Application of the tissue residue approach in ecological risk assessment

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.

Developing As and Cu Tissue Residue Thresholds to Attain the Good Ecological Status of Rivers in Mining Areas

The study was performed on residue-effects datasets from polluted and unpolluted sites in the Nalón River basin (northern Spain). The effects were measured in terms of alteration of field macroinvertebrate communities, and measured as ecological status scores, and number of families and abundance of Ephemeroptera, Plecoptera and Trichoptera (EPT). Non-linear regression models of the field-measured tissue residues in 10 taxa related to the ecological status of the macroinvertebrate communities were used to derive effective tissue residues (ERs). These were estimated for the good/moderate boundary defined by the ecological quality ratio (EQRs) score and for the 50% reduction of EQR and EPT metrics. As, Cu, Hg and Se ERs were calculated for several macroinvertebrate taxa with different feeding styles. The ER dataset allowed us to estimate As and Cu hazardous concentrations (HC), using species sensitivity distribution models, and were interpreted as community thresholds. Further studies for Hg and Se are needed to complete the database required for HC estimation. The reliability and differences of the several thresholds were tested in a risk assessment using a tissue-residue approach (TRA) conducted with field organisms from Cauxa Creek, a tributary from the same basin exposed to high levels of metals in the sediments due to gold mining activities. This risk assessment identified that As and Cu tissue residues satisfactorily explained the reduction in the ecological status of the macroinvertebrate assemblages. Our results indicate that TRA can help in setting future environmental quality standards for the protection of aquatic biota.

Bioaccumulation and chronic toxicity of arsenic and zinc in the aquatic oligochaetes Branchiura sowerbyi and Tubifex tubifex (Annelida, Clitellata)

Oligochaetes feed on bulk sediment and penetrate the sediment through the construction of burrows, making them especially vulnerable to sediment metal contamination. However, the few oligochaete species that have been tested to date are almost exclusively temperate test species. Although the warmwater adapted species Branchiura sowerbyi has been indicated as a promising candidate for tropical sediment toxicity testing, few (especially chronic) studies have been conducted so far to confirm this. Therefore, the aim of the present study was to evaluate the bioaccumulation and chronic 28d lethal and sublethal toxicity of arsenic (As) and zinc (Zn) to both the warmwater-adapted B. sowerbyi and the coldwater-adapted oligochaete Tubifex tubifex for comparison. Arsenic was more toxic to both oligochaete species than Zn. Inter- and intra-species variability in toxicity values of the two test species and other benthic invertebrates was within an order of magnitude. However, B. sowerbyi was the most sensitive species to As even for sediment concentration (EC₅₀: 36.6 ± 2.1 µg/g and 147.1 ± 21.7 µg/g, for B. sowerbyi and T. tubifex, respectively) and for tissue concentration (ER₅₀: 9.2 ± 0.9 µg/g and 887.0 ± 35.0 µg/g, for B. sowerbyi and T. tubifex, respectively). Finally, the Tissue Residue-effects Approach (TRA) using Effective Tissue Residues appears to be a promising way forward in advancing in this since it considers internal body concentrations.

Antimicrobial residues survey by LC-MS in food-producing animals in Lebanon

The treatment of animals with antimicrobial products may lead to the contamination of edible tissues by their residues, which may represent a risk to human health. Therefore, this study aimed to determine the level of antimicrobial residues in food-producing animals (chicken, beef, and milk) in Lebanon. A total of 310 samples were collected and analysed using an LC-MS/MS for the determination of 48 compounds belonging to different families in order to map their compliance according to the European Commission decision 2002/657/EC. Results show that 60% of the analysed samples were not contaminated by any residue, while 12% presented a concentration higher than the MRLs for tetracyclines, sulphonamides, quinolones, and macrolides. Results revealed that chicken were the most contaminated by antimicrobial residues, when compared to beef and milk. The obtained results demonstrate the uncontrolled use of antimicrobials in some Lebanese farms and claim for better management of livestock.

Integrated Assessment of Bioconcentration, Toxicity, and Hazards of Chlorobenzenes in the Aquatic Environment

The evaluation of bioconcentration, toxicity, and hazard (BTH) of persistent lipophilic organic compounds (LOCs) are generally performed as separate rather than integrated assessments. There are adequate data sets in the literature for chlorobenzenes (CBs) consisting of (a) concentrations in aquatic biota (C_B) and water (C_w) in the natural environment, (b) laboratory-derived bioconcentration factors (K_B) and field concentration ratios (CR), the field equivalent factor of K_B, (c) measured internal lethal concentrations (ILC₅₀) and model estimated ILC₅₀ calculated from K_B and lethal concentrations (LC₅₀), and (d) calculated hazard quotients in aquatic biota (HQ_B) and in water (HQ_W). However, there have been no integrated studies of those parameter values based on the respective lipid-based parameters (C_BL, K_BL, CR_L, ILC_50L, HQ_BL) performed. This study utilized the lipid-based parameters for CBs; a group of widely occuring, bioaccumulative, and toxic LOCs, and integrated those parameters into a bioconcentration-toxicity-hazard (BTH_L) index. The values of the parameters were obtained from selected literature with known lipid contents of the aquatic biota. The results showed that the laboratory derived bioconcentration factors, K_BLs, were comparable to the corresponding field based factors, CR_Ls, and the measured internal lethal concentrations, ILC_50L, showed comparable values with the estimated ones. The integrated BTH_L index was less than an order of magnitude or moderately acceptable for the assessment of variability, uncertainty, and predictive power of the index. This integrated assessment can be used to support decision making dealing with CBs in specific and LOCs in general, both in regional and global aquatic environments.

