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Biotic ligand models (BLMs) predict the toxicity of metals in aquatic environments by accounting for metal interactions with cell surface receptors (biotic ligands) in organisms, including water chemistry (metal speciation) and competing cations. Metal binding constants (log KMBL values), which indicate the affinity of metals for cell surface receptors, are fundamental to BLMs, but have only been reported for a few commonly investigated metals and freshwater species. This review evaluated literature toxicity and uptake data for seven key metals (cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), lead (Pb), uranium (U), and zinc (Zn)) and four key competing cations (protons (H), calcium (Ca), magnesium (Mg), and sodium (Na)), to derive average metal binding constants for freshwater organisms/taxa. These constants will improve current BLMs for Cd, Cu, Ni, Pb, and Zn, and aid in developing new BLMs for Co and U. The derived metal binding constants accurately predicted metal toxicity for a wide range of freshwater organisms (75–88% of data were within a factor of two and 88–98% of data were within a factor of three of the ideal 1:1 agreement line), when considering metal speciation, competing cations and the fraction of cell receptors ((fC)M50%) occupied by the metal at the median (50%) effect concentration (EC50). For many organisms, toxicity occurs when 50% of cell surface receptors are occupied by the metal, though this threshold can vary. Some organisms exhibit toxicity with less than 50% receptor occupancy, while others with protective mechanisms show reduced toxicity, even with similar log KMBL values. For Cu, U, and Pb, the toxic effect of the metal hydroxide (as MOH+) must be considered in addition to the free metal ion (M2+), as these metals hydrolyse in circumneutral freshwaters (pH 5.5 to 8.5), contributing to toxicity. [ABSTRACT FROM AUTHOR]

Objectives In this study, considering the changes in the concentration of metal/metalloid and environmental factors over time of the target water system and the toxic effects of metals on various aquatic organisms, determined procedure of ecotoxicologically acceptable metal/metalloid concentration based on a biotic ligand model (BLM) was proposed in detail. As an application example, the ecotoxicologically acceptable Cu concentration for the Numedalslågen river in Norway was calculated. Methods The Cu concentration and environmental factor time series data of the target water system were collected, and EC50[Cu]T, the total concentration of Cu in the water system showing a toxic effect of 50% on the target aquatic organisms, was calculated through BLM. In addition, the predicted no-effect concentration (PNEC) was obtained from the species sensitivity distribution using the acute-chronic ratio and adjustment factor, and the ecotoxicologically acceptable Cu concentration of the target water system was determined through the fixed monitoring benchmark (FMB). Results and Discussion Ecotoxicologically acceptable Cu concentration of the target water system was determined as 1.15 μg/L. Dissolved organic carbon (DOC) showed the highest linear relationship with EC50[Cu]T (R2 = 0.94-0.98) compared to various environmental factors, and the Cu toxicity effect on aquatic organisms tended to decrease as the DOC concentration increased. Ca showed a low linear relationship with EC50[Cu]T (R2 < 0.04), which is presumed to be due to the decrease in Ca2+ concentration due to the complexese formation of DOC and Ca2+, which reduced the competitive effect with Cu2+. Conclusion The proposed procedure provides a useful method for calculating ecotoxicologically acceptable metal concentrations for the protection of aquatic organisms in water systems. In addition, it is expected that it can be used to calculate site-specific metal concentrations that can protect aquatic organisms in the target water system by reflecting the timing of sediment resuspension, which can cause rapid changes in the concentration of metals and environmental factors in the water system, and specific time points such as storm and flood seasons.

Metal bioavailability in solution is mostly driven by two factors: complexation and competition. The first factor, complexation, contributes to decrease the overall reactivity of the metal by reducing the activity of the free metal ion, which is known as the common denominator of metal reactions involving either dissolved ligands or surface functional groups (abiotic or biotic). Ubiquitous in natural ecosystems, natural organic matter is, for several metals, the most important metal complexing ligand. The second factor, competition, contributes to decrease the availability of biotic ligands involved in the membrane transport of metals from the bulk solution to the intracellular medium. In freshwater systems, proton and hardness cation concentrations are the main parameters potentially modulating metal bioavailability. The above reflects the current accepted paradigm. In this paper, two knowledge gaps are identified: i) the role of natural organic matter other than metal complexation that may lead to an increase in metal bioavailability; and ii) the effects of multiple metals other than competition that may trigger biological feedback mechanisms which may, in turn, alter biotic ligand binding properties. More research efforts are needed to decipher the extent of these overlooked potential effects and to improve the predictability of metal bioavailability. [ABSTRACT FROM AUTHOR]

Natural dissolved organic matter (DOM) is a heterogeneous mixture of a variety of organic compounds, with a great importance for the environmental fate of metals and their ecotoxicity. However, its complex nature and variable composition make the understanding of its role a challenge. Lanthanum (La) has a strong affinity for DOM and is one of the rare earth elements that is widely used in many electronic and green technologies, and for which the demand may potentially increase for the foreseeable future. The present study examines the links between the optical and chemical properties of organic matter and its influence on the bioavailability and toxicity of La toward the green microalga Chlorella fusca. A total of four DOMs, two natural organic matter samples from Ontario (Luther Marsh and Bannister Lake) and two Suwannee River fulvic and humic acids, were characterized by absorbance and fluorescence spectroscopy as well as by asymmetrical flow field-flow fractionation. These suggest that Luther Marsh and the Suwannee River humic acid have higher molecular weight and are more aromatic, compared to the other two DOMs. The concentrations of free metal iosn La3+ were measured by an ion exchange technique and a partial ultrafiltration method, and related to biological response. Toxicity tests over 96 h at pH = 5.0 were separately conducted with and without 3mgC·L-1 of each DOM. All DOM samples reduced La bioavailability but as opposed to what can be expected based on the Biotic Ligand Model, the presence of DOM exacerbated the toxicity of La and its accumulation in algal cells when only the free La3+ ion concentration was considered. These results indicate that the role of natural organic matter in modulating metal bioavailability remains to be deciphered. [ABSTRACT FROM AUTHOR]

Chronic copper (Cu) bioavailability models have been successfully implemented in European risk assessment frameworks and compliance evaluations. However, they were developed almost two decades ago, which calls for an update. In the study, we present updated chronic Cu bioavailability models for invertebrates and algae. They consider recent ecotoxicity data sets and use the more recent speciation model Windermere Humic Aqueous Model (WHAM) VII and an optimized model structure (i.e., a generalized bioavailability model [gBAM]). Contrary to the classic biotic ligand model, a gBAM models the effect of pH on Cu2+ toxicity via a log‐linear relationship parametrized through the pH slope SpH. The recalibrated SpH parameters are −0.208 for invertebrates (Daphnia magna, two clones) and −0.975 for algae (Raphidocelis subcapitata and Chlorella vulgaris). The updated models predict 80% to 100% of the observed effect levels for eight different species within a factor of 2. The only exception was one of the two data sets considering subchronic 7‐day mortality to Hyalella azteca: the prediction performance of the updated invertebrate model at pH ≥ 8.3 was poor because the effect of pH on Cu2+ toxicity appeared to be dependent on the pH itself (with a steeper pH slope compared with the updated invertebrate model at pH ≥ 8.1). The prediction performance of the updated Cu bioavailability models was similar to or better than that of the models used for regulatory application in Europe until now, with one exception (i.e., H. azteca). Together with the recently published fish bioavailability model, the models developed in the present study constitute a complete, updated, and consistent bioavailability model set. Overall, the updated chronic Cu bioavailability model set is robust and can be used in regulatory applications. The updated bioavailability model set is currently used under the European Union Registration, Evaluation, Authorisation, and Restriction of Chemicals framework regulation to guide the safe use of Cu. Environ Toxicol Chem 2024;43:450–467. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Efforts to incorporate bioavailability adjustments into regulatory water quality criteria in the United States have included four major procedures: hardness‐based single‐linear regression equations, water‐effect ratios (WERs), biotic ligand models (BLMs), and multiple‐linear regression models (MLRs) that use dissolved organic carbon, hardness, and pH. The performance of each with copper (Cu) is evaluated, emphasizing the relative performance of hardness‐based versus MLR‐based criteria equations. The WER approach was shown to be inherently highly biased. The hardness‐based model is in widest use, and the MLR approach is the US Environmental Protection Agency's (USEPA's) present recommended approach for developing aquatic life criteria for metals. The performance of criteria versions was evaluated with numerous toxicity datasets that were independent of those used to develop the MLR models, including olfactory and behavioral toxicity, and field and ecosystem studies. Within the range of water conditions used to develop the Cu MLR criteria equations, the MLR performed well in terms of predicting toxicity and protecting sensitive species and ecosystems. In soft waters, the MLR outperformed both the BLM and hardness models. In atypical waters with pH <5.5 or >9, neither the MLR nor BLM predictions were reliable, suggesting that site‐specific testing would be needed to determine reliable Cu criteria for such settings. The hardness‐based criteria performed poorly with all toxicity datasets, showing no or weak ability to predict observed toxicity. In natural waters, MLR and BLM criteria versions were strongly correlated. In contrast, the hardness‐criteria version was often out of phase with the MLR and, depending on waterbody and season, could be either strongly overprotective or underprotective. The MLR‐based USEPA‐style chronic criterion appears to be more generally protective of ecosystems than other models. Environ Toxicol Chem 2023;42:2529–2563. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Metal bioavailability in solution is mostly driven by two factors: complexation and competition. The first factor, complexation, contributes to decrease the overall reactivity of the metal by reducing the activity of the free metal ion, which is known as the common denominator of metal reactions involving either dissolved ligands or surface functional groups (abiotic or biotic). Ubiquitous in natural ecosystems, natural organic matter is, for several metals, the most important metal complexing ligand. The second factor, competition, contributes to decrease the availability of biotic ligands involved in the membrane transport of metals from the bulk solution to the intracellular medium. In freshwater systems, proton and hardness cation concentrations are the main parameters potentially modulating metal bioavailability. The above reflects the current accepted paradigm. In this paper, two knowledge gaps are identified: i) the role of natural organic matter other than metal complexation that may lead to an increase in metal bioavailability; and ii) the effects of multiple metals other than competition that may trigger biological feedback mechanisms which may, in turn, alter biotic ligand binding properties. More research efforts are needed to decipher the extent of these overlooked potential effects and to improve the predictability of metal bioavailability.

