A Risk-Management Strategy for PCB-Contaminated Sediments (2001) / Chapter Skim
Currently Skimming:
Analyzing Risks
Analyzing Risks
Pages 118-188
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From page 118... ...
A critical part of this evaluation is the characterization of existing and potential risks to affected parties. In analyzing risks from PCB-contaminated sediments, the primary focus has been on human health and ecological effects from exposure, the emphasis being on the bioaccumulation of PCBs through the aquatic food web and the human health effects associated with the consumption of contaminated seafood.
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From page 119... ...
This chapter provides an overview of the ERA process and discusses the use and limitations of scientific information in each of the steps of a risk assessment of PCB-contaminated sediments. The steps that are described include exposure assessment to PCBs; ecological effects and human health effects from PCB exposure; PCB risk characterization; social, cultural, and economic impacts of PCB contamination; and comparative risk assessment.
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From page 120... ...
The analysis phase for human health and ecological risk assessments includes an identification of exposure pathways, a characterization of exposures, and an assessment of the relationship between exposures and effects. Finally, the risk-characterization phase involves quantifying overall risks to humans and wildlife.
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From page 121... ...
For example, for humans, it might be possible to measure PCB concentrations in food and in human tissues.
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From page 122... ...
of exposure pathways is developed (see Box 6-2~. This conceptual model can then be used to conduct a pathways analysis to determine the level of exposure expected for each trophic level or individual receptor (e.g., see Figure 6-1~.
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From page 123... ...
The concentrations in fish can be used directly by comparing them to dietary toxicity reference values (TRY) or by using them to predict exposures to higher trophic levels.
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From page 124... ...
Omnivorous/Carnivorous Fish/lnvertebrates Turtles/Crayfish Several Fish Species Trophic Level 2 (Secondary Consumer) PCBs In Sediments l Carnivorous/Piscivorous Birds Bald Eagle Peregrine Falcon Brown Pelican Doubl - Crested Cormorant ..
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From page 125... ...
Further details of the analysis phase, such as PCB exposure assessment, and human health and ecological effects are presented below. PCB Exposure Assessment The purpose of an exposure assessment is to determine the concentrations of PCBs in various environmental compartments, including sediment, water, benthic invertebrates, and fish, and to evaluate dietary exposures to PCBs of higher trophic level organisms, such as birds, aquatic mammals, and humans.
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From page 126... ...
Sediment and fish samples collected in Thompson Island Pool (the first impoundment on the upper Hudson River, a few miles downstream of the General Electric plant sites) are shown in Figure 6-2 and provide a dramatic example of PCB weathering in the environment.
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From page 127... ...
This difference indicates that the pattern of relative concentrations of PCBs changes because of such processes as weathering, bioaccumulation, and metabolic processes as the individual congeners move from one atrophic level to the next. nv~ronmental wea~enng changes the relative concentrations of PCB congeners | because of differential solubilities, volatilities, and sorption coefficients (Mackay et al.
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From page 128... ...
0 _ , ~ l~ r~ ~'~ l ~ ~~ s 1l ~ l ll l T ~ lll n ~ ~ ~ l ~ ll n l rn ~ r~^ l ~ n i n N ~) ~ _ FIGURE 6-2 Congener distributions for PCB sources' sediments, and fish in the Upper Hudson River.
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From page 129... ...
consumption rates can be determined from individual diet surveys or foodmarket sale records. In calculating dietary exposure, PCB concentrations in contaminated prey are typically defined on a whole-body basis for birds and aquatic mammals, whereas PCB concentrations in fish fillet are used in
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From page 130... ...
1986~. Because PCBs are a group of compounds and the absolute and relative concentrations of PCBs in sediments are changing as a function of space, time, and trophic level, the method used to quantify PCBs can have a great impact on the risk-assessment process.
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From page 131... ...
For organisms at higher trophic levels, PCB concentrations in contaminated food are used to calculate dietary exposure rates that, for example, may be compared with allowable dosage rates (e.g., reference dose (RfD)
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From page 132... ...
PCB input from contaminated ground water might add to PCB inventories in surface waters and sediments. At some sites, migration of PCBs from contaminated sediments may also be a concern.
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From page 133... ...
To account for preferential binding of PCBs to organic carbon in sediments and lipid content in the organisms, PCB concentrations in bottom-dwelling organisms and sediments are generally related using lipid-normalized accumulations of PCBs in organisms and organic carbon-normaTized PCB concentrations in sediments. Because fish typically have a larger home range than bottom-dwelling organisms, aerial-weighted-average concentrations of PCBs in surface sediments, and not hot spot concentrations, are often considered to be a better indicator of potential PCB concentrations in fish.
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From page 134... ...
