MUTAGENICITY OF EXTRACTS OF LAKE DRINKING-WATER TREATED WITH DIFFERENT DISINFECTANTS IN BACTERIAL AND PLANT-TESTS

Raw water and drinking water samples collected from five treatment pla nts supplied by a northern Italian lake in two periods of the year (su mmer and winter) were studied for their mutagenicity. The water sample s were concentrated on silica C-18 cartridges and the adsorbates were tested at increasing doses with a bacterial short-term mutagenicity te st (Ames test with Salmonella typhimurium TA98 and TA100 strains), whi ch reveals the gene-mutation-inducing ability of pollutants, and with a plant genotoxicity bioassay (Tradescantia/micronucleus test), which determines clastogenicity (chromosome-breaking ability). Raw water sam ples from all treatment plants were found to contain bacterial direct- acting mutagens detectable mainly with TA98 strain. The analyses of dr inking water samples after water treatment showed some interesting res ults: TA98 mutagenicity was reduced when ozone was used together with chlorine dioxide, but TA100 mutagenicity was increased, though only in the summer sample; mutagenicity detectable with both strains was alwa ys reduced after chlorine dioxide disinfection; on the contrary, in al l treatment plants using NaClO TA98 mutagenicity of winter samples inc reased. Raw lake water induced a high number of micronuclei in the Tra descantia/micronucleus lest, showing a strong clastogenicity. This act ivity was higher in the NaClO-treated samples, and lower with the othe r disinfectants. Therefore, disinfection of lake water with ozone and/ or chlorine dioxide seems to be a suitable alternative to the use of N aClO for controlling the formation of nonvolatile mutagens. The concen tration method coupled with the two mutagenicity tests was found to be a simple, rapid and relatively inexpensive system for monitoring trea tment plants and studying the influence of different disinfection syst ems on water mutagenicity. (C) 1998 Elsevier Science Ltd. All rights r eserved.