Natural dissolved organic matter (DOM) is a heterogeneous mixture of a variety of organic compounds, with a great importance for the environmental fate of metals and their ecotoxicity. However, its complex nature and variable composition make the understanding of its role a challenge. Lanthanum (La) has a strong affinity for DOM and is one of the rare earth elements that is widely used in many electronic and green technologies, and for which the demand may potentially increase for the foreseeable future. The present study examines the links between the optical and chemical properties of organic matter and its influence on the bioavailability and toxicity of La toward the green microalga Chlorella fusca. A total of four DOMs, two natural organic matter samples from Ontario (Luther Marsh and Bannister Lake) and two Suwannee River fulvic and humic acids, were characterized by absorbance and fluorescence spectroscopy as well as by asymmetrical flow field-flow fractionation. These suggest that Luther Marsh and the Suwannee River humic acid have higher molecular weight and are more aromatic, compared to the other two DOMs. The concentrations of free metal ion La3+ were measured by an ion exchange technique and a partial ultrafiltration method, and related to biological response. Toxicity tests over 96 h at pH = 5.0 were separately conducted with and without 3 mg C·L−1 of each DOM. All DOM samples reduced La bioavailability but as opposed to what can be expected based on the Biotic Ligand Model, the presence of DOM exacerbated the toxicity of La and its accumulation in algal cells when only the free La3+ ion concentration was considered. These results indicate that the role of natural organic matter in modulating metal bioavailability remains to be deciphered.

The copper (Cu) biotic ligand model (BLM) has been used for ecological risk assessment by taking into account the bioavailability of Cu in freshwater. The Cu BLM requires data for many water chemistry variables, such as pH, major cations, and dissolved organic carbon, which can be difficult to obtain from water quality monitoring programs. To develop an optimized predicted no‐effect concentration (PNEC) estimation model based on an available monitoring dataset, we proposed an initial model that considers all BLM variables, a second model that requires variables excluding alkalinity, and a third model using electrical conductivity as a surrogate for the major cations and alkalinity. Furthermore, deep neural network (DNN) models have been used to predict the nonlinear relationships between the PNEC (outcome variable) and the required input variables (explanatory variables). The predictive capacity of DNN models was compared with the results of other existing PNEC estimation tools using a look‐up table and multiple linear and multivariate polynomial regression methods. Three DNN models, using different input variables, provided better predictions of the Cu PNECs compared with the existing tools for the following four test datasets: Korean, United States, Swedish, and Belgian freshwaters. Consequently, it is expected that Cu BLM–based risk assessment can be applied to various monitoring datasets, and that the most applicable model among the three different types of DNN models could be selected according to data availability for a given monitoring database. Environ Toxicol Chem 2023;42:2271–2283. © 2023 SETAC [ABSTRACT FROM AUTHOR]

Nickel (Ni) is used primarily in the production of alloys like stainless steel and is increasingly being used in the production of batteries for the electric vehicle market. Exposure of Ni to ecosystems is of concern because Ni can be toxic to aquatic organisms. The influence of water chemistry constituents (e.g., hardness, pH, dissolved organic carbon) on the toxicity of Ni has prompted the development and use of bioavailability models, such as biotic ligand models (BLMs), which have been demonstrated to accurately predict Ni toxicity in broadly different ecosystems, including Europe, North America, and Australia. China, a leading producer of Ni, is considering bioavailability‐based approaches for regulating Ni emissions. Adoption of bioavailability‐based approaches in China requires information to demonstrate the validity of bioavailability models for the local water chemistry conditions. The present study investigates the toxicity of Ni to three standard test species (Daphnia magna, Pseudokirchneriella subcapitata, and Danio rerio) in field‐collected natural waters that are broadly representative of the range of water chemistries and bioavailabilities encountered in Chinese lakes and rivers. All experimental data are within a factor of 3 of the BLM predicted values for all tests with all species. For D. magna, six of seven waters were predicted within a factor of 2 of the experimental result. Comparison of experimental data against BLM predictions shows that the existing Ni bioavailability models are able to explain the differences in toxicity that result from water chemistry conditions in China. Validation of bioavailability models to water chemistries and bioavailability ranges within China provides technical support for the derivation of site‐specific Ni water quality criteria in China. Environ Toxicol Chem 2023;42:1257–1265. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Biotic ligand models (BLMs) and the sensitivities of indigenous species are used to assess the environmental risk considering the bioavailability of metals, such as nickel. However, the BLM‐based acute–to–chronic ratio (ACR) is required if the predicted no‐effect concentration (PNEC) cannot be derived from the chronic species sensitivity distribution (SSD). The applicability of the ACR approach for estimating BLM‐based PNEC for nickel from acute toxicity data was evaluated in the present study. The BLM‐based acute SSD for nickel was built using the sensitivities of 21 indigenous species and different taxon‐specific BLMs for each taxonomic group. To predict the acute sensitivity of invertebrates, the chronic crustacean nickel BLM with pH effect term, which can account for nickel toxicity at high pH levels, was used. This was used instead of the existing acute BLM for crustacean, which has too narrow a pH range to cover the pH dependency of toxicity. The final BLM‐based ACR of nickel, determined within a factor of 1.53 from the species‐specific acute and chronic sensitivities of the six species, was more reliable than the typical ACR estimated within a factor of 1.84. A linear relationship (r2 = 0.95) was observed between the PNECs using BLM‐based ACR and the PNECs derived from the BLM‐based chronic SSD of the European Union Risk Assessment Reports. In conclusion, the BLM‐based PNEC for nickel could be derived using the ACR approach, unlike when copper BLM was applied. The BLM‐based ACR for nickel is the first result calculated by directly comparing acute and chronic species sensitivities, and will contribute to the application of BLM‐based risk assessment in broader ecoregions. Environ Toxicol Chem 2023;42:914–927. © 2023 SETAC [ABSTRACT FROM AUTHOR]

A variety of important major and trace elements may competitively inhibit cadmium (Cd) absorption in human cells and reduce Cd toxicity. However, the impact of essential elements on the cytotoxicity of metals can be difficult to quantify and anticipate. Cd acute toxicity to Caco-2 cell viability was studied in culture solutions and modeled by a biotic ligand model (BLM). The individual effects of the cations potassium (K+), calcium (Ca2+), magnesium (Mg2+), ferrous ion(Fe2+), zinc (Zn2+) and manganese (Mn2+) on Cd toxicity were also investigated. The results indicated that the toxicity of Cd in culture solutions to cell viability declined with increasing concentrations of Zn2+ and Mn2+ in the solutions, while K+, Ca2 +, Mg2 + and Fe2+ had no significant effect. Using the BLM, the stability constants for the binding of Cd2 +, Zn2+, and Mn2+ to biotic ligands were determined to be logKCdBL = 5.76, logKZnBL = 4.39 and logKMnBL = 5.31, respectively. Moreover, it was calculated that 51% occupancy of the biotic ligand sites for Cd by Cd was required to cause a 50% reduction in Caco-2 cell viability. A BLM was successfully established using the estimated constants to predict the Cd cytotoxicity to Caco-2 cell viability as a function of solution characteristics, so that the effective concentrations that reduced cell viability by 50% (EC50) could be predicted by the BLM within 1.6 fold changes of the observed EC50. The application's viability and precision for foretelling Cd toxicity in Caco-2 cells are discussed.