Since PCBs have a strong affinity for organic carbon, organic carbon distributions have also been modeled explicitly for a few sites. Further details regarding the modeling components hyclrodynamic transport, sediment transport, organic carbon, PCB fate and transport, an(l bioaccumuiation—are given below.
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135 E~ ' tU ° C,~ ._ ~ oo C~ ...............
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From page 136... ...
1983~) to complex multidimensional hydrodynamic computer simulations (e.g., for the Hudson River (Blumberg et al.
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From page 137... ...
In this regard, sediment-transport modeling results provide critical information in assessing the depth of sediment scour during high-flow events and in identifying mixing of buried PCBs with the biologically active sediment layer, water column, or both. Organic Carbon Since PCBs have a strong affinity for particulate (POC)
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From page 138... ...
Partitioning between freely dissolved and particulate phases are either derived from field measurements or assumed to be a direct function of the octanol-water partitioning coefficient and the fraction of organic carbon on the suspended or sediment solids. To account for differences in PCB partitioning to lowermolecular-weight DOC compounds and octanol, partitioning of PCBs between the freely dissolved and the DOC-bound phases is typically assumed to be a fraction of the octanol-water partition coefficient.
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From page 139... ...
A time sequence of PCB concentrations in the sediments and overlying water is typically used for model calibration. Because several modeling coefficients can be adjusted in the calibration procedure, a good comparison between PCB model results and field data alone does not guarantee the proper selection of all modeling coefficients.
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From page 140... ...
For fish and higher trophic level organisms, PCB exposure from ingestion of contaminated prey will often dominate, and biomagnification of PCBs from one trophic level to the next is likely to occur (see Box 6-5~. Models of PCB bioaccumulation in organisms are available with several levels of detail, ranging from simple empirical models to complex food-web models.
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From page 141... ...
of PCBs Among Trophic Levels A study was conducted on the changes in the absolute and relative concentrations and relative patterns of individual PCB congeners, as well as total PCB concentrations, among trophic compartments. It was determined whether toxic potentials of PCB mixtures change as a function of trophic level when accumulated from the sediments of Saginaw Bay.
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From page 142... ...
For example, projected responses for PCB concentrations in fish from Thompson Island Pool on the upper Hudson River are discussed in Box 6-6. The relative importance of downstream transport, volatilization, burial, dechlorination, and food-chain transfer can also be examined using model simulation results.
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From page 143... ...
Mode] projections for PCB concentrations in Thompson Island Pool fish are shown in Figure 6-5 for five possible remediation scenarios: · No action (no upstream source control)
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From page 144... ...
144 Go - -a Go Us - o [' ~ ~~ no 0 C' .
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From page 145... ...
when the largest amount of sediment is expected to be mobilized. Organic carbon distributions in the sediment and overlying water are usually determined by field!
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From page 146... ...
Due to the fact that the absolute end relative concentrations of PCB congeners can change over time and that different congeners with different chemicalphysical characteristics result in different partitioning- characteristics, the exposure profile can change over time and depending on trophic levels. PCB Effects Assessment The purpose of effects assessment is to determine PCB dose-response and other stressor-response relationships and show evidence that exposure to PCBs or other stressors causes an observed human or ecological response.
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From page 147... ...
Thus, it is generally inappropriate to apply such simple relationships to total PCB concentrations. To account for the changes in the relative concentrations and thus toxic potency, the TEQ approach has been developed.
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From page 148... ...
Theoretically, based on fugacity theory, if the organic carbon in the sediments is equivalent to that in biota, this value should be 1.0. Thus, only about half of the mass of PCB in TABLE 6-1 Average TEQs Calculated from the Average Sum of Non- and Mono-Substituted PCBs and the Resulting TEQs Ratios Across Trophic Levels Sample Sum Non- and Mono-PCB TEQs TEQs Matrix ng/g Lipid SD ng/g lipid SD Trophic Ratios Sedimentl 2.2 x 103 4.2 x 102 1.1 x 10~1 2.2 x 10-2 _ Invertebrate 8.3 x 102 6.8 x 102 3.0 x 10-2 2.0 x 10-2 Invertebrate/ sediment, 0.3 Egg 1.4 x 103 7.8 x 1o2 8.8 x 10-2 4.1 x 10-2 Egg/invertebrate, 3.0 Nestling 2.4 x 103 3.5 x 103 1.l X TO-} 1.6 x 10-~ Nestling/egg, 1.3 iSediment values are ng/g organic carbon.
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From page 149... ...
1993~. Using those data, the relative potencies were calculated based on total PCBs of 1.6 x 10-5, I.8 x 1O-s and 1.1 x 1O-s for tree swallow eggs, newly hatched chicks, and 1 6-day old nestlings, respectively.
