Revision 1
March 19, 1998
by Radiation, Science, and Health, Inc.,
Edited by J. Muckerheide

1.9
Conclusions

"From the limited set of laboratory data on the induction of lung cancer in laboratory rats it appears that, at low exposures, the risk of lung cancer decreases with decreasing concentration, and that exposures of the order of 25 WLM, at an exposure rate of 2 WL do not produce any excess lung cancers. Since 20 WLM is a lifetime exposure comparable to those expected in occupational or indoors conditions and 2 WL is an exposure rate about 20 times higher than current occupational exposures rates and 100 times higher than indoor ones, these observations may be indicative of threshold exposure conditions for the induction of lung cancer by radon progeny."

"From the examination of epidemiological data in underground miners, it appears that the confidence intervals in the risk per unit exposure are so large that it is not possible to exclude harmful effects, the absence of an effect, or even the existence of beneficial effects at exposures lower than about 200 WLM."

"Furthermore, apparent thresholds in the induction of lung cancer have been observed following low doses of alpha radiation in animals (Sanders et al 1988, White et al 1994) and in man, in radium dial painters (Rowland 1997) and Thorotrast-exposed patients (Andersson 1992). Taking these observations together with the fact that the risk of lung cancer due to radon progeny exposure in underground miners is overestimated by neglecting the effect of other potentially cocarcinogenic exposures, it is reasonable to suggest that the risk of lung cancer due to low exposures and very low concentrations of Rn222 progeny may not have any detrimental health effect, and that regulatory requirements should reflect these converging factual observations."