Czech studies of lung cancer risk from radon

Abstract

Epidemiological evidence of lung cancer risk from radon is based mainly on studies of men employed underground in mines. One such study among uranium miners was established in 1970 by Josef Sevc. During the 1980s, another occupational study followed. In 1989, Sevc designed a new large cohort study among inhabitants exposed to high radon concentrations in homes. The paper reports recent results from extended follow-up of the two occupational cohorts and results from the residential study covering the period 1960–1999. A total of 915 and 216 cases of lung cancer were observed in the occupational and residential studies, respectively. These numbers not only allow evaluation of the risk from low and high exposures, but also the effect of temporal modifying factors and a comparison of the risk from occupational and residential exposure. Results of recent follow-up confirmed previous findings that excess relative risk from radon depends linearly on cumulative exposure experienced more than five years previously. In the occupational cohort, this relationship is strongly modified by time since exposure, age at exposure, and exposure rate. The effect from exposure more than 25 years ago was less than 7% of the risk related to exposure 5–14 years ago. Similar temporal patterns were observed in the residential cohort. The effect from unit exposure decreased to 29% after 20 years when compared to a period 5–19 years. In addition, the risk of lung cancer in the latter study is analysed using individual information on smoking habits. The estimate of the excess relative risk per standard unit concentration of radon gas (100 Bq/m³) is in line with findings from other residential studies. Adjustment for smoking did not change the estimate, however the risk among those who had never smoked was found higher by factor of nearly 2. In terms of detriment, the risk from concentrations of radon gas 1 kBq/m³ experienced 5–34 years previously in houses is approximately equal to the risk in mines with exposure rate 1 WLM/y and lasting for the same period.