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From page 150... ...
150 · _ Cd o 0' Cat o Cal · _ C)
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From page 151... ...
Ratios of the relative potencies among trophic levels demonstrated a decrease in the relative toxic potency from sediment to invertebrates but an increase in the relative toxic potency between invertebrates and tree swallow eggs (Table 6-2~. The relative enrichment of TEQs with respect to the original Aroclor mixture in the same trophic level can also be calculated (Table 6-2~.
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From page 152... ...
BSAF calculations based on total PCBs were between ~ and ~ I, and those based on non- and TABLE 6-3 BS~ Valuesa for Each Manx Based on Total PCBs, the Sum of the Non- and Mono-Ortho-Substituted PCB Congeners, and TEQs Matrix Sum of Non- and PCB~o~a~ Mono-PCBs TEQs Invertebrates 11 0.4 0.3 Tree swallow eggs 8.8 0.6 0.8 Tree swallow nestlings 9.3 1.1 1.0 aEach value represents the ratio of the lipid-normalized concentration in tissue divided by the organic carbon-normalized concentration in sediments. Source: Adapted from Froese et al.
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From page 153... ...
BSAF values for total PCBs are often greater than would be expected if based on fugacity theory. The high values might be related to the contribution of PCBs in sediments within the guts of the invertebrates.
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From page 154... ...
l991~. The BSAF values observed for the distribution of total PCBs between sediments and infaunal invertebrates can range by up to 2 orders of magnitude, but a global average value of ~ .7 has been suggested for use in risk assessments when BSAF values have not been determined for a particular site (Landrum and Poore ~ 9884.
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From page 155... ...
Because PCBs usually are associated with, or bound to, sediments, attempts have been made to relate PCB concentrations in sediment to effects concentrations. These effects concentrations, as well as the national ambient water quality criteria for total PCBs, are presented in Appendix G
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From page 156... ...
Causal links between chronic toxicity effects and Aroclor or total PCB concentrations have been reported in a number of laboratory studies. These results, however, might not be directly applicable to field conditions, because they were largely performed using parent Aroclor mixtures and do not account for possible reduction or enrichment in toxic potency by environmental weathering (Williams et al.
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From page 157... ...
Risk assessments are meant to be accurate representations ofthe potential for risk but are designed to be protective rather than predictive. Even though PCBs are a mixture of compounds with different relative potencies, the concentration ofthe entire mixture to which an organism is exposed is determined by the congeners or class of congeners with the maximum toxic potency.
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From page 158... ...
Toxicity data indicate that waterborne or tissue PCB concentrations that might cause adverse effects for Tower trophic level organisms are much greater than PCB concentrations reported for contaminated environments (Niimi et al.
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From page 159... ...
Confounding factors affecting the relationship between sediment concentrations and effects can include differences in PCB 1 · '1 ~ ·1 ', ~ . - ~ ~ - , · ~ ~ b~oava~lab~l~ty as a function ot sediment organic carbon and the presence of co-contaminants.
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From page 160... ...
1997) have been found that correlate effects from PCB dietary exposure to Aroclors and that correlate tissue residue effects levels in eggs to Aroclors, total PCBs, PCB congeners, and TODD and TCDD-equivalents (see Box 6-7~.
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From page 161... ...
(1997) found that PCB 77 decreased in relative abundance both within total PCBs and within its homologue group with increasing trophic level.
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From page 162... ...
Risk assessments based on mink often result in the least allowable concentrations in sediments, and if mink are used as a surrogate in risk assessment, most other species, including humans, should be protected. Lipid-normalized NOAEL values of 1 1 microgram per gram (pg/g)
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From page 163... ...
The effects attributed to exposure to PBS include alteration of enzyme activities, suppression of the immune system, embryo-lethality, and developmental abnormalities. The effects observed in the field have been substantiated in the same wildlife species and surrogate animal models under laboratory conditions.
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From page 164... ...
~ 988~. Similarly, alterations in immunological parameters were most strongly correlated with prenatal rather than postnatal measures of PCB exposure, although the effects from postnatal exposure disappear more quickly (primarily within 2-3 years following exposures)
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From page 165... ...
1994~. Limitations of Human Health Risk Assessments for PCBs The classic problem with determining relative risk due to mixtures of compounds, like PCBs, is posed by the following question, "How do we account for the toxicity of the individual congeners when potencies differ between congeners and between endpoints (effects)
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From page 166... ...
Risk-management decisions might result in competing risks; therefore, it is not appropriate to select extreme safety factors that result in gross overestimation of human and ecological risks from PCB-contaminated sediments. If no alternative risks exist, it might be more appropriate to take a very conservative approach in estimating the risks of PCBs in sediments.
