LUNG-CANCER IN RADON-EXPOSED MINERS AND ESTIMATION OF RISK FROM INDOOR EXPOSURE

Background: Radioactive radon is an inert gas that can migrate from so ils and rocks and accumulate in enclosed areas, such as homes and unde rground mines. Studies of miners show that exposure to radon decay pro ducts causes lung cancer. Consequently, it is of public health interes t to estimate accurately the consequences of daily, low-level exposure in homes to this known carcinogen. Epidemiologic studies of residenti al radon exposure are burdened by an inability to estimate exposure ac curately, low total exposure, and subsequent small excess risks. As a result, the studies have been inconclusive to date. Estimates of the h azard posed by residential radon have been based on analyses of data o n miners, with recent estimates based on a pooling of four occupationa l cohort studies of miners, including 360 lung cancer deaths. Purpose: To more fully describe the lung cancer risk in radon-exposed miners, we pooled original data from 11 studies of radon-exposed underground m iners, conducted a comprehensive analysis, and developed models for es timating radon-associated lung cancer risk. Methods: We pooled origina l data from 11 cohort studies of radon-exposed underground miners, inc luding 65 000 men and more than 2700 lung cancer deaths, and fit vario us relative risk (RR) regression models. Results: The RR relationship for cumulative radon progeny exposure was consistently linear in the r ange of miner exposures, suggesting that exposures at lower levels, su ch as in homes, would carry some risk. The exposure-response trend for never-smokers was threefold the trend for smokers, indicating a great er RR for exposure in never-smokers. The RR from exposure diminished w ith time since the exposure occurred. For equal total exposure, exposu res of long duration (and low rate) were more harmful than exposures o f short duration (and high rate). Conclusions: In the miners, about 40 % of all lung cancer deaths may be due to radon progeny exposure, 70% of lung cancer deaths in never-smokers, and 39% of lung cancer deaths in smokers. In the United States, 10% of all lung cancer deaths might be due to indoor radon exposure, 11% of lung cancer deaths in smokers, and 30% of lung cancer deaths in never-smokers. This risk model estim ates that reducing radon in all homes exceeding the U. S. Environmenta l Protection Agency's recommended action level may reduce lung cancer deaths about 2%-4%. These estimates should be interpreted with caution , because concomitant exposures of miners to agents such as arsenic or diesel exhaust may modify the radon effect and, when considered toget her with other differences between homes and mines, might reduce the g eneralizability of findings in miners.