We measured the mutagen formation potential (MFP) of 42 river water samples from 37 rivers throughout Japan using the Ames mutagenicity assay, to investigate the nationwide level of mutagen precursors contained in river water. The MFP of river water was highest when Salmonella typhimurium strain TA100 was used without metabolic activation. The MFPs ranged from 210 to 20,200 net rev. · l^-1 and the median was 2,520 net rev. · l^-1, which shows that the values varied greatly between samples. About 60% of the samples showed MFPs in the range from 1,500 to 3,500 net rev. · l^-1. Dissolved organic carbon (DOC), E₂₆₀, NH₄-N, NO₂-N, NO₃-N and T-N concentrations were also measured. A strong positive relationship was observed between logarithmically-transformed DOC and MFP. However, the MFP/DOC ratio varied widely from 110 to 2,160 net rev. · mg^-1. We also investigated the relationship between MFP and river basin characteristics such as population density. The results suggest that mutagen precursors are strongly influenced by human activities. In addition, rivers were classified using a cluster analysis of water qualities (MFP, DOC, E₂₆₀, NH₄-N and NO₂-N+NO₃-N).

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The light-dark bottle method and benthic chamber method were used to estimate the gross photosynthetic rate of benthic tidal microalgae. In the light-dark bottle method, 0.5g of wet bottom sediment and an incubation time of 6 hours were employed for the measurement of the photosynthetic rate of the benthic microalgae. The gross primary production of the benthic microalgae at the in situ temperature and photon flux density, determined by the light-dark bottle method, reached 2.1 gC · m^-2 · day^-1 on October 7, 2003 at the experimental tidal flat in Hannan Second District, Osaka Bay. The gross photosynthetic rate per unit chlorophyll a concentration of the benthic microalgae increased with increasing photon flux density in the benthic chamber. Using the present benthic chamber method, together with the in situ photon flux density and chlorophyll a concentration of the bottom sediment, the gross production of the benthic microalgae was estimated to be an average of 0.34gC · m^-2 · day^-1 at the Wakagawa tidal flat on October 3, 2005.

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The highly toxic tributyltin (TBT) compounds used as biocides in ship antifouling paints have been released to aquatic environments. In this study, we investigated the sediment-water partition of organotin compounds using the sediments collected from several ports and harbors. As a result, the adsorption of TBT onto a particle was found to be significantly determined by organic carbon content and temperature and less significantly by pH and salinity. The possibility of the effect of dibutyltin (DBT) adsorption on TBT adsorption was suggested.

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The concentrations of PCBs in sea water and blue mussels ranged from 0.5 to 4.0 ng · l^-1 (mean ± S.D.: 1.8 ± 0.6 ng · l^-1) and from 3.1 to 69.8 ng · g^-1 -wet (24.0 ± 19.0 ng · g^-1-wet), respectively, in the Seto Inland Sea. The main homologues of PCB in seawater and blue mussels were T₄CBs and H₆CBs, respectively, and their content ratios to total PCB were 40∼50%. Homologues with high chlorine content accumulated in blue mussels. By principal component analyses associated with the homologues of PCB in seawater, blue mussels and sediment, it was clearly shown that the sea area in Osaka Bay and Harima-nada were mainly contaminated with low-chlorine-content homologues of PCB which were mainly used in condenser and heating fluid, and that the other sea area was mainly contaminated with high-chlorine-content homologues which were mainly used in paints and varnish. More detailed analyses were possible by the principal component analyses with selected and important isomer data.

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We have been developing a method of establishing a phosphate ion removal, recovery and recycle system using a synthesized Mg-Al-Cl form of hydrotalcite (HT). The powder form of the HT, however, is not ideal for wastewater treatment because of its poor solid-liquid separating efficiency; thus, we have developed a hydrotalcite-carrying fiber (HTCF). The HTCF is made of a porous polymer that carries HT at weight percents of 80-90. The internal structure of the HTCF is composed of a pore structure with continuous holes, so the HTCF is a carrier with a high permeability and exhibits the characteristics of HT sufficiently. In this study, we investigated the characteristics of the HTCF, such as adsorption capacity, desorption rate, regeneration rate and change in regeneration rate with regenerating time by applying the "two- liquid regeneration system". As a result, the HTCF showed a high adsorption rate, a high adsorption capacity, a high desorption rate for phosphate ions and a high regeneration rate, equal to that of HT powder. In addition, the HTCF can be reused more than 10 times, maintaining a regeneration ratio of 80% higher. From these results, it was confirmed that the HTCF is a suitable carrier that exhibits characteristics comparable to those of HT powder and can contribute to the establishment of a zero-emission-formula phosphate removal and recovery system for wastewater.

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