Bioconcentration factors for hydrocarbons and petrochemicals: Understanding processes, uncertainty and predictive model performance

Fish bioconcentration factors (BCFs) are often used to assess substance-specific bioaccumulation. However, reliable BCF data are limited given the practical challenges of conducting such tests. The objectives of this paper are to describe nine rainbow trout studies performed in our lab using tailored dosing and test designs for obtaining empirical BCFs for 21 test substances; gain insights into the structural features and processes determining the magnitude and uncertainty in observed BCFs; and assess performance of six quantitative structure property relationships (QSPRs) for correctly categorizing bioaccumulation given current regulatory triggers. Resulting mean steady-state BCFs, adjusted to a 5% lipid content, ranged from 12 Lkg^-1 for isodecanol to 15,448 Lkg^-1 for hexachlorobenzene which served as a positive control. BCFs for hydrocarbons depended on aromatic and saturated ring configurations and position. Uptake clearances appeared to be modulated by gill metabolism and substance bioavailability, while elimination rates were likely influenced by somatic biotransformation. Current approaches for quantifying uncertainty in experimental BCFs, which take into account only variability in measured fish concentrations, were found to underestimate the true uncertainty in this endpoint with important implications for decision-making. The Vega (KNN/Read-Across) QSPR and Arnot-Gobas model yielded the best model performance when compared to measured BCFs generated in this study.

Selenium and mercury in freshwater fish muscle tissue and otoliths: a comparative analysis

Evaluating potential ecological and human health risks of exposure to bioaccumulative trace elements is typically implemented using analysis of tissue samples. Increasingly, the microchemistry of fish calcified structures is used to elucidate the lifetime exposure to trace elements. In the present study, we measured total mercury (THg), methylmercury (MeHg), and selenium (Se) in muscle tissue and otolith samples from 12 species of fish collected at reference sites and locations influenced by power plant wastewater. Muscle tissue concentrations of Se were sensitive to recent wastewater exposure magnitude, stream type, trophic level, and species (p < 0.001). For Hg, concentrations in muscle tissue and otoliths were affected only by trophic level and species. Levels of THg and Se in muscle tissue and otolith samples were positively correlated for those species with a robust sample size. Some individual fish from 3 species (channel catfish, hybrid striped bass, and freshwater drum) showed significantly increasing or decreasing lifetime concentrations of either THg or Se in otolith samples. Multiple regression analysis indicated that for bluegill muscle tissue Se concentrations could be best explained utilizing water concentrations of selenium, sulfate, and molybdenum (r² = 0.87; p < 0.001). Because of the increased cost and specialized sample processing requirements of analyzing trace elements in otolith structures, it may be prudent to limit these analyses to those species where insights into temporal trends are sought or where evidence indicates that fish move into or out of contaminated water bodies. Environ Toxicol Chem 2019;38:1467-1475. © 2019 SETAC.

Tissue-based assessment of hazard posed by mercury and selenium to wild fishes in two shallow Chinese lakes

Total (all forms of inorganic and organic) concentrations of mercury (Hg) and selenium (Se) were measured in dorsal muscle and eggs of wild fishes from two shallow lakes in China: Tai Lake (Ch: Taihu; TL) and Baiyangdian Lake (BYDL). Hazard quotients (HQs) were calculated by dividing concentrations of Se or Hg in muscle or eggs of fishes by threshold concentrations for effects expressed as tissue residue toxicity reference values (TR-TRVs). Concentrations of Hg in whole bodies of fishes were estimated by concentrations in muscle. Based on concentrations of Hg in whole body, HQs for fishes in TL and BYDL were less than 1.0, which suggests little to moderate potential for effects on these fishes and unaccepted adverse effects of Hg are unexpected for adult fishes. HQs of Se in muscle of common carp from TL were closed to 1.0, and 27% of HQs based on concentrations of Hg in eggs of fishes from BYDL exceeded 1.0. Potential hazard due to Hg on common carp in TL and reproductive effects of Se on fishes from BYDL exhibited need for concern. Ratios of molar concentrations of Se to Hg were greater than 1.0. Thus, there might be some protective effects of Se on effects of Hg on fishes in TL and BYDL.

Ecological risk assessment of perfluooroctane sulfonate to aquatic fauna from a bayou adjacent to former fire training areas at a US Air Force installation

Per- and polyfluoroalkyl substances (PFASs) continue to receive significant attention, with particular concern for PFASs such as perfluorooctane sulfonate (PFOS), which was a constituent of aqueous film-forming foam used widely as a fire suppressant for aircraft since the 1970s. We were interested in the potential for risk to ecological receptors inhabiting Cooper Bayou, which is adjacent to 2 former fire-training areas at Barksdale Air Force Base (LA, USA). Previous research showed higher PFOS concentrations in surface water and biota from Cooper Bayou compared to reference sites. To estimate risk, we compared surface water concentrations from multiple sites within Cooper Bayou with several PFOS chronic toxicity benchmarks for freshwater aquatic organisms (∼0.4-5.1 μg PFOS/L) and showed probability of exceedances from 0.04 to 0.5, suggesting a potential for adverse effects in the most contaminated habitats. A tissue-residue assessment similarly showed some exceedance of benchmarks but with a lower probability (maximum = 0.17). Both fire-training areas have been inactive for more than a decade, so exposures (and, thus, risks) are expected to decline. Several uncertainties limit confidence in our risk estimates including highly dynamic surface water concentrations and limited chronic toxicity data for relevant species. Also, we have little data concerning organisms higher in the food chain which may receive higher lifetime exposures given the potential for PFOS to bioaccumulate and the longevity of many of these organisms. Overall, the present study suggests that PFOS can occur at concentrations that may cause adverse effects to ecological receptors, although additional, focused research is needed to reduce uncertainties. Environ Toxicol Chem 2018;37:2198-2209. © 2018 SETAC.

Developing and applying metamodels of high resolution process-based simulations for high throughput exposure assessment of organic chemicals in riverine ecosystems

As defined by Wikipedia (https://en.wikipedia.org/wiki/Metamodeling), "(a) metamodel or surrogate model is a model of a model, and metamodeling is the process of generating such metamodels." The goals of metamodeling include, but are not limited to (1) developing functional or statistical relationships between a model's input and output variables for model analysis, interpretation, or information consumption by users' clients; (2) quantifying a model's sensitivity to alternative or uncertain forcing functions, initial conditions, or parameters; and (3) characterizing the model's response or state space. Using five models developed by the US Environmental Protection Agency, we generate a metamodeling database of the expected environmental and biological concentrations of 644 organic chemicals released into nine US rivers from wastewater treatment works (WTWs) assuming multiple loading rates and sizes of populations serviced. The chemicals of interest have log n-octanol/water partition coefficients (logK_OW) ranging from 3 to 14, and the rivers of concern have mean annual discharges ranging from 1.09 to 3240m³/s. Log-linear regression models are derived to predict mean annual dissolved and total water concentrations and total sediment concentrations of chemicals of concern based on their logK_OW, Henry's Law Constant, and WTW loading rate and on the mean annual discharges of the receiving rivers. Metamodels are also derived to predict mean annual chemical concentrations in fish, invertebrates, and periphyton. We corroborate a subset of these metamodels using field studies focused on brominated flame retardants and discuss their application for high throughput screening of exposures to human and ecological populations and for analysis and interpretation of field data.

Assessing the relevance of ecotoxicological studies for regulatory decision making

Regulatory policies in many parts of the world recognize either the utility of or the mandate that all available studies be considered in environmental or ecological hazard and risk assessment (ERA) of chemicals, including studies from the peer-reviewed literature. Consequently, a vast array of different studies and data types need to be considered. The first steps in the evaluation process involve determining whether the study is relevant to the ERA and sufficiently reliable. Relevance evaluation is typically performed using existing guidance but involves application of "expert judgment" by risk assessors. In the present paper, we review published guidance for relevance evaluation and, on the basis of the practical experience within the group of authors, we identify additional aspects and further develop already proposed aspects that should be considered when conducting a relevance assessment for ecotoxicological studies. From a regulatory point of view, the overarching key aspect of relevance concerns the ability to directly or indirectly use the study in ERA with the purpose of addressing specific protection goals and ultimately regulatory decision making. Because ERA schemes are based on the appropriate linking of exposure and effect estimates, important features of ecotoxicological studies relate to exposure relevance and biological relevance. Exposure relevance addresses the representativeness of the test substance, environmental exposure media, and exposure regime. Biological relevance deals with the environmental significance of the test organism and the endpoints selected, the ecological realism of the test conditions simulated in the study, as well as a mechanistic link of treatment-related effects for endpoints to the protection goal identified in the ERA. In addition, uncertainties associated with relevance should be considered in the assessment. A systematic and transparent assessment of relevance is needed for regulatory decision making. The relevance aspects also need to be considered by scientists when designing, performing, and reporting ecotoxicological studies to facilitate their use in ERA. Integr Environ Assess Manag 2017;13:652-663. © 2016 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Baseline tissue concentrations of metal in aquatic oligochaetes: Field and laboratory approaches

