Wildlife ecological risk assessment in the 21st century: Promising technologies to assess toxicological effects.

Despite advances in toxicity testing and the development of new approach methodologies (NAMs) for hazard assessment, the ecological risk assessment (ERA) framework for terrestrial wildlife (i.e., air-breathing amphibians, reptiles, birds, and mammals) has remained unchanged for decades. While survival, growth, and reproductive endpoints derived from whole-animal toxicity tests are central to hazard assessment, nonstandard measures of biological effects at multiple levels of biological organization (e.g., molecular, cellular, tissue, organ, organism, population, community, ecosystem) have the potential to enhance the relevance of prospective and retrospective wildlife ERAs. Other factors (e.g., indirect effects of contaminants on food supplies and infectious disease processes) are influenced by toxicants at individual, population, and community levels, and need to be factored into chemically based risk assessments to enhance the "eco" component of ERAs. Regulatory and logistical challenges often relegate such nonstandard endpoints and indirect effects to postregistration evaluations of pesticides and industrial chemicals and contaminated site evaluations. While NAMs are being developed, to date, their applications in ERAs focused on wildlife have been limited. No single magic tool or model will address all uncertainties in hazard assessment. Modernizing wildlife ERAs will likely entail combinations of laboratory- and field-derived data at multiple levels of biological organization, knowledge collection solutions (e.g., systematic review, adverse outcome pathway frameworks), and inferential methods that facilitate integrations and risk estimations focused on species, populations, interspecific extrapolations, and ecosystem services modeling, with less dependence on whole-animal data and simple hazard ratios. Integr Environ Assess Manag 2024;20:725-748. © 2023 His Majesty the King in Right of Canada and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Toxicological effects assessment for wildlife in the 21st century: Review of current methods and recommendations for a path forward.

Model species (e.g., granivorous gamebirds, waterfowl, passerines, domesticated rodents) have been used for decades in guideline laboratory tests to generate survival, growth, and reproductive data for prospective ecological risk assessments (ERAs) for birds and mammals, while officially adopted risk assessment schemes for amphibians and reptiles do not exist. There are recognized shortcomings of current in vivo methods as well as uncertainty around the extent to which species with different life histories (e.g., terrestrial amphibians, reptiles, bats) than these commonly used models are protected by existing ERA frameworks. Approaches other than validating additional animal models for testing are being developed, but the incorporation of such new approach methodologies (NAMs) into risk assessment frameworks will require robust validations against in vivo responses. This takes time, and the ability to extrapolate findings from nonanimal studies to organism- and population-level effects in terrestrial wildlife remains weak. Failure to adequately anticipate and predict hazards could have economic and potentially even legal consequences for regulators and product registrants. In order to be able to use fewer animals or replace them altogether in the long term, vertebrate use and whole organism data will be needed to provide data for NAM validation in the short term. Therefore, it is worth investing resources for potential updates to existing standard test guidelines used in the laboratory as well as addressing the need for clear guidance on the conduct of field studies. Herein, we review the potential for improving standard in vivo test methods and for advancing the use of field studies in wildlife risk assessment, as these tools will be needed in the foreseeable future. Integr Environ Assess Manag 2024;20:699-724. © 2023 His Majesty the King in Right of Canada and The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC). Reproduced with the permission of the Minister of Environment and Climate Change Canada. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Interspecies scaling of toxicity reference values in human health versus ecological risk assessments: A critical review.

Risk assessments that focus on anthropogenic chemicals in environmental media-whether considering human health or ecological effects-often rely on toxicity data from experimentally studied species to estimate safe exposures for species that lack similar data. Current default extrapolation approaches used in both human health risk assessments and ecological risk assessments (ERAs) account for differences in body weight between the test organisms and the species of interest, but the two default approaches differ in important ways. Human health risk assessments currently employ a default based on body weight raised to the three-quarters power. Ecological risk assessments for wildlife (i.e., mammals and birds) are typically based directly on body weight, as measured in the test organism and receptor species. This review describes differences in the experimental data underlying these default practices and discusses the many factors that affect interspecies variability in chemical exposures. The interplay of these different factors can lead to substantial departures from default expectations. Alternative methodologies for conducting more accurate interspecies extrapolations in ERAs for wildlife are discussed, including tissue-based toxicity reference values, physiologically based toxicokinetic and/or toxicodynamic modeling, chemical read-across, and a system of categorical defaults based on route of exposure and toxic mode of action. Integr Environ Assess Manag 2024;20:749-764. © 2023 SETAC.

