Mortality in the chrysotile asbestos mines and mills of Quebec

Our plain-English summary of Mortality in the chrysotile asbestos mines and mills of Quebec, by J.C. McDonald, A.D. McDonald, G.W. Gibbs, et al (Archives of Environmental Health, 1971).

The study

• Authors: J.C. McDonald, A.D. McDonald, G.W. Gibbs, J. Siemiatycki, C.E. Rossiter
• Journal: Archives of Environmental Health
• Published: 1971;22(6):677-86
• Cited by: 99 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. 001367).

Abstract

Of 11,788 persons born 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.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This study followed 11,788 people, born 1891 to 1920, employed at least a month by Quebec asbestos mining companies, which ran mines, mills and a small asbestos products factory. Of these, 10,421 (88.4%) were traced; by November 1, 1966, 2,457 had died. Dust indexes combined job time with estimated dust levels (approximate before 1949). From 1950 to 1966, traced men alive in 1950 had 1,674 deaths, versus 1,824 expected from Quebec rates. In the highest dust category (5% of the cohort), age-standardized mortality was about 20% higher than in the rest. There were 101 respiratory cancer deaths, three from malignant mesothelioma. The authors put the lung cancer excess between zero and 30 deaths, most probably ten to 20. Lung cancer rates per 1,000 men were 6.7 with the least dust and shortest employment, 35.3 with the most. The authors judged the true difference closer to threefold than fivefold, citing tracing and autopsy biases. They wrote that this strongly suggests chrysotile is less likely than forms such as crocidolite to cause lung and pleural cancer, or that insulation and processing workers face additional factors.

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: Cohort mortality study of past and current employees, using company work histories, a job-based dust exposure index, and death records
• Who was studied: 11,788 persons (11,323 men, 465 women) born 1891 to 1920 inclusive, employed one calendar month or more by asbestos mining companies in the Eastern Townships region of Quebec. These companies' operations included mines, mills and a small factory making mixed asbestos products. Vital status was determined as of Nov 1, 1966. 10,421 (88.4%) were traced and 2,457 had died.
• Exposure: Chrysotile asbestos dust in mines, mills, and a small products factory. A dust index was built for each worker by summing years in each job multiplied by the estimated average dust concentration (millions of particles per cubic foot, mpcf).
• Main results:
  • Men traced and alive in 1950, followed 1950 to 1966 (with adjustment for men who started work after 1950): 1,674 deaths observed versus 1,824 expected from Quebec death rates
  • Men in the highest dust-index category (5% of the cohort): age-standardized all-cause mortality about 20% higher than the other groups
  • The excess in the highest dust category was accounted for by malignant, circulatory and respiratory diseases in about equal proportions
  • After review of death certificates and autopsy information, there were 101 deaths from cancer of the bronchus, trachea or lung (100 men, one woman). These included 97 bronchus or lung, 1 trachea, and 3 malignant mesothelial tumors.
  • Men: 94 certified lung cancer deaths observed versus 91 expected from provincial rates, or 61 expected from mining-region rates. The authors put the excess somewhere between zero and 30, most probably 10 to 20 deaths.
  • Lung cancer equivalent average death rate per 1,000 men: 6.7 for the lowest amount and duration of exposure versus 35.3 for the highest, a fivefold difference
  • In the parametric analysis, lung cancer rates in the four lowest dust-index levels were significantly different from the highest exposure group
  • The authors judged the true lung cancer difference between maximally and minimally exposed men to be probably closer to threefold than fivefold
  • Of 28 deaths coded as pneumoconiosis, 23 were asbestosis (plus 4 silicosis and 1 anthracosis). The greatest excess was in the highest dust group employed 10 to 29 years.
  • Three mesothelioma deaths among nearly 2,500 deaths in the cohort. The authors contrasted this with US insulation workers and a London asbestos factory in other studies.
  • Women: 440 of 465 traced, 45 had died, one from lung cancer. The authors did not analyze women further.
• The authors' conclusion: The authors wrote that their findings strongly suggest either that chrysotile is less likely to cause malignant disease of the lung and pleura than other forms of asbestos such as crocidolite, or that insulation and processing workers are exposed to additional factors
• Limitations the authors state:
  • Dust exposure estimates before 1949 were only approximate
  • Records of at least 560 persons in one company had been destroyed
  • No direct smoking data for ex-employees
  • Tracing was poorest for men employed less than a year, making their low lung cancer rate hard to accept
  • Autopsy rates rose with exposure, likely exaggerating the lung cancer difference by an unknown amount
  • The comparison of mesothelioma figures with other studies is not entirely comparable

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

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

Related studies

• The health of chrysotile asbestos mine and mill workers of Quebec — J.C. McDonald, M.R. Becklake, et al. (1974)
• Lung function profiles in the chrysotile asbestos mines and mills of Quebec — M.R. Becklake, G. Fournier-Massey, et al. (1976)
• Rheumatic complaints and pulmonary response to chrysotile dust inhalation in the mines and mills of Quebec — F.M. White, J. Swift, et al. (1974)
• Long-term mortality experience of chrysotile miners and millers in Thetford Mines, Quebec — W.J. Nicholson, I.J. Selikoff, et al. (1979)
• Late progression of radiographic changes in Canari chrysotile mine and mill exworkers — J.R. Viallat, C. Boutin, et al. (1983)
• The 1891-1920 birth cohort of Quebec chrysotile miners and millers: mortality 1976-88 — J.C. McDonald, F.D. Liddell, et al. (1993)

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