Dosimetric Approaches to Risk Assessment for Indoor Exposure to Radon Daughters

The ICRP has weighted its judgement of the excess risk of lung cancer from occupational exposure to radon daughters towards the evaluation of an effective dose equivalent per unit intake and thus exposure. The OECD/NEA and UNSCEAR have applied this approach to evaluate absorbed doses from exposure of the general public, taking into account the different conditions of exposure. They concluded that the effective dose equivalent (and hence lifetime risk) per unit exposure in domestic environments is about half that in mines, corresponding to a conversion coefficient of 5 mSv per WLM. An alternative concept of dosimetric assessment is being considered by the NCRP (USA), where the risk per unit exposure for the general public is derived from the ratio of doses absorbed by bronchial cells under mine and domestic exposure conditions and a reference risk coefficient extrapolated from the range of lung cancer rates reported for uranium miners. This approach leads to a numerically higher estimate of the conversion coefficient of 12 mSv per WLM. These two different approaches to dosimetric analysis are reviewed and the sensitivity of risk estimates to the underlying assumptions and uncertainties of dosimetric models and other critical parameters is examined. It is concluded that whichever dosimetric approach is used, exposure to potential alpha energy is an adequate index of the excess lifetime risk of lung cancer over the range of environmental conditions associated with high exposures in the home.