Validation of Nickel Bioavailability Models for Algae, Invertebrates, and Fish in Chinese Surface Waters.

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.

Updating the Chronic Freshwater Ecotoxicity Database and Biotic Ligand Model for Nickel for Regulatory Applications in Europe.

Bioavailability has been taken into account in the regulation of nickel in freshwater ecosystems in Europe for over a decade; during that time a significant amount of new information has become available covering both the sensitivity of aquatic organisms to nickel toxicity and bioavailability normalization. The ecotoxicity database for chronic nickel toxicity to freshwater organisms has been updated and now includes 358 individual data points covering a total of 53 different species, all of which are suitable for bioavailability normalization to different water chemistry conditions. The bioavailability normalization procedure has also been updated to include updates to the bioavailability models that enable more sensitive water chemistry conditions to be covered by the model predictions. The updated database and bioavailability normalization procedure are applicable to more than 95% of regulated European surface water conditions and have been used to calculate site-specific criteria for a variety of different water chemistry scenarios, to provide an indication of how the sensitivity to nickel varies between different water types. The hazardous concentration for 5% of a species (HC5) values for this diverse selection of water types range from 1.6 to 36 µg L-1 , clearly demonstrating the importance of accounting for nickel bioavailability in freshwaters. This updated database and bioavailability normalization procedure provide a robust basis for the derivation of regulatory thresholds for chronic nickel toxicity in freshwaters such as predicted no-effect concentrations and Environmental Quality Standards and are protective of the results of several mesocosm studies. Environ Toxicol Chem 2023;42:566-580. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Assessing the Extent of Environmental Risks From Nickel in European Freshwaters: A Critical Reflection of the European Commission's Current Approach.

Nickel (Ni) has a been a Priority Substance under the European Water Framework Directive since 2008. As such it is deemed to present an European Union-wide risk to surface waters. Since 2013, the Ni Environmental Quality Standard (EQS) has been bioavailability-based, and new European Guidance supports accounting for bioavailability in assessing Ni compliance with the EQS. The European Commission has developed an approach to determine whether Priority Substances present a sufficient European Union-wide risk to justify an ongoing statutory monitoring programme, effectively to deselect a substance. This is a key step to ensure that finite monitoring resources are targeted at delivering environmental benefit, when there is an ever-growing burden of determinands to measure for all regulators. When the European Commission performed this exercise for Ni without accounting for bioavailability, they concluded that Ni should not be deselected, and Ni is an European Union-wide risk. Performing this same exercise with the same methodology, using regulatory monitoring data for over 300 000 samples, from more than 19 000 sites across Europe, and accounting for bioavailability, as detailed in the Directive, >99% of sites comply with the Ni EQS. Nickel shows very low risks for all of the criteria identified by the European Commission that need to be met for deselection. Accounting for bioavailability is key in the assessment of Ni risks in surface waters to deliver ecologically relevant outcomes. Environ Toxicol Chem 2022;41:1604-1612. © 2022 NiPERA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Environmental risk of nickel in aquatic Arctic ecosystems.

The Arctic faces many environmental challenges, including the continued exploitation of its mineral resources such as nickel (Ni). The responsible development of Ni mining in the Arctic requires establishing a risk assessment framework that accounts for the specificities of this unique region. We set out to conduct preliminary assessments of Ni exposure and effects in aquatic Arctic ecosystems. Our analysis of Ni source and transport processes in the Arctic suggests that fresh, estuarine, coastal, and marine waters are potential Ni-receiving environments, with both pelagic and benthic communities being at risk of exposure. Environmental concentrations of Ni show that sites with elevated Ni concentrations are located near Ni mining operations in freshwater environments, but there is a lack of data for coastal and estuarine environments near such operations. Nickel bioavailability in Arctic freshwaters seems to be mainly driven by dissolved organic carbon (DOC) concentrations with bioavailability being the highest in the High Arctic, where DOC levels are the lowest. However, this assessment is based on bioavailability models developed from non-Arctic species. At present, the lack of chronic Ni toxicity data on Arctic species constitutes the greatest hurdle toward the development of Ni quality standards in this region. Although there are some indications that polar organisms may not be more sensitive to contaminants than non-Arctic species, biological adaptations necessary for life in polar environments may have led to differences in species sensitivities, and this must be addressed in risk assessment frameworks. Finally, Ni polar risk assessment is further complicated by climate change, which affects the Arctic at a faster rate than the rest of the world. Herein we discuss the source, fate, and toxicity of Ni in Arctic aquatic environments, and discuss how climate change effects (e.g., permafrost thawing, increased precipitation, and warming) will influence risk assessments of Ni in the Arctic.

