2. Hazards for uranium miners
(September 1995) In addition to the hazards of conventional mining, uranium miners are exposed to the risk of contracting lung cancer; this results from the inhalation of radioactive dusts and the radioactive gas radon. Radon-222 is formed from the decay of radium-226, a radionuclide contained in the uranium ore. Investigations (for example the study [Sevc1988] conducted on Czech uranium miners) show a sixfold increase of lung cancer risk with uranium miners; but also other respiratory diseases show higher incidences. Lung cancer typically develops with a latency period of 15 to 30 years; the link between occupational exposure in a uranium mine and the incidence of the disease therefore is not always obvious.
During the early "wild" years of uranium mining, protective measures for the miners were rarely taken worldwide. Miners in these early years thus took the highest risk of contracting lung cancer. In the year 1955, radon concentrations in Wismut's mines typically were approximately 100,000 Bq/m3, with peaks of 1.5 million Bq/m3 [Jacobi1992]. From the end of the fifties, the ore was kept wet during drilling to avoid generation of dust, and the mines were intensively ventilated to lower the radon concentrations. The doses received from radon decay products thus decreased from 150 WLM to 4 WLM per year (WLM = Working Level Month is a unit for the dose from radon decay products, which are causative for cancer development).
In the Rumanian uranium mine Avram Iancu high radon concentrations of up to 60,000 Bq/m3were even monitored in recent times, due to insufficient ventilation of the mine [RSRP1993].
According to [Jacobi1992], the doses received in Wismut's mines in the early years should not be estimated at 150 WLM, but at 200 WLM per year. The true value can hardly be determined, since Wismut never performed direct individual monitoring of the doses received by the miners. Before 1955, no monitoring was performed at all - only estimates can be made for this early period. Later, radon decay product concentrations were sampled at representative locations within the mines for short periods of time. The doses received by the miners were calculated from these sampling results. While this method allows a certain overview on the doses received, its results cannot be compared with those of continuous individual monitoring.
In France, however, individual dose meters are used from 1983. From 1989, they are obligatory for all miners who risk exceeding 30 % of the radiation dose limit. [Tirmarche1993], [Bernhard1991]
Between 1946 and 1990, 7163 uranium miners who had been employed with Wismut died from lung cancer. For 5237 of them, the occupational exposure was recognized as the cause of the disease [AKURA1993]. Until mid-1990, the limit for recognition was 450 WLM; then it was lowered to 200 WLM. One year of work in the uranium mines during the early years is therefore already sufficient to attribute an observed lung cancer to the occupational exposure.
An assessment of international studies on lung cancer incidences with uranium miners showed that with reference to age at exposure and age at cancer incidence, even a total exposure of only 40 WLM can be sufficient to be regarded causative. Such a dose could also be obtained by work exclusively during the mine's later years, while the recognition was so far granted only for work during the mine's early years. At exposures of 150 WLM and higher, an observed lung cancer can be attributed to the work in the uranium mines, practically independent of the exposure history. [Jacobi1992]
A specific situation is given for the workers employed in the final stage of the uranium mills. Since they handle the concentrated final product, their main risk results from inhalation of contaminated dust. For these workers, the most severe hazards result from the chemical toxicity of the uranium, causing kidney function deterioration.