Impact of Bioavailability Incorporation on Ecological Risk Assessment of Nickel, Copper, and Zinc in Surface Waters

In this study, biotic ligand models (BLMs) were used to conduct bioavailability-incorporated risk assessment of metals (Ni, Cu, and Zn) in Japanese rivers. Site-specific species sensitivity distributions were constructed and site-specific risk characterization ratios (RCRs: ratios of dissolved concentrations of metals to site-specific HC5 (dissolved metal concentrations that protect 95% of species in an ecosystem)) were derived. The obtained site-specific RCRs, which are bioavailability-incorporated risk levels, were compared with RCRs without bioavailability consideration (generic RCRs). Incorporating bioavailability lowered the site-specific RCRs of Ni compared to the corresponding generic RCRs, and the numbers of sites at risk (site-specific RCR > 1) decreased in most rivers, indicating that conventional risk assessment without the consideration of bioavailability overestimated the risk of Ni. Similarly, for Cu, site-specific RCRs and the percentage of sampling sites at risk were lower than those without bioavailability consideration at sampling sites where the dissolved organic carbon and hardness in river water were high. The site-specific RCRs of Zn were higher than the generic RCRs in most rivers with soft waters, and the percentage of sampling sites at risk was higher than that calculated without the consideration of bioavailability.