A Review of Water Quality Factors that Affect Nickel Bioavailability to Aquatic Organisms: Refinement of the Biotic Ligand Model for Nickel in Acute and Chronic Exposures.

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.

Comparison of Multiple Linear Regression and Biotic Ligand Models to Predict the Toxicity of Nickel to Aquatic Freshwater Organisms.

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.

Development of a bioavailability-based risk assessment framework for nickel in Southeast Asia and Melanesia.

Nickel laterite ore deposits are becoming increasingly important sources of Ni for the global marketplace and are found mainly in tropical and subtropical regions, including Indonesia, the Philippines, Papua New Guinea, Cuba, and New Caledonia. There are few legislatively derived standards or guidelines for the protection of aquatic life for Ni in many of these tropical regions, and bioavailability-based environmental risk assessment (ERA) approaches for metals have mainly been developed and tested in temperate regions, such as the United States and Europe. This paper reports on a multi-institutional, 5-y testing program to evaluate Ni exposure, effects, and risk characterization in the Southeast Asia and Melanesia (SEAM) region, which includes New Caledonia, Papua New Guinea, the Philippines, and Indonesia. Further, we have developed an approach to determine if the individual components of classical ERA, including effects assessments, exposure assessments, and risk characterization methodologies (which include bioavailability normalization), are applicable in this region. A main conclusion of this research program is that although ecosystems and exposures may be different in tropical systems, ERA paradigms are constant. A large chronic ecotoxicity data set for Ni is now available for tropical species, and the data developed suggest that tropical ecosystems are not uniquely sensitive to Ni exposure; hence, scientific support exists for combining tropical and temperate data sets to develop tropical environmental quality standards (EQSs). The generic tropical database and tropical exposure scenarios generated can be used as a starting point to examine the unique biotic and abiotic characteristics of specific tropical ecosystems in the SEAM region. Integr Environ Assess Manag 2021;17:802-813. © 2021 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Empirical Bioavailability Corrections for Nickel in Freshwaters for Australia and New Zealand Water Quality Guideline Development.

Bioavailability-based approaches have been developed for the regulation of metals in freshwaters in several countries. Empirical multiple linear regression (MLR) models have been developed for nickel that can be applied to aquatic organisms. The MLR models have been compared against the use of previously developed biotic ligand models (BLMs) for the normalization of an ecotoxicity dataset compiled for the derivation of a water quality guideline value that could be applied in Australia and New Zealand. The MLR models were developed from data for a number of specific species and were validated independently to confirm their reliability. An MLR modeling approach using different models for algae, plants, invertebrates, and vertebrates performed better than either a pooled MLR model for all taxa or the BLMs, in terms of its ability to correctly predict the results of the tests in the ecotoxicity database based on their water chemistry and a fitted species-specific sensitivity parameter. The present study demonstrates that MLR approaches can be developed and validated to predict chronic nickel toxicity to freshwater ecosystems from existing datasets. The MLR approaches provide a viable alternative to the use of BLMs for taking account of nickel bioavailability in freshwaters for regulatory purposes. Environ Toxicol Chem 2021;40:113-126. © 2020 SETAC.

Acute and chronic toxicity of nickel on freshwater and marine tropical aquatic organisms.

Water quality guidelines and ecological risk assessment of chemical substances like nickel (Ni) in tropical regions such as South East Asia and Melanesia are often based on temperate information as a result of fewer Ni ecotoxicity data available for tropical species. This leaves an unknown margin of uncertainty in the risk assessment in the tropics. In order to fill this data gap, this study was designed to conduct standard toxicity tests on Ni with two freshwater species (acute tests) and three marine species (acute and chronic tests) originated from tropical Hong Kong. All tests were carried out using measured concentrations of Ni with control mortality below 15%. The median lethal concentrations (LC50s) were determined as 2520 (95% confidence interval: 2210, 2860) and 426 (351, 515) µg Ni L-1 for the freshwater gastropods Pomacea lineata (48 h) and Sulcospira hainanensis (96 h), respectively, while 96 h LC50s of 4300 (3610, 5090), 18,200 (6470, 51,200), 62,400 (56,800, 68,500), and 71,700 (68,200, 75,400) µg Ni L-1 were derived for the marine copepod Tigriopus japonicus, the gastropod Monodonta labio, juvenile and adult of the marine fish Oryzias melastigma, respectively. The chronic effect concentration of 10% (EC10) based on the intrinsic rate of increase of the population of T. japonicus was 29 (12, 69) µg Ni L-1. In terms of growth inhibition, the chronic EC10 for M. labio was 34 (17, 67) µg Ni L-1. The results also indicated that T. japonicus in maturation stage (LC10: 484 (349, 919) µg Ni L-1) was less sensitive than its nauplii stage (LC10: 44 (27, 72) µg Ni L-1). This study represents an important addition of high-quality toxicity data to the tropical Ni toxicity database which can be used for future ecological risk assessment of Ni and derivation of its water quality guidelines in tropical regions.

