Occupational and geographical factors in the epidemiology of malignant mesothelioma.

In most industrialised countries mortality from malignant mesothelioma has risen steeply since about 1950 and is likely to go on doing so well into the next century. This increase, which has lagged behind the level of asbestos use by some 30 or more years, is most evident in men but less clear in women. Amphibole asbestos fibre types, crocidolite in particular, carry the greatest risk and chrysotile the least. Studies in chrysotile miners and millers, in whom the overall frequency of mesothelioma is low suggest the risk is mainly determined by the presence of contamination with amphibole fibres in the tremolite series. There is wide variation in mesothelioma incidence geographically and occupationally. Regions with the highest rates are those where crocidolite is mined; within countries, dockyard areas are most affected, probably because of amphibole use for insulation in naval ships. Occupations at high risk, apart from crocidolite miners and millers, include shipyard and insulation workers and those employed in construction trades. Data on exposure-response are scanty although occupational cohort studies suggest that risk is related to both duration and intensity of exposure. More specific confirmation of an exposure-response relationship has been obtained from lung fibre analysis in a limited number of case-referent studies.