EPA's perspective on risks from residential radon exposure.

Indoor radon has been judged to be the most serious environmental carcinogen which the EPA must address for the general public. The optimal strategy for dealing with this problem depends on the magnitude of the risk, how the risk is distributed within the population, as well as the effectiveness and costs of mitigation measures. Based on current exposure and risk estimates, radon exposure in single-family houses may be a causal factor in roughly 20,000 lung cancer fatalities per year. Most of these projected fatalities are attributable to exposures in houses with average or moderately elevated radon levels (below 10 pCi/L). Hence to appreciably reduce radon-induced lung cancers, remediation efforts must include houses not highly elevated in radon. From either an individual risk or a cost-benefit standpoint, reduction of a few pCi/L per home appears to be justified. The optimal strategy for dealing with the indoor radon problem depends on the magnitude of the risk per unit exposure, the distribution of exposures in houses, and the effectiveness and costs of mitigation. EPA's current views with respect to these factors and the associated uncertainties are discussed.