A cohort study in southern China of tin miners exposed to radon and radon decay products

Abstract

Several studies of underground miners have demonstrated that exposure to radioactive radon gas (more precisely, 222Rn and its short-lived decay products) at levels historically found in mines increases the risk of lung cancer. Because of small numbers of lung cancers, previous studies have had limited power to evaluate temporal and other characteristics of patterns of risk. Herein we report on a historical cohort study of male employees of the Yunnan Tin Corporation in southern China. The cohort consists of 17,143 workers with 175,143 person-years of observation and 981 lung cancer events. Eighty percent of the workers were employed underground and exposed to radon. The excess relative risk increased linearly with exposure, rising 0.6% per working level month (95% confidence interval = 0.4-0.8). In the mines, workers were also exposed to arsenic-containing dusts. Adjustment for arsenic exposure, a known lung carcinogen, reduced the effect of radon exposure to 0.2% per working level month (95% confidence interval = 0.1-0.2). The excess relative risk/working level month declined significantly with attained age and with radon exposure rate as measured by the cumulative working level month divided by duration of exposure. It also declined significantly with years from last exposure and with time since exposure, but these declines were consistent only after adjustment for arsenic exposure. In this cohort, 41% of the underground workers were first exposed when < 15 y old; however, lung cancer risk did not vary consistently with age at first radon exposure. A joint analysis of radon exposure and smoking status (smoker vs. nonsmoker) rejected both an additive and a multiplicative association; the relationship was consistent with an intermediate association.