Uranium mining

The most problematic decay product is radium-226 for three reasons: its salts are mainly soluble; it has a long half-life (1,760 years); and it emits gamma rays. Another dangerous nuclide is radon-222 (half-life 3.8 days). Because it is an odourless, colourless gas, it and its progeny, although invisible, are readily distributed in the environment. Exposures to radon gas are considered to be the second leading cause of lung cancer worldwide after smoking tobacco.80 The US Environmental Protection Agency (EPA) has estimated that indoor radon exposure causes or contributes to about 21,000 lung-cancer deaths in the United States annually.81

Partly for these reasons, the ICRP estimated that a lifetime excess absolute risk of 5 × 10-⁴ per Working Level Month (WLM)82 should be used as the risk coefficient for radon-induced lung cancer, doubling its previous estimate.83 These cancer risks are expressed using either the Excess Relative Risk (ERR) model or the Excess Absolute Risk (EAR) model. ERR is the proportional increase in risk over the background rate (i.e. where people are not exposed). EAR is the additional risk above the background rate. However, several ICRP authors later added that the risk would have actually increased to 7 × 10-4 per WLM if lung cancer rates among Euro-American males had been used instead of inappropriate ICRP reference rates (namely males and females and Euro-American and Asian populations).84 In other words, the estimated risk rates for most uranium mine workers have approximately tripled rather than doubled since 1993. This increased awareness of uranium mining’s risks has not been reflected in tighter safety standards for uranium workers.

URANIUM MINING

Although many uranium mines are now closed, the past history of uranium mining throughout the world remains bleak, with many accidents and reports of ill health among uranium miners. Older epidemiology studies indicated significant excesses of lung cancer among uranium mining workers.85

Perhaps the best-documented example in Europe is the Wismut mine complex in former East Germany. The Soviet-run uranium mine complex was in operation until 1996. 59,000 of these miners employed between 1946 and 1989 were examined. Researchers found a significant increase in lung cancer risk with increasing radon exposure (ERR/WLM = 0.0019).86 An update of this study found that the lung-cancer risk actually increased threefold (to ERR/WLM = 0.006) with the extended observation period to 2013.87 Also, the authors found 3,942 miners from the cohort had died from lung cancer during their increased observation period from 1946 to 2013. Unfortunately, the new study omits the number of deaths from extra-pulmonary cancers, heart diseases and cerebro-vascular diseases which had been observed in the earlier cohort study.

80 Darby, S., Hill, D., Auvinen, A., Barros-Dios, J.M., Baysson, H., Bochicchio, F., Deo, H., Falk, R., Forastiere, F., Hakama, M. and

Heid, I. 2005, Radon in homes and risk of lung cancer: collaborative analysis of individual data from 13 European case-control studies, Bmj, 330(7485), pp. 223. 81 Pawel, D.J. and Puskin, J.S. 2004, The US Environmental Protection Agency’s assessment of risks from indoor radon, Health physics, 87(1), pp. 68-74. 82 One working level (WL) refers to the concentration of short-lived decay products of radon in equilibrium of 3,700 Bq/m³ (100 pCi/L) in air. A working level month (WLM) is the exposure to one working level for 170 hours per month. It is conventionally assumed that 1 WLM = ~10 mSv. 83 Tirmarche, M., Harrison, J.D., Laurier, D., Paquet, F., Blanchardon, E. and Marsh, J. 2010, Lung cancer risk from radon and progeny and statement on radon, Annals of the ICRP, 40(1), pp.1-64. 84 Tirmarche, M., Harrison, J., Laurier, D., Blanchardon, E., Paquet, F. and Marsh, J. 2012, Risk of lung cancer from radon exposure: contribution of recently published studies of uranium miners, Annals of the ICRP, 41(3-4), pp.368-377. 85 Grosche, B., Kreuzer, M., Kreisheimer, M., Schnelzer, M. and Tschense, A. 2006, Lung cancer risk among German male uranium miners: a cohort study, 1946–1998, British journal of cancer, 95(9), pp. 1280. 86 Kreuzer, M., Grosche, B., Schnelzer, M., Tschense, A., Dufey, F. and Walsh, L. 2010, Radon and risk of death from cancer and cardiovascular diseases in the German uranium miners cohort study: follow-up 1946–2003, Radiation and environmental biophysics, 49(2), pp.177-185. 87 Kreuzer, M., Sobotzki, C., Schnelzer, M. and Fenske, N. 2017, Factors modifying the radon-related lung cancer risk at low exposures and exposure rates among German uranium miners, Radiation research, 189(2), pp.165-176.