Target Lipid Model and Empirical Organic Carbon Partition Coefficients Predict Sediment Toxicity of Polychlorinated Biphenyls to Benthic Invertebrates.

Quantifying causal exposure-response relationships for polychlorinated biphenyl (PCB) toxicity to benthic invertebrates can be an important component of contaminated sediment assessments, informing cleanup decisions and natural resource injury determinations. Building on prior analyses, we demonstrate that the target lipid model accurately predicts aquatic toxicity of PCBs to invertebrates, providing a means to account for effects of PCB mixture composition on the toxicity of bioavailable PCBs. We also incorporate updated data on PCB partitioning between particles and interstitial water in field-collected sediments, to better account for effects of PCB mixture composition on PCB bioavailability. To validate the resulting model, we compare its predictions with sediment toxicity data from spiked sediment toxicity tests and a variety of recent case studies from sites where PCBs are the primary sediment contaminant. The updated model should provide a useful tool for both screening-level and in-depth risk analyses for PCBs in sediment, and it should aid in diagnosing potential contributing factors at sites where sediment toxicity and benthic community impairment are observed. Environ Toxicol Chem 2023;42:1134-1151. © 2023 SETAC.

Ecological Risk Analysis for Benzalkonium Chloride, Benzethonium Chloride, and Chloroxylenol in US Disinfecting and Sanitizing Products.

Use of three topical antiseptic compounds-benzalkonium chloride (BAC), benzethonium chloride (BZT), and chloroxylenol (PCMX)-has recently increased because of the phaseout of other antimicrobial ingredients (such as triclosan) in soaps and other disinfecting and sanitizing products. Further, use of sanitizing products in general increased during the coronavirus (COVID-19) pandemic. We assessed the environmental safety of BAC, BZT, and PCMX based on best available environmental fate and effects data from the scientific literature and privately held sources. The ecological exposure assessment focused on aquatic systems receiving effluent from wastewater-treatment plants (WWTPs) and terrestrial systems receiving land-applied WWTP biosolids. Recent exposure levels were characterized based on environmental monitoring data supplemented by modeling, while future exposures were modeled based on a hypothetical triclosan replacement scenario. Hazard profiles were developed based on acute and chronic studies examining toxicity to aquatic life (fish, invertebrates, algae, vascular plants) and terrestrial endpoints (plants, soil invertebrates, and microbial functions related to soil fertility). Risks to higher trophic levels were not assessed because these compounds are not appreciably bioaccumulative. The risk analysis indicated that neither BZT nor PCMX in any exposure media is likely to cause adverse ecological effects under the exposure scenarios assessed in the present study. Under these scenarios, total BAC exposures are at least three times less than estimated effect thresholds, while margins of safety for freely dissolved BAC are estimated to be greater than an order of magnitude. Because the modeling did not specifically account for COVID-19 pandemic-related usage, further environmental monitoring is anticipated to understand potential changes in environmental exposures as a result of increased antiseptic use. The analysis presented provides a framework to interpret future antiseptic monitoring results, including monitoring parameters and modeling approaches to address bioavailability of the chemicals of interest. Environ Toxicol Chem 2022;41:3095-3115. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Ecological risk assessment of per- and polyfluorinated alkyl substances: Foreword.

During the last 5 years, data and guidance to support ecological risk assessment of per- and polyfluorinated alkyl substance (PFAS) have become increasingly available. The studies presented in this special series exemplify and advance this progress. Among the highlights are a whole-colony honey bee toxicity study, a critical evaluation of contrasting evidence to understand avian toxicity of PFAS, a bioaccumulation model incorporating PFOS precursor transformation, and an assessment of PFAS monitoring and regulatory needs on the African continent. This foreword closes with a summary of research needs identified from the special series. Integr Environ Assess Manag 2021;17:670-672. © 2021 SETAC.

