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 plants supplied by a northern Italian lake in two periods of the year (summer and winter) were studied for their mutageni- city. The water samples were concentrated on silica C18 cartridges and the adsorbates were tested at increasing doses with a bacterial short-term mutagenicity test (Ames test with Salmonella typhimurium TA98 and TA100 strains), which reveals the gene-mutation-inducing ability of pollutants, and with a plant genotoxicity bioassay (Tradescantia/micronucleus test), which determines clastogenicity (chromo- some-breaking ability). Raw water samples from all treatment plants were found to contain bacterial direct-acting mutagens detectable mainly with TA98 strain. The analyses of drinking water samples after water treatment showed some interesting results: 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 always reduced after chlorine dioxide disinfec- tion; on the contrary, in all treatment plants using NaClO TA98 mutagenicity of winter samples increased. Raw lake water induced a high number of micronuclei in the Tradescantia/micronucleus test, showing a strong clastogenicity. This activity was higher in the NaClO-treated samples, and lower with the other disinfectants. Therefore, disinfection of lake water with ozone and/or chlorine dioxide seems to be a suitable alternative to the use of NaClO for controlling the formation of nonvolatile mutagens. The concentration method coupled with the two mutagenicity tests was found to be a simple, rapid and relatively inexpensive system for monitoring treatment plants and studying the infuence of different dis- infection systems on water mutagenicity.