Abstract
The aquatic toxicity of heavy metals is affected by water chemistry such as hardness, pH, and dissolved organic carbon. Biotic ligand models（BLMs）for predicting heavy metal toxicity in consideration of water chemistry have been developed and used for risk assessment. Most of the currently used BLMs were developed in the United States and European Union countries, and thus the target biological species of the models tend to be the species living in those countries. In this study, we investigated the toxicity of copper on medaka（Oryzias latipes）in water having lower hardness and also investigated that how the toxicity varies as a function of Ca and Mg concentrations. By using the toxicity data, we developed a BLM for the fish. We conducted a series of tests of Cu toxicity to juvenile medaka in water with relatively low hardness, ranging from 18.1 to 22.4 mg/L CaCO3, which is typical of Japanese surface water, and Ca and Mg concentrations（and hence water hardness）are raised separately. We found that Cu toxicity decreased with increasing Ca concentration, whereas increasing the Mg concentration resulted in only a slight decrease in Cu toxicity. A BLM was then developed using these ecotoxicity data. The observed and BLM-predicted 10%, 50%, and 90% lethal concentrations were mostly within a factor of 2 of each other, and hence we concluded that predictability of our BLM is reasonably good.
