage sludge ranged from less than 0.1 to 7 ppb dry weight.
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From page 229... ...
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 J)
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From page 230... ...
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.
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From page 231... ...
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.
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From page 232... ...
232 Ct s~ B C~ .= cd o z D ;= O O ~ ·m 4— C~ Ct o L~ o (J ~C Ct ~5 U CJ C} ~ ~ ~:5 ~ ~ 00 0 ~ ~ ~ ~ ~ C~ ~ 00 ~ U~ O O ~ O ~ O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O O 0.
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From page 234... ...
234 .~ s in pa o CD o O ·s ~ ~ o ~ m Ct V c~c¢ o LO o o V TIC Cat Cat V G 3 ~ Cat ~ ~ - ^ ~ C)
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From page 235... ...
Appropriate toxicity values will need to be based on the likely exposure duration (short-term vs. chronic)
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From page 236... ...
7. Chronic toxicity The level at which an odorant can result in long-term health impact.
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From page 237... ...
237 ~ o .~ · _ o rid r sit o In o U)
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From page 238... ...
A comparison of the pollutant Units 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)
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From page 239... ...
Additionally, limitations in the chemical selection process apply to inorganic, as well as organic, pollutants. Recommendation: A revised multipathway risk assessment should beperformed for~he c:~rre7't;regulatedpoll~ta'~s, withpartic~larattentio'~paid to arsenic and to i7'direci exposure pathwaysfor cadmium and mercury.
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From page 240... ...
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.
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From page 241... ...
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.
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From page 242... ...
Jal~atior's because of data gaps. The research program should have the goal of identifj~ir~g addiilor~al chemicals that should be included i,; ro~li~ze 6iofolids surveys and in future risk assessments.
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From page 243... ...
1996. The form and bioavailability of nonionic organic chemicals in sewage sludge-amended agricultural soils.
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From page 244... ...
GP100. Presentation at the 6th International Conference on the Biogeochemistry of Trace Elements, Guelph, Ontario, Canada, July 29-August 2, 2001.
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From page 245... ...
1999. Overestimation bias and other pitfalls associated with the estimated 99.9th percentile in acute dietary exposure assessments.
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From page 246... ...
1995. A Guide to the Biosolids Risk Assessments for the EPA Part 503 Rule.
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From page 247... ...
1996b. Soil Screening Guidance: TechnicalBackground Document.
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From page 248... ...
2001b. Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites.
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From page 249... ...
2000. Nitro musks, nitro mush amino metabolites and polycyclic musks in sewage sludges.
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From page 250... ...
Begley.1998. Removal of alcohol ethoxylates, alkyl ethoxylate sulfates, and linear alkylbenzene sulfonates in wastewater treatment.
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From page 251... ...
2000b. Assessing the Bioavailability of Organic Chemicals in Soil for Use in Human Health Risk Assessments.
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From page 252... ...
1997. Effect of processing mode on trace elements in dewatered sludge products.
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From page 253... ...
2000. Potential health effects of odor from animal operations, wastewater treatment, and recycling of byproducts.
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From page 254... ...
1997. Long-term effects of biosolids applications on heavy metal bioavailability in agricultural soils.
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From page 255... ...
1983. Soil ingestion-a major pathway of heavy metals into livestock grazing contaminated land.
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From page 256... ...
2001. Effects of short-term in viva exposure to polybrominated diphenyl ethers on thyroid hormones and hepatic enzyme activities in weanling rats.
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