Clinical measurement in Quebec chrysotile miners: use for future protection of workers

Our plain-English summary of Clinical measurement in Quebec chrysotile miners: use for future protection of workers, by M.R. Becklake (Annals of the New York Academy of Sciences, 1979).

The study

• Author: M.R. Becklake
• Journal: Annals of the New York Academy of Sciences
• Published: 1979;330:23-9
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 004033).

Abstract

There is a relationship between dust exposure, on the one hand, and serious disease and death, on the other, in chrysotile asbestos mine and mill workers of Quebec. Studies in current working populations indicate that prevalence of abnormality increases with increasing exposure. However, the relationship is weak and offers only a partial explanation of between-subject variability. In addition, there is no certain way to detect or predict change. Because of the relative nonspecificity of the health measurements examined and their poor relationship to exposure, control should be based on environmental monitoring, with biologic monitoring considered in a complementary role. This leaves the clinician with the dilemma of how best to advise the worker in whom questionable changes have been detected. At present, there appears little doubt that the decision must remain essentially clinical, based, on one hand, on all available information about the man, his job, and the plant or mine in which he works, from which an estimate of likely outcome must be made, and, on the other hand, on the social and human factors concerned, including the fact that removal from exposure does not necessarily prevent the appearance of abnormality.

In plain English

This paper was the author's overview of clinical information (questionnaires, lung function tests and chest X-rays) from a 12-year research program on Quebec chrysotile mine and mill workers. It summarized published and forthcoming studies, mainly of non-cancer disease. Dust exposure was measured in million particles per cubic foot years (mpcf-y). Deaths attributed to pneumoconiosis were 28 times more frequent in men exposed above 600 mpcf-y than in men exposed below 100 mpcf-y. Among older men exposed above 800 mpcf-y, 34% had small irregular opacities on X-ray, 39% had pleural changes (Thetford area) and 43% reported breathlessness (dyspnea), so at least half showed no response according to these indicators. Abnormalities rose with exposure, but the relationships were weak. In a study of 86 former workers, parenchymal (lung tissue) changes occurred in about 12% and pleural changes in about 20% of men with substantial dust exposure before leaving. The author concluded that worker protection should rest on environmental dust monitoring, with medical monitoring as a complement. The author noted the findings may not apply to other fiber types or manufacturing.

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: Overview (review) by the author of clinical findings from a multidisciplinary research program's own prevalence and follow-up studies, published or forthcoming
• Who was studied: Quebec chrysotile mine and mill workers. They were drawn from a 1966 register of about 28,000 people who had worked in the industry since 1878. Studies included 1015 current workers examined in 1967-8, with 277 and 445 of them restudied; 267 men with X-rays spanning about 20 years; and 86 men who had left the industry.
• Exposure: Chrysotile asbestos dust in mining and milling. It was expressed as an accumulated index in million particles per cubic foot years (mpcf-y), based on particle counts rather than fiber counts.
• Main results:
  • Deaths attributed to pneumoconiosis were more frequent (relative risk x 28) in the group exposed to more than 600 mpcf-y than in the group exposed to less than 100 mpcf-y. This excludes asbestos-related cancer deaths.
  • In older men exposed to more than 800 mpcf-y, prevalence was 34% for small irregular opacities (1/0 or more), 39% for any pleural changes (Thetford area) and 43% for dyspnea.
  • At least half of the men in this highly exposed group showed no response according to these indicators. The author took this to imply differences between individuals in susceptibility.
  • Signs thought to reflect pulmonary fibrosis were more common in higher exposure groups. However, the exposure-response relationships were not strong.
  • In follow-up after 7-8 years, progression in any feature was more frequent in those who already had an abnormality in that feature. In some men lung function changes appeared before X-ray changes, and in others the reverse.
  • In 267 men with five X-rays spanning an average of 20 years, the status of the first film accounted for most of the variation in progression.
  • In a study of 86 men who had left the industry in the previous 10-15 years, parenchymal changes occurred in about 12% and pleural changes in about 20% of men with substantial exposure before leaving (average dust index 498 mpcf-y over an average of 20 years).
  • In current miners, an obstructive lung function profile was almost as frequent as a restrictive profile and was slightly more evidently related to dust exposure. The association of smoking with the obstructive profile was easily demonstrated.
• The authors' conclusion: The author concluded that, because the clinical measurements are nonspecific and poorly related to exposure, control should rest on environmental monitoring, with biologic (medical) monitoring complementary. Advice to individual workers with questionable changes must remain a clinical judgment.
• Limitations the authors state:
  • The exposure index did not distinguish exposure patterns: short, heavy exposures could be equated with lower, longer ones. The author also noted it was based on area rather than personal sampling.
  • Measuring exposure as particle counts rather than fiber counts may not be the most appropriate way to predict pulmonary fibrosis.
  • The findings come from chrysotile mining in Quebec and may not apply to other fiber types or exposure settings such as manufacturing.
  • The paper covers mainly non-cancer disease. The mortality findings exclude asbestos-related cancer.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Medical terms in this study, explained in our Lexicon: Quebec Chrysotile, Chrysotile.

Related studies

• Magnetic lung measurements of relation to occupational exposure in asbestos miners and millers of Quebec — D. Cohen, T.S. Crowther, et al. (1981)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: development from 1904 and mortality to 1992 — F.D. Liddell, A.D. McDonald, et al. (1997)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)
• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)
• The health of chrysotile asbestos mine and mill workers of Quebec — J.C. McDonald, M.R. Becklake, et al. (1974)
• A report on the health of asbestos, Quebec miners 1940 — M. Greenberg (2005)

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