Metal tissue residue evaluation in benthic macroinvertebrates is an important component of an integrated approach to ecological risk assessment of metals and metalloids in the Nalón River basin (North Spain), where historic mining activities took place. The purpose of this study was to know the baseline tissue concentration of 7 metals (Cd, Cu, Cr, Hg, Ni, Pb, and Zn) and one metalloid (As) in aquatic oligochaetes, sediment burrower organisms, representative of the collector-gatherer functional feeding group in the macroinvertebrate community. Metal concentration was measured in sediment and field aquatic oligochaetes at several reference (minimally disturbed) sites of the Nalón River basin, selected following Water Framework Directive criteria. Metal tissue residues were measured separately in field microdriles and lumbricids and compared with tissue concentrations measured in the aquatic oligochaete Tubifex tubifex exposed to reference sediments from the Nalón and other Cantabrian River basins in 28-d chronic laboratory bioassays. Metal tissue residues in bioassay organisms attained usually higher levels than in field worms, in special for As, Cu, Hg and Zn, although metal levels were within the same order of magnitude. The baseline values for metals were calculated from 90^th percentile (P90) values in field aquatic oligochaetes (microdriles and lumbricids). The P90 for Hg, As and Zn could efficiently discriminate Toxic and Non-Toxic sites, while baseline values calculated for the other metals deserve further research due either to the low range of values found in the present study, or to the regulation of the metal body concentration, as in the case of Cu.

Improving Toxicity Assessment of Pesticide Mixtures: The Use of Polar Passive Sampling Devices Extracts in Microalgae Toxicity Tests

Complexity of contaminants exposure needs to be taking in account for an appropriate evaluation of risks related to mixtures of pesticides released in the ecosystems. Toxicity assessment of such mixtures can be made through a variety of toxicity tests reflecting different level of biological complexity. This paper reviews the recent developments of passive sampling techniques for polar compounds, especially Polar Organic Chemical Integrative Samplers (POCIS) and Chemcatcher® and the principal assessment techniques using microalgae in laboratory experiments. The progresses permitted by the coupled use of such passive samplers and ecotoxicology testing as well as their limitations are presented. Case studies combining passive sampling devices (PSD) extracts and toxicity assessment toward microorganisms at different biological scales from single organisms to communities level are presented. These case studies, respectively, aimed (i) at characterizing the "toxic potential" of waters using dose-response curves, and (ii) at performing microcosm experiments with increased environmental realism in the toxicant exposure in term of cocktail composition and concentration. Finally perspectives and limitations of such approaches for future applications in the area of environmental risk assessment are discussed.

Contaminants of emerging concern in a large temperate estuary

This study was designed to assess the occurrence and concentrations of a broad range of contaminants of emerging concern (CECs) from three local estuaries within a large estuarine ecosystem. In addition to effluent from two wastewater treatment plants (WWTP), we sampled water and whole-body juvenile Chinook salmon (Oncorhynchus tshawytscha) and Pacific staghorn sculpin (Leptocottus armatus) in estuaries receiving effluent. We analyzed these matrices for 150 compounds, which included pharmaceuticals, personal care products (PPCPs), and several industrial compounds. Collectively, we detected 81 analytes in effluent, 25 analytes in estuary water, and 42 analytes in fish tissue. A number of compounds, including sertraline, triclosan, estrone, fluoxetine, metformin, and nonylphenol were detected in water and tissue at concentrations that may cause adverse effects in fish. Interestingly, 29 CEC analytes were detected in effluent and fish tissue, but not in estuarine waters, indicating a high potential for bioaccumulation for these compounds. Although concentrations of most detected analytes were present at relatively low concentrations, our analysis revealed that overall CEC inputs to each estuary amount to several kilograms of these compounds per day. This study is unique because we report on CEC concentrations in estuarine waters and whole-body fish, which are both uncommon in the literature. A noteworthy finding was the preferential bioaccumulation of CECs in free-ranging juvenile Chinook salmon relative to staghorn sculpin, a benthic species with relatively high site fidelity.

Application of molecular endpoints in early life stage salmonid environmental biomonitoring

Molecular endpoints can enhance existing whole animal bioassays by more fully characterizing the biological impacts of aquatic pollutants. Laboratory and field studies were used to examine the utility of adopting molecular endpoints for a well-developed in situ early life stage (eyed embryo to onset of swim-up fry) salmonid bioassay to improve diagnostic assessments of water quality in the field. Coastal cutthroat trout (Oncorhynchus clarki clarki) were exposed in the laboratory to the model metal (zinc, 40μg/L) and the polycyclic aromatic hydrocarbon (pyrene, 100μg/L) in water to examine the resulting early life stage salmonid responses. In situ field exposures and bioassays were conducted in parallel to evaluate the water quality of three urban streams in British Columbia (two sites with anthropogenic inputs and one reference site). The endpoints measured in swim-up fry included survival, deformities, growth (weight and length), vitellogenin (vtg) and metallothionein (Mt) protein levels, and hepatic gene expression (e.g., metallothioneins [mta and mtb], endocrine biomarkers [vtg and estrogen receptors, esr] and xenobiotic-metabolizing enzymes [cytochrome P450 1A3, cyp1a3 and glutathione transferases, gstk]). No effects were observed in the zinc treatment, however exposure of swim-up fry to pyrene resulted in decreased survival, deformities and increased estrogen receptor alpha (er1) mRNA levels. In the field exposures, xenobiotic-metabolizing enzymes (cyp1a3, gstk) and zinc transporter (zntBigM103) mRNA were significantly increased in swim-up fry deployed at the sites with more anthropogenic inputs compared to the reference site. Cluster analysis revealed that gene expression profiles in individuals from the streams receiving anthropogenic inputs were more similar to each other than to the reference site. Collectively, the results obtained in this study suggest that molecular endpoints may be useful, and potentially more sensitive, indicators of site-specific contamination in real-world, complex exposure scenarios in addition to whole body morphometric and physiological measures.

