The ICRP's lung cancer risk from protracted exposure to radon and its progeny.

On the basis of the results of the recent combined analyses of epidemiological studies, the International Commission on Radiological Protection (ICRP) revised the lifetime excess absolute risk of radoninduced lung cancer to 5 10 per working level month (WLM). When applying this new coefficient in risk assessment, it should first be understood that the coefficient is associated with a chronic exposure scenario, i.e. a constant low-level exposure per year for many years. Secondly, the coefficient expresses the excess risk from radon exposure to the natural baseline risk by an increment dependent on radon progeny exposure in the unit of (WLM) and the coefficient represents an absolute risk in addition to the baseline risk that is independent of the baseline risk. Thirdly, it is the nominal risk coefficient for radon-induced lung cancer. A nominal risk coefficient means, according to the ICRP, the sexand age-averaged lifetime risk estimated for a representative population. For residential radon exposure (7000 h y indoors and an equilibrium factor of 0.4), one WLM equals a 1-y exposure to a radon gas concentration of 227 Bq m. Since the results of national radon surveys are reported exclusively in radon gas concentration in the units of Bq m, the lung cancer absolute risk of 5 10 per WLM can be converted to 2.2 10 per 100 Bq m for indoor radon exposure. Data for the populations of Canada, the USA and the UK along with the global data are shown in Table 1. This table gives population statistics, population-weighted average radon concentrations and estimated lung cancer deaths due to radon exposure available in the literature – . The worldwide population statistics, average radon concentration as well as estimated lung cancer deaths related to radon are also included in Table 1 8, . A nominal risk coefficient can be applied to a population. The ICRP-predicted number of lung cancer deaths due to indoor radon exposure, NLC,Rn, for a given population will be