Dissolved copper (Cu) can contribute to toxicity in aquatic systems impacted by acid mine drainage (AMD), and its bioavailability is influenced by aqueous complexation with organic ligands that predominantly include fulvic acids (FAs). Because the geochemical fractionation of FAs that accompanies sorption to hydrous aluminum oxides (HAOs) and hydrous iron oxides (HFOs) can alter Cu complexation with FA, we investigated FAs isolated from three categories of water (pristine, AMD, and in situ‐fractionated mixtures of pristine and AMD collected at stream confluences) in three mining‐impacted alpine watersheds in central Colorado, USA. We also conducted geochemical fractionation of field‐collected FAs and Suwannee River FAs by precipitating HAOs and HFOs in the laboratory. Spectral properties of the FAs (e.g., UV‐VIS absorbance) were altered by geochemical fractionation, and in acute toxicity tests with an aquatic invertebrate (Daphnia magna) Cu was more toxic in the presence of in situ‐ and laboratory‐fractionated FAs (median effect concentration [EC50] 19–50 µg Cu L−1) than in the presence of nonfractionated FAs (EC50 48–146 µg Cu L−1). After adjusting for the strain‐specific sensitivity of our D. magna, we improved the accuracy of Biotic Ligand Model predictions of Cu EC50 values for AMD‐related FAs by using an "effective dissolved organic carbon" based on spectral properties that account for among‐FA differences in protectiveness against Cu toxicity. However, some differences remained between predicted and measured EC50 values, especially for FAs from AMD‐related waters that might contain important metal‐binding moieties not accounted for by our measured spectral indices. Environ Toxicol Chem 2023;42:449–462. © 2022 SETAC [ABSTRACT FROM AUTHOR]

Multiple linear regression (MLR) models for predicting zinc (Zn) toxicity to freshwater organisms were developed based on three toxicity‐modifying factors: dissolved organic carbon (DOC), hardness, and pH. Species‐specific, stepwise MLR models were developed to predict acute Zn toxicity to four invertebrates and two fish, and chronic toxicity to three invertebrates, a fish, and a green alga. Stepwise regression analyses found that hardness had the most consistent influence on Zn toxicity among species, whereas DOC and pH had a variable influence. Pooled acute and chronic MLR models were also developed, and a k‐fold cross‐validation was used to evaluate the fit and predictive ability of the pooled MLR models. The pooled MLR models and an updated Zn biotic ligand model (BLM) performed similarly based on (1) R2, (2) the percentage of effect concentration (ECx) predictions within a factor of 2.0 of observed ECx, and (3) residuals of observed/predicted ECx versus observed ECx, DOC, hardness, and pH. Although fit of the pooled models to species‐specific toxicity data differed among species, species‐specific differences were consistent between the BLM and MLR models. Consistency in the performance of the two models across species indicates that additional terms, beyond DOC, hardness, and pH, included in the BLM do not help explain the differences among species. The pooled acute and chronic MLR models and BLM both performed better than the US Environmental Protection Agency's existing hardness‐based model. We therefore conclude that both MLR models and the BLM provide an improvement over the existing hardness‐only models and that either could be used for deriving ambient water quality criteria. Environ Toxicol Chem 2023;42:393–413. © 2022 SETAC [ABSTRACT FROM AUTHOR]

This study aimed to establish ecotoxicologically acceptable Cu concentrations for soil-residing species by integrating the biotic ligand model and the species sensitivity distribution. Statistical analyses were performed on 35 soil solution samples collected from four distinct land use sites: residential, agricultural, forested, and industrial regions. The environmental parameters of these samples, including pH, dissolved organic carbon (DOC), Ca2⁺, Mg2⁺, K⁺, and Na⁺ concentrations, exhibited wide variations across the four regions. Specifically, pH and the concentrations of Mg2⁺, K⁺, and Na⁺ showed significant variability. Additionally, a strong correlation was observed between pH and Ca2⁺, as well as between the DOC concentration and Mg2⁺ and Na⁺. Using the biotic ligand model, we derived the half-maximal effective activities of Cu (EC 50 {Cu 2+ }) for 10 soil organisms based on the chemical compositions of the soil solution samples. Additionally, a species sensitivity distribution approach was employed to determine the 5% hazardous concentration (HC5) for soil biota, which was closely associated with DOC and Na⁺ concentrations, with Mg2⁺ playing a secondary role. We attributed these relationships to the formation of DOC complexes that mitigate Cu toxicity, along with competitive interactions with cations. Notably, HC5 values did not differ significantly across sampling sites (p = 0.523). Clustering based on environmental factors grouped the samples into four clusters, each containing soils from different land use types. However, the third cluster included an outlier from agricultural soil due to its unusually high pH and DOC levels. These findings suggest that it is crucial to consider site-specific soil characteristics when determining ecotoxicologically acceptable Cu concentrations, and soil solution characteristics do not always align with specific land use patterns. [Display omitted] • Biotic ligand model and species sensitivity distribution were integrated. • From 35 soil samples, ecotoxicologically acceptable Cu concentrations were derived. • Soil solution characteristics do not consistently align with specific land uses. • Site-specific soil solution characteristics are good indicators of bioavailability. [ABSTRACT FROM AUTHOR]

Copper (Cu) is a contaminant of potential concern for a uranium mine whose receiving waters are in the World Heritage–listed Kakadu National Park in northern Australia. The physicochemical characteristics of the freshwaters in this region enhance metal bioavailability and toxicity. Seven tropical species were used to assess the chronic toxicity of Cu in extremely soft freshwater from a creek upstream of the mine. Sensitivity to Cu was as follows: Moinodaphnia macleayi > Chlorella sp. > Velesunio sp. > Hydra viridissima > Amerianna cumingi > Lemna aequinoctialis > Mogurnda mogurnda. The 10% effect concentrations (EC10s) ranged from 1.0 µg/L Cu for the cladoceran Moinodaphnia macleayi to 9.6 µg/L for the fish M. mogurnda. The EC50s ranged from 6.6 µg/L Cu for the mussel Velesunio sp. to 22.5 µg/L Cu for M. mogurnda. Geochemical modeling predicted Cu to be strongly bound to fulvic acid (80%–99%) and of low bioavailability (0.02%–11.5%) under these conditions. Protective concentrations (PCs) were derived from a species sensitivity distribution for the local biota. The 99% PC (PC99), PC95, PC90, and PC80 values were 0.5, 0.8, 1.0, and 1.5 µg/L Cu, respectively. These threshold values suggest that the current Australian and New Zealand default national 99% protection guideline value for Cu (1.0 µg/L) would not provide adequate protection in freshwaters of low hardness, particularly for this area of high conservation value. The continuous criterion concentration predicted by the Cu biotic ligand model for conditions of low pH (6.1), low dissolved organic carbon (2.5 mg/L), low hardness (3.3 mg/L), and 27 °C was 0.48 µg/L Cu, comparable with the PC99. Consideration of the natural water quality conditions of a site is paramount for protective water quality guidelines. Environ Toxicol Chem 2022;41:2808–2821. © 2022 Commonwealth of Australia. Environmental Toxicology and Chemistry © 2022 SETAC. [ABSTRACT FROM AUTHOR]

