Cancer risk assessment: importance of identifying mechanisms of action.

The process by which regulatory standards are established for drinking water contaminants is based on extrapolating animal toxicity data to humans using a standard mathematical model. The assumptions and judgments involved introduce a relatively high degree of uncertainty and conservativeness into both the qualitative and quantitative aspects of the process. Setting standards based on knowledge of specific mechanisms of carcinogenicity would decrease the uncertainty involved in risk assessment. Understanding these mechanisms is necessary for arriving at the most appropriate mathematical construct for calculating more rational standards.