Demonstrating the Reliability of bio-met for Determining Compliance with Environmental Quality Standards for Metals in Europe.

The importance of considering the bioavailability of metals in understanding and assessing their toxicity in freshwaters has been recognized for many years. Currently, biotic ligand models (BLMs) are being applied for the derivation and implementation of environmental quality standards (EQS) for metals under the Water Framework Directive in Europe. bio-met is a simplified tool that was developed for implementing bioavailability-based EQS for metals in European freshwaters. We demonstrate the reliability of the relationship between the full BLM predictions and the thresholds (hazardous concentration affecting 5% of species [HC5] values) predicted by bio-met in 3 stages, for the metals copper, nickel, and zinc. First, ecotoxicity data for specific species from laboratory tests in natural waters are compared with predictions by the individual species BLMs included in the full BLMs. Second, the site-specific HC5 values predicted by bio-met for the natural waters used for ecotoxicity testing are compared with those provided by the full BLMs. The reliability of both relationships is demonstrated for all 3 metals, with more than 80% of individual species BLM predictions being within a factor of 3 of the experimental results, and 99% of bio-met local HC5 predictions being within a factor of 2 of the full BLM result. Third, using a larger set of European natural waters in addition demonstrates the reliability of bio-met over a broad range of water chemistry conditions. bio-met is therefore an appropriate tool for performing compliance assessments against EQS values in Europe, due to the demonstrated consistency with the toxicity test data. Environ Toxicol Chem 2020;39:2361-2377. © 2020 SETAC.

Deriving a Chronic Guideline Value for Nickel in Tropical and Temperate Marine Waters.

The absence of chronic toxicity data for tropical marine waters has limited our ability to derive appropriate water quality guideline values for metals in tropical regions. To aid environmental management, temperate data are usually extrapolated to other climatic (e.g., tropical) regions. However, differences in climate, water chemistry, and endemic biota between temperate and tropical systems make such extrapolations uncertain. Chronic nickel (Ni) toxicity data were compiled for temperate (24 species) and tropical (16 species) marine biota and their sensitivities to Ni compared. Concentrations to cause a 10% effect for temperate biota ranged from 2.9 to 20 300 µg Ni/L, with sea urchin larval development being the most sensitive endpoint. Values for tropical data ranged from 5.5 to 3700 µg Ni/L, with copepod early-life stage development being the most sensitive test. There was little difference in temperate and tropical marine sensitivities to Ni, with 5% hazardous concentrations (95% confidence interval) of 4.4 (1.8-17), 9.6 (1.7-26), and 5.8 (2.8-15) µg Ni/L for temperate, tropical, and combined temperate and tropical species, respectively. To ensure greater taxonomic coverage and based on guidance provided in Australia and New Zealand, it is recommended that the combined data set be used as the basis to generate a jurisdiction-specific water quality guideline of 6 µg Ni/L for 95% species protection applicable to both temperate and tropical marine environments. Environ Toxicol Chem 2020;39:2540-2551. © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Evaluation of Acute and Chronic Toxicity of Nickel and Zinc to 2 Sensitive Freshwater Benthic Invertebrates Using Refined Testing Methods.

