Journal of Oceanography, Vol. 62 (No. 6), pp. 767-775, 2006
Masahiro Sakata1*, Kohji Marumoto2, Masahiro Narukawa3 and Kazuo Asakura4
1Institute for Environmental Sciences, University of Shizuoka, Yada, Shizuoka 422-8526, Japan
2National Institute for Minamata Disease, Hama, Minamata, Kumamoto 867-0008, Japan
3Solar-Terrestrial Environment Laboratory, Nagoya University, Honohara, Toyokawa, Aichi 442-8507, Japan
4Environmental Science Research Laboratory, Central Research Institute of Electric Power Industry, Abiko, Abiko, Chiba 270-1194, Japan
(Received 23 February 2006; in revised form 15 May 2006; accepted 8 June 2006)
Abstract: The mass balance and sources of mercury in Tokyo Bay were investigated on the basis of observations from December 2003 to January 2005. Estimated input terms included river discharge (70 kg yr-1) and atmospheric deposition (37 kg yr-1), and output terms were evasion (49 kg yr-1), export (13 kg yr-1) and sedimentation (495 kg yr-1). Thus, the outputs (557 kg yr-1) considerably exceeded the inputs (107 kg yr-1). In addition, the imbalance between the inputs and outputs of mercury was much larger than that of other trace metals (Cd, Cr, Cu, Pb and Zn), which suggests that there are other major inputs of mercury to Tokyo Bay. The mercury concentrations in rivers correlated significantly with the concentrations of Al and Fe, major components of soil. In Japan, large amounts of organomercurous fungicides (about 2500 tons as Hg) were used extensively in fields in the past, and most of the mercury was retained in the soil. In this study, the mercury concentration in rivers was measured primarily in ordinary runoff. These observations 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 in river water during a typhoon. The mercury concentrations in stormwater runoff increased to 16-50 times the mean value in ordinary runoff, which is much higher than the increases for other metals. This tends to support the hypothesis.