Mesotheliomas, minerals, and man-made mineral fibres.

Editorial Mesotheliomas, minerals, and man-made mineral fibres In spite of much research and frequent international meetings no clear advice can yet be given on the prevention of mesotheliomas. After the original observations of Wagner et al,' the evidence from South Africa has been consistent with t'he view that only crocidolite causes meso-thelioma. Although conditions in the African chrysotile and amosite mines and mills have been sufficiently dusty to produce the other asbestos-related diseases, mesotheliomas have been almost exclusively confined to the crocidolite mines and mills and their environs.2 Anthophyllite, commercially the least important form of asbestos, was mined in Finland with a lot of environmental dust pollution and although a high proportion of the population developed pleural plaques no mesotheliomas have occurred.3 The main source of chrysotile (other than Russia) is Canada and a few more mesotheliomas have been reported in the mining area than would be expected for thie low background level of the disease.4 However , during the 1939-45 war South African crocidolite was processed at some of these mines and also some of the Canadian chrysotile is contaminated with tremolite. Similar contamination occurs in Cyprus where the tremolite is used for stucco and whitewash. Mesotheliomas have occurred in Cyprus but strife has prevented a Full epidemiological investigation. However, in the Western consumer countries the situation is confused. Dust-induced meso-theliomas have an average latent interval of about 40 years, so that the cases recogniLsed since 1960 result from industrial conditions before and during the 1939-45 war. Records are scanty and memories are short, so reliable information as to dust levels or even the type of fibre used is h,ard to obtain. One of the most serious examples of mesothelioma induction is among gas mask workers in Britain and Canada. The civilian masks were made with filters containing chryso-tile and the military respirators with crocidolite (probably from South Africa although the specification was for Australian). Although many more civilian gas masks were made, all but one of the 100 or more cases have arisen among those who made the military gas masks. The one "civilian" case has not been fully investigated. A similar high incidence of mesothelioma has been reported by Selikoff and his colleagues arising from a dusty factory where amosite insulation material was made during the war.5 No chrysotile exposures with an exceptionally high risk of mesothelioma have been reported so far. Although more information will be …