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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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To investigate the formation of mobile organic plutonium, we analyzed the plutonium contents of the fulvic (FA) and humic (HA) acids from the soil samples obtained at Nishiyama, Nagasaki, Japan. The percentages of the plutonium bound strongly to HA and to FA vs. the total plutonium in the soil were 5-10% and 1%, respectively, at the depth of 0-0.1 m, much higher values than those of 137Cs and uranium. After being weathered for 51 years under a temperate climate, the initial highfired oxides of fallout plutonium have become as chemically reactive plutonium from nuclear fuel reprocessing plants.

The direct analysis of mercury in sediment samples from Minamata Bay, Kumamoto, Japan was studied using laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). Two sediment and one soil certified reference material were analysed and used to construct the calibration curve. Direct analysis of sediment samples without internal standardization yielded satisfactory results. Elemental speciation and particle size within the studied range did not appear to significantly affect the measurements. With the LA-ICP-MS system, a sample throughput of 10 per h and a detection limit of 0.02 mg kg 21 was achieved. Analytical results of 14 sediment samples using the present system were in good agreement with those obtained by isotope dilution cold vapour generation ICP-MS.