John Wiley & Sons, Ltd.

Applying biotic ligand models and Bayesian techniques: Ecological risk assessment of copper and nickel in Tokyo rivers

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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 six rivers in Tokyo in order 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 copper 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 nickel was a concern at only one of the six sites. BLM corrections affected these conclusions in the case of copper but were moot in the case of nickel. 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 © 2012 SETAC

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