MORTALITY IN URANIUM MINERS IN WEST BOHEMIA - A LONG-TERM COHORT STUDY

A cohort of 4320 uranium miners in West Bohemia who started work at th e mines during 1948 to 1959 and worked there for at least four years w ere followed up to the end of 1990 to determine cause specific mortali ty risks in relation to exposures in the mines. The miners had experie nced high radon exposures, on average 219 working level months during their uranium mining careers, for which detailed measurements were ava ilable. They had also been exposed to high arsenic levels in one of th e two major mines, and to dust. New follow up methods, not previously used for occupational cohorts in Czechoslovakia, were utilised. By the end of follow up 2415 (56%) of the cohort were known to have died. Ov erall mortality was significantly raised compared with that in the gen eral population (relative risk (RR) = 1.56, 95% confidence interval (9 5% CI) 1.50-1.63), with significantly raised risks of lung cancer (RR = 5.08, 95% CI 4.71-5.47), accidents (RR = 1.59, 95% CI 1.34-1.87), ho micide (RR = 5.57, 95% CI 2.66-10.21), mental disorders (RR = 5.18, 95 % CI 2.83-8.70), cirrhosis (RR = 1.51, 95% CI 1.16-1.94), and nonrheum atic circulatory diseases (RR = 1.16, 95% CI 1.08-1.25). The relative risk of lung cancer was greatest four to 14 years after entry to the m ines. Relative risks for homicide and accidents were raised up to 25 y ears from entry but not after this. Substantial significantly raised r isks at 15 to 24 years after entry occurred for cirrhosis, non-rheumat ic circulatory diseases, and pneumonia and other respiratory infection s. Sizeable significantly raised risks at 25 and more years after entr y, but not earlier, were present for mental disorders, tuberculosis, a nd nonmalignant non-infectious respiratory conditions. No specific cau ses showed risks significantly related to age at entry to mining. Risk of lung cancer was significantly positively related to radon exposure , estimated arsenic exposure, and duration of work in the mines, but n o other cause was significantly positively related to these variables. The raised risk of lung cancer in uranium miners, which is well estab lished, is related aetiologically to radon exposure, and in the presen t cohort it may also in part have been due to exposure to arsenic. The raised risks of accidents, tuberculosis, and noninfectious respirator y diseases have also been seen in other uranium mining cohorts, and ar e likely to reflect the dangerous and dusty working conditions and the confined spaces in which work occurred. The cirrhosis and homicide de aths probably relate to the lifestyle associated with mining. The rais ed risk of circulatory diseases does not seem to be related to radon o r arsenic exposure; its causes are unclear. The use of multiple follow up methods was found to be critical to correct ascertainment of morta lity in the cohort.