Mercury tissue residue approach in Chironomus riparius: Involvement of toxicokinetics and comparison of subcellular fractionation methods

Along with the growing body of evidence that total internal concentration is not a good indicator of toxicity, the Critical Body Residue (CBR) approach recently evolved into the Tissue Residue Approach (TRA) which considers the biologically active portion of metal that is available to contribute to the toxicity at sites of toxic action. For that purpose, we examined total mercury (Hg) bioaccumulation and subcellular fractionation kinetics in fourth stage larvae of the midge Chironomus riparius during a four-day laboratory exposure to Hg-spiked sediments and water. The debris (including exoskeleton, gut contents and cellular debris), granule and organelle fractions accounted only for about 10% of the Hg taken up, whereas Hg concentrations in the entire cytosolic fraction rapidly increased to approach steady-state. Within this fraction, Hg compartmentalization to metallothionein-like proteins (MTLP) and heat-sensitive proteins (HSP), consisting mostly of enzymes, was assessed in a comparative manner by two methodologies based on heat-treatment and centrifugation (HT&C method) or size exclusion chromatography separation (SECS method). The low Hg recoveries obtained with the HT&C method prevented accurate analysis of the cytosolic Hg fractionation by this approach. According to the SECS methodology, the Hg-bound MTLP fraction increased linearly over the exposure duration and sequestered a third of the Hg flux entering the cytosol. In contrast, the HSP fraction progressively saturated leading to Hg excretion and physiological impairments. This work highlights several methodological and biological aspects to improve our understanding of Hg toxicological bioavailability in aquatic invertebrates.

Accumulation dynamics and acute toxicity of silver nanoparticles to Daphnia magna and Lumbriculus variegatus: implications for metal modeling approaches

Frameworks commonly used in trace metal ecotoxicology (e.g., biotic ligand model (BLM) and tissue residue approach (TRA)) are based on the established link between uptake, accumulation and toxicity, but similar relationships remain unverified for metal-containing nanoparticles (NPs). The present study aimed to (i) characterize the bioaccumulation dynamics of PVP-, PEG-, and citrate-AgNPs, in comparison to dissolved Ag, in Daphnia magna and Lumbriculus variegatus; and (ii) investigate whether parameters of bioavailability and accumulation predict acute toxicity. In both species, uptake rate constants for AgNPs were ∼ 2-10 times less than for dissolved Ag and showed significant rank order concordance with acute toxicity. Ag elimination by L. variegatus fitted a 1-compartment loss model, whereas elimination in D. magna was biphasic. The latter showed consistency with studies that reported daphnids ingesting NPs, whereas L. variegatus biodynamic parameters indicated that uptake and efflux were primarily determined by the bioavailability of dissolved Ag released by the AgNPs. Thus, principles of BLM and TRA frameworks are confounded by the feeding behavior of D. magna where the ingestion of AgNPs perturbs the relationship between tissue concentrations and acute toxicity, but such approaches are applicable when accumulation and acute toxicity are linked to dissolved concentrations. The uptake rate constant, as a parameter of bioavailability inclusive of all available pathways, could be a successful predictor of acute toxicity.

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.

Risk assessment of butyltins based on a fugacity-based food web bioaccumulation model in the Jincheng Bay mariculture area: I. Model development

A fugacity-based model was developed to simulate the bioaccumulation of butyltins in the food web of the Jincheng Bay mariculture area. The predicted biological tissue residues of tributyltin (TBT), dibutyltin (DBT), and monobutyltin (MBT) were 0.04-17.09, 0.14-53.54, and 0.27-108.77 ng-Sn g(-1), respectively, and the predicted values in six mollusca agreed well with the measured ones. The lipid-normalized concentrations did not significantly increase across trophic levels, indicating no biomagnification across aquatic food webs. These results were highly consistent with those observed both in the laboratory and field, which had been reported in numerous references. The explanation, from calculating their flux equilibrium in the food web, was that butyltins were primarily taken in via respiration from the water column by marine organisms. The sensitivities of the model parameters were analyzed, revealing that the hydrophobicity of butyltins played the dominant role in their bioaccumulation phenomena. The verified model predictions of the biotic tissue concentrations of the butyltins could be readily applied to perform internal ecological risk and human health risk assessments in this area.

Risk assessment of butyltins based on a fugacity-based food web bioaccumulation model in the Jincheng Bay mariculture area: II. Risk assessment

A fugacity-based food web bioaccumulation model was constructed, and the biotic concentrations of butyltins in the food web of the Jincheng Bay mariculture area were estimated accordingly, using the water and sediment concentrations described in the accompanying paper (Part I). This paper presents an ecological risk assessment (ERA) and a human health risk assessment (HHRA) of the butyltins, based on the estimated tissue residues in the marine life in this area. The results showed that the ecological risk probability was greater than 0.05. At this level, management control is critical since sensitive marine species would be profoundly endangered by butyltin contamination. Few if any detrimental effects, however, would be generated for humans from exposure to butyltins through seafood consumption. The fugacity-based model can refine the ERA and HHRA of pollutants in marine areas, provide a basis for protecting marine ecology and the security of fishery products, and thus help determine the feasibility of a proposed aquaculture project.

