Reliability of up-to-date risk factor between residential radon and lung cancer

Full text: The WHO launched an international radon project in January, 2005 because two major scientific articles on the residential-radon-and-lung-cancer risk have been published. Furthermore, the ICRP has just issued a new recommendation (Publ. 103). In the publication, radon issues have been mentioned using these references. They show that there is a significant correlation between radon exposures and lung cancer risks even with a somewhat lower radon concentration than an internationally recommended level (200 Bq m-3). In most cases, residential radon concentrations were measured by passive integrating radon monitors based on the alpha track detection techniques in their studies. We examined detection responses for the presence of thoron with some typical alpha track detectors (Kf K: Germany, Radtrak: USA and NRPB: UK), which were widely used in many epidemiological studies. In addition, we measured indoor radon and thoron concentrations in cave dwellings in Gansu Province, China, in which the National Cancer Institute (NCI) conducted a large-scale epidemiological study. The NCI concluded that there was also a significant correlation between the two aforementioned parameters, which was a similar value to recently acceptable one. However, our results on radon concentrations were obviously different from them because there was much thoron in that area. The present study demonstrates whether these risk factors are really correct throughout our data or not. Tokonami (2005) has pointed out that some of popular alpha track detectors are sensitive to thoron (220Rn). This finding implies that radon readings will be overestimated and consequently may lead to biased estimates of lung cancer risk. The present study describes thoron interference on accurate radon measurements from the viewpoint of both experimental studies and field experiences. (author)