東京湾における水銀汚染の現状とその負荷源

抄録

The pollution and sources of mercury in Tokyo Bay were investigated on the basis of about one year of observations. The outputs (557 kg yr^-1) of mercury considerably exceeded the inputs (107kg yr^-1), and the imbalance between the inputs and outputs for mercury was much larger than that for Cd, Cr, Cu, Pb and Zn. These suggest that there are other major inputs of mercury to Tokyo Bay. In Japan, large amounts of organomercurous fungicides were extensively used in fields in the past, and most of the mercury from these was retained in soil. In this study, the mercury concentration in rivers was measured primarily in ordinary runoff. These lead to the hypothesis that field soil discharged into stormwater runoff is a major source of mercury in Tokyo Bay. As a preliminary approach to validating this hypothesis, we measured the concentrations of mercury and other trace metals (Cd, Cr, Cu, Pb and Zn) in river water during a typhoon. The increase in mercury concentration in stormwater runoff was much higher than the increases in other metal concentrations, which tends to support the hypothesis.