The occurrence, biodegradation and DNA lesion of glyoxal derivatives as ozonation products, glyoxal and methylglyoxal were compared from the viewpoint of consequences for human health effect. The ozonation of three kinds of humic acids from different origins resulted in the tendency of more formation of glyoxal than methylglyoxal. Methylglyoxal showed high basepair substitution mutagenicity but was easily decomposed by glyoxalase system or S9 mix, compared to glyoxal. In rat hepatocytes, glyoxal induced 2-3 times more apparent frequency of DNA single-strand breaks than methylglyoxal, while only methylglyoxal induced DNA crosslink at about 1/10 frequency of the DNA single-strand breaks. During the process of ozone treatment pilot-scale plant, glyoxal showed 2 times higher formation after ozonation than methylglyoxal, and the concentration after chlorination was higher than that of chlorinated water from the conventional process because of less elimination of glyoxal by granular activated carbon-filtration. Therefore, all the results indicate that glyoxal should be prior to methylglyoxal as regards the toxicological assessment of ozonation products in drinking water.

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A sensitive and precise method was examined for the determination of molybdenum in environmental sediments by electrothermal atomic absorption spectrometry. The ground sample was digested with HF/HNO₃/HClO₄ or fused with sodium carbonate, then molybdenum was determined by standard addition method. Both use of a pyrolytic graphite-coated tube and addition of matrix modifier (Palladium (II) + magnesium nitrate) was effective for increasing sensitivity and precision. Constant absorbance was obtained in the charring temperature range of 1,400-1,600°C. Analytical results of molybdenum obtained by two proposed digestion methods agreed each other and were in good agreement with the certified or reference values for the environmental certified reference materials. Molybdenum concentrations in river, lake and marine sediments in Kanagawa prefecture were detected in the range of 0.545-2.66μg·g^-1 (average 1.24μg·g^-1). The detection limit of the proposed methods was 0.034μg·g^-1 for 0.5g of sediment.

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This paper describes how to determine the amount of oxygen required for the catalytic wet-oxidation treatment of wastewater which contains highly concentrated organic substances and/or ammonia. Here is an outline of the rescach results.
(1) A simplified formula was developed to calculate an amount of oxygen required for oxidative decomposition and thus to determine a total oxygen demand (TOD) for various nitrogen compounds, which has been complicated so far. Using the simplified formula, the required oxygen amont can be more accurately determined with the TOD of wastewater as well as the analysis of nitrogen compounds such as ammonia in wastewater.
(2) It was also clear that using the air amount obtained by the simplified formula, organic substances, ammonia and other pollutants in wastewater-night soil and gas liquid in particular-can be efficiently treated.

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Effects of the ratio of molecular weight (MW)/molecular weight cut-off (MWCO) on the flux of organic substance and clay in ultrafiltration were evaluated by fouling model materials and clay. Fouling model materials selected were protein (BSA, α-lactalbumin, γ-Globulin), polysaccharide (MW9,300, 70,000, 250,000, 515,000), fulvic acid (NW8,000) and humic acid (MW8,000-200,000, 8,000-50,000, 8,000-10,000, c.a200,000), and kaolin was selected as a clay material. The polysulfone membrane (MWCO10,000, 50,000 and 200,000) were used as an ultrafiltration membrane.
The flux of protein and polysaccharide with coexistence of kaolin increased in the case of the ratio of MW/MWCO being greater than one, but ded not increase in the case of the MW/MWCO ratio being below one. In contrast, the flux of fulvic acid and humic acid with coextence of kaolin decreased regardless of the ratio of MW/MWCO.
The addition of dispersion agent and coagulant in the organic substances and kaolin mixture solution changed the size distribution of kaolin, and resulted in the change of the flux. When the transmembrane pressure was changed from 100kPa to 200kPa, the flux of BSA and humic acid decreased with coextence of kaolin.
It was suggested that the decline of the flux with coexistence of kaolin was due to the change of the resistance of kaolin cake layer corresponding the change of kaolin size distribution with charge and filtration pressure.

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We intend to use rice straw as a organic substance for denitrification to remove nitrogen from soil percolate, and examined its feasibility by column experiments. We prepared the soil columns of 52 mm inner diameter with rice straw put in as a mono-layer, and supplied 20 mg-N per litter potassium nitrate solution to them from the upper surface at the rate of 24, 47 or 94 mm per day. Nitrate hardly was observed in the effluent from the column supplied at 94 mm per day for 114 days, and nitrate nitrogen removal during the period was 490 mg-N, which was roughly 5% of the amount of rice straw. Other columns fed at lower rate exhibited much lower nitrogen removal, the decrease in nitrogen concentration did not observed after 40 days of operation in these columns.
From the fact that the column fed at the largest flow rate showed the largest amount of denitrification, and from the examination of mass balance of nitrogen in soil and rice straw, we concluded that the removal of nitrogen by the column fed at 94 mm per day was mainly due to denitrification.
We conclude that we can use rice straw as a organic material source for denitrification to remove nitrate from soil percolate. The anoxic condition at the place where rice straw should be put in is essential to the effective use of rice straw.

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The Ames mutagenicity levels of tap water at 23 cities in Japan were investigated during a year for indicating the need of evaluation and control of gene toxicity of tap water. The mutagenicity values were ranged from under the detection limit to 9,200 net rev.·l^-1, and their difference was about 30 times. The mutagenicity values higher than 3,000 net rev.·l^-1 were about one fourth of them. There was no significant relation between the mutagenicitv of tap water and the kinds of the water treatment process or the water source except ground water. The mutagenicity values tended to be higher in winter and spring, and their annual means at each city were ranged from 290 net rev.·l^-1 to 4,400 net rev.·l^-1. It means that there is 15 times difference of the gene injury risk in these areas. Furthermore, the relations between the mutagenicity values and the conventional water qualities were not clear. Consequently, it was indicated that the Ames mutagenicity was available for evaluation and control of water safety in addition to the conventional water qualities. Especially, the mutagenicity of tap water should be evaluated and controlled in the area where the mutagenicity was clearly higher (above 3,000 net rev.·l^-1) than the other areas.

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Antialgal bioactive compounds were extracted from macrophyte (Egeria densa, Cabomba caloliniana, Myriophyllum spicatum) with methanol (MeOH). The MeOH extract was fractionated on the basis of polarity and molecular weight. Each fraction was assayed for algae (Selenastrum capricornutum and Microcystis aeruginosa). Microbial degradability of antialgal bioactive compounds was also investigated.
Algal growth was inhibited by the most polar fraction of the MeOH extract, and its fractionation on the basis of molecular weight showed that algal growth inhibition was caused by substances whose molecular weight were below 1,000. The lowly polar fraction extracted from Myriophyllum spicatum inhibited growth of M. aeruginosa, while growth of S. capricornutum was not affected. It was also shown that the antialgal bioactive compounds were easily degraded in the condition of coexistence with heterotrophic bacteria.

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