Asbestosis in long-term employees of an Ontario asbestos-cement factory

Our plain-English summary of Asbestosis in long-term employees of an Ontario asbestos-cement factory, by M.M. Finkelstein (The American Review of Respiratory Disease, 1982).

The study

• Author: M.M. