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Epidemiological studies of many groups of miners, of various ores, have shown that exposure to radon daughters is associated with increased lung cancer risk. These results, together with surveys of indoor radon levels, suggest that indoor exposure might present a hazard for the general population. However, the magnitude of risk at the comparatively low levels found indoors is uncertain, since the exposure of mining groups, on which risk estimates are based, is in general higher. Surveys of radon gas in British coalmines have shown levels of a similar order of magnitude to those indoors, and it therefore appeared that coalminers might be a suitable occupational group in which to study the effects of low-level exposure to radon daughters. The present study group consists of 19418 male industrial coalmine workers who attended either or both of two medical surveys carried out at 10 British collieries during the 1950s and early 1960s. Deaths in this group up to 31 December 1989 were notified by the Office of Population Censuses and Surveys. Cumulative exposures to radon and thoron daughters acquired during working time were calculated for a subgroup of 14956 men using data from two sources: a set of 146 measurements of daughter levels made at the 10 collieries during the 1970s, and extensive information on time worked underground and on the surface, gathered as part of the British National Coal Board's Pneumoconiosis Field Research. An overlapping subgroup of 14145 men were categorized by smoking habit. Death rates for two causes - lung cancer and stomach cancer - were tabulated by colliery, calendar time period, age, smoking category, and lagged cumulative exposure to radon or thoron daughters. Relationships between death rates and exposure were investigated by Poisson regression analysis. In a series of matched case-referent studies, relationships between exposure and mortality from these two causes of death, and eight others, were analysed by conditional logistic regression. External comparisons of mortality were made for lung cancer and all-causes only; exposure-response was not examined. |