Toxicity reference values for methylmercury effects on avian reproduction: Critical review and analysis.

Effects of mercury (Hg) on birds have been studied extensively and with increasing frequency in recent years. The authors conducted a comprehensive review of methylmercury (MeHg) effects on bird reproduction, evaluating laboratory and field studies in which observed effects could be attributed primarily to Hg. The review focuses on exposures via diet and maternal transfer in which observed effects (or lack thereof) were reported relative to Hg concentrations in diet, eggs, or adult blood. Applicable data were identified for 23 species. From this data set, the authors identified ranges of toxicity reference values suitable for risk-assessment applications. Typical ranges of Hg effect thresholds are approximately 0.2 mg/kg to >1.4 mg/kg in diet, 0.05 mg/kg/d to 0.5 mg/kg/d on a dose basis, 0.6 mg/kg to 2.7 mg/kg in eggs, and 2.1 mg/kg to >6.7 mg/kg in parental blood (all concentrations on a wet wt basis). For Hg in avian blood, the review represents the first broad compilation of relevant toxicity data. For dietary exposures, the current data support TRVs that are greater than older, commonly used TRVs. The older diet-based TRVs incorporate conservative assumptions and uncertainty factors that are no longer justified, although they generally were appropriate when originally derived, because of past data limitations. The egg-based TRVs identified from the review are more similar to other previously derived TRVs but have been updated to incorporate new information from recent studies. While important research needs remain, a key recommendation is that species not yet tested for MeHg toxicity should be evaluated using toxicity data from tested species with similar body weights. Environ Toxicol Chem 2017;36:294-319. © 2016 SETAC.

Critical perspectives on mercury toxicity reference values for protection of fish.

Environmental management decisions at mercury-contaminated sediment sites are predicated on the understanding of risks to various receptors, including fish. Toxicity reference values (TRVs) for interpreting risks to fish have been developed to assess mercury concentrations in fish or fish prey. These TRVs were systematically evaluated based on several lines of evidence. First, their conceptual basis and specific derivation were evaluated, including a close review of underlying toxicity studies. Second, case studies were reviewed to investigate whether TRVs are predictive of effects on fish populations in the field. Third, TRVs were compared with available information regarding preindustrial and present-day background concentrations of mercury in fish. The findings show that existing TRVs are highly uncertain, because they were developed using limited data from studies not designed for TRV derivation. Although field studies also entail uncertainty, several case studies indicate no evidence of adverse effects despite mercury exposures that exceed the available TRVs. Some TRVs also fall within the range of background mercury concentrations in predatory or prey fish. Lack of information on the selenium status of mercury-exposed fish is a critical confounding factor, and the form of methylmercury used in toxicity testing may also contribute to differences between TRV-based predictions and field observations of mercury effects on fish. On balance, the available information indicates that several of the TRVs reviewed are lower than necessary to protect fish populations. The 20% effect concentration from a previously published dose-response analysis appears closer to an effect threshold, based on available laboratory data. Additional research is needed to provide a stronger basis to establish dose-response relationships for mercury effects on fish.

Growth and reproductive effects from dietary exposure to Aroclor 1268 in mink (Neovison vison), a surrogate model for marine mammals.

Polychlorinated biphenyls (PCBs) from the commercial mixture Aroclor 1268 were historically released into the Turtle-Brunswick River estuary (southeastern Georgia, USA) from industrial operations. Sum PCBs (ΣPCBs) in blubber samples from Turtle-Brunswick River estuary bottlenose dolphins (Tursiops truncatus) have been reported at concentrations more than 10-fold higher than those observed in dolphins from adjacent regional estuaries. Given that toxicity data specific to Aroclor 1268 and applicable to marine mammals are limited, predicting the toxic effects of Aroclor 1268 in dolphins is uncertain, particularly because of its unique congener profile and associated physiochemical characteristics compared with other PCB mixtures. American mink (Neovison vison) were chosen as a surrogate model for cetaceans to develop marine mammalian PCB toxicity benchmarks. Mink are a suitable surrogate species for cetaceans in toxicity studies because of similarities in diet and taxonomic class, and a characteristic sensitivity to PCBs provides a potential safety factor when using mink toxicology data for cross-species extrapolations. Effects of dietary exposure to Aroclor 1268 on reproduction, growth, and mortality in mink were compared with both a negative control and a positive control (3,3',4,4',5-pentachlorobiphenyl, PCB 126). Aroclor 1268 dietary ΣPCB concentrations ranged from 1.8 µg/g feed wet weight to 29 µg/g feed wet weight. Whelp success was unaffected by Aroclor 1268 exposure at any level. Treatment mean litter size, kit growth, and kit survival were adversely affected relative to the negative control at dietary ΣPCB concentrations of 10.6 µg/g feed wet weight and greater.

