In this study, we investigated the formation condition of bromate ions following chlorination of purified water or of well water containing bromide ions. The formation of bromate ions occurred at room temperature but increased with temperature or pH. In the presence of ultraviolet rays, bromate ions formed rapidly and in high concentrations, but could be almost completely controlled by shading during chlorination. Light irradiation of chlorine-treated well water containing bromide ions also led to formation of bromate ions at concentrations ranging from ND to 60.8 μg·l^-1, but concentrations differed greatly between different well water samples. This difference was thought to be the result of differing concentrations of organic matter contained within the different well water samples. We suggest that bromate ion formation is suppressed by the high chlorine concentration used for trihalomethane formation when the organic matter concentration is high, and that these two formation reactions competed for chlorine. There is also a possibility that some organic matter, such as humic materials, directly controls the formation reaction of the bromate ion.

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Concentrations of Ag, Pb, and Hg in samples of aquatic insects and feeding sources such as algae and leaves were determined at four sites along the Ginzan River, Which receives drainage from a mined land. Nitrogen (δ¹⁵N) and carbon (δ¹³C) isotope analyses of the samples were carried out to assess whether feeding sources or the trophic level influenced metal accumulation in each faunal taxon. The individual dry mass was also measured to examine the effect of body size on metal accumulation. The relationship between metal concentrations and level of δ¹⁵N in fauna indicated biodilutions for Pb (3 sites) and Ag (1 site) through the food webs. This must be caused by high concentrations of metals in algae and fine particulate organic matter (FPOM) as the main feeding sources for harvivores and detorivores. The relative contribution of autochthonous and allochthonous energy sources to each taxon's biomass had no effect on the concentrations of Ag, Pb, and Hg in the fauna. The individual dry mass was negatively correlated with the concentrations of Ag (3 sites), Pb (1 site), and Hg (4 sites) in fauna.

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In this study, the authors propose simplified model experiments which show the phenomena of water pollution in rivers and closed bodies of water and of eutrophication in closed bodies of water, using a piece of tofu and two cups of clean water. Tofu is used to representative of organic matter. The water without organic matter (tofu) in the cup remains clear forever, but the water containing a piece of tofu in the cup gradually becomes polluted in a few days. The water containing a piece of tofu is polluted with phytoplankton, and becomes green in two to three weeks which shows the phenomenon of eutrophication. In this study, the authors explained the phenomena of water pollution and eutrophication which occur in the cup by analyzing water quality using transparency, pH, BOD, SS, T-N, T-P and chl-a. The simplified model experiments proposed in this study are very useful for the environmental education at primary and junior high schools.

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The water quality of Lake Hashie and the Kanzawa and Nishikatsura rivers, which flow into the lake, was measured to identify the main cause of eutrophication in the lake. A land use survey was also carried out of the watershed of Lake Hashie. The total nitrogen (TN) and total phosphorus (TP) concentrations in the lake and rivers were relatively high, in the ranges of 1-15 and 0.1-1.5mg·l^-1, respectively. The TN and TP concentrations of the lake were increased by the influx of water from the rivers. From the results of the land use survey, nitrogen and phosphorus loads from stockbreeding and farmland in the upper basins may have caused the pollution of the rivers. Therefore, to prevent the eutrophication of Lake Hashie, the proper disposal or recycling of livestock waste and the optimum use of chemical fertilizer in the farmland are recommended in the upper basins of the Kanzawa and Nishikatsura rivers.

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To supply safe and high-quality drinking water to the inhabitants of the volcanic Izu-Oshima island during periods of volcanic inactivity, quality analysis of groundwater from 17 sites and multivariate analysis were performed. The analytical indices were divided into four groups by cluster and correlation analyses : (a) 11 indices (Na, Ca, Cl^-, etc.) were that related to seawater intrusion, (b) 6 indices (HCO₃^-, B, As, Li, SiO₂ and water temperature) were that related to water-rock interaction in the volcanic area (WRI), (c) 2 indices (pH and NO₃^--N) were that inversely related to WRI and (d) the 4 other indices. Principal component analysis revealed that 68% of the original data set could be explained by only 2 principal components and that the water quality was influenced mainly by seawater intrusion and WRI. The first principal component corresponded to the overall influences of seawater intrusion as the major factor and WRI as the minor factor. The second principal component represented the influence of WRI. The samples of groundwater were grouped according to scores of each first and second principal component. Although the sites of water wells were contiguous, they showed different water quality owing to the influences of seawater intrusion and WRI. Concentrations of arsenic and boron in groundwater from some sites were strongly influenced by WRI and exceeded the Japanese criteria for drinking water. This indicates the importance of monitoring these elements in the groundwater of Izu-Oshima island.

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