The US Environmental Protection Agency (USEPA) is reviewing the protectiveness of the national ambient water quality criteria (WQC) for nickel (Ni) and zinc (Zn) and compiling toxicity databases to update the WQC. An amphipod (Hyalella azteca) and a unionid mussel (Lampsilis siliquoidea) have shown high sensitivity to Ni and Zn in previous studies. However, there remained uncertainties regarding the influence of test duration (48 vs 96 h) and the presence and absence of food in acute exposures with the amphipod, and there were also concerns about poor control of amphipod growth and reproduction and mussel growth in chronic exposures. We conducted acute 48- and 96-h water-only toxicity tests to evaluate the influence of feeding and test durations on the toxicity of dissolved Ni and Zn to the amphipod; we also used recently refined test methods to conduct chronic Ni and Zn toxicity tests to evaluate the sensitivity of the amphipod (6-wk exposure) and the mussel (4- and 12-wk exposures). The 96-h 50% effect concentrations (EC50s) of 916 µg Ni/L and 99 µg Zn/L from acute amphipod tests without feeding decreased from the 48-h EC50s by 62 and 33%, respectively, whereas the 96-h EC50s of 2732 µg Ni/L and 194 µg Zn/L from the tests with feeding decreased from the 48-h EC50s by 10 and 26%, indicating that the presence or absence of food had apparent implications for the 96-h EC50. Our chronic 6-wk EC20s for the amphipod (4.5 µg Ni/L and 35 µg Zn/L) were 50 to 67% lower than the 6-wk EC20s from previous amphipod tests, and our chronic 4-wk EC20s for the mussel (41 µg Ni/L and 66 µg Zn/L) were similar to or up to 42% lower than the 4-wk EC20s from previous mussel tests. The lower EC20s from the present study likely reflect more accurate estimates of inherent sensitivity to Ni and Zn due to the refined test conditions. Finally, increasing the chronic test duration from 4 to 12 wk substantially increased the toxicity of Zn to the mussel, whereas the 4- and 12-wk Ni effect needs to be re-evaluated to understand the large degree of variation in organism responses observed in the present study. Environ Toxicol Chem 2020;39:2256-2268. © 2020 SETAC.

Toxicity of Nanoparticulate Nickel to Aquatic Organisms: Review and Recommendations for Improvement of Toxicity Tests.

We reviewed the literature on toxicity of nanoparticulate nickel (nano-Ni) to aquatic organisms, from the perspective of relevance and reliability in a regulatory framework. Our main findings were 1) much of the published nano-Ni toxicity data is of low or medium quality in terms of reporting key physical-chemical properties, methodologies, and results, compared with published dissolved nickel studies; and 2) based on the available information, some common findings about nanoparticle (NP) toxicity are not supported for nano-Ni. First, we concluded that nanoparticulate elemental nickel and nickel oxide, which differ in chemical composition, generally did not differ in their toxicity. Second, there is no evidence that the toxicity of nano-Ni increases as the size of the NPs decreases. Third, for most organisms tested, nano-Ni was not more toxic on a mass-concentration basis than dissolved Ni. Fourth, there is conflicting evidence about whether the toxicity is directly caused by the NPs or by the dissolved fraction released from the NPs. However, no evidence suggests that any of the molecular, physiological, and structural mechanisms of nano-Ni toxicity differ from the general pattern for many metal-based nanomaterials, wherein oxidative stress underlies the observed effects. Physical-chemical factors in the design and conduct of nano-Ni toxicity tests are important, but often they are not adequately reported (e.g., characteristics of dry nano-Ni particles and of wetted particles in exposure waters; exposure-water chemistry). Environ Toxicol Chem 2020;39:1861-1883 © 2020 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

A Mystery Tale: Nickel Is Fickle When Snails Fail-Investigating the Variability in Ni Toxicity to the Great Pond Snail.

Dissolved Ni concentrations inhibiting the growth of juvenile great pond snails (Lymnaea stagnalis) have been documented to vary from about 1 to 200 µg L-1 Ni. This variability makes L. stagnalis either a moderately sensitive or the most sensitive freshwater species to chronic Ni exposure tested to date. Given the role of sensitive species in environmental risk assessment frameworks, it is particularly important to understand this variability, i.e., to characterize the factors that modulate Ni toxicity and that may confound toxicity test outcomes when uncontrolled. In the present study, we tested if this variability was due to analytical (growth calculation: biomass versus growth rate), environmental (water quality), lab-specific practices, and/or snail population differences among earlier studies. Specifically, we reanalyzed previously published Ni toxicity data and conducted additional measurements of Ni aqueous speciation, short-term Ni uptake, and chronic Ni toxicity with test waters and snail cultures used in previous studies. Corrections for Ni bioavailability and growth calculations explained a large degree of variability in the published literature. However, a residual 16-fold difference remained puzzling between 2 studies: Niyogi et al. (2014) (low ECxs) and Crémazy et al. (2018) (high ECxs). Indeed, differences in metal bioavailability due to water chemistry, lab-specific practices, and snail population sensitivity could not explain the large variation in Ni toxicity in these 2 very similar studies. Other potentially important toxicity-modifying factors were not directly evaluated in the present work: test duration, diet, snail holding conditions, and snail age at onset of testing. The present analysis highlights the need for further studies to elucidate 1) the mechanisms of growth inhibition in Ni-exposed L. stagnalis and 2) the important abiotic and biotic factors affecting this biological response. Until these processes are understood, substantial uncertainties will remain about inclusion of this species in Ni environmental risk assessment. Integr Environ Assess Manag 2020;16:983-997. © 2020 SETAC.

