extrapolation outside the range of the miner data, led to uncertainty limits of 2 to 21%, with a central estimate of about 11%.

Effects of Radon Exposure Other Than Lung-Cancer

Health effects of exposure to radon progeny other than lung-cancer have been of concern, including other malignancies and non-malignant respiratory diseases in miners. The findings of several ecologic studies in the general population have indicated a possible effect of radon exposure in increasing risk for several types of non-lung-cancers and leukemias. A pooled analysis of 11 miner studies, differing in one study from the data used by the committee, showed no evidence of excess risk for cancers other than the lung. The committee concluded that the findings in the miners could be reasonably extended to the general population and that there is no basis for considering that effects would be observed in the range of typical exposures of the general population that would not be observed in the underground miners exposed at generally much higher levels.

The committee reviewed new studies of non-malignant respiratory disease in uranium miners. A case series of uranium miners with pulmonary fibrosis supported the possibility that exposures to radon progeny may cause fibrosis of the pulmonary interstitium, but the case series is insufficient to establish a causal link to radon progeny specifically.

CONCLUSIONS

Radon is one of the most extensively investigated human carcinogens. The carcinogenicity of radon is convincingly documented through epidemiologic studies of underground miners, all showing a markedly increased risk of lung-cancer. The exposure-response relationship has been well characterized by analyses of the epidemiologic data from the miner studies, and a number of modifiers of the exposure-response relationship have been identified, including exposure rate, age, and smoking. For residences in the United States, a large national survey provides information on typical exposures and on the range of exposures.

On the basis of the epidemiologic evidence from miners and understanding of the genomic damage caused by alpha particles, the committee concluded that exposure to radon in homes is expected to be a cause of lung-cancer in the general population. According to the committee's two preferred risk models, the number of lung-cancer cases due to residential radon exposure in the United States was projected to be 15,400 (exposure-age-duration model) or 21,800 (exposure-age-concentration model). Although these represent the best estimates that can be made at this time, the committee's uncertainty analyses using the constant relative risk model suggested that the number of cases could range from about 3,000



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