Enzyme induction and histopathology elucidate aryl hydrocarbon receptor-mediated versus non-aryl hydrocarbon receptor-mediated effects of Aroclor 1268 in American mink (Neovison vison).

Polychlorinated biphenyl (PCB) concentrations reported in preferred prey and blubber of bottlenose dolphins from the Turtle-Brunswick River estuary (Georgia, USA) suggest the potential for adverse effects. However, PCBs in Turtle-Brunswick River estuary dolphins are primarily derived from Aroclor 1268, and predicting toxic effects of Aroclor 1268 is uncertain because of the mixture's unique composition and associated physiochemical characteristics. These differences suggest that toxicity benchmarks for other PCB mixtures may not be relevant to dolphins exposed to Aroclor 1268. American mink (Neovison vison) were used as a surrogate model for cetaceans to characterize mechanisms of action associated with Aroclor 1268 exposure. Mink share similarities in phylogeny and life history with cetaceans and are characteristically sensitive to PCBs, making them an attractive surrogate species for marine mammals in ecotoxicity studies. Adult female mink and a subsequent F1 generation were exposed to Aroclor 1268 through diet, and effects on enzyme induction, histopathology, thyroid hormone regulation, hematology, organ weights, and body condition index were compared to a negative control and a 3,3',4,4',5-pentachlorobiphenyl (PCB 126)-positive control. Aroclor 1268 dietary exposure concentrations ranged from 1.8 µg/g wet weight to 29 µg/g wet weight. Anemia, hypothyroidism, and hepatomegaly were observed in mink exposed to Aroclor 1268 beyond various dietary thresholds. Cytochrome P450 induction and squamous epithelial proliferation jaw lesions were low in Aroclor 1268 treatments relative to the positive control. Differences in enzyme induction and the development of squamous epithelial proliferation jaw lesions between Aroclor 1268 treatments and the positive control, coupled with effects observed in Aroclor 1268 treatments not observed in the positive control, indicate that mechanisms additional to the aryl hydrocarbon receptor-mediated pathway are associated with Aroclor 1268 exposure.

Critical review of mercury sediment quality values for the protection of benthic invertebrates.

Sediment quality values (SQV) are commonly used-and misused-to characterize the need for investigation, understand causes of observed effects, and derive management strategies to protect benthic invertebrates from direct toxic effects. The authors compiled more than 40 SQVs for mercury, nearly all of which are "co-occurrence" SQVs derived from databases of paired chemistry and benthic invertebrate effects data obtained from field-collected sediment. Co-occurrence SQVs are not derived in a manner that reflects cause-effect, concentration-response relationships for individual chemicals such as mercury, because multiple potential stressors often co-occur in the data sets used to derive SQVs. The authors assembled alternative data to characterize mercury-specific effect thresholds, including results of 7 laboratory studies with mercury-spiked sediments and 23 studies at mercury-contaminated sites (e.g., chloralkali facilities, mercury mines). The median (± interquartile range) co-occurrence SQVs associated with a lack of effects (0.16 mg/kg [0.13-0.20 mg/kg]) or a potential for effects (0.88 mg/kg [0.50-1.4 mg/kg]) were orders of magnitude lower than no-observed-effect concentrations reported in mercury-spiked toxicity studies (3.3 mg/kg [1.1-9.4 mg/kg]) and mercury site investigations (22 mg/kg [3.8-66 mg/kg]). Additionally, there was a high degree of overlap between co-occurrence SQVs and background mercury levels. Although SQVs are appropriate only for initial screening, they are commonly misused for characterizing or managing risks at mercury-contaminated sites. Spiked sediment and site data provide more appropriate and useful alternative information for characterization and management purposes. Further research is recommended to refine mercury effect thresholds for sediment that address the bioavailability and causal effects of mercury exposure. Environ Toxicol Chem 2015;34:6-21. © 2014 SETAC.

