Naturally occurring asbestos in eastern Australia: a review of geological occurrence, disturbance and mesothelioma risk. Marc Hendrickx ENVIRONMENTAL GEOLOGY Volume 57, Number 4 (2009), 909-926, DOI: 10.1007/s00254-008-1370-5 http://www.springerlink.com/content/cg74621r55613pn1/
Carbonate-hosted asbestos occurrences in South Australia: review of geology and implications for mesothelioma. Marc Hendrickx Australian Journal of Earth Sciences, Volume 56, Number 5, July 2009 , pp. 639-654(16) http://www.ingentaconnect.com/content/tandf/aes/2009/00000056/00000005/art00001
This project aims to investigate the geology of asbestos in eastern Australia (Queensland, New South Wales, Victoria and Tasmania) and South Australia with a view to assessing the potential health implications for mesothelioma, a rare form of cancer caused by asbestos exposure.
Potential asbestos-bearing rocks account for about 0.2% of the land area of eastern Australia and about 2.5% of the land area of South Australia. In the eastern states the main mode of occurrence is in serpentinised ophiolite complexes along the boundaries of major tectonic domains that contain sporadic deposits of cross fibre and slip fibre veins of chrysotile asbestos. Smaller deposits of chrysotile and amphibole asbestos occur in metamorphosed mafic and ultramafic rocks associated with the Macquarie Volcanic Arc in central New South Wales. Amphibole asbestos is also known from Proterozoic and Palaeozoic amphibolite and from Devonian basalt. In South Australia asbestos is hosted by carbonates, mainly dolomites in the Hutchison Group in the eastern Gawler Craton, and metasomatised dolomite and limestone in the Adelaide Geosyncline. The main asbestos minerals in South Australia are asbestiform magnesio-riebeckite (AMR) and fibrous tremolite in the Adelaide Geosyncline and chrysotile in the Gawler Craton.
Natural asbestos-bearing materials in eastern and southern Australia have been disturbed by mining, road construction, agriculture and forestry, urban development and natural weathering processes.
International epidemiological studies indicate that populations regularly exposed to amphibole fibres from natural sources for a long period of time are at greatest risk with respect to mesothelioma. All reported associations between asbestos exposure from disturbance of natural asbestos-bearing materials and mesothelioma are due to varieties of amphibole asbestos; no cases involving chrysotile asbestos alone have been repoted.
Only a very small portion of the population of eastern and South Australia is considered at risk of being exposed to fibres from disturbance of natural asbestosoccurrences. While amphibole asbestos disturbed by human activities and natural weathering has the potential to account for some deaths from mesothelioma the overall incidence rate for those exposed to asbestos from natural sources is estimated to be less than 1 in 1,000,000. Persons considered most at risk of potential exposure include: rural workers and communities in towns 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.
Government authorities need to take geological factors into account to reduce the likelihood of unplanned disturbance of natural asbestos-bearing materials, particularly those containing asbestiform amphiboles. Increased awareness of the location of known and potential occurrences, and of the health risks should help reduce the incidence of accidental asbestos exposure.
Toxicological studies are required to better understand the potential health risks associated with AMR. Epidemiological studies suggest the risks of mesothelioma for those exposed to chrysotile fibres alone from natural sources are negligible.
Based on knowledge of the geology of asbestos in Australia and medical studies that have established NOA as a source of exposure elsewhere, the risks to the general population in eastern and South Australia from exposure to fibres from natural sources is negligible. Only those outcrops close to human settlements that have undergone significant long term anthropogenic disturbance through mining, quarrying, excavation or repeated disturbance through ploughing are considered a risk of releasing fibres in quantities large enough to be considered a significant health risk. In eastern and South Australia, such outcrops are generally in areas of low population density. Rocks containing asbestos that have not been disturbed are probably not a significant source of asbestos fibre. For such outcrops there is no mechanism that can release individual fibres in sufficient quantities and size that would make them bio-available. A key factor is that if asbestos is not disturbed and fibres are not released then it is not a health risk.
The overall message about the risks of NOA in eastern and South Australia can therefore be summed up as “No need for alarm”.
Government authorities should take similar precautions to reduce the risks of exposure for all forms of asbestos regardless of the source. In areas where potential asbestos-bearing rocks and soil occur, planning authorities need to seek additional geological and geotechnical advice to reduce the likelihood of unplanned disturbance of asbestos-bearing materials. With engineering controls in place there is a safe means of working in these environments.
The derivative geological maps and associate information produced in this thesis provide a means for non-geologists in planning positions in local, state and federal governments to properly manage development in areas of natural asbestos-bearing materials thereby avoiding future accidental disturbance of NOA.