OBJECTIVE: Evaluation of cytotoxic and genotoxic load of drinking water in relationship to the source of supplies, the disinfection process, and the piping system. SETTING: Two treatment/distribution networks of drinking water, the first (#1) located near the source, the second (#2) located near the mouth of a river supplying the plants. DESIGN: Water samples were collected before (F) and after (A) the disinfection process and in two points (R1 and R2) of the piping system. The samples, concentrated on C18, were tested for DNA damage in human leukocytes by the Comet assay and for gene conversion, reversion and mitochondrial mutability in Saccharomyces cerevisiae D7 strain. MAIN OUTCOME MEASURES: The approach used in this study is able to identify genotoxic compounds at low concentration and evaluate their antagonism/synergism in complex mixtures. RESULTS: Comet assay results show that the raw water quality depends on the sampling point, suggesting that a high input of environmental pollutants occurred during river flowing; they also show that the disinfection process can both detoxify or enhance biological activity of raw water according to its quality and that the piping systems do not affect tap water cytotoxic/genotoxic load. The yeast tests indicate the presence of some disinfection by-products effective on mitochondrial DNA. CONCLUSION: The biological assays used in this study are proven to be able to detect the presence of low concentrations of toxic/genotoxic compounds and assess the sources of their origin/production.
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