Polycyclic aromatic hydrocarbon body residues and lysosomal membrane destabilization in mussels exposed to the Dubai Star bunker fuel oil (intermediate fuel oil 380) spill in San Francisco Bay

Following the spill of bunker fuel oil (intermediate fuel oil 380, approximately 1500-3000 L) into San Francisco Bay in October 2009, polycyclic aromatic hydrocarbon (PAH) concentrations in mussels from moderately oiled areas increased up to 87 554 ng/g (dry wt) and, 3 mo later, decreased to concentrations found in mussels collected prior to oiling, with a biological half-life of approximately 16 d. Lysosomal membrane destabilization increased in mussels with higher PAH body burdens.

Tissue-based environmental quality benchmarks and standards

Although the use of tissue concentrations (residues) of chemical contaminants as the dose metric to characterize chemical toxicity to aquatic organisms has been gaining acceptance over the past 20 years, tissue concentrations are less commonly used in water quality management and have yet to be formally adopted as benchmarks or environmental quality standards (EQS). This synthesis paper addresses advantages and disadvantages for the development and application of tissue-based EQS as an alternative and supplement to exposure-based EQS determined with water and sediment concentration data. Tissue-based EQS can be readily developed in parallel with conventional toxicity tests, and achieved by quantification of chemical concentrations in tissue alongside traditional concentration-response toxicity testing. Tissue-residue toxicity metrics can be used as benchmarks for screening and monitoring water and sediment quality, to derive equivalent water or sediment EQS, and for ecological risk assessments and weight of evidence approaches for assessing ecosystem impairment. Tissue-based toxicity metrics and associated EQS provide several advantages; however, there are some limitations to consider and key knowledge gaps to fill.

Toxicity and critical body residues of Cd, Cu and Cr in the aquatic oligochaete Tubifex tubifex (Müller) based on lethal and sublethal effects

The aim of the present study was to estimate critical body residues (CBRs) of three metals [cadmium (Cd), copper (Cu), chromium (Cr)] in the aquatic oligochaete Tubifex tubifex based on lethal (LBR) and sublethal effects (CBR), and to discuss the relevance of the exposure to sediment for deriving CBR. Toxicity parameters (LC50, EC50, LBR50 and CBR50) were estimated for each metal by means of data on survival and on several sublethal variables measured in short-term (4 days), water-only exposures and in long-term, chronic (14 and 28 days) exposures using metal-spiked sediment. Sublethal endpoints included autotomy in short-term exposure, as well as reproduction and growth in chronic bioassays. LBR50 and CBR50 were 3-6 times higher in sediment than in water-only exposure to Cd and about 2-11 times higher for Cu, depending on the measured endpoint; however, for Cr these parameters varied only by a factor of 1.2. Cu and Cr LBR50 and CBR50 values in 96 h water-only exposure were very similar (survival 2.39 μmol Cu g(-1) dw, 2.73 μmol Cr g(-1) dw; autotomy 0.53 μmol Cu g(-1) dw, 0.78 μmol Cr g(-1) dw). However, in metal-spiked sediments, 28 d CBR50 values for autotomy, reproduction and growth ranged 6.76-29.54 μmol g(-1) dw for Cd, 3.88-6.23 μmol g(-1) dw for Cu, 0.65 μmol g(-1) dw for Cr (calculated only on total number of young). Exposure conditions (time and presence/absence of sediment) seem to be influential in deriving metal CBR values of Cd and Cu, while appear to be irrelevant for Cr. Thus, CBR approach for metals is complex and tissue residue-toxicity relationship is not directly applicable so far.

Toxicity of lead and zinc to developing mussel and sea urchin embryos: critical tissue residues and effects of dissolved organic matter and salinity

