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Health Effects of Exposure to Radon: BEIR VI
Lung-cancer risks associated with radon exposure were characterized in several ways. The LRR was used to describe the lifetime risk of lung-cancer among people continually exposed to radon throughout the course of their lifetime relative to the risk among unexposed individuals.
The percentage of lung-cancer cases that can be attributed to residential exposure to radon is of particular interest for risk management. The committee used data from the National Residential Radon Survey in combination with its 2 categorical risk models to estimate the AR posed by residential radon exposures. The ARs were estimated to be in the range 10–15%. These estimates are somewhat higher than the estimate of about 8% based on the data and methods of BEIR IV. About 30% of the AR was associated with homes having concentrations above 148 Bqm-3 (4 pCiL-1).
Although the AR percentages were comparable for ever-smokers and never-smokers under the multiplicative model, the number of radon-related lung-cancer cases was much higher among ever-smokers than for never-smokers under the multiplicative model. Of the approximately 157,000 lung-cancer deaths occurring annually, radon was estimated to play a role in about 15,000 to 22,000 cases. Of these, 13,000 to 19,000 were in ever-smokers and 1,000 to 3,000 in never-smokers, depending on the choice of the model. These computed values represent the best estimates of the lung-cancer risk attributable to radon that can be made at this time.
The committee recognized that these estimates are subject to uncertainty, including kinds of uncertainty that are not captured by statistical confidence limits on risk estimates. Consequently, the committee attempted a quantitative analysis of the uncertainty associated with estimates of the population AR. This analysis was itself limited, inasmuch as characterization of such sources of uncertainty as exposure measurement error in the miner data is difficult. Using data whenever possible and expert judgment otherwise, the committee attempted to describe the sources of uncertainty in its 2 categorical risk models.
The best estimates of the population AR were in the range 10 to 14% on the basis of the committee's preferred risk models. The quantitative analysis conducted by the committee provided limits within which the AR was considered to lie with 95% certainty. For the exposure-age-concentration model, the uncertainty interval ranged from about 9 to 25%, with central estimates of about 14%. This reflects a substantial degree of uncertainty in the AR, although the uncertainty distributions indicated that values near the central estimates were much more likely than values near the upper and lower limits. For the exposure-age-duration model, the AR ranged from 7 to 17%, and centered at about 10%. The committee also computed uncertainty limits for the simple constant-relative-risk model fitted to the miner data below 0.175 Jhm-3 (50 WLM), which is based on observations in miners closest to residential exposure levels. The latter analysis, which minimizes the degree of extrapolation outside the range of the miner data, led to uncertainty limits of 2–21%, with a central estimate of about 12%.