[Production of mutagenic compounds during the water purification treatment of surface water].

In the last years many studies have reported the presence of mutagenic/carcinogenic compounds in treated waters. These substances can be present in raw water, but are also produced during drinking water purification. Mutagens are formed as by-products of chemical reactions between oxidants/disinfectants used in treatments and organic load of the raw water (humic and fulvic acids). The aim of this study was to evaluate the production of mutagenic substances during the main phases of the Po river water treatment ("PO3" plant) in Turin. Water samples (50 litres), collected from February 1989 to August 1990, were concentrated with XAD-2/XAD-8 resins mixture. Extracts were tested for mutagenicity at different doses (1, 2.5, 5 and 10 litres) by Ames Salmonella assay, using TA 100 and TA 98 strains, without microsome fraction (S9). Raw water was rarely mutagenic while, in particular at the highest doses (5 and 10 litres), sometimes showed toxic effect. After ozonation treatment only few samples were mutagenic with TA 100 strain, while 43% of the samples were mutagenic with TA 98. The following treatment of clariflocculation and chlorination with NaClO produced mutagens in 95% of the samples assayed with TA 100 and in 85% of the samples assayed with TA 98. The next GAC/sand filtration step seems to reduce the mutagenic load produced in the previous phases. Finally, drinking water after chlorination with ClO2 showed weak mutagenicity at 1 litre dose (26% and 21% of positive samples with TA 100 and TA 98 respectively) and this effect increased at the higher dosages.(ABSTRACT TRUNCATED AT 250 WORDS)