The quantitative risks of mesothelioma and lung cancer in relation to asbestos exposure

Mortality reports on asbestos exposed cohorts which gave information on exp osure levels from which las a minimum) a cohort average cumulative exposure could be estimated were reviewed. At exposure levels seen in occupational cohorts it is concluded that the exposure specific risk of mesothelioma fro m the three principal commercial asbestos types is broadly in the ratio 1:1 00:500 for chrysotile, amosite and crocidolite respectively, For lung cance r the conclusions are less clear cut, Cohorts exposed only to crocidolite o r amosite record similar exposure specific risk levels (around 5% excess lu ng cancer per f/ml.yr); but chrysotile exposed cohorts show a less consiste nt picture, with a clear discrepancy between the mortality experience of a cohort of chrysotile textile workers in Carolina and the Quebec miners coho rt. Taking account of the excess risk recorded by cohorts with mixed fibre exposures (generally<1%), the Carolina experience looks uptypically high, I t is suggested that a best estimate lung cancer risk for chrysotile alone w ould be 0.1%, with a highest reasonable estimate of 0.5%. The risk differen tial between chrysotile and the two amphibole fibres for lung cancer is thu s between 1:10 and 1:50, Examination of the inter-study dose response relationship for the amphibole fibres suggests a non-linear relationship for all three cancer endpoints ( pleural and peritoneal mesotheliomas. and lung cancer), The peritoneal meso thelioma risk is proportional to the square of cumulative exposure, lung ca ncer risk lies between a linear and square relationship and pleural mesothe lioma seems to rise less than linearly with cumulative dose. Although these non-linear relationships provide a best fit to the data, statistical and o ther uncertainties mean that a linear relationship remains arguable for ple ural and lung tumours (but not for peritoneal tumours, Based on these considerations, and a discussion of the associated uncertain ties, a series of quantified risk summary statements for different levels o f cumulative exposure are presented. Crown Copyright (C) 2000 Published by Elsevier Science Ltd on behalf of British Occupational Hygiene Society. All rights reserved.