Assessing the risks of Rn exposure: the influence of cigarette smoking

The principal hazard associated with exposure to Rn progeny is lung cancer. However, most lung cancer is caused by smoking, which raises a dual problem of deriving Rn-progeny cancer risk estimates from miner populations who, in large part, are smokers and applying these estimates to the general population whose lung cancer risk, in large part, is determined by smoking habits. We examine current risk estimates for Rn-progeny-induced lung cancer using a cohort life table methodology. Estimates of lifetime probability of dying of lung cancer, average loss in life expectancy due to premature lung cancer death, and loss in life expectancy per premature lung cancer death are calculated for the general population for 1969 and 1978, nonsmokers, and smokers. These calculations demonstrate that such risk estimates are affected by smoking, and by trends in smoking habits, in several ways. Major smoking-related factors in this interaction are the proportion of smokers in the mining population used to derive lung cancer risk estimates, the proportion of smokers in the "general" population, and the assumed interaction (additive or multiplicative) between lung cancer risk, Rn-progeny exposure, and smoking history. At this time the data are not sufficient to recommend one particular modeling approach. However, our evaluation demonstrates that broad statements about Rn-progeny lung cancer risk such as "x cancers/10(6) person working level month," while informative, are incomplete without further specification. Any risk assessment must clearly state the population assumed to be at risk and the risk model assumed to be operating. Finally, the caveats appropriate to these assumptions should also be enunciated.