Relations between drinking water mutagenicity and water quality parameters

The formation of mutagenic activity in drinking waters containing various amounts of organic matter was studied in Finland. It was found possible to model the mutagenicities of chlorinated drinking waters as a function of the total organic carbon (TOC), of the chlorine dose, and as a minor factor, of the amount of ammonia. The equation was the sum of the two chlorination steps, each of them of the same form: [mutagenicity in TA 100]= A(1−e−kc) , where c=[TOC] [Cl2]. Here [TOC] is the concentration of total organic carbon and [Cl2] the chlorine dose, in units of mg per liter; A and K are constants. The regression coefficient R for the measured mutagenicities in TA 100 and the modelled mutagenicities was 0.854 in 86 drinking water samples. Ozone or chlorine dioxide preoxidation combined with chlorine postdisinfection resulted in lower mutagenicities than if chlorine was used in both steps. The mutagenicities were slightly higher in winter than in summer.