Enclosure 10 - Dust Exposure and Radiographic Appearance in Quebec Asbestos Workers

Our plain-English summary of Enclosure 10 - Dust Exposure and Radiographic Appearance in Quebec Asbestos Workers, by C.E. Rossiter, L.J. Bristol, P.H. Cartier, et al.

The study

• Authors: C.E. Rossiter, L.J. Bristol, P.H. Cartier, G.W. Gibbs, J.C. Gilson, T.R. Grainger, J. Siemiatycki, G.K. Sluis-Cremer, J.C. McDonald
• Published: McGill University
• Type of article: Conference paper
• Our copy: from Johns-Manville's own medical library. The article is still under copyright, so we describe it here rather than post it.

In plain English

This conference report came from a McGill University study of Quebec chrysotile asbestos miners and millers. With the full analysis unfinished, the authors compared dust exposure with X-ray findings only for employees and former employees of one Thetford Mines company. Job histories were converted into three exposure measures: years employed, total dust exposure, and total dust weighted by physical effort. Each worker's latest chest X-ray was read using the UICC/Cincinnati classification. Within five-year birth groups, the profusion of small irregular opacities was related to all three dust measures and also to age. Small rounded opacities were related mainly to total dust, and the other two measures added little. Irregularity of the cardiac (heart) border was related most to effort-weighted dust, a conclusion the authors said remained in some doubt. Pleural thickening and pleural calcification did not vary significantly with dust within birth groups, but the authors summarized both as related to age. Pleural plaques were seen in 45 of 282 people born before 1921 at this company (16.0%), compared with 10% for the rest of Thetford Mines.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Cross-sectional analysis of chest radiographs against individual dust exposure indices, including analysis within five-year birth cohorts, drawn from a larger ongoing study of the Quebec asbestos industry; conference report
• Who was studied: Employees and ex-employees of one asbestos mining company in Thetford Mines, Quebec, Canada. This was the first established company and was still in production. The wider study covered 27,000 workers, and the latest radiographs of 15,689 workers were read. Some pleural findings were also given for the Asbestos area and the rest of Thetford Mines.
• Exposure: Chrysotile asbestos dust in the mines and mills, without exposure to other asbestos or to other dusts found in manufacturing plants. Exposure was measured by three indices: years employed in the industry, total dust exposure based on dust assessments for each job, and total dust weighted by the physical effort of each job.
• Main results:
  • Across the company's workers, the closest correlation was between the profusion of irregular small opacities and years of exposure (r=0.437).
  • Within birth cohorts, all three exposure indices contributed about equally to the relation with irregular small opacities (multiple correlation coefficient 0.200, P<0.001).
  • Profusion of irregular small opacities depended on age as well as on dust exposure.
  • For small rounded opacities, total dust gave the greatest contribution to the relation, and the other two indices added little.
  • For irregularity of the cardiac border, dust weighted by physical effort contributed most to the relation. There was significant variation between cohorts, so the authors considered this conclusion still in some doubt.
  • In the within-cohort analysis, neither pleural thickening nor pleural calcification varied significantly with dust.
  • In the authors' summary, pleural thickening and pleural calcification were related to age but not to any dust index in the cohort analysis.
  • Pleural calcification was read by one or more of the six readers on 0.8% of radiographs from the Asbestos area, compared with 5.4% from Thetford Mines.
  • Among people born before 1921, pleural plaques were seen in 45 of 282 (16.0%) at this company, compared with 10% for the rest of Thetford Mines.
• The authors' conclusion: The authors concluded that the profusion of small irregular opacities was related to all three dust indices, with age itself an important factor. Small rounded opacities were related to total dust. Irregularity of the cardiac border was related to dust weighted by effort. Pleural thickening and calcification were related to age but not to any dust index. Pleural plaques were concentrated in those who had worked in or near this mine.
• Limitations the authors state:
  • The full analysis was not yet complete, so the report covered only one company.
  • In the analysis across all workers, the effects of age and years of exposure were confounded. This led to the within-cohort analysis.

Topics

Medical terms in this study, explained in our Lexicon: Quebec Chrysotile, Thetford Mines, Chest X-Ray, UICC, Pleural Thickening, Pleural Calcification, Pleural Plaques.

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