²²²Rnを対象とした自然放射線の室内曝露に関わる被害評価手法の構築と係数の開発

抄録

Objective. Radiation is one of the impact categories in LCA, but this category has not been evaluated in product LCA in general. However, the accident of Fukushima nuclear power plant raised people’s interests in radiation. According to the World Health Organization, radon (²²²Rn) is the second most frequent cause of lung cancer in public, after smoking. Main pathway of radiation exposure to radon is indoor inhalation. However, there are still few studies for the development of the life cycle impact assessment (LCIA) method of environmental radiation considering the exposure pathway and radon. This study is aimed at the development of the impact assessment method of irradiation caused by inhalation of radon in living environment.
Methods. The method is composed of 4 analysis; fate analysis, exposure analysis, effect analysis and damage analysis. Fate analysis was carried out using the parameters in typical housing in Japan. We estimated inteRnal and exteRnal exposures using conversion factors and the result of fate analysis. Risk of cancer in each organ and loss of life expectancy by cancer were applied in effect analysis and damage analysis respectively. Damage factor, main output of this study can be expressed as loss of life expectancy caused by a unit of emission of radon. Damage factor enables us to compare with the health effects caused by another impact category such as global warming and air pollution.
Results and Discussion. Damage factors obtained from this study ranges from 4.4 × 10⁻¹¹ to 1.5 × 10⁻¹⁰ (DALY/Bq), which was consistent with the existing study. Lung cancer was the primary impact for damage factor. Damage factor of female was estimated higher than that of male. The damage factor of young people becomes higher, because the sensitivity of inteRnal inhalation exposure of young people is estimated higher. These results were applied to a case study of housing. The result revealed that the health impact of radon was twice of that of global warming.
Conclusions. A methodology evaluating health damages due to the exposure to radon emitted to indoor air from the use of building materials. Damage factor was consistent with the existing study. This study enabled us to calculate damage assessment in LCA considering Japanese conditions and the differences of exposure age and sex. These considerations are expected to improve the reliability of LCIA. The development of LCIA method which takes into account the differences in the various conditions of housing and the updated epidemiological studies are required.