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From page 167... ...
Ecological Risk from Chemical Exposure The potential risks of PCB exposure to ecological receptors are evaluated by comparing the results of exposure assessment (e.g., measured or modeled concentrations of chemicals in receptors of concern) with TRVs.
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From page 168... ...
Variations in exposure are expected within an identified subpopulation because of individual differences in fish consumption rates, body weight, and PCB concentrations in consumer! fish.
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From page 169... ...
in estimating CDI values. The primary, although not exclusive, source of information for CSFs and RfDs used in Superfund risk assessments is the EPA Integrated Risk Information System (IRIS)
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From page 170... ...
If a certain contaminant pathway of either in-place or external sources of PCBs is not included or not properly characterized in the conceptual model, errors will be propagated throughout the analysis. · Natural variation and parameter error: Natural variations in measurement of PCB concentrations, lipid content, age, body weight, feeding rate, and duration of exposure for an endpoint species might result in errors in specifying parameters for exposure assessment.
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From page 171... ...
~ 998~. Furthermore, increased ambient-air PCB concentrations can occur during remediation operations because of increased physical disturbance of the sediments.
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From page 172... ...
· Loss of benefits to recreational swimmers and boaters: Although scientific information suggests that human health risk from incidental contact with river water and sediments is low, some individuals might avoid swimming and boating in contaminated areas because of a fear of being exposed to PCBs. ~ Increased costs of drinking water: Although dissolved PCB concentrations in waters overlying PCB-contaminated sediments are typically below the maximum contaminant level goal for PCBs in drinking water (0.5 high)
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From page 173... ...
Lawrence River has caused many of the men to leave the reservation to find work, resulting in a breakdown of family and a loss of tribal traditions. COMPARATIVE RISK ASSESSMENT Determining an overall assessment of risk from PCB-contaminated sediments is a challenging task that requires sound scientific information and consensus-building among affected parties.
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From page 174... ...
For example, should short-term increases in PCB exposure levels during remedial activity be acceptable in achieving Tong-term reduction of risk? To foster an open discussion of risks, summary information should be tabulated and periodically disseminated to all affected parties.
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From page 175... ...
1988) has separated risk into the more easily measured "hazard" and the more subjective and emotion-laden "outrage." Some of the factors that affect "outrage" were garnered by the committee during their visit to the Hudson River, and discussion with affected parties include the following: · Many of the public groups from along the lower Hudson River expressed a preference for dredging whatever PCB-contaminated sediments could be removed.
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From page 176... ...
Risk assessments and risk-management decisions should be conducted on a site-specific basis and should incorporate all available scientific information. Current management options can reduce risks but cannot completely eliminate PCBs and PCB exposure from contaminated-sediment sites.
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From page 177... ...
Because the composition of PCB mixtures in the environment changes over time, risk characterizations should be based on the specific congeners present at a site. New studies on the toxicity and fate of PCBs in the environment are being conducted, and the results from these studies should be used to inform risk assessments at contaminates]
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From page 178... ...
Models used to describe all relevant PCB exposure pathways—Tom the contaminated sediments, through the aquatic food web, and to specific receptors must consider exposures to sensitive populations, including but not limited to the elderly, pregnant women, infants, and children; culturally or economically unique populations; and sensitive and endangered wildlife and their habitats. These models, which have inherent uncertainty, require calibration that should be conducted by multiple researchers.
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From page 179... ...
1995. PCB congeners and hexachlorobenzene biota sediment accumulation factors for Macoma nasuta exposed to sediments with different total organic carbon contents.
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From page 180... ...
1995b. Isomerspecific analysis of polychlorinated biphenyls and 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs)
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From page 181... ...
1998. Bioaccumulation of polychlorinated biphenyls from sediments to aquatic insects and tree swallow eggs and nestlings in Saginaw Bay, Michigan, USA.
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From page 182... ...
1993. A model for predicting the bioaccumulation of hydrophobic organic chemicals in aquatic food webs: application to Lake Ontario.
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From page 183... ...
2000. Toxicity reference values for the toxic effects of polychlorinated biphenyls to aquatic mammals.
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From page 184... ...
1983. Physical chemical properties of polychlorinated biphenyls.
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From page 185... ...
l 999. Effects of environmental exposure to polychlorinated biphenyls and dioxins on cognitive abilities in Dutch children at 42 months of age.
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From page 186... ...
l999b. PCBs in the Upper Hudson River.
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From page 187... ...
1992. Mortality among workers exposed to polychlorinated biphenyls.
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From page 188... ...
1995. Immunologic effects of background prenatal and postnatal exposure to dioxins and polychlorinated biphenyls in Dutch infants.
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