Probabilistic application of a fugacity model to predict triclosan fate during wastewater treatment.

The fate and partitioning of the antimicrobial compound, triclosan, in wastewater treatment plants (WWTPs) is evaluated using a probabilistic fugacity model to predict the range of triclosan concentrations in effluent and secondary biosolids. The WWTP model predicts 84% to 92% triclosan removal, which is within the range of measured removal efficiencies (typically 70% to 98%). Triclosan is predominantly removed by sorption and subsequent settling of organic particulates during primary treatment and by aerobic biodegradation during secondary treatment. Median modeled removal efficiency due to sorption is 40% for all treatment phases and 31% in the primary treatment phase. Median modeled removal efficiency due to biodegradation is 48% for all treatment phases and 44% in the secondary treatment phase. Important factors contributing to variation in predicted triclosan concentrations in effluent and biosolids include influent concentrations, solids concentrations in settling tanks, and factors related to solids retention time. Measured triclosan concentrations in biosolids and non-United States (US) effluent are consistent with model predictions. However, median concentrations in US effluent are over-predicted with this model, suggesting that differences in some aspect of treatment practices not incorporated in the model (e.g., disinfection methods) may affect triclosan removal from effluent. Model applications include predicting changes in environmental loadings associated with new triclosan applications and supporting risk analyses for biosolids-amended land and effluent receiving waters.

Terrestrial ecological risk evaluation for triclosan in land-applied biosolids.

Triclosan is an antimicrobial compound found in many consumer products including soaps and personal care products. Most triclosan is disposed of down household drains, whereupon it is conveyed to wastewater treatment plants. Although a high percentage of triclosan biodegrades during wastewater treatment, most of the remainder is adsorbed to sludge, which may ultimately be applied to land as biosolids. We evaluated terrestrial ecological risks related to triclosan in land-applied biosolids for soil microbes, plants, soil invertebrates, mammals, and birds. Exposures are estimated using a probabilistic fugacity-based model. Triclosan concentrations in biosolids and reported biosolids application rates are compiled to support estimation of triclosan concentrations in soil. Concentrations in biota tissue are estimated using an equilibrium partitioning model for plants and worms and a steady-state model for small mammals; the resulting tissue concentrations are used to model mammalian and avian dietary exposures. Toxicity benchmarks are identified from a review of published and proprietary studies. The results indicate that adverse effects related to soil fertility (i.e., disruption of nitrogen cycling) would be expected only under "worst-case" exposures, under certain soil conditions and would likely be transient. The available data indicate that adverse effects on plants, invertebrates, birds, and mammals due to triclosan in land-applied biosolids are unlikely.

Probabilistic risk evaluation for triclosan in surface water, sediments, and aquatic biota tissues.

Triclosan, an antimicrobial compound used in personal care products, occurs in the aquatic environment due to residual concentrations in municipal wastewater treatment effluent. We evaluate triclosan-related risks to the aquatic environment, for aquatic and sediment-dwelling organisms and for aquatic-feeding wildlife, based on measured and modeled exposure concentrations. Triclosan concentrations in surface water, sediment, and biota tissue are predicted using a fugacity model parameterized to run probabilistically, to supplement the limited available measurements of triclosan in sediment and tissue. Aquatic toxicity is evaluated based on a species sensitivity distribution, which is extrapolated to sediment and tissues assuming equilibrium partitioning. A probabilistic wildlife exposure model is also used, and estimated doses are compared with wildlife toxicity benchmarks identified from a review of published and proprietary studies. The 95th percentiles of measured and modeled triclosan concentrations in surface water, sediment, and biota tissues are consistently below the 5th percentile of the respective species sensitivity distributions, indicating that, under most scenarios, adverse affects due to triclosan are unlikely.

Erratum: Probabilistic application of a fugacity model to predict triclosan fate during wastewater treatment.