Lead (Pb) EC50 values in the very sensitive early development phases (48-72h post-fertilization) of the mussels Mytilus galloprovincialis and Mytilus trossolus and sea urchin Strongylocentrotus purpuratus in 100% sea water were: M. trossolus - 45 (95% C.I.=22-72) μgL(-1); M. galloprovincialis - 63 (36-94) μgL(-1); S. purpuratus - 74 (50-101) μgL(-1). Salinity thresholds for normal development varied: M. trossolus>21ppt; M. galloprovincialis>28ppt; S. purpuratus≥30ppt. Addition of two spectroscopically distinct dissolved organic matters (DOM) from fresh water (Nordic Reservoir) and sea water (Inshore) moderately decreased the toxicity of Pb to both mussels, but not in a concentration-dependent fashion, with only an approximate doubling of EC50 over the range of 1.4-11.2mgCL(-1). Independent Pb binding capacity determinations for DOC explained the lack of a relationship between DOM concentration and toxicity. Salinity had no effect on Pb toxicity down to 21ppt in M. trossolus, and low salinity (21ppt) did not enhance the protective effect of DOC. Both DOMs increased the toxicity of Pb in developing sea urchin embryos, in contrast to mussels. Relative to Pb, the organisms were 6-9 fold less sensitive to Zn on a molar basis in 100% seawater with the following Zn EC50s: M. trossolus - 135 (103-170) μgL(-1); M. galloprovincialis - 172 (126-227) μgL(-1), S. purpuratus - 151 (129-177) μgL(-1). Nordic Reservoir and Inshore DOM (2-12mgCL(-1)) had no significant effect on Zn toxicity to mussels, in accord with voltammetry data showing an absence of any strong ligand binding for Zn by DOMs. As with Pb, DOMs increased Zn toxicity to urchin larvae. Critical Tissue Residues (CTR) based on whole body concentrations of Pb and Zn were determined for M. galloprovincialis at 48h and S. purpuratus at 72h. The median lethal CTR values (LA50s), useful parameters for development of saltwater Biotic Ligand Models (BLMs), were approximately 4-fold higher on a molar basis for Zn than for Pb. The latter were not altered by DOM exposure, despite increased EC50 values, in accord with the tenets of the BLM.

Ecotoxicity and risk to human fish consumers of polychlorinated biphenyls in fish near the Hanford Site (USA)

The purpose of this study was to quantify three groups of polychlorinated biphenyl (PCB) congeners (i.e., dioxin-like toxic equivalents [TEQ], non-dioxin-like PCBs, total PCBs) in fish in several species, tissues, and locations in the Columbia River near the Hanford Site. For TEQ and total PCBs, fish ecotoxicity and risk to human fish consumers were also evaluated. Non-dioxin-like PCBs were not assessed for toxicity, due to lack of available benchmarks. In sturgeon liver, TEQ was significantly higher (P<0.05) within the Hanford Site study areas, relative to upriver. However, this same spatial relationship in sturgeon liver did not attain statistical significance for non-dioxin-like PCBs and total PCBs. Non-dioxin-like PCBs and total PCBs were significantly higher (P<0.05) in whitefish fillet than in other species (except carp) and significantly higher (P<0.05) in carp fillet, relative to bass. All PCB residues in carcass were significantly elevated (P<0.005) in comparison to fillet. In addition to PCB source, many factors (e.g., dietary composition, tissue lipid content, fish mobility and home range, age, toxicokinetic processes, seasonal adaptations) influence patterns in PCB bioaccumulation across species, tissues, and locations. TEQ and total PCB residues in liver, fillet, and carcass, observed in this study, were below corresponding no effect residues for TEQ and Aroclors in the literature for fish survival, growth, and reproduction. In contrast, TEQ and total PCBs in fillet in this study exceeded USEPA tissue screening levels for cancer (1E-6 risk) and noncancer (hazard quotient [HQ]=1) toxicity for human fish consumers. Key uncertainties in these comparisons to assess toxicity relate to variation in fish species sensitivity to PCBs and use of Aroclor data in the literature to represent total PCBs.

Toxicity reference values and tissue residue criteria for protecting avian wildlife exposed to methylmercury in China

MeHg is the most biologically available and toxic from of mercury, and has the potential to bioaccumulate and biomagnify as it moves up the food chain. These characteristics result in MeHg exposure to avian wildlife at high trophic levels that can produce adverse effects. The toxicity of MeHg to birds was reviewed, and using available data, TRVs and TRCs were derived for protecting birds in China. The TRV and TRC values were based on concentrations of MeHg in diet (or fish tissue based) and tissues of birds. Two methods were applied to derive TRVs from concentrations in the diet or in tissues. These were the CSA and SSD approaches. Results of published studies show that reproductive productivity of while ibis was the most sensitive endpoint for MeHg exposure, and study results on white ibises were used for deriving the TRV and TRC values, which included applying a UF of 2.0. For the SSD approach, data for ten species were used to construct the SSD for MeHg, and to calculate the dietary-based TRV and TRC values. Using the CSA approach, the TRV was based on MeHg in the diet and was derived as 5.0 ng MeHg/g (bm).day; for feathers and blood, the TRV's were 3.16 μg THg/g (wwt), and 0.365 μg THg/g (wwt), respectively. The corresponding TRCs were 15.47 ng MeHg/g (wwt), 3.16 μg THg/g (wwt)respectively. The dietary-based TRV and TRC derived by SSD were 3.09 ng MeHg (bm)/day and 9.56 ng MeHg/g (wwt) respectively. However, birds tissue residue-based criteria were not available because insufficient MeHg effects data existed to construct an SSD for birds. We compared the criteria derived in our study to those developed by others, and concluded that our results provided more reasonable protection to Chinese avian wildlife. By comparing the criteria derived values we calculated to actual MeHg levels in fish and bird tissues, we concluded that these criteria values are useful indicators for screening-level risk assessments of avian wildlife in Chinese aquatic systems. The results of this meta-analysis might therefore have important implications for assessing the risk of Hg exposure to birds and for environmental management in China and in other regions. Moreover, because humans and top avian wildlife consumers are at the same trophic level, these criteria may also be used as a reference for human health risk assessment. The diet of birds consists of aquatic species from different trophic levels. However, the structure of the food web for avian wildlife and the environmental factors that effect their exposure to MeHg vary among aquatic systems. Therefore, further research results are needed on the food web structure of avian wildlife in Chinese aquatic systems to provide more insight into what constitutes adequate protection for avian wildlife.

