The contents and chemical forms of mercury in sediments from Kagoshima Bay, in comparison with Minamata Bay and Yatsushiro Sea, southwestern Japan

抄録

Sediments collected from Kagoshima Bay, Minamata Bay and Yatsushiro Sea were analyzed for organic mercury, mercury(II) oxide, mercury(II) sulfide and residual mercury through sequential extraction followed by cold vapor atomic absorption spectrometry. Results show that mercury(II) sulfide (38.4∼96.1%, geometric mean 71.4%) is the most prevalent mercury compound in the sediments followed by mercury(II) oxide (<0.9∼42.9%, geometric mean 5.65%). Organic mercury is present only in a very small quantity (0.21∼12.8%, geometric mean 2.55%). Residual mercury shows a wide range of content in the sediments (2.6∼44.3%, geometric mean 10.5%). The abnormally high mercury concentration observed in the sediment samples from Northern Kagoshima Bay is caused by the condensation of submarine fumarolic gases including elemental mercury and hydrogen sulfide, which are depositing in the surface sediments. This is in accord with the fact that mercury(II) sulfide is the most prevalent mercury compound there. Organic mercury content is high in the vicinity of the submarine fumarole, where mercury(II) sulfide content is very high.