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 mutagenicity. 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 (chromosome-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 disinfection; 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 influence of different disinfection systems on water mutagenicity.