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Radon, your home or mine?

Radon and radon decay products have been causing lung cancers among underground miners for more than 400 years (1). In 1556, Agricola (2) described a mysterious lung disease afflicting miners of the Black Forest regions of Eastern Europe, mentioning that the occupation was so hazardous that some women lost as many as seven husbands to this terrible consumption. Inhaled radon and radon progeny were subsequently indicted as the culprits (3), although in some mines arsenic and other factors also contributed to the untimely deaths from lung cancer. Alpha particles emitted during the radon decay cascade resulted in large depositions of energy in bronchial cells, jumbling DNA and eventually leading to cancer. Cumulative working level months (WLMs) as high as 4,000 (approximately 20 Gy, or 200 Sv lung equivalent dose) have been estimated among early miners of the Colorado Plateau (4, 5). During the past 30 years, epidemiological studies of underground miners have provided an enormous amount of information on radon-induced lung cancer. The 11 major studies of uranium, fluorspar, tin and iron miners now include 65,000 men and 2,700 lung cancers. It is estimated that 40% (or 1,080) of these lung cancers are attributable to underground radon exposure (6). In contrast, the most recent study of 87,000 atomic bomb survivors recorded 939 lung cancer deaths, of which 7% (or 67) were attributable to the atomic radiation (7). Perhaps the most striking epidemiological feature of the 11 studies of underground miners is that a straight line adequately describes the relationship between cumulative radon exposure and lung cancer risk, although the individual slopes differ. This linear relationship has been apparent for nearly 25 years (5). Thus it might not seem too surprising that risks based on the low exposure range would be similar to those based on high-exposure data, as presented in this issue of Radiation Research by Lubin and colleagues (8). This relatively straightforward conclusion, however, is more important than it might seem at first glance. First, in years past there were insufficient data to even evaluate risks at low radon concentrations. In the early Colorado Plateau study (4), only 4 lung cancer deaths occurred among miners exposed to less than 120 WLM (0.6 Gy; 6.0 Sv). The combined series (8) includes sufficient numbers to directly address the risk of lung cancer among miners exposed to less than 100 WLM, and 562 lung cancer deaths were available to do so.