Question 4
Asbestos in the workplace: Can asbestos be handled without undue risk to the workers? What is the risk to workers handling chrysotile asbestos at today's controlled exposure levels?
Answer:
Lung fibrosis, lung cancer and mesothelioma have been definitely correlated with exposure to airborne respirable fibres of asbestos. This correlation has been ascertained for both intensity (dose) and duration of exposure. The correlation is especially strong for mesothelioma and exposure to the amphibole varieties of asbestos.
With regard to intensity (or exposure levels) of exposure, this aspect has been examined more recently, especially with regard to the very low exposure levels to chrysotile only.
Results of recently reported cohorts surveys, where the health experience at very low exposure levels to chrysotile only was examined, support the following statements:
- There are low levels of exposure to chrysotile asbestos in the workplace, where no excess morbidity (disease) and mortality have been detected.
- There is no undue risk to workers handling chrysotile asbestos, at today's controlled exposure levels (~ 1 f/cc).
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References for Question 4:
Berry G, and Newhouse ML (1983). British Journal of Industrial Medicine 40(1):1-7
A mortality (1942-1980) study carried out in a factory producing friction materials, using almost exclusively chrysotile. Compared with national death rates, there were no detectable excess deaths due to lung cancer, gastrointestinal cancer, or other cancers. The exposure levels were low, with only 5% of men accumulating 100 fibre-years/ml. The authors state: "The experience at this factory over a 40-year period showed that chrysotile asbestos was processed with no detectable excess mortality".
Newhouse ML, and Sullivan KR (1989). British Journal of Industrial Medicine 46(3):176-179.
The 1983 study (referred to above), has been extended by seven years. The authors confirm that there was no excess of deaths from lung cancer or other asbestos related tumours, or from chronic respiratory disease. After 1950, hygienic control was progressively improved at this factory, and from 1970, levels of asbestos have not exceeded 0.5-1.0 f/ml. The authors conclude: "It is concluded that with good environmental control, chrysotile asbestos may be used in manufacture without causing excess mortality".
Thomas HF, Benjamin IT, Elwood PC, and Sweetnam PM (1982). British Journal of Industrial Medicine 39(3):273-276.
In an asbestos-cement factory using chrysotile only, 1,970 workers were traced, and their mortality experience was examined. There was no appreciably raised standardized mortality ration (SMR) for the causes of death investigated, including all causes, all neoplasms, cancer of the lung and pleura, and cancers of the gastrointestinal tract. The authors indicate: "Thus the general results of this mortality survey suggest that the population of the chrysotile asbestos-cement factory studied are not at any excess risk in terms of total mortality, all cancer mortality, cancers of the lung and the bronchus, or gastrointestinal cancers".
McDonald JC, Liddell DK, Dufresne A, and McDonald AD (1993). British Journal of Industrial Medicine 50:1073-1081.
This study is undoubtedly the largest cohort of asbestos workers ever studied and followed for the longest period is that of the miners and millers of the chrysotile mines in Québec. The cohort, which was established in 1966, comprises some 11,000 workers born between 1891-1920 and has been followed ever since. Optimal use was made of all available dust measurements to evaluate for each cohort member his exposure in terms of duration, intensity and timing. Findings on mortality have been published on five occasions, and the most recent report provides an update of the results of analysis of mortality for the period 1976-1988 inclusive. One of the central findings of this update is that over several narrow categories of exposure up to 300 mpcf.y, the SMRs for lung cancer fluctuated around unity, with no evidence of trend and increased steeply above that exposure level. Still more recently, the same authors confirmed their original findings with a mortality update up to 1992: Liddell FDK, McDonald AD and McDonald JC. Ann. Occup. Hyg. 41:13-35 (1997).
