G. W. Gibbs

Mortality in the Chrysotile Asbestos Mines and Mills of Quebec

Of 11,788 persons bom between 1891 and 1920 employed in the Quebec asbestos mining industry, 88.4% were traced. Of these 2,457 (23.6%) had died. Exposure indexes for each worker were calculated from job dust levels and duration of employment. The overall mortality was lower than expected for the population of Quebec but in the highest dust category, comprising 5% of the cohort, the age-standardized rate was 20% higher than in the other groups. Respiratory, cardiovascular, and malignant disease in equal proportions accounted for the excess. There were 101 deaths from respiratory cancer including three from malignant mesothelioma, an estimated excess of about 15 deaths. The difference in rates for respiratory cancer between those maximally and minimally exposed was fivefold and, though perhaps exaggerated, was apparently determined by accumulated dust exposure and duration of employment.

The health of chrysotile asbestos mine and mill workers of Quebec.

The results of studies of respiratory symptoms and function, roentgenographic changes, and mortality in relation to dust exposure in the Quebec chrysotile industry, which has employed some 28,000 workers, are brought together and their implications for control examined. Breathlessness on exercise, diminished inspiratory capacity, parenchymal and pleural changes, and respiratory disease mortality were related to dust exposure and to each other. Respiratory cancer was also related to dust exposure. The overall excess of deaths from respiratory cancers, including five with malignant mesothelioma, was at most 50% above expectation, based on age-specific rates for Quebec and the mining region. If safety standards are set, they should be based on epidemiological evidence. From these data for the chrysotile producing industry of Quebec, a resonable figure, based on a 1% risk of acquiring clinically significant disease, would lie between 2 to 4 million particles per cubic foot, calculated for a working life of 50...

Magnetic lung measurements in relation to occupational exposure in asbestos miners and millers of Quebec

Abstract Fe3O4 particles (ferrimagnetic) are usually attached to asbestos fibers (nonferrimagnetic) in the chrysotile asbestos mining and milling industries; therefore, a magnetic measurement of Fe3O4 in the lungs of workers in these industries could help determine the amount of asbestos which has been inhaled and retained in their lungs. As a first assessment of this method, magnetic measurements were made of Fe3O4 in the lungs of 115 miners and millers in Quebec. These measurements at an industrial site were found to be feasible and practical; however, the amount of Fe3O4 seen in the lungs of those with welding exposure was large enough to mask the Fe3O4 contributed by asbestos, and this subgroup was considered separately. For the remainder (nonwelders), the amount of Fe3O4 was plotted against a total dust exposure index (asbestos and other dust) estimated for each worker. Although the correlation between these quantities was not high, it was statistically significant at the 1% level. Because retained asbestos is likely to increase with increasing exposure to total dust, this correlation suggests that a magnetic lung measurement of a chrysotile miner or a miller does reflect, to some extent, the amount of asbestos in his lung. There was considerable scatter in the data, partly due to individual variations in deposition and clearance, to which this method is sensitive. When the data of only the nonsmokers were plotted, the amount of Fe3O4 was greater than for the total group of nonwelders. This is consistent with previous findings that less dust is deeply deposited in the lungs of smokers, due to constriction of small airways.

Dust-fiber relationships in the Quebec chrysotile industry.

Epidemiological studies of Quebec chrysotile miners and millers have related various indices of health to dust exposure, as measured with the midget impinges The interpretation of these relationships in terms of fiber necessitates the conversion of midget impinger (particle + fiber) counts to membrane filter (fiber) equivalents. An investigation in which 87 side-by-side midget impinger-membrane filter samples were taken at five mines and mills showed that the correlation was poor and no single conversion factor was justified. Until more detailed information on the relationships between midget impinger and membrane filter counts can be obtained, it is recommended that safety standards, at least in this industry, should continue to be based on dust counts, for which there is considerable epidemiological support, rather than on fiber counts, for which there is no direct evidence.

Etiology of pleural calcification: a study of Quebec chrysotile asbestos miners and millers.

