Biological indicators of chrysotile exposure.

Chrysotile asbestos is retained in lung tissue, where it may be used as a marker of exposure. Studies include analysis of sputum and bronchoalveolar lavage fluid, but principally lung parenchyma from autopsy or surgically resected specimens. Asbestos bodies form on chrysotile fibres but are generally not a good indicator of human exposure to chrysotile because of their greater probability of formation on amphiboles. Chrysotile fibre analyses in lung have advantages and limitations. Chrysotile concentration is related to the level of environmental and occupational exposure, but in the latter situation owing to deposition, fibre alteration and clearance cumulative exposure and interval between end-exposure and death clearly affect results. Autopsy case series are biased toward increased proportions of asbestos-related diseases as compared to epidemiological cohort data. Analytical problems include potential contamination by chrysotile at autopsy, from fixatives, from post-fixative processing and in the analytical laboratory itself. These may have greatest effect in studies of individuals with low exposure, for tissue other than lung, and for short chrysotile fibres. Selection of control subjects should be contemporaneous with that of cases, and control subjects should fully reflect the hospital population at the time of case death. Limited data are available on fibre analysis in pleural tissue. More are needed. Issues requiring attention include avoidance of contamination, selection of controls, and sample site selection (parietal pleura, or tumour or plaque). For mesothelioma, two case-control studies of lung fibre burden show the principal relationship to be with long amphiboles, but some methodological problems exist. Lung cancer shows no such fibre-type differences. Asbestosis seems to be associated with long-fibre chrysotile and tremolite in one study and short fibres in others. Overall, lung retained dose is a useful indicator of chrysotile exposure if used cautiously in inference, and is very useful in the evaluation of historical exposures and industrial hygiene data in epidemiological studies.