Bioavailability levels of trace metals and its potential risk to aquatic species in urban river

Urban rivers are complex due to the drainage from municipal waste treatment plants (MWTPs), emissions from traffic sources including wearing of tires and brakes, atmospheric corrosion (galvanized materials) from houses, and human wastes. In Japan, MWTPs contribute a relatively large amount of the emissions of dissolved metals to urban rivers, and these dissolved metals are accumulated in the rivers and pose adverse effect to aquatic organisms. It is known that bioavailability and toxicity of dissolved metals to aquatic organisms depend on their chemical speciation; free ions, inorganic complexes and easily dissociable complexes likely represent as a bioavailable fraction. In this study, to estimate bioavailability and its biological effect to aquatic species of trace metals in urban river, Neya River (affected by some municipal waste treatment plants) in Osaka, Japan was selected as sampling area, and diffusive gradients in thin fi lms (DGT) method combined with model prediction using WHAM 7.0 were deployed to assess bioavailable levels of some metals (Ni, Cu, Zn, and Pb). To assess the potential risks associated with metal bioavailability, site-specific 95% protection levels (HC5) and risk characterizations ratios (RCR) were derived, using species sensitivity distribution (SSD). High levels of bioavailability values for metals were recorded at sites adjacent to MWTPs. Model calculation results for bioavailuable Zn was consistent with measured result by DGT. Model calculation results for Cu and Ni were higher than the measured results by DGT. The possible reason was that there were likely high levels of organic chelators (humic substances and anthropogenic ligands) in the Neya River. Risk assessment (RCR values) results suggested that there was high risk to aquatic organisms in our sampling river