A carcinogenicity study with mutagenic organic concentrates of drinking-water in the Netherlands.

The carcinogenicity in male and female Wistar SSP TOX rats of organic drinking-water concentrates that are positive in the Ames test was studied at three doses. The organic mutagenic concentrates were prepared weekly from drinking-water from one location in The Netherlands by adsorption onto XAD-4/8 resins and elution with dimethylsulphoxide. The organic concentrates in dimethylsulphoxide were mixed with non-mutagenic drinking-water before exposure of the rats. Dose levels were based on multiples of expected human exposure levels. For the calculation the average human daily intake of drinking-water was taken as 2 litres for a body weight of 70 kg. There was no significant increase in tumour induction when male Wistar SSP TOX rats were exposed for 106 wk to 4.5, 14 or 40 times the expected human exposure level and females to 7,22 or 68 times the human level. The development and types of tumours were similar in the treated and control groups. The numbers of animals with tumours and of animals that died as a result of tumours in the exposed groups did not differ significantly from those in the control groups. These results suggest that these organic mutagenic drinking-water concentrates did not contain very potent carcinogens in effective concentrations.