In the present study, we assessed the use of existing user‐friendly bioavailability tools to predict metal bioavailability and the risk of toxicity in a typical Nigerian surface water. The effect of prevailing water chemistry on toxicity of metals was also assessed in laboratory studies. Surface water samples were collected at four locations downstream in the Ogun River in Lagos State, and water chemistry analysis was carried out using standard methods. Relevant parameters were inputted into the Bio‐Met software and Metal Bioavailability Assessment Tool (M‐Bat), which are run on a Microsoft Excel spreadsheet, to obtain the site‐specific hazardous concentrations affecting 5% of the population (HC5)/predicted‐no‐effect concentrations (PNECs) for selected metals and risk characterization ratios (RCRs) at locations downstream in the river. Assessments using the bioavailability tools showed that two locations, Owode‐Onirin and Kara, were more sensitive to Zn and Pb inputs compared to the other locations. The RCRs for Cu, Zn, and Pb, respectively, were >1 at all locations, indicating a potential risk of toxicity to aquatic life. Results from laboratory studies conformed with predictions from the bioavailability tools because Zn and Pb were more toxic to aquatic organisms in surface water collected from Owode‐Onirin and Kara locations, respectively, compared to toxicity in surface water from other locations. The issue of bioavailability in metal pollution control is widely accepted and has been incorporated into water quality guidelines (WQGs) in the United States, the United Kingdom, and Europe. In the absence of regulations incorporating bioavailability in developing countries including Nigeria, it is essential to assess the applicability of existing methods incorporating bioavailability to surface waters in this region. Findings from such studies will facilitate the development of region‐specific WQGs for metals which will be protective of locally relevant aquatic life. Environ Toxicol Chem 2022;41:2537–2547. © 2022 SETAC [ABSTRACT FROM AUTHOR]

The equilibrium partitioning sediment benchmarks (ESBs) derived by the US Environmental Protection Agency (USEPA) in 2005 provide a mechanistic framework for understanding metal bioavailability in sediments by considering equilibrium partitioning (EqP) theory, which predicts that metal bioavailability in sediments is determined largely by partitioning to sediment particles. Factors that favor the partitioning of metals to sediment particles, such as the presence of acid volatile sulfide (AVS) and sediment organic matter, reduce metal bioavailability to benthic organisms. Because ESBs link metal bioavailability to partitioning to particles, they also predict that measuring metals in porewater can lead to a more accurate assessment of bioavailability and toxicity to benthic organisms. At the time of their development, sediment ESBs based on the analysis of porewater metal concentrations were limited to comparison with hardness‐dependent metals criteria for the calculation of interstitial water benchmark units (IWBUs). However, the multimetal biotic ligand model (mBLM) provides a more comprehensive assessment of porewater metal concentrations, because it considers factors in addition to hardness, such as pH and dissolved organic carbon, and allows for interactions between metals. To evaluate the utility of the various sediment and porewater ESBs, four Hyalella azteca bioassay studies were identified that included sediment and porewater measurements of metals and porewater bioavailability parameters. Evaluations of excess simultaneously extracted metals, IWBUs, and mBLM toxic units (TUs) were compared among the bioassay studies. For porewater, IWBUs and mBLM TUs were calculated using porewater metal concentrations from samples collected using centrifugation and peepers. The percentage of correct predictions of toxicity was calculated for each benchmark comparison. The mBLM‐based assessment using peeper data provided the most accurate predictions for the greatest number of samples among the evaluation methods considered. This evaluation demonstrates the value of porewater‐based evaluations in conjunction with sediment chemistry in understanding toxicity observed in bioassay studies. Integr Environ Assess Manag 2022;18:1335–1347. © 2021 SETAC Key Points: Evaluation of risks associated with metal‐contaminated sediments using porewater chemistry and the mBLM bioavailability model can provide additional and more accurate assessments compared with excess SEM and carbon normalized excess SEM.Metal concentrations in sediment porewaters derived from peepers were a more accurate characterization of exposure to benthic organisms compared with porewaters collected by centrifugation.Porewater evaluation may be especially useful for sediments that fall in between the upper and lower boundaries for excess SEM and carbon‐normalized excess SEM and are therefore characterized as "uncertain" by these methods. [ABSTRACT FROM AUTHOR]

Extraction of soil samples with dilute CaCl2 solution in a routinely performed batch test has potential to be used in site‐specific assessment of ecotoxicological risks at metal‐contaminated sites. Soil extracts could potentially give a measure of the concentration of bioavailable metals in the soil solution, thereby including effects of soil properties and contaminant "aging." We explored the possibility of using a 0.001 M CaCl2 batch test combined with biotic ligand models (BLMs) for assessment of ecotoxicity in soils. Concentrations of Cu2+ and Zn2+ in soil extracts were linked to responses in ecotoxicity tests (microbial processes, plants, and invertebrates) previously performed on metal‐spiked soils. The batch test data for soils were obtained by spiking archived soil materials using the same protocol as in the original studies. Effective concentration values based on free metal concentrations in soil extracts were related to pH by linear regressions. Finally, field‐contaminated soils were used to validate model performance. Our results indicate a strong pH‐dependent toxicity of the free metal ions in the soil extracts, with R2 values ranging from 0.54 to 0.93 (median 0.84), among tests and metals. Using pH‐adjusted Cu2+ and Zn2+ concentrations in soil extracts, the toxic responses in spiked soils and field‐contaminated soils were similar, indicating a potential for the calibrated models to assess toxic effects in field‐contaminated soils, accounting for differences in soil properties and effects of contaminant "aging." Consequently, evaluation of a standardized 0.001 M CaCl2 batch test with a simplified BLM can provide the basis for an easy‐to‐use tool for site‐specific risk assessment of metal toxicity to soil organisms. Environ Toxicol Chem 2022;41:1540–1554. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Environmental context: Having appropriate and robust models used for developing water quality guidelines is critical for sound environmental management. Methods used to validate models have only been demonstrated appropriate for a small portion of data types used in these models. This study has found that models using certain data types would be more appropriately validated using alternative evaluation criteria. This study serves as an important reference for developing and evaluating robust models. Rationale: Bioavailability-based toxicity models for metals often have performance assessed by whether it can predict toxicity data within a factor of 2 of their paired observed toxicity data. This method has only been verified for median effect values (EC50) for acute fish and daphnia data, however toxicity models have been developed for a much broader range of effect levels (i.e. EC10/EC20) and species (e.g. microalga). This study tested whether the factor-of-2 rule is appropriate for a wider range of organisms and effect concentrations than previously studied. Methodology: Toxicity estimate data from repeated tests conducted under the same conditions were collated to assess variation in results and compare this variation to a range of 4 (a factor of 2 above and below the mean) and a range of 9 (a factor of 3 above and below the mean) to assess if a factor-of-3 rule may be more appropriate for some species and effect levels. Results and discussion: Overall, the factor-of-2 rule is broadly applicable for metal toxicity to a range of species for EC50 data. The EC10 datasets highlighted that larger variability exists in low effect levels and supported the use of a factor-of-3 rule, while the either the factor-of-2 or factor-of-3 rule could be applied to microalgae. The level of performance evaluation chosen may depend on the application of the bioavailability model. This study also found that while repeated toxicity test data is routinely generated, it is rarely published. Publication of such data would enable expansion of the present study to include inter-laboratory comparisons, an important consideration as most bioavailability models are based on data pooled from multiple sources. Environmental context. Having appropriate and robust models used for developing water quality guidelines is critical for sound environmental management. Methods used to validate models have only been demonstrated appropriate for a small portion of data types used in these models. This study has found that models using certain data types would be more appropriately validated using alternative evaluation criteria. This study serves as an important reference for developing and evaluating robust models. [ABSTRACT FROM AUTHOR]

