Abstract
Although it has been well established that radon exposure to high level radon in mining environment is a risk factor for lung cancer, it was not clear whether radon exposure in homes was a risk or not. Recently it has been revealed by large scale pool analyses of lung cancer case-controls studies that a level of 100 Bq/m3 in door radon does elevate a risk for lung cancer significantly. The levels of in door radon in Japan were estimated below the half level of world mean. However, there is a concern that the levels might elevate along with the increase of energy-saving houses with higher airtightness and lower ventilation rate. In the study, (1) we will measure radon at 3900 homes in Japan in order to obtain the population-weighted mean of in door radon in Japan, and (2) estimate the attributable fraction of radon for lung cancer among smokers and non-smokers in Japan.
A passive radon-thoron discriminative detector (RadoSys) will be set at either living or bed rooms for 6 months. Information will be obtained by questionnaire about possible confounding factors such as house structure, ventilation rate and location that will be used to grade the outdoor radon levels into three categories. In the present report, we will discuss about 820 and 900 measurements done from Oct. 2007 - Feb. 2008 and Mar. 2008 - Aug. 2008. At present, we have 820 measurements covering 28 metropolitan and prefectures. The distribution of indoor radon was compatible with log-normal distribution (Kolmogorov-Smirnov Test, p = 0.355), arithmetic mean and SD were 21.3 Bq/m3 and 21.0, geometric mean and geometric SD were 16.9 Bq/m3 and 1.95, lowest and highest values were 0.3 Bq/m3 and 437.9 Bq/m3, respectively. In door radon levels were statistically elevated if compared with those levels measured by RERF from 1993 to 1996.
