Temporal patterns of exposure and nonmalignant pulmonary abnormality in Quebec chrysotile workers

Our plain-English summary of Temporal patterns of exposure and nonmalignant pulmonary abnormality in Quebec chrysotile workers, by R. Copes, D. Thomas, M.R. Becklake (Archives of Environmental Health, 1985).

The study

• Authors: R. Copes, D. Thomas, M.R. Becklake
• Journal: Archives of Environmental Health
• Published: 1985;40(2):80-7
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001221).

Abstract

Questionnaire, radiographic, and lung function information for 983 Quebec chrysotile workers at work in 1966 was used to develop five clinical response scales (i.e., parenchymal and pleural fibrosis, airflow limitation, chronic bronchitis, and airway reactivity). The relationship of the scales to variables describing temporal patterns of exposure was studied, taking into account cumulative exposure, age, and smoking. All response scales related to variables containing only time information, and in all cases temporal patterns of exposure influenced exposure response relationships. For pulmonary fibrosis, the strongest relationships were to cumulative exposure; for pleural fibrosis to exposure peaks and residence time of dust in the lung; for airway reactivity to early and recent exposure; and for airflow limitation and chronic bronchitis to smoking and to dust level and load over time. These results add to the gathering evidence that exposures to environments containing airborne asbestos may result in airway abnormalities.

In plain English

This study reanalyzed questionnaire, chest X-ray and lung function data collected earlier for 983 male workers aged 21 to 65 employed by mining companies in Quebec's Asbestos and Thetford Mines areas in 1966. The authors built five scores (parenchymal lung fibrosis, pleural fibrosis, airflow limitation, chronic bronchitis, airway reactivity). They tested whether the timing and pattern of each man's dust exposure explained these scores beyond cumulative exposure, age and smoking. For every score, the strongest crude correlations were with time-only variables such as years since first exposure. Cumulative exposure was the best predictor only for parenchymal fibrosis. Pleural fibrosis related more to how long dust had been in the lung and to heavy or peak exposures. Smoking had the strongest effect on chronic bronchitis, and airway reactivity related to early and recent dust levels. The variables explained little of the differences between workers, and timing added at most 2.5%. The authors concluded that different exposure patterns appear to matter for different outcomes, including airway abnormalities. They noted that many associations were tested and that dust was measured as particles, not fibers.

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 previously collected data, using factor analysis to build response scales and regression analysis to relate them to exposure variables
• Who was studied: 983 of 1,015 men in an age-weighted sample of male workers aged 21-65 employed on October 31, 1966 by mining companies in the Asbestos and Thetford Mines areas of Quebec
• Exposure: Chrysotile mine and mill dust. Annual exposures were estimated from work histories and dust levels measured in million particles per cubic foot. The measures were cumulative exposure plus 11 variables describing the timing, peaks and duration of exposure.
• Main results:
  • For all five response scales, the highest crude correlations were with variables containing only time information. For example, time since first exposure correlated .35 with parenchymal fibrosis and .25 with pleural fibrosis.
  • For none of the scales did the temporal pattern of exposure add more than 2.5% to the explained variation. The explanatory variables accounted for only a small amount of the variability.
  • Parenchymal fibrosis was the only scale for which cumulative exposure was the best predictor in the complete model.
  • For pleural fibrosis, the time dust had been resident in the lung and dust inhaled during heavy or peak exposures were more closely related to outcome than cumulative exposure.
  • For airflow limitation, both smoking and dust effects were strong. Exposures received early in a worker's career appeared more important than recent ones.
  • For chronic bronchitis, smoking had the strongest effect. Dust exposure had an effect that was smaller but of the same general order.
  • For airway reactivity, both early dust levels (exposure in the first 5 years) and recent dust levels were positively related, but peak exposures were not.
• The authors' conclusion: The authors concluded that temporal patterns of exposure may influence exposure-response relationships for parenchymal and pleural fibrosis and also for airway abnormalities, with different exposure patterns appearing to matter for different outcomes.
• Limitations the authors state:
  • Many associations were examined, so some may be due to chance, and the exposure variables were highly correlated with each other.
  • Errors in exposure assessment, especially in dust concentration, may bias the estimated exposure-response relationships.
  • Dust was counted as particles, many possibly rock dust. For bronchitis and possibly airflow limitation, the relationship may reflect total dust load rather than asbestos fibers.
  • The findings may not apply to present-day workers, whose exposures and smoking habits differ.

Topics

Medical terms in this study, explained in our Lexicon: Quebec Chrysotile, Fibrosis, Cumulative Exposure, Pulmonary Fibrosis.

Related studies

• The health of chrysotile asbestos mine and mill workers of Quebec — J.C. McDonald, M.R. Becklake, et al. (1974)
• Rheumatic complaints and pulmonary response to chrysotile dust inhalation in the mines and mills of Quebec — F.M. White, J. Swift, et al. (1974)
• Lung function profiles in the chrysotile asbestos mines and mills of Quebec — M.R. Becklake, G. Fournier-Massey, et al. (1976)
• Clinical measurement in Quebec chrysotile miners: use for future protection of workers — M.R. Becklake (1979)
• Asbestos, asbestosis, and lung cancer: observations in Quebec chrysotile workers — B.W. Case, A. Dufresne (1997)
• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)

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