Question 3
What is the risk associated with the presence of asbestos at concentration levels found in the general environmental air?
Answer:
Asbestos fibres in the general environmental air have been present long before manís exploitation of the mineral. This phenomenon is due to the natural erosion from geological formations quite common throughout the world, and the total amount of asbestos emitted from natural sources is much greater than that emitted from industrial sources.
In general, the ambient air concentrations rarely exceed 0.001 f/cc.
At these low levels, the risk is undetectably low, indeed much lower than other risks, such as natural background radiation. Such a low risk has been labelled: "acceptable" by the WHO, or "not significant", by the Ontario Royal Commission on Asbestos or "further control not justified", by the Royal Society, London.
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Question 4 >>
References for Question 3:
Churg A (1986). American Review of Respiratory Disease, 134 (1):125-127.
Study comparing health effects in residents of chrysotile mining towns, where levels are from 200 to 500 times higher than in most North American cities, to those seen in urban residents. In spite of higher levels in these mining towns, no evidence of higher asbestos-related diseases were found. The author concludes: "These observations should provide reassurance that exposure to chrysotile asbestos from urban air or in public buildings will not produce detectable disease".
This is in agreement with other reports on residents of chrysotile mining towns in Québec, which have consistently failed to demonstrate excess respiratory disease incidence. These are:
McDonald AD, and McDonald JC (1980). Cancer 46(7): 1650-1656.
Siemiatycki J. (1982). Health effects on the general population (mortality in the general population in asbestos mining areas). Proceedings, World Symposium on Asbestos, Montreal, 25-27 May, pp.337-348.
Pampalon R, Siemiatycki J, et Blanchet M, (1982). Pollution environnementale par l'amiante et santé publique au Québec. Union Médicale du Canada 111(5): 475-489.
McDonald JC, (1985). Health implications of environmental exposure to asbestos. Environmental Health Perspectives 62:319-328.
Report of the Royal Commission on Matters of Health and Safety Arising from the Use of Asbestos in Ontario (1984). Eds. JS Dupré, JF Mustard, RJ Uffen. Published by the Ontario Ministry of the Attorney General 2:666.
"Considering all of the above data together, we conclude that asbestos fibre concentrations in the ambient air are extremely low. Counts of fibres longer than 5 microns taken by electron microscope are often less than 0.001 f/cc. If we consider the fibres that would be seen by an optical microscope, it is extremely rate in Ontario to have concentrations greater than 0.001 f/cc. The recent Ontario data suggest that fibre levels are lowest where population density is lowest, although the earlier Ontario data did not reveal this relationship. In Chapter 9 we conclude that the health risks presented to building occupants from exposure to 0.001 optically visible fibres per cubic centimetre is not significant. It follows that the fibre levels discussed in this section present a clearly insignificant health risk. We see no reason to worry about the health effects of the prevalent level of asbestos fibres in the outdoor air in Ontario".