The fate and partitioning of the antimicrobial compound, triclosan, in wastewater treatment plants (WWTPs) is evaluated using a probabilistic fugacity model to predict the range of triclosan concentrations in effluent and secondary biosolids. The WWTP model predicts 84% to 92% triclosan removal, which is within the range of measured removal efficiencies (typically 70% to 98%). Triclosan is predominantly removed by sorption and subsequent settling of organic particulates during primary treatment and by aerobic biodegradation during secondary treatment. Median modeled removal efficiency due to sorption is 40% for all treatment phases and 31% in the primary treatment phase. Median modeled removal efficiency due to biodegradation is 48% for all treatment phases and 44% in the secondary treatment phase. Important factors contributing to variation in predicted triclosan concentrations in effluent and biosolids include influent concentrations, solids concentrations in settling tanks, and factors related to solids retention time. Measured triclosan concentrations in biosolids and non-United States (US) effluent are consistent with model predictions. However, median concentrations in US effluent are over-predicted with this model, suggesting that differences in some aspect of treatment practices not incorporated in the model (e.g., disinfection methods) may affect triclosan removal from effluent. Model applications include predicting changes in environmental loadings associated with new triclosan applications and supporting risk analyses for biosolids-amended land and effluent receiving waters.

Geochemical stability of chromium in sediments from the lower Hackensack River, New Jersey.

Elevated levels of chromium, partly attributable to historical disposal of chromite ore processing residue, are present in sediment along the eastern shore of the lower Hackensack River near the confluence with Newark Bay. Due to anaerobic conditions in the sediment, the chromium is in the form of Cr(III), which poses no unacceptable risks to human health or to the river ecology. However, as water quality conditions have improved since the 1970s, aerobic conditions have become increasingly prevalent in the overlying water column. If these conditions result in oxidation of Cr(III) to Cr(VI), either under quiescent conditions or during severe weather or anthropogenic scouring events, the potential for adverse ecological effects due to biological exposures to Cr(VI) is possible, though the reaction kinetics associated with oxidation of Cr(III) to Cr(VI) are unfavorable. To investigate the stability of Cr(III) in Hackensack River sediments exposed to oxic conditions, sediment suspension and oxidation experiments and intertidal sediment exposure experiments that exposed the sediments to oxic conditions were conducted. Results revealed no detectable concentrations of Cr(VI), and thus no measurable potential for total chromium oxidation to Cr(VI). Furthermore, total chromium released from sediment to elutriate water in the oxidation and suspension experiments ranged from below detection (<0.01 mg/L) to 0.18 mg/L, below the freshwater National Recommended Water Quality Criteria (NRWQC) of 0.57 mg/L for Cr(III). These results support conclusions of a stable, in situ geochemical environment in sediments in the lower Hackensack River with respect to chromium. Results showed that chemicals other than Cr(VI), including copper, lead, mercury, zinc, and PCBs, were released at levels that may pose a potential for adverse ecological effects.

Using a Sediment Quality Triad approach to evaluate benthic toxicity in the Lower Hackensack River, New Jersey.

A Sediment Quality Triad (SQT) study consisting of chemical characterization in sediment, sediment toxicity and bioaccumulation testing, and benthic community assessments was performed in the Lower Hackensack River, New Jersey. Chemistry data in sediment and porewater were evaluated based on the equilibrium partitioning approach and other published information to investigate the potential for chemical effects on benthic organisms and communities. Relationships were supported by laboratory toxicity and bioaccumulation experiments to characterize chemical effects and bioavailability. Benthic community results were evaluated using a regional, multimetric benthic index of biotic integrity and four heterogeneity indices. Evidence of slight benthic community impairment was observed in five of nine sediment sample stations. Severe lethal toxicity to amphipods (Leptocheirus plumulosus) occurred in four of these five stations. Although elevated total chromium concentrations in sediment (as high as 1900 mg/kg) were the rationale for conducting the investigation, toxicity was strongly associated with concentrations of polycyclic aromatic hydrocarbons (PAHs) rather than total chromium. PAH toxic units (SigmaPAH TU) in sediment and SigmaPAH concentrations in laboratory organisms from the bioaccumulation experiment showed a clear dose-response relationship with toxicity, with 0% survival observed in sediments in which SigmaPAH TU > 1-2 and SigmaPAH concentrations in Macoma nasuta were >2 micromol/g, lipid weight. Metals detected in sediment and porewater, with the possible exception of copper, did not correlate with either toxicity or levels in tissue, likely because acid-volatile sulfide levels exceeded concentrations of simultaneous extracted metals at all sample locations. The study reinforces the value of using multiple lines of evidence approaches such as the SQT and the importance of augmenting chemical and biological analyses with modeling and/or other approaches to evaluate chemical bioavailability and toxicity of sediments.

