Abstract
Recently it has been revealed by the large scale pool analyses of lung cancer case-controls studies that a level of 100 Bq/m3 in door radon did elevate a risk for lung cancer significantly. The levels of in door radon in Japan were estimated to be 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 air tightness and lower ventilation rate. In the study, (1) we will measure indoor radon at 3900 homes in Japan in order to obtain the population-weighted mean of in door radon in Japan, and (2) we will estimate the attributable fraction of radon for lung cancer among smokers and non-smokers in Japan utilizing a mathematic model by EPA.
A passive radon-thoron discriminative detector (RadoSys) was set at either living or bed room for 6 months. In the present report, we will discuss about 2800 measurements done from Oct. 2007 ~Aug. 2009. At present, we have 2122 measurements covering 45 prefectures excluding Hiroshima and Nara. The distribution of indoor radon was compatible with log-normal distribution and those distributions in spring-summer and autumn-winter seasons could be adjusted by multiplying correction factors. Here we report data of 2122 houses: arithmetic mean (after correction) and SD were 15.2± 17.4 Bq/m3, geometric mean and geometric SD were 11.5 ×÷ 2.0 Bq/m3, lowest and highest values were 0.1 and 332 Bq/m3, respectively. Judging from mean and SD of log-normal transformed data, the probability of in door radon more than 100 Bq/m3 is about 0.1%, but in high radon areas such as Iwate and Okinawa, such a probability will be several percent. In these areas more intensive survey must be conducted.