Environmental context: The growth in demand for platinum has led to an increase in the presence of this metal in the environment but little is known about its toxicity to aquatic organisms. The presence of organic matter should contribute to decreasing metal bioavailability but the opposite was found for platinum. How ubiquitous natural organic matter can alter the accumulation and effects of platinum group elements remains to be fully elucidated. Rationale: There is a growing interest for platinum in ecotoxicology, mainly because of its use in automobile exhaust catalysts. When it reaches aquatic ecosystems, platinum can interact with ligands such as natural organic matter. According to the Biotic Ligand Model, the formation of such complexes should reduce metal bioavailability. As a consequence, toxicity should decrease in the presence of organic matter. Methodology: This study focused on the uptake of platinum by two microalgae species (Chlorella fusca and Chlamydomonas reinhardtii) and its subsequent inhibitory effects on growth (96 h). Cells were exposed to platinum (5–300 µg L−1) at three concentrations (0, 10 and 20 mg C L−1) of standard Suwannee River humic acid (SRHA). Platinum bound to humic acid was determined experimentally using partial ultrafiltration to relate metal uptake and toxicity to speciation. Results: Unexpectedly, results show that platinum toxicity, expressed as ultrafiltrable Pt (not bound to humic acid) and total Pt concentrations, is enhanced in the presence of humic acid for both algae. For C. fusca , the half maximal effective concentration (EC50) values decreased from 93 to 37 and 35 µg L−1 of ultrafiltrable Pt in the presence of 10 and 20 mg C L−1 SRHA and from 89 to 36 and 0.31 µg L−1 for C. reinhardtii. Discussion: In contradiction with the Biotic Ligand Model, the results show that the presence of SRHA can significantly and importantly increase platinum uptake and toxicity as determined in two unicellular green algae, C. reinhardtii and C. fusca. The present work raises the issue of the impact of platinum on microalgae under realistic environmental conditions (ubiquitous presence of organic matter), primary producers being of great ecological importance. Environmental context. The growth in demand for platinum has led to an increase in the presence of this metal in the environment but little is known about its toxicity to aquatic organisms. The presence of organic matter should contribute to decreasing metal bioavailability but the opposite was found for platinum. How ubiquitous natural organic matter can alter the accumulation and effects of platinum group elements remains to be fully elucidated. [ABSTRACT FROM AUTHOR]

A hydroponic trial was conducted to study the effect of chloride salinity in simulated effluent on Cd accumulation by tobacco. Leaf surface area (LSA) and root surface area (RSA) measurements were incorporated as possible determinants of Cd uptake rate by plants. Results showed that individual plant differences in Cd content were normalized when including RSA to express Cd uptake rates by plants but not including LSA. A biotic ligand model (BLM) fitted to predict Cd uptake, estimated active and almost linear uptake of the free Cd2+ ion by tobacco plants, while virtually no changes in the chloride complex (CdCl+) uptake were predicted, presumably due to a rapid saturation of the hypothetical root sorption sites at the concentrations used in this trial. Nicotiana tabacum var. K326 is evidenced to be a species potentially suitable for biological wastewater treatment using rhizofiltration at concentrations commonly found in salt-affected wastewater, with high Cd accumulation (185 to 280 mg/kgd.m.) regardless of water salinity and tolerance up to 80 mmol/L NaCl.

In the real world, metals are generally present as mixtures, but evaluating their mixture toxicity is still a daunting challenge. The classic conceptual models of concentration addition (CA) and independent action (IA) have been widely used by simply adding doses and responses to predict mixture effects assuming there is non-interaction. In cases where interactions do occur in a mixture, both CA and IA are no longer applicable for quantifying the toxicity, because interpretation of the observed joint effects is often limited to overall antagonism or synergism. In metal mixtures, interactive effects may occur at various levels, such as the exposure level, the uptake level, and the target level. A comprehensive understanding of the mechanisms of joint toxicity is therefore needed to incorporate the interactive effects of mixture components in predicting mixture toxicity. With this in mind, numerous bioavailability-based methods may be considered, with diverse mechanistic perspectives, such as the biotic ligand model (BLM), the electrostatic toxicity model (ETM), the WHAM-Ftox approach, a toxicokinetic-toxicodynamic (TK-TD) and an omics-based approach. This review therefore timely summarizes the representative predictive tools and their underlying mechanisms and highlights the importance of integrating mixture interactions and bioavailability in assessing the toxicity and risks of metal mixtures. [ABSTRACT FROM AUTHOR]

Although the concept and modeling of metal bioavailability and toxicity have been well developed based largely on laboratory experiments with standard test species, additional evidence is required to demonstrate their applicability for macroinvertebrates typically found in natural lotic ecosystems. We conducted 10‐day stream mesocosm experiments to test the hypothesis that increased water hardness (in the present study, the calcium [Ca] concentration was increased by adding CaCl2) would mitigate the effects of copper (Cu) on natural benthic macroinvertebrate communities. Exposure of macroinvertebrate communities to 25 μg/L Cu for 10 days in stream mesocosm experiments resulted in significant decreases in total abundance, in number of taxa, and in abundance of many macroinvertebrate taxa. However, the addition of Ca to stream mesocosms and the associated increase in water hardness up to 250 mg/L CaCO3 did not mitigate these effects of Cu on macroinvertebrate communities. The results showed that the hardness‐based water quality criteria for Cu of the US Environmental Protection Agency were not protective under the conditions of relatively high hardness, low alkalinity, and circumneutral pH. In contrast, the water quality criteria based on the biotic ligand model predicted little protective effects of Ca on Cu toxicity, which is consistent with our results. Additional experiments are required to understand the influence of modifying factors on the toxicity of metals to macroinvertebrate communities. Environ Toxicol Chem 2022;41:1304–1310. © 2022 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Nickel (Ni) ecotoxicity is dictated by water chemistry characteristics such as pH, water hardness, and amount of dissolved organic carbon. Bioavailability models have been developed to predict Ni toxicity and validated for European, Australian, and US natural waters. In this study, chronic toxicity tests in Ni-spiked Japanese river waters were conducted on a strain of Daphnia magna to test whether the chronic toxicity differs among Japanese natural waters with different water chemistries. Based on the results of chronic Ni toxicity tests, we assessed the performance of existing D. magna bioavailability models, which were developed in artificial waters (Model 1) and calibrated in European natural waters (Model 2), in terms of the accuracy and the bias of model predictions. Furthermore, we also calibrated the two models by using toxicity test results to develop a bioavailability model for Ni chronic toxicity to the strain of D. magna in Japanese river waters. The 10%, 20%, and 50% effect concentrations (EC10, EC20, and EC50) of dissolved Ni on reproduction of the D. magna strain were within ranges from 8.1 to 44.9 μg/L, 9.0 to 57.1 μg/L, and 10.9 to 86.1 μg/L, respectively. Results indicate that differences in water chemistry among Japanese river waters influenced chronic Ni toxicity to the model organism. Model 1predicted 43% of the observed EC10, EC20, and EC50 values within a factor of 2 and 100%, 100%, and 43% within a factor of 3, respectively. Model 2 predicted 14%, 14%, and 29% of the observed EC10, EC20, and EC50 values within a factor of 2 and 43% within a factor of 3. The values of model bias based on the geometric mean of ratios of EC10, EC20 and EC50 values predicted by each of the two models and observed EC10, EC20, and EC50 values were 0.71, 0.65, and 0.62 for Model 1 and 0.27, 0.26, and 0.29 for Model 2, respectively. After calibrating two models using the results of toxicity tests, refined Model 1 predicted 71%, 57%, and 57% of observed EC10, EC20, and EC50 values within a factor of 2 and 100%, 86%, and 100% within a factor of 3; refined Model 2 predicted 71% of observed EC10, EC20, and EC50 values within a factor 2 and 100%, 86%, and 86% within a factor of 3, respectively. Our results indicate that calibrating the Ni bioavailability models in Japanese natural waters increased their predictive capacity by a factor of up to approximately five. [ABSTRACT FROM AUTHOR]

Heavy metals are occurring in the aquatic environment as the result of natural or anthropogenic inputs, and depending on concentration, availability and resilience time, they can differently affect the animal wellness. Numerous studies reveal that more than 99% of metals in seawater are complexed with organic ligands suggesting the major role of organic complexation on metal behavior. Moreover, the amphilic character of marine natural organic matter makes this substance a relevant medium for interactions with charged and uncharged metal molecules. Here we review mechanisms and factors that control marine organic matter composition and its interactions with metals. Organic matter–metal complexes modify metal bioavailability and, in turn, change effects on living organisms. [ABSTRACT FROM AUTHOR]

