Ambient air concentrations of asbestos fibres were measured during the period 20 June to 12 August, 1980 at three locations; Danville, Asbestos and Wottenville in the eastern townships of Quebec. Measurements were made with low-volume samplers and measurement periods ranged from 3 to 13 days. Fibre counts were made by means of electron microscopy. Our results indicate that overall fibre concentrations are related to atmospheric stability and to the direction of the prevailing wind with respect to the source of emission. Fibre concentrations are then related to total dust content of the ambient air for the town of Asbestos. Spatial variations of mortality are in turn related to the variations in the concentration of ambient air dust particles.
Mortality and workers' compensation patterns were studied among 1,064 Ontario asbestos insulation workers. A proportional mortality analysis of 153 asbestos worker deaths found increased mortality from malignant diseases (65 deaths observed; 35.1 expected), cancers of the lungs and pleura (32 deaths observed; 11.5 expected), peritoneal mesothelioma (4 deaths), and respiratory diseases (14 deaths observed; 7.9 expected). Despite the publicity given to asbestos-associated diseases, dependents of many men potentially eligible for workers compensation awards have not received pensions because claims were not filed. These findings suggest that much occupationally related disease is not being recognized in Ontario.
Workers' compensation systems attempt to evaluate claims for occupational disease on an individual basis using the best guidelines available to them. This may be difficult when there is more than one risk factor associated with the outcome, such as asbestos and cigarette smoking, and the occupational exposures is not clearly responsible for the disease. Apportionment is an approach that involves an assessment of the relative contribution of work-related exposures to the risk of the disease or to the final impairment that arises for the disease. This article discusses the concept of apportionment and applies it to asbestos-associated disease. Lung cancer is not subject to a simple tradeoff between asbestos exposure and smoking because of the powerful biological interaction between the two exposures. Among nonsmokers, lung cancer is sufficiently rare that an association with asbestos can be assumed if exposure has occurred. Available data suggest that asbestos exposure almost invariably contributes to risk among smokers to the extent that a relationship to work can be presumed. Thus, comparisons of magnitude of risk between smokers and nonsmokers are irrelevant for this purpose. Indicators of sufficient exposure to cause lung cancer are useful for purposes of establishing eligibility and screening claims. These may include a chest film classified by the ILO system as 1/0 or greater (although 0/1 does not rule out an association) or a history of exposure roughly equal to or greater than 40 fibres/cm3 x y. (In Germany, 25 fibres/cm3 x y is used.) The mere presence of pleural plaques is not sufficient. Mesothelioma is almost always associated with asbestos exposure and the association should be considered presumed until proven otherwise in the individual case. These are situations in which only risk of a disease is apportioned because the impairment would be the same given the disease whatever the cause. Asbestosis, if the diagnosis is correct, is by definition an occupational disease unless there is some source of massive environmental exposure; it is always presumed to be work-related unless proven otherwise. Chronic obstructive airways disease (COAD) accompanies asbestosis but may also occur in the context of minimal parenchymal fibrosis and may contribute to accelerated loss of pulmonary function. In some patients, particularly those with smoking-induced emphysema, this may contribute significantly to functional impairment. An exposure history of 10 fibre x years is suggested as the minimum associated with a demonstrable effect on impairment, given available data. Equity issues associated with apportionment include the different criteria that must be applied to different disorders for apportionment to work, the management of future risk (eg. risk of lung cancer for those who have asbestosis), and the narrow range in which apportionment is really useful in asbestos-associated disorders. Apportionment, attractive as it may be as an approach to the adjudication of asbestos-related disease, is difficult to apply in practice. Even so, these models may serve as a general guide to the assessment of asbestos-related disease outcomes for purposes of compensation.
Cancer mortality of men with diagnosed asbestosis was studied in Finland. Of the 174 men registered as having asbestosis, 56 had died before 1977, whereas the number of expected deaths based on the Finnish male population was only 23.4. The respective figures for lung cancer were 19 observed and 2.1 expected. The mean age of these 19 lung cancer patients was 57.8 yr, and lung cancer was the cause of death (underlying cause) in 35% of all diseased men with asbestosis. The proportion of lung cancer mortality from all deaths among Finnish men 55-64 yr old is 10.8%, which is clearly lower than that among the men with asbestosis. No excess of other malignancies was found in Finland among workers with asbestosis.
Primary prevention carried out today can reduce the disease incidence in the future decades. The present disease panorama is the consequence of past asbestos exposure mainly before the 1970s. The peak incidence of asbestos-induced diseases will be reached around 2010 in Finland. The number of asbestos-related premature deaths is at present annually about 150 which exceeds the figure of fatal work accidents. Asbestos-related cancer will increase still for 15-20 years and reach its maximum, about 300 cases, in 2010, and will start to decrease after that. More than 20,000 asbestos-exposed workers have participated in the medical screening and follow-up. The termination of exposure, antismoking campaigns, improved diagnostics and careful attention to compensation issues, as well as other potentials for prevention, were the central issue of the Asbestos Program of the Finnish Institute of Occupational Health. An important objective of research work is to improve early diagnostics, and thereby treatment prospects, in case of asbestos-induced cancers.