Mortality among long-term employees of an Ontario asbestos-cement factory

Our plain-English summary of Mortality among long-term employees of an Ontario asbestos-cement factory, by M.M. Finkelstein (British Journal of Industrial Medicine, 1983).

The study

• Author: M.M. Finkelstein
• Journal: British Journal of Industrial Medicine
• Published: 1983;40(2):138-44
• Cited by: 57 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000607).

Abstract

Mortality was studied among a group of 328 employees of an Ontario asbestos-cement factory who had been hired before 1960 and who had been employed for a minimum of nine years. The group of 87 men who had worked in the rock wool/fibre glass operations, or who had been otherwise minimally exposed to asbestos, had mortality rates similar to those of the general Ontario population, while the group of asbestos-exposed employees had all-cause mortality rates double those of the Ontario population, mortality rates due to malignancies five times higher than expected, and deaths attributed to lung cancer eight times more frequent than expected. According to the best evidence available, 10 of 58 deaths among the production workers were due to malignant mesothelioma and 20 to lung cancer. The men dying of mesothelioma were younger than the men dying of lung cancer with mean ages at death of 51 and 64 years respectively. An exposure model was constructed on the basis of the available air sampling data, and individual exposure histories were calculated. These exposure histories were used to investigate the exposure-response relationships for asbestos-associated malignancies.

In plain English

This study followed deaths among long-term workers at an Ontario asbestos-cement factory. The author studied men hired before 1960 who had worked there at least nine years: 186 production workers, 55 maintenance workers, and 87 men in rock wool/fibre glass work or otherwise minimally exposed to asbestos, followed until 31 October 1980. The pipe process used both chrysotile and crocidolite. The minimally exposed men died at the rate expected for Ontario men. Among production workers, 20 to 33 years after first exposure, there were 50 deaths against 23.4 expected and 17 lung cancer deaths against 2.0 expected. Of 58 deaths among production workers, 10 were from malignant mesothelioma (5 pleural, 5 peritoneal) and 20 from lung cancer. One maintenance worker also died of pleural mesothelioma. Mesothelioma deaths occurred at a mean age of 51 and lung cancer deaths at 64. Mesothelioma rates were related to estimated cumulative exposure, but lung cancer rates did not rise steadily with it. The author noted small numbers and crude exposure estimates, and concluded that workers at this factory exposed to historical dust conditions had increased mortality from respiratory and malignant diseases.

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: Retrospective cohort mortality study. Deaths were compared with those expected from Ontario population rates by the man-years method, and there were internal comparisons by estimated cumulative exposure.
• Who was studied: 339 men hired before 1960 who had worked at least nine years at an Ontario asbestos-cement factory. 11 who could not be classified were excluded, leaving 186 production workers, 55 maintenance workers and 87 men in rock wool/fibre glass operations or otherwise minimally exposed to asbestos. They were followed up until 31 October 1980.
• Exposure: Asbestos-cement manufacture. The pipe process generally used both chrysotile and crocidolite in each batch, and the board operation used only chrysotile. Individual cumulative exposures for production workers were estimated from air sampling data, for example 40, 20 and 0.2 fibres/ml for willows operators in 1949, 1969 and 1979.
• Main results:
  • The minimally exposed (control) workers had mortality equal to that expected for the general male population of Ontario. They had 14 deaths observed against 13.3 expected at 20 to 33 years from first exposure.
  • The asbestos-exposed employees had all-cause mortality double that of the Ontario population, malignancy mortality five times higher than expected, and lung cancer deaths eight times more frequent than expected. Among production workers at 20 to 33 years from first exposure there were 50 deaths from all causes against 23.4 expected (ratio 2.1). Among production plus maintenance workers there were 61 against 30.6 (ratio 2.0).
  • Production workers, 20 to 33 years from first exposure, comparison based on death certificate codings: 17 lung cancer deaths observed against 2.0 expected (observed/expected 8.5; the author gives the SMR as 850).
  • Production workers, 20 to 33 years from first exposure: 29 deaths from all malignancies observed against 5.7 expected (observed/expected 5.1).
  • Using best-evidence classification, 10 of the 58 deaths among production workers were from malignant mesothelioma (5 pleural, 5 peritoneal), a proportional mortality of 17%. One maintenance worker also died of pleural mesothelioma.
  • All of the men who died of mesothelioma had been exposed to both chrysotile and crocidolite in the pipe plant.
  • The 10 production workers with mesothelioma had a mean age at death of 51 years, and none was over 60.
  • 20 of the 58 deaths among production workers were from lung cancer, a proportional mortality of 34%. These men had a mean age at death of 64 years (range 55 to 78).
  • Mesothelioma death rates were related to estimated cumulative exposure. Crude rates per 1000 man-years at 20 to 33 years from first exposure were 2.5 (1 death) in group A (8 to 69 fibre-years/ml), 4.6 (2 deaths) in group B (69 to 121) and 11.9 (6 deaths) in group C (122 to 420). The author described the relation as compatible with a linear function through the origin, but with large uncertainties.
  • Lung cancer rates did not rise steadily with estimated cumulative exposure. Group C, the highest-exposure group, had the lowest lung cancer rate, and the author was unable to determine the exposure-response relation for lung cancer.
  • Of the 241 asbestos-exposed production and maintenance workers, 71 (29%) had been certified as disabled by asbestosis.
• The authors' conclusion: The author concluded that workers at this asbestos-cement factory, exposed to historical dust conditions (described as probably not atypical of the industry), experienced increased mortality from respiratory and malignant diseases.
• Limitations the authors state:
  • The numbers of men were so small that only large increases in risk could be detected as statistically significant.
  • The exposure estimates were crude. Cumulative exposures were judged accurate only to within a factor of three or five.
  • The high relative risks are partly due to selecting only long-term employees, which excluded shorter-term workers who are presumably at lower risk.
  • Untraced men were assumed to be alive, which could lead to underestimated standardised mortality ratios.
  • Smoking histories were fragmentary, and smoking may have confounded the lung cancer findings.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos-Cement, Lung Cancer, Malignant Mesothelioma, Mesothelioma, Air Sampling.

Related studies

• Asbestosis in long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1982)
• Mortality among employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1984)
• Mortality among employees of an Ontario factory manufacturing insulation materials from amosite asbestos — M.M. Finkelstein (1989)
• Long-term follow-up mortality study of petroleum refinery and chemical plant employees — S.P. Tsai, E.L. Gilstrap, et al. (1996)
• Radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer in Ontario asbestos-cement workers — M.M. Finkelstein (1997)
• Mortality rates among employees potentially exposed to chrysotile asbestos at two automotive parts factories — M.M. Finkelstein (1989)

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