Carbonate-hosted asbestos occurrences in South Australia: review of geology and implications for mesothelioma
Stratigraphic units with the potential for carbonate-hosted asbestos account for <3% of the land area of South Australia. Known asbestos occurrences are small, low grade and commonly weathered. The main mode of occurrence is as cross-fibre and slip-fibre veins of asbestiform magnesio-riebeckite (AMR) in metasomatised dolomites, and fibrous tremolite associated with talc mineralisation in the Adelaide Geosyncline. Small occurrences of chrysotile asbestos are hosted by dolomites in the Hutchison Group in the eastern Gawler Craton. Hyperspectral mapping could be used to locate additional asbestos mineralisation. Disturbance of natural asbestos-bearing materials in South Australia has been through mining, agriculture and natural weathering processes. Release of respirable asbestos fibres from rocks and soils is feasible and could potentially account for some cases of mesothelioma in South Australia. Only a very small portion of the population is considered at risk of being exposed to fibres from disturbance of natural asbestos fibres. Persons considered most at risk of potential exposure include: rural workers and communities residing close to areas of intense agricultural disturbance of asbestos-bearing soils; construction workers involved in large-scale earthworks projects in areas underlain by asbestos-bearing rocks and soils; and quarry workers who unwittingly disturb asbestos-bearing materials. Populations regularly exposed to amphibole fibres for a long period of time are at greatest risk with respect to mesothelioma. Epidemiological studies suggest that the risks of mesothelioma for those exposed to chrysotile fibres alone are negligible. Toxicological studies are required to better understand the potential health risks associated with AMR. Current medical reporting of asbestos in South Australia does not include detailed residential or occupational histories required to undertake a statistically significant study of the possible health effects of asbestos from natural sources. Government authorities and private enterprises need to take geological factors into account to reduce the likelihood of unplanned disturbance of natural asbestos-bearing materials.
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