Polychlorinated ethanes and methanes were reductively dechlorinated using iron powder E-200 (supplied by Dowa Iron Powder Co., Ltd.) in the aqueous layer. Time courses of their concentrations were observed and the intermediates and final degradation products were determined quantitatively. The degradation reaction of these compounds showed a pseudo-first-order rate process and the rate constants were calculated. Tetrachloroethanes and tetrachloromethane were easily degraded in the aqueous layer, but dichloroethanes, chloroethane, dichloromethane and chloromethane were only slightly degraded. The rate constants and the reaction products of polychlorinated ethane isomers, that is, 1,1,2,2-tetrachloroethane and 1,1,1,2-tetrachloroethane, or 1,1,1-trichloroethane and 1,1,2-trichloroethane, were significantly different from each other. This denotes that the main degradation pathways of these compounds are different. The possibility of using iron powder for the remediation of soil and groundwater contaminated with chlorinated organic compounds is discussed.

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In order to take an effective countermeasure based on measurements of toxicities by bioassays, information about the possible toxicity controlling chemicals is necessary. In this study, a new method of identifying toxicity-controlling chemicals using bioassay database and actual toxicity data is presented, and its feasibility is examined through its application to on 25 waste landfill leachates as models of environmental water. By comparing two important parameters describing dose-response relationship (the EC₅₀ value and the slope) between the landfill leachate samples and 255 kinds of chemicals, whose bioassay database has been recently organized in Japan, in some samples, we successfully listed possible candidates of toxicity-controlling chemicals as targets for chemical analysis, such as biophenol-A and chlorophenols. Subsequently-performed chemical analyses successfully showed the presence of such chemicals, and the concentration of these chemicals partly explained the observed toxicity of these samples. The new presented methodology is specifically effective in listing possible toxicity-controlling chemicals based on two important parameters of a dose-response relationship, and thereby enables targeted and cost-effective chemical analysis.

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The inactivation of microorganisms in seawater using a combined system of photocatalysis, hydrogen peroxide and UV-C irradiation was investigated. It was noted that the photocatalysis reaction time required for the complete suppression of photoreactivation in coliforms after UV-C irradiation was much shorter than that required for the complete inactivation of coliforms by direct disinfection of filtrated seawater. The minimum concentration of hydrogen peroxide required for the complete suppression of photoreactivation in coliforms after UV-C irradiation was lower than that required for the complete inactivation of coliforms by direct disinfection of filtrated seawater. The photocatalysis reaction time required for the complete inactivation of coliforms was the shortest in the combined system of UV-C→H₂O₂→TiO₂/UV-A, which resulted in the largest amount of disinfected seawater. The stable treatment using teh UV-C→H₂O₂→TiO₂/UV-A combined system was undertaken in the pilot tests plant for 6 days, during which bromate ion, and oxidation by-product, was not detected in the treated seawater.

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The result of source identification of polychlorinated dibenzo-p-dioxins, dibenzofurans (PCDD/Fs) and dioxin-like PCBs (co-PCBs) in Japanese river water is presented for the first time. River water and atmospheric deposition samples were collected from different locations in Tokyo Metropolis and Kanagawa Prefecture. The river water samples exhibited a range from 190 to 520 pg·l^-1 for total mono through octachlorinated PCDD/Fs and a range from 21 to 220 pg·l^-1 for total co-PCBs. Dichlorinated dibenzo-p-dioxins (DiCDDs) were the most abundant homologue in the river water samples (54-89% of total PCDD/Fs), while monochlorinated dibenzofurans (MoCDFs) were the most abundant homologue in the atmospheric deposition samples (24-51% of total PCDD/Fs). The concentrations of total TEQ ranged from 0.12 to 0.80 pg-TEQ·l^-1 in the river water samples, and total TEQ was dominated by particulate phase PCDD/Fs and co-PCBs, accounting for 62-97%. The congener profiles of the river water were basically similar to those of the atmospheric deposition (combustion). Several congeners in the river water, however, showed significantly higher proportions within each homologue than those in the atmospheric deposition. Part of these results could be explained by the effects of the impurities of triclosan, which is widely used as a germicide and antiseptic. Multiple regression analysis was used to estimate the contributions of different sources to total TEQ in the river water. The result showed that 73-92% of total TEQ originated from a combustion source.

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The mass change of nitrogen in Lake Biwa was shown, and its cycle was discussed and compared with the input/output loading. Nitrogen exists at 10.5X10³ ton in average, and its minimum and maximum mass are 7.6X10³ ton, 13.4X10³ ton, respectively. Its average mass is equivalent to 133% of the annual input loading, resulting in 1.6 months of residence time, which is shorter than 5.5 years of hydraulic retention time. This indicates that nitrogen in the lake is removed by settling onto the lake bottom or denitrification, and the removed mass is estimated to be 71% of the input loading. Phytoplanktons mainly utilize ammonium nitrogen in epilimnion whose mass is only 1% of the total mass in the lake. rather than other inorganic nitrogen amounting to more than ten-fold of ammonium nitrogen. During the stratification period, almost all decomposed nitrogen in the organic matter is oxidized into nitrate, and half of them is likely to be removed by denitrification.

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Estrogenic compounds are widely known to be present in water sources for public water supply and in aquatic environments at trace levels. However, the synergistic interactions of estrogenic chemicals in water have been scarcely reported. Therefore, the effects of p-nonylphenol (NP), bisphenol A (BPA), 17β-estradiol (E2), and their mixture on the induction of serum vitellogenin (VTG) in Japanese medaka were investigated in this study. Mature male medaka was exposed to NP, BPA and E2, and their mixture to evaluate their estrogenic activities by using a water-flow-through a chemical-exposure system installed in a clean room. VTG concentration in the sample was analyzed using a Medaka vitellogenin ELISE kit (Metocean Environment Inc., Transgenic Inc.). The lowest observed effect concentrations (LOEC) of vitellogenin by NP, BPA, and E2 exposures were 50μg·l^-1, 500μg·l^-1 and 5ng·l^-1, respectively. No observed effect concentrations (NOEC) by NP, BPA, and E2 exposures were 10μg·l^-1, 200μg·l^-1 and 1ng·l^-1, respectively. A significant increase in VTG level was observed when medakas were exposed to the mixture of these chemicals at NOEC. In addition, the mixture of these chemicals at LOEC showed a higher rate of VTG induction than single chemicals.

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