CARCINOGENIC MICROPOLLUTANTS IN DRINKING-WATER - RISKS AND REGULATION

A number of common contaminants in drinking water, arising as by-products of chlorination or from industrial pollution, have been shown to cause cancer in laboratory animals. The initiating event in the process of chemical carcinogenicity is usually considered to be the induction of a mutation in the DNA of a somatic cell. The process theoretically may not have a threshold. There are however some substances which are capable of producing cancer in animal studies but which cannot be shown to have genotoxic activity. The former are usually regulated by estimating the concentration in drinking vater which gives rise to an acceptable risk of additional cancers in exposed populations. The mathematical models used in the process have many built in assumptions and will usually overestimate the true risk which could be zero. The latter, non-genotoxic carcinogens, are considered to operate through a mechanism which has a threshold and are usually regulated by applying uncertainty, or safety, factors to the no observed effect level in animal studies. Carcinogens often occur in vater in mixtures and at present ve have no appropriate means of taking this into account. However there is a sufficient margin of safety built into the regulatory approach to be confident that drinking vater is not a significant source of cancer in most populations.