Abstract
It is generally accepted that the bioavailability and toxicity of trace metals in surface water to aquatic life depend on the speciation of metal, not on total or dissolved metal concentration. Metal speciation is a function of water chemistry including temperature, pH, organic content, and the compositions and concentrations of ions and solid phases in solution. To develop efficient and effective methods of assessing and managing the risk posed by metals to aquatic life, it is important to determine the effects of water chemistry on the bioavailability of metals in surface water . For this reason, we have employed the technique called diffusive gradients in thin-films (DGT) in the study of several Japanese rivers, including meta-contaminated rivers adjacent to abandoned mines, to gain information on the bioavailability of metals in Japanese water systems. The measurements of labile metals as determined by the DGT technique suggest that the biologically available fractions of metals in urban rivers are relatively low compared with those in rivers adjacent to abandoned mines. The fractions of Zn and Cd appear to be higher than that of Cu. An inverse relationship was found between labile- Cu fraction and dissolved organic carbon (DOC). Our result suggested that large amount of Zn and Cd occurred as hydrated ions or small inorganic complexes in water of the rivers studied, whereas most of the Cu occurred as Cu-organic complexes. This study demonstrates the importance of obtaining metal speciation data in the pragmatic risk assessment and management of metals in water environments, especially in urban rivers with high natural and anthropogenic organic contents.
