The Royal Commission on Asbestos finds that the health hazard posed by asbestos depends on the quantity of asbestos fibres an individual breathes and on the dimensions of those fibres.
The three members of the Royal Commission on Asbestos were J. Stefan Dupré, professor of political science at the University of Toronto, who acted as chairman; Dr. J. Fraser Mustard, professor of pathology at McMaster University and President of the Canadian Institute for Advanced Research; and, Robert J. Uffen, professor of engineering and geophysics at Queen's University.
The Commission's three-volume Report, running over 900 pages, features an exhaustive analysis of the health effects of asbestos. This analysis is based in part on the scientific literature and in part on sworn testimony given by an international who's who of asbestos experts during more than fifty days of formal Commission hearings. The expert witnesses underwent examination and cross-examination by representatives of industry, labour and government.
Of the asbestos fibres that can be inhaled, the most hazardous asbestos fibres are no longer than 5 or perhaps 8 microns, and thinner than 1.5 microns. A micron is a millionth of a metre. Thinner fibres can more easily penetrate into the lung tissue. While shorter fibres can be surrounded by protective cells in the lungs, longer fibres cannot be surrounded. Thus they retain the potential to cause cancer while they remain in the lungs, which may be for decades.
The Commission further concludes that the three types of asbestos that are of major commercial importance differ significantly in the dimension of their fibres. Crocidolite asbestos and amosite asbestos are more hazardous than chrysotile asbestos because fibres of crocidolite and amosite are more likely to conform to the most hazardous dimensions. They are also more likely to become airborne and hence to be respirable. The resulting hazard leads the Commission to recommend that the use of crocidolite and amosite asbestos be prohibited in Ontario. The Commission's conclusions that health risks differ among fibre types is shared by occupational health agencies in Ontario and the United Kingdom.
The Commission reaches a conclusion that breaks new ground when it states that the type of industrial process in which any given type of asbestos is used also influences the dimensions of the fibres released into the air, and thus the hazard faced by workers. The manufacture of asbestos brakelinings, which involves drilling and grinding of chrysotile asbestos is much less likely to generate fibres of hazardous dimensions than textile manufacturing, which involves spinning and weaving. The health experience in textile plants has been so adverse that the Commission recommends that textile spinning and weaving be prohibited in Ontario.
For a given fibre type and a given industrial process the Commission concludes that the risk of disease depends upon the quantity of fibre breathed. While asbestosis, a form of lung fibrosis, has been common among workers exposed to high asbestos concentrations in the past, the Commission believes that under the regulations it has recommended, asbestosis will become a disease of the past. In the case of lung cancer and mesothelioma, a cancer of the lining of the lung or abdomen, the relationship between the quantity of fibres breathed and the risk of disease cannot be stated with scientific certainty. According to the Commission, however, prudence dictates the assumption that the risk of disease is proportional to the extent of fibre exposure. This implies that any exposure involves some risk of disease, although at very low exposure levels, such as in the outdoor air, this risk is insignificant.
For years there has been evidence that the risk of lung cancer for a smoker who breathes asbestos is greater than the sum of the risk from each activity alone. The Commission accepts this evidence as establishing that smoking may multiply the risk of lung cancer for an asbestos-exposed worker by a factor of 5. It concludes that "smoking coupled with asbestos work is like pouring gasoline on a fire."
In addition to concluding that the risk of disease differs among the major asbestos fibre types and between different industrial processes, the Commission concludes that mesothelioma is caused differentially by the different fibre types. Mesothelioma is most likely to result from crocidolite exposure, has a strong association with amosite exposure, and has a weak association with chrysotile exposure.
The primary evidence regarding the dangers of breathing asbestos fibres arises from disease caused by the large quantity of asbestos breathed by asbestos workers over the three decades during and after World War II. These high exposures have left a tragic legacy of disease and death. The exposure of the general public to asbestos fibres is thousands of times less than these exposures. There is no evidence of significant health risks to the general public from exposure to asbestos in the ambient air and in buildings unless the person is breathing in the immediate vicinity of loose asbestos that is being disturbed. The health risk posed by asbestos is therefore a workplace health risk rather than a general public health risk.
The Commission links the health hazards of asbestos to inhalation, not swallowing. Neither biological nor epidemiological evidence indicates that swallowing asbestos creates a health risk. In addition, the fibres found in water, often numbering millions per litre, are very short. The Commission concludes that concern about asbestos in drinking water, beverages and food is not justified.