Evaluation of indoor radon risk for discussion on national action in Japan

Sakoda, Akihiro   ; Ishimori, Yuu  

International organizations such as WHO and ICRP recommended reference levels with the range of 100300 Bq/m against residential radon exposure. In Japan, indoor radon activity concentration is generally low, and a national plan and reference level have not been set so far. This study aimed to evaluate the risks of indoor radon among Japanese populations and to discuss the effectiveness of an assumed reference level in terms of reduction in the number of lung cancer deaths. The US EPA model was used to calculate lifetime risks and population attributable fractions for ever smokers and never smokers using the recent Japanese-specific information such as demographic data and smoking prevalence. The result indicated that the number of lung cancer deaths was very low (i.e., less than 10 in 2020) among the population exposed to more than 100 Bq/m. This means that even if a reference level of 100 Bq/m is set, the statistically significant reduction in lung cancer deaths could not be observed. Given the risk evaluation, we believe that expected national actions in Japan are to support individuals who consider taking measures for the own risk perception and control of lifetime risk, rather than to introduce regulations. Comprehensive argument and judgement would also be desired for better public health, based on information on not only radon but also other common modifiable risk factors.