Toxicity and mutagenecity of urban wastewater treated with different purifying processes

Abstract The toxicity and mutagenecity of 1000-fold concentrates of 5 litre samples of wastewater from five different towns (containing 500, 600, 15000, 50000 and 190000 inhabitants) with different sewage treatment processes were determined. Two kinds of samples, including municipal wastewater entering the sewage treatment plants and the effluents discharged into the environment were analysed. After concentration through resins, overall toxicity was evaluated using the bioassay employing Photobacterium phosphoreum and samples were classified according to Vasseur et al. (1986) as 'Non-toxic', 'Slightly toxic', 'Toxic' or 'Highly toxic'. Mutagenecity was evaluated using the mutagenecity index determined by the Ames test, and samples were classified as 'Non-mutagenic', 'Slightly mutagenic', or 'Mutagenic', according to the 'two-fold' rule. The results obtained varied considerably; such that in some plants the toxicity values decreased during treatment whereas in others they remained unmodified or increased. None of the extracts analysed proved to be mutagenic. The data on toxicity and mutagenecity of the samples are apparently not correlated.