One of the most visible tragedies by industrial water pollution is Minamata disease, methylmercury poisoning caused by eating contaminated fish, which has killed more than 100 people and paralyzed several thousand people around Minamata Bay, Japan and the adjacent Yatsushiro Sea since 1956. The cause of Minamata disease was confirmed, not by analyzing environmental samples such as sediments (containing more than 600 ppm of Hg) or fish (at least 20 ppm) at the bay, but by symptoms of Minamata disease patients that resembled previous mercury poisoning reported in a European medical journal. Mercury dispersion was traced for 22 years to collect mercury concentration measurements in Yatsushiro Sea surface sediments at 24 fixed stations. The analytical results of mercury revealed four trends of mercury movement from the bay: 1) a rapid increase in Hg concentrations up to 1984; 2) a dramatic decrease in mercury concentrations after an artificial mercury decontamination project began in 1984; 3) a strange drop in mercury contents due to an historical rainfall in the region in 1982 and; 4) natural decontamination, which has been underway since 1985. The tragedy at Minamata has provided many lessons which have shaped the scientific field in environmental research, especially in the area of water quality.

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