Novel control and steady-state correction method for standard 28-day bioaccumulation tests using Nereis virens

Evaluation of dredged material for aquatic placement requires assessment of bioaccumulation potentials for benthic organisms using standardized laboratory bioaccumulation tests. Critical to the interpretation of these data is the assessment of steady state for bioaccumulated residues needed to generate biota sediment accumulation factors (BSAFs) and to address control correction of day 0 contaminant residues measured in bioassay organisms. This study applied a novel performance reference compound approach with a pulse-chase experimental design to investigate elimination of a series of isotopically labeled polychlorinated biphenyl ((13)C-PCBs) in the polychaete worm Nereis virens while simultaneously evaluating native PCB bioaccumulation from field-collected sediments. Results demonstrated that all (13)C-PCBs, with the exception of (13)C-PCB209 (> 80%), were eliminated by more than 90% after 28 d. The three sediment types yielded similar (13)C-PCB whole-body elimination rate constants (k(tot)) producing the following predictive equation: log k(tot)  =  - 0.09 × log K(OW)  - 0.45. The rapid loss of (13)C-PCBs from worms over the bioassay period indicated that control correction, by subtracting day 0 residues, would result in underestimates of bioavailable sediment residues. Significant uptake of native PCBs was observed only in the most contaminated sediment and proceeded according to kinetic model predictions with steady-state BSAFs ranging from 1 to 3 and peaking for congeners of log K(OW) between 6.2 and 6.5. The performance reference compound approach can provide novel information about chemical toxicokinetics and also serve as a quality check for the physiological performance of the bioassay organism during standardized bioaccumulation testing.

Advancing environmental toxicology through chemical dosimetry: external exposures versus tissue residues

The tissue residue dose concept has been used, although in a limited manner, in environmental toxicology for more than 100 y. This review outlines the history of this approach and the technical background for organic chemicals and metals. Although the toxicity of both can be explained in tissue residue terms, the relationship between external exposure concentration, body and/or tissues dose surrogates, and the effective internal dose at the sites of toxic action tends to be more complex for metals. Various issues and current limitations related to research and regulatory applications are also examined. It is clear that the tissue residue approach (TRA) should be an integral component in future efforts to enhance the generation, understanding, and utility of toxicity testing data, both in the laboratory and in the field. To accomplish these goals, several key areas need to be addressed: 1) development of a risk-based interpretive framework linking toxicology and ecology at multiple levels of biological organization and incorporating organism-based dose metrics; 2) a broadly applicable, generally accepted classification scheme for modes/mechanisms of toxic action with explicit consideration of residue information to improve both single chemical and mixture toxicity data interpretation and regulatory risk assessment; 3) toxicity testing protocols updated to ensure collection of adequate residue information, along with toxicokinetics and toxicodynamics information, based on explicitly defined toxicological models accompanied by toxicological model validation; 4) continued development of residue-effect databases is needed ensure their ongoing utility; and 5) regulatory guidance incorporating residue-based testing and interpretation approaches, essential in various jurisdictions.

Tissue residue approach for chemical mixtures

At the SETAC Pellston Workshop "The Tissue Residues Approach for Toxicity Assessment," held in June 2007, we discussed mixture toxicology in terms of the tissue residue approach (TRA). This article reviews the literature related to the TRA for mixtures of chemicals and recommends a practical, tiered approach that can be implemented in regulatory or risk assessment applications. As with the toxicity of individual chemicals, addressing mixture toxicity by means of the TRA has a number of significant advantages. Early work provided a theoretical basis and experimental data to support the use of TRA for mixtures; later work provided a field-based validation of the integration. However, subsequent development has been hindered by the lack of mixture toxicity data expressed in tissue or preferably target-site concentrations. We recommend a framework for addressing the toxicology of mixtures that integrates the TRA and mixture toxicology in a 3-tier approach. Tier I uses concentration addition (CA) to estimate the toxicity of mixtures regardless of the mechanism of action of the components. However, the common approach that uses a bioaccumulation factor (BAF) to predict TR from the exposure-water concentration for organics must be modified slightly for metals because, unlike organics, the BAF for a metal changes as 1) the aqueous exposure concentration changes, and 2) the concentration of other metals changes. In addition, total tissue residues of a metal are not a good predictor of toxicity, because some organisms store high concentrations of metals internally in detoxified forms. In tier I, if the combination of measured concentrations in the mixture exceeds that predicted to produce adverse effects or above-reference levels, it is necessary to proceed to tier II. Tier II is a mixed model that employs CA and independent action to estimate mixture toxicity. Tiers I and II estimate the toxicity of mixtures to individual species. In tier III, the TRA is integrated with the multisubstance potentially affected fraction (ms-PAF) method to derive TR levels that are protective of a selected percentage of species in aquatic communities (e.g., hazardous concentration for 5% of the species [HC5]).