An evaluation of cause-effect relationships between polychlorinated biphenyl concentrations and sediment toxicity to benthic invertebrates.

Cause-effect sediment-quality benchmarks for the protection of benthic invertebrates are needed for polychlorinated biphenyls (PCBs) to support predictive risk assessments and retrospective evaluations of the causes of observed sediment toxicity. An in-depth evaluation of PCB aquatic toxicity and organic carbon partitioning was conducted to predict sediment effect concentrations using the equilibrium partitioning (EqP) approach. This evaluation was limited to invertebrate toxicity data, because PCBs may exert toxicity to invertebrates and fish via different toxicological mechanisms. As a result of differences in organic carbon partitioning among PCBs of differing levels of chlorination, the estimated EqP benchmarks increase with increasing degree of chlorination for various commercial and environmental PCB mixtures. Studies of spiked sediment toxicity using PCBs were reviewed, and their results generally were consistent with EqP predictions. Additionally, toxicity and benthic community data were reviewed for eight PCB-contaminated sites; these data also showed agreement with EqP predictions. None of these lines of evidence supports previously proposed, empirical sediment-quality guidelines for PCBs. Reasons for the lack of agreement between cause-effect and association-based benchmarks are discussed, and areas of future research to further refine EqP predictions for PCBs are identified.

Post-fire surface water quality: comparison of fire retardant versus wildfire-related effects.

An understanding of the environmental effects of the use of wildland fire retardant is needed to provide informed decision-making regarding forest management. We compiled data from all post-fire surface water monitoring programs where the fire retardant constituents ammonia, phosphorus, and cyanide were measured, and data were available in the public domain. For streams near four major wildfires, we evaluated whether these chemicals originated primarily from fire or from retardant use. We compared measured concentrations in streams where chemical wildland fire retardant was applied with concentrations in streams draining areas where retardant was not used. Correlations with calcium provided an additional line of evidence, because calcium concentrations in ash are much higher than in retardant. Ammonia, phosphorus, and total cyanide were found in streams in burned areas where retardant was not used, at concentrations similar to those found in areas where retardant was applied. Concentrations of weak acid dissociable cyanide were generally non-detected or very low, whether or not wildland fire retardant was used in the watershed. These results indicate that the application of wildland fire retardant had minimal effects on proximate surface water quality. Cyanide concentrations in post-fire stormwater runoff were not affected by the presence of ferrocyanide in the retardant formulas and were due to pyrogenic sources.

Modification of the equilibrium partitioning approach for volatile organic compounds in sediment.

Although weakly hydrophobic chemicals such as volatile organic compounds (VOCs) tend not to persist in sediments, they may nevertheless be present in some sediments because of recent or ongoing releases. Standard methods are not available for assessing risks to benthic invertebrates due to VOCs in sediment. More strongly hydrophobic organic chemicals are frequently assessed by using the equilibrium partitioning (EqP) approach, which predicts the bioavailable fraction of chemical (the concentration dissolved in pore water) from the sediment-sorbed fraction, assuming that partitioning is at equilibrium. As typically applied, the EqP approach is ineffective for assessing VOCs in sediment, because the standard EqP equation fails to account for the contribution of dissolved chemical to the total chemical concentration in sediment. For chemicals with low organic carbon-water partition coefficients (Kocs), this results in nonsensical sediment-quality benchmarks that are more conservative (i.e., lower) than benchmarks calculated by assuming 100% bioavailability. A modified EqP equation is presented that accounts for the dissolved fraction of total chemical concentrations in sediment. Results of the standard and modified EqP equations converge with increasing Koc and are essentially identical at log Koc values exceeding approximately 3.5.