Airborne Asbestos Health Assessment Update
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Recent data from population studies strengthened the association of asbestos with disease. Lung cancer and mesothelioma are the most important asbestos-related causes of death. The data suggest that the excess risk of lung cancer from asbestos exposure is proportional to cumulative exposure (duration X intensity) and underlying risk in the absence of exposure. Risk of death from mesothelioma appears proportional to cumulative exposure in a given period. Animal studies confirm the human epidemiological results. All major asbestos varieties produce lung cancer and mesothelioma, with only limited differences in carcinogenic potency. One can extrapolate the risks of asbestos cancers from occupational exposures, although the uncertainty is approximately tenfold or greater. Calculations of asbestos unit risk values are uncertain and based on subjective estimates because of the following limitations in data: (1) extrapolation from high occupational levels to much lower ambient levels; (2) the uncertainty of mass-to-fiber conversion; (3) statistical uncertainties; (4) various biases and confounding aspects of medical data; and very importantly, (5) nonrepresentative exposure estimates.