Population models are increasingly being used to extrapolate individual‐level effects of chemicals, including metals, to population‐level effects. For metals, it is also important to take into account their bioavailability to correctly predict metal toxicity in natural waters. However, to our knowledge, no models exist that integrate metal bioavailability into population modeling. Therefore, our main aims were to 1) incorporate the bioavailability of copper (Cu) and zinc (Zn) into an individual‐based model (IBM) of rainbow trout (Oncorhynchus mykiss), and 2) predict how survival‐time concentration data translate to population‐level effects. For each test water, reduced versions of the general unified threshold model of survival (GUTS‐RED) were calibrated using the complete survival‐time concentration data. The GUTS‐RED individual tolerance (IT) showed the best fit in the different test waters. Little variation between the different test waters was found for 2 GUTS‐RED‐IT parameters. The GUTS‐RED‐IT parameter "median of distribution of thresholds" (mw) showed a strong positive relation with the Ca2+, Mg2+, Na+, and H+ ion activities. Therefore, mw formed the base of the calibrated GUTS bioavailability model (GUTS‐BLM), which predicted 30‐d x% lethal concentration (LCx) values within a 2‐fold error. The GUTS‐BLM was combined with an IBM, inSTREAM‐Gen, into a GUTS‐BLM‐IBM. Assuming that juvenile survival was the only effect of Cu and Zn exposure, population‐level effect concentrations were predicted to be 1.3 to 6.2 times higher than 30‐d laboratory LCx values, with the larger differences being associated with higher interindividual variation of metal sensitivity. The proposed GUTS‐BLM‐IBM model can provide insight into metal bioavailability and effects at the population level and could be further improved by incorporating sublethal effects of Cu and Zn. Environ Toxicol Chem 2021;40:2764–2780. © 2021 SETAC [ABSTRACT FROM AUTHOR]

Increasing evidence demonstrates that hexavalent tungsten (W(VI)) can affect the survival of various organisms. This study explored the influences of pH and common anions on W(VI) toxicity on wheat and established a biotic ligand model (BLM) for predicting W(VI) toxicity. It was found that as the pH value increased from 6.0 to 8.5, the EC50[W(VI)]T values increased greatly from 24.7 to 46.6 μM, indicating that increasing pH values can alleviate W(VI) toxicity. A linear relationship between the ratio of HWO4- to WO42- and EC50{WO42-} indicated that WO42- and HWO4- were two toxic species of W(VI). The toxicity of W(VI) decreased as the H2PO4- and SO42- activities increased but not when the activities of Cl- and NO3- increased, demonstrating that the competition from H2PO4- and SO42- significantly influenced W(VI) toxicity. By applying BLM theory, the stability constants for HWO4-, WO42-, H2PO4-, and SO42- were obtained: logKWO4BL = 4.08, logKHWO4BL = 6.44, logKH2PO4BL = 2.09, and logKSO4BL = 1.87, fWBL50% = 0.300, β = 1.99. Results demonstrated that BLM outperformed the free metal activity model(FIAM) in predicting W(VI) toxicity when considering the influences of pH, W(VI) species, and H2PO4- and SO42- competition for active ligand sites.

The potential for Ni toxicity in seawater is of concern because of mining and processing activities in coastal regions. Determining Ni speciation is vital to understanding and predicting Ni toxicity and for bioavailability-based nickel risk assessment. The goal of this study was to characterize the complexation of Ni in relation to toxicity using embryological development of purple sea urchin (S. purpuratus). It was predicted that free ion [Ni2+] would be a better predictor of toxicity than total dissolved Ni concentrations (NiD). Synthetic ligands with known logKf values (Ethylenediaminetetraacetic acid (EDTA), Nitrilotriacetic acid (NTA), tryptophan (TRP), glutamic acid (GA), histidine (HD), and citric acid (CA)) were used to test the assumptions of the biotic ligand model (BLM) for Ni in seawater. [NiD] was measured by graphite furnace atomic absorption spectroscopy (GFAAS) and Ni2+ was first quantified using the ion-exchange technique (IET) and then concentrations were measured by GFAAS; [Ni2+] was also estimated using aquatic geochemistry modelling software (Visual Minteq). The mean EC50 values for [NiD] in unmodified artificial seawater control was 3.6 µM (95% CI 3.0–4.5) [211 µg/L 95% CI 176–264] and the addition of ligands provided protection, up to 6.5-fold higher [NiD] EC50 for EDTA. Compared to the control, measured EC50 values based on total dissolved nickel were higher in the presence of ligands. As predicted by BLM theory, [Ni2+] was a better predictor of Ni toxicity with 17% variability in EDTA and CA media while there was 72% variability in the prediction of Ni toxicity with total dissolved Ni. The results of this research provide support for the application of BLM- based prediction models for estimating Ni impacts in seawater.

Toxicity‐modifying factors can be modeled either empirically with linear regression models or mechanistically, such as with the biotic ligand model (BLM). The primary factors affecting the toxicity of nickel to aquatic organisms are hardness, dissolved organic carbon (DOC), and pH. Interactions between these terms were also considered. The present study develops multiple linear regressions (MLRs) with stepwise regression for 5 organisms in acute exposures, 4 organisms in chronic exposures, and pooled models for acute, chronic, and all data and compares the performance of the Pooled All MLR model to the performance of the BLM. Independent validation data were used for evaluating model performance, which for pooled models included data for organisms and endpoints not present in the calibration data set. Hardness and DOC were most often selected as the explanatory variables in the MLR models. An attempt was also made at evaluating the uncertainty of the predictions for each model; predictions that showed the most error tended to show the highest levels of uncertainty as well. The performances of the 2 models were largely equal, with differences becoming more apparent when looking at the performance within subsets of the data. Environ Toxicol Chem 2021;40:2189–2205. © 2021 SETAC [ABSTRACT FROM AUTHOR]

A review of nickel (Ni) toxicity to aquatic organisms was conducted to determine the primary water quality factors that affect Ni toxicity and to provide information for the development and testing of a biotic ligand model (BLM) for Ni. Acute and chronic data for 66 aquatic species were compiled for the present review. The present review found that dissolved organic carbon (DOC) and hardness act as toxicity‐modifying factors (TMFs) because they reduced Ni toxicity to fish and aquatic invertebrates, and these effects were consistent in acute and chronic exposures. The effects of pH on Ni toxicity were inconsistent, and for most organisms there was either no effect of pH or, in some cases, a reduction in toxicity at low pH. There appears to be a unique pH effect on Ceriodaphnia dubia that results in increased toxicity at pHs above 8, but otherwise the effects of TMFs were consistent enough across all organisms and endpoints that a single set of parameters in the Ni BLM worked well with all acute and chronic toxicity data for fish, amphibians, aquatic invertebrates, and aquatic plants and algae. The unique effects of pH on C. dubia may be due to mixture toxicity involving both Ni and bicarbonate. The implications of this mixture effect on BLM modeling and a proposed set of BLM parameters for C. dubia are addressed in the review. Other than this exception, the Ni BLM with a single set of parameters could successfully predict toxicity to all acute and chronic data compiled in the present review. Environ Toxicol Chem 2021;40:2121–2134. © 2021 SETAC [ABSTRACT FROM AUTHOR]

An increasing number of metal bioavailability models are available for use in setting regulations and conducting risk assessments in aquatic systems. Selection of the most appropriate model is dependent on the user's needs but will always benefit from an objective, comparative assessment of the performance of available models. In 2017, an expert workshop developed procedures for assessing metal bioavailability models. The present study applies these procedures to evaluate the performance of biotic ligand models (BLMs) and multiple linear regression (MLR) models for copper. We find that the procedures recommended by the expert workshop generally provide a robust series of metrics for evaluating model performance. However, we recommend some modifications to the analysis of model residuals because the current method is insensitive to relatively large differences in residual patterns when comparing models. We also provide clarification on details of the evaluation procedure which, if not applied correctly, could mischaracterize model performance. We found that acute Cu MLR and BLM performances are quite comparable, though there are differences in performance on a species‐specific basis and in the resulting water quality criteria as a function of water chemistry. In contrast, the chronic Cu MLR performed distinctly better than the BLM. Observed differences in performance are due to the smaller effects of hardness and pH on chronic Cu toxicity compared to acute Cu toxicity. These differences are captured in the chronic MLR model but not the chronic BLM, which only adjusts for differences in organism sensitivity. In general, we continue to recommend concurrent development of both modeling approaches because they provide useful comparative insights into the strengths, limitations, and predictive capabilities of each model. Environ Toxicol Chem 2021;40:1649–1661. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

