In this study, we determined the concentrations of 29 polynuclear aromatic hydrocarbons (PAHs) and related oxidants (four kinds) in river, drinking and heated water samples. The composition of PAHs in drinking water differed from that of PAHs in river water, and the concentrations of dibenzofuran, fluorene, 9-fluorenone and antraquinone in drinking water were higher than those in river water. The total concentration of PAHs in drinking water in the neighborhood around a water purification plant was the same as that of PAHs in river water (the main stream). However, the total concentration of PAHs in drinking water supplied from water purification plants was higher in distant areas than in the neighborhood around the water plant. From to the concentrations and detection frequencies of PAHs in drinking water, those of dibenzofuran, fluorene, 9-fluorenone and antraquinone were the highest, whereas the PAHs showing the second highest concentrations and detection frequencies were naphthalene, biphenyl and phenanthrene. Furthermore, the total concentration of PAHs peaked during summer at 200-300 ng · l^-1 and showed a trough at 10-30 ng · l^-1. The total concentration of PAHs in drinking water collected from a specific district in the Tokyo metropolitan area was about 200 ng · l^-1 during summer. Compared with unheated drinking water, the concentrations of individual PAHs, total PAHs and PAH oxidation products are decreased in drinking water that has been heated using an electric pot or a kettle. The daily intakes of total PAHs are estimated to be 20-60 ng during winter and 200-600 ng during summer for people who drink only 2000 ml of tap water, and 15-45 ng during winter and 150-450 ng during summer for people who drink 1000 ml of tap water and 1000 ml of heated water.

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To evaluate the bottom sediment and water quality change of dam reservoirs, laboratory column experiments using dredged bottom sediment and water of the dam reservoir were conducted for 18 months. The environmental, microbiological and mineralogical changes of the sediment and water in the columns were investigated. Nitrate-reducing and iron-reducing reactions occurred in the 10-12cm depth of the column, and the environment became anaerobic. Denitrification and methane generation due to microorganisms similar to paddy field were observed in the layer, however, the activity of sulfate-reducing bacteria was low. It showed the absence of the sulfate and supply of energy sources in the sediments. No mineralogical change in the sediments was observed under the anaerobic condition.

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River water quality formation on Iriomote Island of the Ryukyus was studied to understand the environment of an isolated subtropical island. The concentrations of the major ions in the water of five rivers and pH of each precipitation were measured for one year in 2005. The water quality was mainly classified into the alkali noncarbonate-type by mixing solutes of two different origins, i.e., sea salt and salt resulting from chemical weathering. In the five rivers, HCO₃^- concentrations ranged from 8 to 34 mg/l, and the Urauchi River, whose catchment area was the widest of the rivers on the island and was covered with siliceous sandstone, was characterized by a very low HCO₃^- concentration as a result of the chemical weathering of noncarbonate minerals. The average pH of the precipitation on this island was 4.7 except for the time of typhoons, and the river water chemistry reflected acid deposition. The total concentration of dissolved cations due to the chemical weathering of rocks (nss-cations) was equivalent to the sum of HCO₃^- and nss-SO₄^2- concentrations, suggesting that acid deposition contributes to 10 - 20 % of the total chemical weathering. A further increase in the input level of acidic substances transported from long distances may negatively influence the quality of terrestrial water.

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