Characteristics of radon and current status of its regulation

Ishimori, Yuu  

The average of indoor radon concentrations in Japan is one fifth of that in Nordic countries, and no regulations of indoor radon have been introduced in Japan. Even if the regulation of 100-200 Bq/m is implemented in Japan, it would not contribute to the significant reduction of lung cancers. Since so-called "radon exposure" is the internal (lung) exposure not from radon itself but from its progeny, there have not been much data on the distribution of radon in the body. Measured data by Nussburm & Hursh (1957) is the sole source of information and is still used. Recently we obtained partition coefficients of radon using mice. In our experiment system, doses from the radon exposure with 2000 Bq/m for 24h are the order of 1Gy in lung and 0.1Gy in others. The observed activation of antioxidant enzymes following the radon inhalation may be attributed to the local energy transfer at cell and molecular levels. To discuss these biological responses in comparison to the LNT model, the dose-response relationship must be offered.