A site-specific, ecologically acceptable concentration of Cu in soil pore water was determined with four trophic levels of soil-residing organisms. Specifically, soil pore water was periodically collected from a site contaminated with heavy metals using in-situ samplers. Dissolved Cu concentration, Ca2+, Mg2+, Na+, K+, Cl-, SO42-, NO3-, dissolved organic carbon, pH, and temperature were analyzed to derive a half-maximal effective concentration of Cu (EC50[Cu]T) using a biotic ligand model (BLM). The BLM parameters, such as binding constants (logKXBL) and the fraction of biotic ligand sites occupied by Cu ions (f), were adapted from previous studies. The EC50{Cu2+} values were used to construct a species sensitivity distribution (SSD) curve from which the hazardous concentration, protecting 95% of the soil-residing organisms (HC5), was determined. Using ten BLM-based acceptable concentrations of Cu obtained by combining BLM and SSD, time series analysis was conducted with the fixed monitoring benchmark method to obtain maximum Cu concentration as an endpoint exhibiting no-adverse-effect which was found to be 0.084 mg/L of Cu in soil pore water at the test site. This study provides a systematic tool for determining an ecologically acceptable concentration of Cu in the soil by incorporating soil pore water chemistry and time series analysis. [ABSTRACT FROM AUTHOR]

A hydroponic trial was conducted to study the effect of chloride salinity in simulated effluent on Cd accumulation by tobacco. Leaf surface area (LSA) and root surface area (RSA) measurements were incorporated as possible determinants of Cd uptake rate by plants. Results showed that individual plant differences in Cd content were normalized when including RSA to express Cd uptake rates by plants but not including LSA. A biotic ligand model (BLM) fitted to predict Cd uptake, estimated active and almost linear uptake of the free Cd2+ ion by tobacco plants, while virtually no changes in the chloride complex (CdCl+) uptake were predicted, presumably due to a rapid saturation of the hypothetical root sorption sites at the concentrations used in this trial. Nicotiana tabacum var. K326 is evidenced to be a species potentially suitable for biological wastewater treatment using rhizofiltration at concentrations commonly found in salt-affected wastewater, with high Cd accumulation (185 to 280 mg/kgd.m.) regardless of water salinity and tolerance up to 80 mmol/L NaCl. [ABSTRACT FROM AUTHOR]

There has been an increased emphasis on incorporating bioavailability‐based approaches into freshwater guideline value derivations for metals in the Australian and New Zealand water quality guidelines. Four bioavailability models were compared: the existing European biotic ligand model (European Union BLM) and a softwater BLM, together with 2 newly developed multiple linear regressions (MLRs)—a trophic level‐specific MLR and a pooled MLR. Each of the 4 models was used to normalize a nickel ecotoxicity dataset (combined tropical and temperate data) to an index condition of pH 7.5, 6 mg Ca/L, 4 mg Mg/L, (i.e., approximately 30 mg CaCO3/L hardness), and 0.5 mg DOC/L. The trophic level‐specific MLR outperformed the other 3 models, with 79% of the predicted 10% effect concentration (EC10) values within a factor of 2 of the observed EC10 values. All 4 models gave similar normalized species sensitivity distributions and similar estimates of protective concentrations (PCs). Based on the index condition water chemistry proposed as the basis of the national guideline value, a protective concentration for 95% of species (PC95) of 3 µg Ni/L was derived. This guideline value can be adjusted up and down to account for site‐specific water chemistries. Predictions of PC95 values for 20 different typical water chemistries for Australia and New Zealand varied by >40‐fold, which confirmed that correction for nickel bioavailability is critical for the derivation of site‐specific guideline values. Environ Toxicol Chem 2021;40:100–112. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

The generalized bioavailability model (gBAM) has been proposed as an alternative to the biotic ligand model (BLM) for modeling bioavailability and chronic toxicity of copper (Cu). The gBAM combines a log‐linear effect of pH on free Cu2+ ion toxicity with BLM‐type parameters for describing the protective effects of major cations (calcium [Ca]2+, magnesium [Mg]2+, and sodium [Na]+). In the present study, a Windermere Humic Aqueous Model (WHAM) VII‐based gBAM for fish was parametrized based on an existing chronic (30‐d) dataset of juvenile rainbow trout (Oncorhynchus mykiss). The model, with defined parameters (pH slope parameter [SpH] = 0.4449 and biotic ligand competition constants [log KCaBL = 4.0, log KMgBL = 3.4, and log KNaBL = 3.0]), was shown to accurately predict the effects of pH, dissolved organic carbon, Ca, and Mg on chronic Cu toxicity to juvenile rainbow trout at the effect levels relevant for environmental risk assessment (i.e., median prediction error of 1.3‐fold for 10 and 20% lethal concentrations). The gBAM predicted the effect of pH more accurately than a previously published Cu BLM for juvenile rainbow trout, especially at pH > 8. We also evaluated the cross‐species and cross‐life stage applicability of the newly developed juvenile rainbow trout gBAM using existing chronic Cu toxicity data with early life stages of fathead minnow (Pimephales promelas) and rainbow trout. We did this because using a single bioavailability model for all fish species and life stages is practical from a regulatory point of view. Although the early life stage datasets exhibit considerable uncertainties, 91% of the considered toxicity values at the effect levels most relevant in European environmental regulations (10% effect on survival or growth) were predicted within a 2‐fold error. Overall, the chronic Cu gBAM we developed is a valuable alternative for the existing chronic Cu BLM for rainbow trout and performs sufficiently well to be used in risk assessment according to currently accepted standards of bioavailability model performance (from the current European regulatory point of view). However, our analysis also suggests that bioavailability relations differ between different fish life stages and between endpoints (e.g., mortality vs growth), which is currently not accounted for in environmental risk assessments. Environ Toxicol Chem 2020;39:2424–2436. © 2020 SETAC [ABSTRACT FROM AUTHOR]

Regulatory jurisdictions worldwide are increasingly incorporating bioavailability‐based toxicity models into development of protective values (PVALs) for freshwater and saltwater aquatic life (e.g., water quality criteria, standards, and/or guidelines) for metals. Use of such models for regulatory purposes should be contingent on their ability to meet performance criteria as specified through a model‐validation process. Model validation generally involves an assessment of a model's appropriateness, relevance, and accuracy. We review existing guidance for validation of bioavailability‐based toxicity models, recommend questions that should be addressed in model‐validation studies, discuss model study type and design considerations, present several new ways to evaluate model performance in validation studies, and suggest a framework for use of model validation in PVAL development. We conclude that model validation should be rigorous but flexible enough to fit the user's purpose. Although a model can never be fully validated to a level of zero uncertainty, it can be sufficiently validated to fit a specific purpose. Therefore, support (or lack of support) for a model should be presented in such a way that users can choose their own level of acceptability. We recommend that models be validated using experimental designs and endpoints consistent with the data sets that were used to parameterize and calibrate the model and validated across a broad range of geographically and ecologically relevant water types. Environ Toxicol Chem 2019;39:101–117. © 2019 SETAC [ABSTRACT FROM AUTHOR]

We conducted acute lethality tests with white sturgeon (Acipenser transmontanus) and Ceriodaphnia dubia exposed to copper and zinc at dissolved organic carbon concentrations ranging from 0.5 to 5.5 mg/L. Dissolved organic carbon had minimal effects on zinc toxicity but did have a protective effect on acute copper toxicity, which was equal to that predicted by the copper biotic ligand model (BLM). The BLM‐adjusted copper median effect concentrations for A. transmontanus ranged from 2.4 to 8.2 mg/L. Environ Toxicol Chem 2019;38:2682–2687. Published 2019 Wiley Periodicals, Inc. on behalf of SETAC. This article is a US government work, and as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]

