Mercury contamination in the Yatsushiro Sea, south-western Japan: spatial variations of mercury in sediment

• Published in: The Science of the total environment Vol. 257; no. 2; pp. 121 - 132
• Main Authors: Tomiyasu, Takashi, Nagano, Ayako, Yonehara, Norinobu, Sakamoto, Hayao, Rifardi, Ōki, Kimihiko, Akagi, Hirokatsu
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier B.V 10.08.2000; Elsevier Science
• Subjects: Applied sciences; Chemical Industry; Dispersion of pollutant; Earth sciences; Earth, ocean, space; Engineering and environment geology. Geothermics; Environmental Monitoring; Exact sciences and technology; Geologic Sediments - chemistry; Japan; Japan, Minamata Bay; Japan, Yatsushiro Sea; Marine sediment; Mercury - analysis; Mercury pollution; Pollution; Pollution sources. Measurement results; Pollution, environment geology; Soil and sediments pollution; Soil Pollutants - analysis; Water Movements; Water Pollutants, Chemical - analysis; Water Pollutants, Chemical - pharmacokinetics; Yatsushiro Sea; Kyushu; Asia; East China Sea; Japan; INW, Japan, Kyushu, Kumamoto Prefect., Yatsushiro-kai Sea; INW, Japan, Kyushu, Kumamoto Prefect., Minamata Coast; Dispersion of pollutant; Mercury pollution; Marine sediment; Yatsushiro Sea; Background concentration; Pollution; Marine sediments; Chemical analysis; Content; Vertical profile; Mercury Organic compounds; Spatial variation; Mercury; Coastal zone; Heavy metal
• ISSN: 0048-9697; 1879-1026
• DOI: 10.1016/S0048-9697(00)00502-7

Mercury-contaminated effluent was discharged into Minamata Bay from a chemical plant over a 20-year period until 1965 (from 1958 to 1959, effluent was discharged into Minamata River), causing Minamata disease. In an effort to characterize the extent of the contamination in the Yatsushiro Sea, the vertical and horizontal distributions of mercury in sediment were investigated. Sediment was sampled at 62 locations in the southern part of the sea from 4 to 6 March 1996. In the lower layers of the long cores of sediment, the total amount of mercury was at a relatively uniform low concentration. We interpret these low values to represent the background concentration absent of anthropogenic influence. The background value thus estimated for the Yatsushiro Sea was 0.059±0.013 mg kg −1 (mean±S.D., n=51). The highest concentration in each sample ranged from 0.086 to 3.46 mg kg −1 (mean, 0.57 mg kg −1). The higher values were obtained at stations near Minamata Bay and the Minamata River (the sources of the pollution). Concentrations decreased with distance from the source. An inspection of the vertical profiles of mercury concentration in cores suggested that the deposited mercury had not been fixed in sediment but had been transported, despite 30 years having past since the last discharge of contaminated effluent. At nine stations, extractable inorganic and organic mercury concentrations were determined differentially. Inorganic mercury is the predominant species in sediment and organic mercury comprising approximately 1% of the total.