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

1.2.6.3
Radon

1.2.6.3.2
Miners Studies

"There is ample evidence that prolonged exposure to large concentrations of airbourne of Rn-222 progeny is the cause of an increased risk of lung cancer in man (Lubin et al 1994) and in animals (Monchaux et al 1994). At sufficiently high exposures, there is a clear relationship between the cumulative exposure received by individual persons or animals in a given cohort and the overall incidence of pulmonary cancer in that cohort. It is also clear that, at high exposures, the risk of pulmonary cancer increases with increasing cumulative exposure. This leaves no doubts of a causal relationship between exposure to Rn progeny and the risk of pulmonary cancer. However, a causal relationship between Rn-222 progeny and pulmonary cancer is more difficult to establish at lower exposures. From 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 lower than about 200 WLM."

"The risk of lung cancer at low exposures to Rn-222 progeny is extrapolated from the risk observed in underground miners at high exposures. However, depending on the specific mines in which they worked, the miners have also inhaled several other potentially carcinogenic substances, such as diesel exhaust products containing carcinogenic hydrocarbons, arsenic, mineral fibres, or haematite. In addition to Rn-222 decay products, uranium miners have inhaled mixtures of radioactive ore dust particles and/or Rn-222 decay products, and they were exposed to the field of gamma radiation emitted from the ore body. These factors may have acted synergistically with, or in complement to, the inhalation of Rn-222 progeny in the induction of lung cancer. Furthermore, in most of the miner cohorts large, or even huge uncertainties exist concerning the exposure of Rn-222 progeny attributed to each worker. Uncertainties in Rn-222 progeny exposures are due to any combination of the following factors: Absence of measurements when the workers were being exposed, low sampling frequency, variability in time and space of the concentration of Rn-222 progeny and unrecorded employment in mines other than that for which exposure records exist. These factors, compounded by the fact that, with few exceptions, all excess lung cancers are attributed to the exposure to Rn-222 decay products alone (neglecting the possible role of other cocarcinogens) make it difficult to draw firm conclusions concerning the influence of low exposures to Rn-222 progeny alone in the induction of lung cancer in underground miners."

"The body of information concerning the effects of low exposures to Rn-222 progeny is limited to the experiments conducted at the CEA-COGEMA laboratory of Razes (France) (COGEMA 1994, Morlier et al 1992), and to those inducted at the Pacific Northwest National Laboratories (PNNL) (Gilbert et al 1996)...

"Dose rate alone (concentration) is a determining factor in the induction of lung cancer by Rn-222 progeny, and that the risk of lung cancer decreases with decreasing concentration of radon progeny, that is, decreasing dose rate. The decrease of risk with decreasing concentration is also noted by Gilbert et al (1996) but, in PNNL contained about 2 to 4% uranium, and also about 80% SiO2 (Cross 1988) and higher radon progeny concentration (the lowest concentration in PNNL experiments was 10WL, which is about 100 times higher than today’s mine concentration and 5 times higher than the low concentration in the CEA-COGEMA experiment."

"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 (Rowlands 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 Rn-222 progeny may not have any detrimental health effect, and that regulatory requirements should reflect these converging factual observations."