State of the Science on Metal Bioavailability Modeling: Introduction to the Outcome of a Society of Environmental Toxicology and Chemistry Technical Workshop.

A Society of Environmental Toxicology and Chemistry technical workshop was held in December 2017 to critically evaluate the current state of the science of metal bioavailability modeling. The availability of mechanistic models such as the biotic ligand model and the rapid development of empirical models such as multiple linear regressions means that choices are available in terms of bioavailability normalization approaches that can be used in metal risk assessments and the development of risk-based protective values for aquatic life. A key goal of the workshop was to provide potential users of metal bioavailability models with the information required to make appropriate decisions when choosing among mechanistic and empirical models. Workshop participants focused on the state of the science of metal bioavailability modeling, mechanistic and empirical model frameworks, validation of bioavailability models, and application of bioavailability models in risk-based decision-making approaches. The output of this workshop provides the necessary scientific information to incorporate bioavailability normalization in regulations pertaining to metals in freshwater systems. Environ Toxicol Chem 2019;39:42-47. © 2019 SETAC.

Comparison of the Chronic Toxicity of Nickel to Temperate and Tropical Freshwater Species.

Reliable ecotoxicity data are required to derive thresholds protective for aquatic life that are scientifically defensible and practically implementable as environmental risk assessment and management tools. Much of the data that have been used to derive thresholds for environmental quality have been collected for temperate species. There are concerns that due to a lack of data for the different species present in tropical ecosystems, they may not be adequately protected by thresholds derived from temperate species. In the present study, chronic ecotoxicity data for nickel and freshwater species from different climatic regions have been collated. Comparisons were performed between tropical and temperate datasets on the basis of the threshold values and overall distributions of the ecotoxicity data, as well as between groups of species and closely related species from different climatic regions. The analysis indicated that the sensitivities of tropical and temperate species cover similar ranges. An approach based on the inclusion of as diverse a range of taxa as possible is recommended to ensure the protection of sensitive species in both temperate and tropical ecosystems. Environ Toxicol Chem 2019;38:1211-1220. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Validation of the nickel biotic ligand model for locally relevant species in Australian freshwaters.

Australian freshwaters have relatively low water hardness and different calcium (Ca) to magnesium (Mg) ratios compared with those in Europe. The hardness values of a substantial proportion of Australian freshwaters fall below the application boundary of the existing European nickel biotic ligand models (Ni BLMs) of 2 mg Ca/L. Toxicity testing was undertaken using Hydra viridissima to assess the predictive ability of the existing Ni BLM for this species in extremely soft waters. This testing revealed an increased competitive effect of Ca and Mg with Ni for binding to the biotic ligand in soft water (<10 mg CaCO3 /L) than at higher water hardness. Modifications were made to the Ni BLM by increasing the binding constants for Ca and Mg at the biotic ligand to account for softer waters encountered in Australia and the more important competitive effect of Ca and Mg on Ni toxicity. To validate the modified Ni BLM, ecotoxicity testing was performed on 5 Australian test species in 5 different natural Australian waters. Overall, no single water chemistry parameter was able to indicate the trends in toxicity to all of the test species. The modified Ni BLMs were able to predict the toxicity of Ni to the test species in the validation studies in natural waters better than the existing Ni BLMs. The present study suggests that the overarching mechanisms defining Ni bioavailability to freshwater species are globally similar and that Ni BLMs can be used in all freshwater systems with minor modifications. Environ Toxicol Chem 2018;37:2566-2574. © 2018 SETAC.