Default assumptions in carcinogen risk assessment used by regulatory agencies.

Uncertain components in carcinogen risk assessment are bridged in different ways in various regulatory agencies, depending on the goal of risk assessment. The U.S. EPA's goal in carcinogen risk assessment is to derive an estimate of the upper bound to risk. Generic default assumptions, designed to obtain a plausible upper bound to risk, are used to bridge uncertain components. The EC, and several member countries, seek estimates of the incidence of cancer likely to occur in the human population. Little or no use is made of genetic default assumptions. Uncertain elements of risk assessment are handled on a case-by-case basis, applying scientific judgement in light of the data available for each individual substance.