Relationship of the raw water quality to mutagens detectable by the Ames Salmonella/microsome assay in a drinking-water supply

Mutagenic activity of non-volatile compounds in dichloromethane extracts of a drinking-water supply derived by conventional treatment (flocculation, sedimentation, sand filtration and chlorination) of river water, was related to the concentration of volatile halogenated hydrocarbons. Limited relationship also existed between mutagenic activity and the total organic carbon content of both the raw and treated water. The dry mass of extracts from neither raw nor treated water correlated with these parameters. Mutagenic activity of the treated water increased during spring, possibly as a result of the first showers of the rainy season washing mutagen precursors into the river, rising temperature, and actively growing algae increasing the concentration of mutagen precursors in the river. After increased river flow, mutagenic activity of the treated water decreased and reached a stable summer level. Mutagenic activity was not detected in the raw water, which indicates that mutagens in partially purified wastewater effluents discharged into the river about 40 km upstream, were removed or inactivated in the river environment. Properties of the drinking-water extracts showed that the mutagens formed during treatment of the water supply consisted mainly of neutral organic compounds inducing frameshift mutations without liver activation. Although the specific activity of mutagens in the extracts does not indicate that the treated water constituted a health hazard, the results illustrate that regular surveillance of potential carcinogens in drinking-water derived by conventional treatment of water subject to pollution may be important.