Methodological problems in ecologic studies of the asbestos-cancer relationship

Abstract

Past researchers dealing with worker populations and, rarely, populations residing around sites where asbestos is mined or manufactured, have shown a relationship between such exposure and mesothelioma. These studies have dealt mainly with males, and have not replicated those findings in a couple of studies that asbestos increased risk of lung, stomach, and large bowel cancer. In order to extend the knowledge of the effects of asbestos further and to consider another type of exposure, residential, we examined the incidence of all sites of cancer, studied separately, in the asbestos-mining counties of Quebec, the first-ring counties surrounding them, the other rural counties, and the urban counties of Quebec. As have previous studies, we found higher risks of mesothelial tumors, and in addition, an added risk for cancer of the lip, salivary gland, and small instestine for males. The females showed higher risk for cancer of the pleura, lip, kidney, salivary gland, and melanoma. Risks increased in a dose-response fashion with an increase in proximity to the mines. We caution that these findings are limited by deriving from an ecological design, and that cancers appearing now are probably the result of a long latent period, during which time the kinds of exposures may have changed markedly because of changes in mining techniques and air pollution controls.