Biological effects of radon

Biological Effects of Radon

Radon is a well-known and well established carcinogen that is responsible for the majority of radioactivity exposure of individuals in most countries throughout the world (Catelinois, Rogel, Laurier, Billon, Hemon, Verger, Tirmarche 2006). The most prominent and pervasive biological risk associated with radon exposure is a significantly increased risk of lung cancer. Studies involving underground miners were the first to detail this serious biological effect resulting from radon exposure, and subsequent studies have outlined the risks associated with indoor radon exposure in several different contexts.

Concerns regarding residential exposure to radon in the United States became prominent in the early 1980s with the identification of the Watras home, which was the home of a nuclear power plant engineer whose home demonstrated radiation levels that were 700 times greater than levels considered safe for exposure to humans. This wake-up call regarding the reality of radon exposure in the United States lagged behind Europe, where the issue of indoor radon exposure had already been recognized and studied (Samet 2006). Based on accumulated evidence, it was determined in 1999 by the U.S. National Research Council Committee on the Biological Effects of Ionizing Radiation that residential exposure to radon was a significantly important risk factor for lung cancer, and that these risks were estimated appropriately by a linear nonthreshold model (Samet 2006). However, Samet (2006) purported that individual case-control studies have not consistently demonstrated significant, direct evidence of excessive risks for lung cancer at residential exposure levels.

Studies of underground miners have yielded estimates that indoor radon exposure may account for approximately 6000 to 36,000 deaths due to lung cancer each year in the United States (Lubin & Boice 1997). However, due to the vast and inherent differences between underground mines and residential dwellings, these estimates are met with substantial uncertainties (Lubin & Boice 1997). Lubin and Boice (1997) explained how case control studies that directly addressed the risk of lung cancer from indoor radon exposure yielded positive, weakly positive or negative findings. Therefore the risk of lung cancer due to radon exposure can only indirectly be ascertained through studies involving miners, cellular studies, and experimental animal studies. In order to further understand the potential risk of lung cancer due to radon exposure, these researchers conducted a meta-analysis of all case-control studies that involved at least 200 subjects and utilized indoor radon measurements that were long-term. Results of this meta-analysis indicated that the risk of lung cancer from indoor radon exposure is not likely to be significantly greater than the risk predicted from miner studies. Furthermore, the results also determined that the negative exposure response that was reported in some ecologic studies more likely resulted from model misspecification or uncontrolled confounding, and could therefore be rejected. Based on these results, Lubin and Boice (1997) concluded that studies of underground miners remain the most optimal source of data for the assessment of lung cancer risk due to indoor radon exposure.

Since radon is a widely known and established carcinogen, researchers have found it important to investigate the biological risks associated with exposure. Catelinois et al. (2006) sought to assess the lung cancer risk in France due to the inhalation of radon. In particular, these researchers examined exposure-response results of both studies involving miners as well as case control studies, and furthermore investigated the interaction between radon and tobacco. The results of this study indicated that the estimated number of deaths due to lung cancer that could be attributed to radon exposure ranged from 543 to 3108 with a 90% uncertainty level. The specific number of deaths was dependent on the particular model being adhered to. From this number, the researchers suggested that 2.2% to 12.4% of these lung cancer deaths may actually be due to indoor radon exposure (Catelinois et al. 2006).