RADON-PROGENY EXPOSURE AND LUNG-CANCER RISK IN A COHORT OF NEWFOUNDLAND FLUORSPAR MINERS

Although radon is a well-established lung carcinogen, there are uncert ainties concerning the exposure-response relationship, whether exposur es in early life are particularly hazardous, and how smoking affects t he risks associated with radon exposure. A cohort study of the mortali ty experience of 1,743 underground fluorspar miners and 321 surface wo rkers from 1950 to 1984 reported previously has been extended to inclu de 6 additional years of follow-up (1985-1990). A statistically signif icant relationship was noted between radon-progeny exposure and risk o f lung cancer mortality. Our analysis found no effect for age at first exposure. Attained age was strongly predictive of excess relative ris k (ERR) per working level month (WLM) of radon exposure, falling from 0.025 for those aged less than 50 years to 0.002 for those 70 years or older. An inverse exposure-rate effect was also observed, wherein for equal total exposure, a high exposure rate (and short duration) is le ss harmful than a low exposure rate (and long duration). The ERR/WLM i ncreased from 0.0019 for exposures of less than 10 years to 0.0076 for exposures of 20 or more years. The analysis of time-since-exposure wi ndows revealed a greater ERR/WLM for exposures received in more recent periods, similar to the result for time since last exposure. Excess r elative risks per WLM were higher for current smokers than for nonsmok ers (never and former smokers). Analyses were consistent with a multip licative relationship between radon-progeny exposure and current smoki ng and the risk of lung cancer. The assessment of radon exposure and l ung cancer risk should incorporate the effects of exposure rate, time since exposure, smoking status and attained age. (C) 1998 by Radiation Research Society.