Cancer mortality in chrysotile mining and milling: exposure-response.

New material was presented from pending publications arising from the follow-up to 1988 of the Quebec cohort of over 10,000 chrysotile miners and millers born 1891-1920. In reviewing these and previous findings, the following conclusions were drawn; they are supported, insofar as this is possible, by the only other relevant information, that from Balangero, in Northern Italy. There is strong evidence that the risk of lung cancer as a result of exposure to chrysotile at concentrations of less than 15 million particles per cubic foot is vanishingly small. At higher concentrations, the relative risk of lung cancer is elevated, but less so in smokers of 20 or more cigarettes a day than in others. The magnitude of this risk cannot be evaluated with any certainty, but this is unimportant as these higher concentrations (above about 50 f ml-1) are well outside the range of experience nowadays. There is no evidence that the risk of laryngeal cancer or of stomach cancer are adversely affected by exposure to chrysotile. Nor is there evidence of increased risks of other abdominal malignancies or of kidney cancer among chrysotile miners and millers. The risk of mesothelioma in chrysotile miners and millers is very low compared with the risks in populations exposed to amphiboles or to mixtures of fibres including even small proportions of amphiboles.