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Biotic ligand models (BLMs) have been broadly accepted and used in ecological risk assessment of heavy metals for toxicity normalization with respect to water chemistry. However, the importance of assessing bioavailability by using BLMs has not been widely recognized among Japanese stakeholders. Failing to consider bioavailability may result in less effective risk management than would be possible if currently available state-of-the-art methods were used to relate bioavailable concentrations to toxic effects. In this study, an ecological risk assessment was conducted using BLMs for 6 rivers in Tokyo to stimulate discussion about bioavailability of heavy metals and the use of BLMs in ecological risk management in Japan. In the risk analysis, a Bayesian approach was used to take advantage of information from previous analyses and to calculate uncertainties in the estimation of risk. Risks were judged to be a concern if the predicted environmental concentration exceeded the 5th percentile concentration (HC5) of the species sensitivity distribution. Based on this criterion, risks to stream biota from exposure to Cu were judged not to be very severe, but it would be desirable to conduct further monitoring and field surveys to determine whether temporary exposure to concentrations exceeding the HC5 causes any irreversible effects on the river ecosystem. The risk of exposure to Ni was a concern at only 1 of the 6 sites. BLM corrections affected these conclusions in the case of Cu but were moot in the case of Ni. The use of BLMs in risk assessment calculations for Japanese rivers requires water quality information that is, unfortunately, not always available. Integr Environ Assess Manag 2013; 9: 63-69. © 2012 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 (EC 10 , EC 20 , and EC 50 ) 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 EC 10 , EC 20 , and EC 50 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 EC 10 , EC 20 , and EC 50 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 EC 10 , EC 20 and EC 50 values predicted by each of the two models and observed EC 10 , EC 20 , and EC 50 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 EC 10 , EC 20 , and EC 50 values within a factor of 2 and 100%, 86%, and 100% within a factor of 3; refined Model 2 predicted 71% of observed EC 10 , EC 20 , and EC 50 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., (© 2022. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The ecotoxicity of nickel depends on water quality characteristics such as pH and dissolved organic carbon. Bioavailability models to predict nickel toxicity have been developed for and validated in European natural waters. In this study, we examined the acute toxicity of nickel to the strain of Daphnia magna that is used for toxicity tests in Japan, using water samples from five Japanese rivers. Based on the results of these toxicity tests, we examined the predictive capacity of the bioavailability model for acute nickel toxicity to D. magna and validated the model. The 50% effect and lethal concentrations (EC50 and LC50) of dissolved nickel for D. magna ranged from 0.52 to 4.0 mg/L and from 0.62 to 5.3 mg/L, respectively. Our results indicate that acute nickel toxicity varied as a result of the different water quality conditions in Japanese rivers. The bioavailability model predicted EC50 and LC50 values in water samples from Japanese rivers by errors more than a factor of 2, while the bioavailability models validated with the results of our toxicity tests were able to accurately predict these values with errors less than a factor of 2. Therefore, our results indicate that the bioavailability model validated using the results of the toxicity tests conducted using Japanese water samples could accurately predict acute nickel toxicity to the strain of D. magna. [ABSTRACT FROM AUTHOR]