Radon and its decay products in the indoor environment: radiation exposure and risk estimation.

Radon, a member of the uranium decay chains, enters the indoor environment from the building subsoil, walls and the drinking water. In areas with high radium content of rocks and soil, considerable indoor levels of radon are measured. A sample of 32 conventional homes in Southeastern Switzerland, an area with generally high uranium concentrations in the subsoil, showed an arithmetic mean radon concentration in living quarters and cellars of 307 Bq/m3 (8.3 pCi/l) and 1410 Bq/m3 (38.1 pCi/l), respectively. Using UNSCEAR82 conversion factors, the annual effective dose equivalent in this area amounts to 9 mSv (900 mrem). The corresponding dose to the stem cells of the tracheobronchial tissue is about 100 mSv/a (10 rem/a). Life time exposure in such dwellings is in the range of occupational doses collected in modern uranium mines and leading to a significant increase in the lung cancer risk.