Risk management for plausibly hormetic environmental carcinogens: the case of radon

Risk management typically involves efforts to reduce human exposures by establishing regulations that limit the concentration of the substance in environmental media. In cases where a substance is widely used in commerce or is naturally occurring in the environment, compliance costs can be substantial because of nationwide requirements to add expensive control technologies. Uncertainties in a dose-response function further impact risk management decisions because they may correspond to large differences in health benefit per unit exposure reduction. These problems are highlighted in the case of plausibly hormetic environmental carcinogens, for which a linear-no-threshold (LNT) dose-response model has been the traditional regulatory default assumption. In this case, model uncertainty is pivotal, and risk management is consequently inherently controversial. However, marginal cost functions that arise for plausibly hormetic carcinogens are expected to possess a common analytic feature that may be particularly useful for this type of risk management problem. Specifically, marginal cost functions in this context are expected to have roots reflecting contaminant concentration values above which regulatory goals may be optimally placed subject to cost constraints. Here we illustrate this heuristic feature in the case of residential radon, using both a LNT model and a biologically plausible hormetic model to predict associated risks of lung cancer mortality.