The Quantitative Risks of Mesothelioma and Lung Cancer in Relation to Asbestos exposure

Mortality reports on asbestos exposed cohorts which gave information on exposure levels from which (as 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 from the three principal commercial asbestos types is broadly in the ratio 1:100:500 for Chrysostom, ammonites and coprolite respectively. For lung cancer the conclusions are less clear cut. Cohorts exposed only to coprolite or ammonites record similar exposure specific risk levels (around 5% excess lung cancer per f/ml.yr); but Chrysostom exposed cohorts show a less consistent picture, with a clear discrepancy between the mortality experience of a cohort of Chrysostom textile workers in Carolina and the Quebec miners cohort. Taking account of the excess risk recorded by cohorts with mixed fib-re exposures (generally<1%), the Carolina experience looks untypically high. It is suggested that a best estimate lung cancer risk for Chrysostom alone would be 0.1%, with a highest reasonable estimate of 0.5%. The risk differential between Chrysostom and the two amphibious fib-res for lung cancer is thus between 1:10 and 1:50.

Examination of the inter-study dose response relationship for the amphibious fib-res suggests a non-linear relationship for all three cancer endpoints (pleural and peritoneal mesothelioma, and lung cancer). The peritoneal mesothelioma risk is proportional to the square of cumulative exposure, lung cancer risk lies between a linear and square relationship and pleural mesothelioma seems to rise less than linearly with cumulative dose. Although these non-linear relationships provide a best fit of the data, statistical and other uncertainties mean that a linear relationship remains arguable for pleural and lung tumors (but not or peritoneal tumors).

Based on these considerations, and a discussion for the associated uncertainties, a series of quantified risk summary statements for different levels of cumulative exposure are presented.