Some scientific judgments in the assessment of the risk of environmental contaminants

The assessment of risk due to environmental contaminants depends, in part, on scientific data. When such data are incomplete, as is usually the case, assumptions based on scientific judgments are made to analyze the consequences. Specifically, when health related data needed to assess the risk posed by environmental contaminants are missing or incomplete, it becomes necessary to make assumptions using scientific judgment to estimate the risk. Different scientists can and do make different assumptions, and the resulting differences in opinion can result in controversy. The present discussion presents a few of the consensus judgments of the Science Advisory Board (SAB) of the U.S. Environmental Protection Agency concerning the health effects and risk for such environmental contaminants as 1,2-dichloroethylene, dichloromethane, para-dichlorobenzene, polychlorinated biphenyls, perchloroethylene, and xylene, as well as the implications of the more likely cancer mechanisms, the exposure routes, and pharmacokinetics to the risk assessment process. In some of these examples, the scientific data have been developed to the extent that specific judgments by groups such as the SAB can result in greater confidence that one is correct in the assessment of risk. Because of the uncertainties in current scientific knowledge for many environmental contaminants, judgments differ and there is no right or wrong opinion.