In the present study, we aimed to test the protectiveness of the bioavailability‐normalization procedure, with its associated hazardous concentrations for x% of the species (HCx), that is currently implemented to derive environmental threshold concentrations for nickel (Ni) in European environmental legislative frameworks. We exposed a natural plankton‐dominated community to 3 constant Ni concentrations, that is, a control with no Ni added (background Ni of 1.2–4 µg/L) and the bioavailability‐normalized HC5 and HC50 of 24 and 97 µg dissolved Ni/L, respectively, during a 56‐d microcosm experiment under high dissolved organic carbon (DOC) conditions (DOC of 14 mg/L at test initiation). The effects of the bioavailability‐normalized HC5 and HC50 values were evaluated at the levels of community structure (community composition and plankton group abundances), community functioning (measured as indirect physicochemical proxies for overnight respiration and carbon fluxes), and individual species abundances. The bioavailability‐normalized HC50 treatment had clear effects (defined as effects occurring on at least 2 consecutive sampling days) on both the structure and functioning of the investigated aquatic community. Through its effect on community functioning (i.e., reduced pH and DOC), Ni also influenced its own bioavailability. Clear direct effects of Ni were observed for only 3 species (the Cyanobacteria Oscillatoria sp. 1 and the rotifers Asplanchna/Testidunela sp. and Trichocerca group similis). Most other effects occurring in the plankton community in the HC50 treatment were indirect and likely driven by the direct effect of Ni on the Cyanobacteria Oscillatoria sp. 1, which was the dominant phytoplankton species in the control microcosms. In contrast, the bioavailability‐normalized HC5 did not induce clear effects on community structure and functioning endpoints: these were only affected on individual sampling days. Clear (direct) effects were observed for only 2 plankton species (the rotifer Trichocerca group similis and the Cyanobacteria Oscillatoria sp. 1), but their abundances recovered to control levels at the end of the study. In addition, a few species (1 phytoplankton and 3 zooplankton species) were affected in the HC5 treatment only on the last sampling day. It is uncertain whether these species would have shown clear effects over a longer exposure duration. Thus, our study shows that the bioavailability‐normalized HC5 of Ni at high DOC induced clear effects on a few individual species. However, the overall conclusion is that the bioavailability‐normalized HC5 of Ni as derived through the procedure that is currently implemented in European legislative frameworks protects against clear effects on community structure and function. Environ Toxicol Chem 2019;38:1923–1939. © 2019 SETAC. [ABSTRACT FROM AUTHOR]

Copper is essential, but can be toxic to aquatic organisms when present in high concentrations. In freshwater crustaceans, copper inhibits enzymes related to ionic and osmoregulation and to the ammonia efflux, that leads to Na+ imbalance and inhibition of ammonia excretion. In the animals inhabiting estuarine or seawater, mechanisms of copper toxicity is not clear, but had been described as disruption of ionregulation and metabolism. To clarify the mechanism of copper toxicity in crustaceans inhabiting variable salinity, this work investigated whether copper affects ammonia excretion and enzymes used for ammonia balance and osmoregulation in the blue crab Callintectes sapidus acclimated to salinity 2 and 30 ppt. To achieve this, juveniles of the blue crab were exposed to 63.5 µg/L of copper at both salinities for 96 h. This is an environmentally realistic copper concentration. Results of ammonia efflux, free amino acids and Na+ concentrations in hemolymph, Na+/K+-ATPase, H+-ATPase and, carbonic anhydrase (CA) activities in gills were consistent with the osmoregulatory pattern adopted by the blue crab, which hyperosmoregulates at salinity 2 ppt and osmoconforms at 30 ppt. At 30 ppt copper reduced free amino acid in hemolymph of crabs, suggesting an effect of the metal on osmotic performance. At 2 ppt, copper significantly increased the H+-ATPase activity involved in ammonia excretion. This may be a compensatory response of crabs to maintain low levels of ammonia in their hemolymph; which can be increased by copper exposure. Results presented here are useful for the improvement of the Biotic Ligand Model (BLM) to predict copper toxicity for saltwater environments. [ABSTRACT FROM AUTHOR]

There is a lack of appropriate models to delineate the toxicity of rare earth elements (REEs) while taking into account the factors that affect bioavailability. Here, standardized wheat (Triticum aestivum L.) root elongation tests were conducted to examine the impact of exposure conditions (i.e., varying Ca, Mg, Na, K and pH levels) on Y and Ce toxicity. Cation competition and electrostatic theory were examined for their applicability in explaining the observed variations in toxicity. Only Ca2+ and Mg2+ significantly alleviated the toxicity of Y3+ and Ce3+, while Na+, K+ and H+ showed no significant effects. Based on the cation competition, the derived binding constants for the hypothetical biotic ligands of wheat log K CaBL , log K MgBL , log K YBL , and log K CeBL were 3.87, 3.59, 6.70, and 6.48, respectively. The biotic ligand model (BLM) succeeded in predicting toxicities of Y and Ce, with more than 93% of the variance in toxicity explained. Given the BLM requires large data sets for deriving model parameters, attempts were further made to explore a simpler electrostatic based model to quantify REEs toxicity. The results demonstrated that the predictive capacity of the electrostatic approach, which considers ion activities at the plasma membrane surface, was comparable to that of BLM with at least 87% of the variations in toxicity explained. This suggested that the electrostatic theory can serve as a surrogate to BLM in modeling Y and Ce toxicities. Therefore, we recommend the BLM and electrostatic-based model as effective approaches to incorporate bioavailability in quantifying REEs toxicity in the presence of various levels of other major cations. Image 1 • Toxicity of Y/Ce to wheat was examined under various levels of coexisting cations. • The same toxicity-modifying factors (i.e., Ca2+ and Mg2+) held for different REEs. • The biotic ligand model theory was applicable for trivalent Y3+ and Ce3+ ions. • ETM required fewer parameters than BLM in predicting the toxicity of REEs. Ca and Mg induced toxicity variations of REEs can be interpreted and reconciled with either cation competition or electrostatic theory. [ABSTRACT FROM AUTHOR]

Few studies have been conducted so far into the effects of humic substances (HS) on aquatic organisms and their influence on the toxicity of chemical pollutants in the tropics. The aim of the present study was therefore to evaluate the direct effects of locally-derived tropical natural HS on the cladoceran Daphnia similis, the midge Chironomus xanthus and the fish Danio rerio. The influence of a HS concentration series on the acute toxicity of copper to these organisms was also assessed through laboratory toxicity testing. The HS did not exert direct acute effects on the test organisms, but long-term exposure to higher HS concentrations provoked a stress response (increase in feces production) to D. rerio and exerted effects on chironomid adult emergence and sex ratio. The biotic ligand model proved to be a useful tool in converting total copper concentrations to the appropriate bio-available fraction to which tropical aquatic organisms are exposed. [ABSTRACT FROM AUTHOR]

Since the mid‐1970s, thousands of studies have evaluated the toxicity of various chemicals to aquatic organisms. Results from many of these studies have been used to develop species sensitivity distributions (SSDs) or genus sensitivity distributions (GSDs) for deriving water quality guidelines. Recently, there has been more emphasis on evaluating the toxicity of chemicals to sensitive organisms rather than the entire range of sensitivities. The SSD approach is intended to inform the derivation of guidelines for the protection of all species, not just those that were included in the SSD. The overemphasis of the more sensitive end of the SSD can contribute to a skew in the observed distribution such that the shape of the distribution is distorted from what it would be if all species could be tested, which ultimately affects the derived guideline value. The freshwater acute Cu GSD derived by the US Environmental Protection Agency (USEPA) is one that exemplifies this trend, with one‐third of the genera in the GSD belonging to only 3 taxonomic families, all of which are nearer to the sensitive end of the distribution. The stronger representation of the more sensitive families does not seem to mirror the overall abundance of species within those families in nature. This tendency toward testing sensitive organisms is not seen in the chronic Cu SSD. In the present study, Cu toxicity literature is reviewed and long‐term trends in the availability of toxicity information for species of varying sensitivity are examined. As part of the present review, the apparent bias that favors the publication of toxicity data for sensitive taxa is demonstrated, and implications for the representativeness of SSDs and their use in developing water quality guidelines are discussed. Integr Environ Assess Manag 2019;00:000–000. © 2019 SETAC Key Points: Copper toxicity data have been trending toward increasingly sensitive organisms over the last couple of decades.Daphnids, unionid mussels, and salmonids are among the families most represented in the acute species sensitivity distribution (SSD).Fitting a statistical distribution to an SSD with an overabundance of sensitive organisms can result in an effect on the water quality standard, most likely making it unnecessarily low. [ABSTRACT FROM AUTHOR]