A review of 15,689 chest radiographs of Quebec chrysotile miners and millers, representing the latest film prior to November 1, 1966, for all such persons ever x-rayed, identified 206 men with pleural calcification. Of these, 198 had worked in the Thetford Mines area, 6 at Asbestos, and 2 at St. Remi de Tingwick; 2.5%, 0.08%, and 1% of the films from these areas, respectively. A series of case-control studies revealed that pleural calcification was concentrated in men employed at a small group of mines in Thetford Mines and occurred more often among miners and maintenance personnel than among millers. Calcification was not related to past history of illness or injury, place of residence, or employment in other industries. The distribution of pleural calcification in this Quebec industry suggests that it is related to some characteristic of airborne dust or mineral closely associated with the chrysotile that is encountered during mining in Thetford Mines but not in other mining areas. Possible minerals include mica, talc, and breunnerite.

Physical Parameters of Airborne Asbestos Fibres in Various Work Environments—Preliminary Findings

The results of a pilot investigation to describe the physical parameters, length, aspect ratio, mass and shape of airborne fibres in a variety of industries producing processing and handling chrysotile, amosite and crocidolite are described. Samples of airborne dust were collected on nucleopore membrane filters and examined by scanning electron microscopy. The diameters and lengths of airborne fibres collected during the dumping of raw amosite at an asbestos products plant were greater than those of fibres collected during the application of amosite insulation. Chrysotile fibres collected in the carding area of an asbestos textile plant also tended to have smaller diameters than fibres collected in the dryer and bagging areas of an asbestos mill. The measurements of fibre dimensions indicate that the degree of protection afforded a worker by optical counts using the membrane filter technique is likely to depend on variety of asbestos and stage of processing. Preliminary results are not in conflict with experimental data suggesting that asbestosis might be related to the mass of airborne dust and primary malignant mesothelial tumors to exposure to fibres in a specific range of fibre diameter and length.

The Organic Content of Canadian Chrysotile

The organic content of commercially milled Canadian chrysotile was found to range from 0.5 to 20.0 mg per 100 gm, depending on the source and grade of fiber. These yields exceeded those from field specimens in all cases except one, and indicated contamination by mining and milling processes. An elemental analysis showed the organic extracts to contain carbon (81.94 to 86.03%), hydrogen (11.47 to 13.14%), and minor amounts of other elements. Infrared and gas chromatographic examination confirmed n-alkanes to be the major constituents. The concentration of polycyclic aromatic hydrocarbons in milled fiber was considered too low to play an important role in carcinogenesis. The importance and sources of n-alkanes and total organic contamination are discussed.

The organic geochemistry of chrysotile asbestos from the Eastern Townships, Quebec

Abstract Extractions of selected specimens of chrysotile from the Eastern Townships of Quebec yielded small quantities of organic material. Infrared and gas Chromatographic studies indicate the presence of predominantly n-alkanes. These were probably derived by distillation from Precambrian sediments although a magmatic origin is not completely ruled out. Sample collection, handling, methods of analysis and problems associated with such studies of chrysotile are discussed.

Some Problems Associated with the Storage of Asbestos in Polyethylene Bags

Abstract Samples of milled Canadian chrysotile asbestos, collected and stored in polyethylene bags, were found on extraction with benzene to yield oils in substantially greater quantity and with at least one different constituent from those collected and stored in glass jars. The constituent isolated from the asbestos collected in certain polyethylene bags is yellow and shows a strong absorption band at 421 mμ. Extracts of polyethylene bags do not contain this compound, but the compound is formed on the introduction of asbestos into the bag. The relevance to sample collection for subsequent organic analysis and to animal experiments for tests of carcinogenic activity of samples of asbestos and other substances is discussed.

Collection and storage of samples in organic geochemistry

Abstract Recent studies have shown that serious organic contamination of asbestos samples occurred by collection and storage in polyethylene bags. The implications of this and other contamination problems in organic geochemistry are discussed.