Leukemia among uranium miners--late effects of exposure to uranium dust?

The paper reports recent observations among Czech uranium miners. The study includes two groups of underground miners exposed in periods 1948-63 and 1968-88. A total of 9960 workers have been followed to the end of 1999 representing 267 thousands person-years. By the end of 1999, a total of 29 cases of leukaemia were observed. The standardized mortality ratio is 1.31, 90%CI: 0.88-1.88. In relation to cumulated exposure to radon progeny, no statistical association is seen (p = 0.172), but the trend with duration of underground work is significant (p = 0.015). These contrasting results suggest that the risk of leukaemia is probably related to other components in the underground environment. On the basis of the ICRP respiratory tract and biokinetic models using extrapolation of measurements of long lived radionuclides from uranium dust and external gamma radiation in Czech uranium mines since the 1970s, annual doses to the red bone marrow were estimated in the range 10-30 mSv. About 2/3 of the total dose for jobs involving drilling is due to inhalation of uranium and its decay products with ore dust, about 1/4 is due to gamma radiation, and only 5% of the dose is from radon and its progeny. The risk coefficient (excess relative risk per sievert) corresponding to these estimates is ERR/Sv = 7.1 (90%CI: 3.6 – 13.9). The dose estimates are subject to a considerable uncertainty. Therefore, in the absence of more exact estimates, it is more practical to assess the risk using only duration of exposure modified according to job category. As the red bone marrow estimates for hewers are about two-fold, the modification consists in accounting only half of the year for job categories other than hewer. Using this approach, the ERR per year is 0.15 (90%CI: 0.08 – 0.27).