Organic extracts of raw water from 11 water courses of SLo Paulo State, Brazil, were collected during one year bimonthly and tested for mutagenicity using the Ames test, with strains TA98 and TAlOO of Salmonella typhimurium with and without metabolic activation. The samples were extracted with XADz resin and eluted with methanol and methylene chloride. From the 75 samples analyzed, 14 showed positive responses and 8 were considered marginal, making up 29% of mutagenic samples. The percentage of mutagenic samples in October (spring) was 9%, increasing to 64% in February (summer), and decreased to 9% again in August (winter). Paraiba do Sul river showed the higher percentage of mutagenic samples (67%) and Capivari river the highest mutagenic sample (1787 and 3265 revertants per liter for TA98 without and with S9, respectively).The amplitude of the mutagenic response was 39-3265 revertants per liter for TA98 and 83-467 for TA100. The mutagenic samples showed direct and indirect mutagens, and TA98 detected the majority of responses, indicating prevalence of frameshift mutagens in these samples. 0

During the last decade, studies carried out in several countries throughout the world have disclosed the presence of halogenated hydrocarbons and other potentially carcinogenic compounds in drinking water, causing public concern with respect to the quality of drinking water. Considering this problem, chlorinated drinking water from seven water treatment plants in São Paulo and from its water sources were tested for mutagenicity in the Ames/Salmonella assay. Different volumes of raw and treated waters were concentrated by XAD‐2 resin, and eluted in methanol and methylene chloride. Organic extracts ressuspended in DMSO were assayed for dose response in Salmonella typhimrium strains TA98 and TA100, with and without metabolic activation, using the plate incorporation technique. Results showed higher incidence of mutagenic activity in water samples after chlorination than in raw water. The majority of positive responses were decreased by addition of metabolic activation, confirming the presence of direct‐acting mutagens, produced during water chlorination, although significant mutagenicity was also observed in the presence of S9. Mutagenic levels ranged from 104 to 569 revertants/L in raw water, and in chlorinated drinking water, between 10 and 418 revertants/L. Based on the results obtained in this study, it is essential to study and identify mutagenic compounds evolving from the chlorination processes, and to determine, for water treatment plants with high incidence of mutagenic compounds, the procedures to avoid or eliminate this problem, as well as to establish an effective monitoring program.

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