水道水の変異原性の季節変動とその解析

Abstract

The Ames Salmonella/microsome assay (Ames test) is a convenient method for screening mutagens in our diet including those in drinking water. In this study, we assayed the mutagenicity levels of tap water in Kitakyushu-city and of humic acid solutions treated with chlorine. The amount of chlorine added was calculated to maintain the residual chlorine level constant at 20°C as in city office tap water. The samples were concentrated with adsorbent (CSP800) and the mutagenic activity was assayed with Salmonella typhimurium TA100 and TA98 strains with or without S9 mix. The tap water was analyzed for volatile organic compounds and some factors in conventional water quality monitoring every two months from March 1998 to January 2000. The tap water samples tested showed mutagenicity on strain TA100 without S9 mix. The mutagenicity of the samples tended to be higher from winter to spring than that from summer to fall.Chlorine-treated humic acid solutions were used as a model to examine the effect of the concentrations of humic acid and chlorine, and the temperature on the mutagenicity. The descending order of sensitivity to mutagenicity was TA100 without S9 mix, TA98 without S9 mix, and TA100 with S9 mix; no mutagenicity was observed for TA98 with S9 mix. Mutagenicity seemed to increase with increasing concentrations of humic acid and chlorine, and with lowering the water temperature. The observed seasonal variation of mutagenicity of the tap water may be partly explained by the rainfall and the water temperature during the rainy season, from summer to fall, because the organic substances of river water decreased and the water temperature increased over that season.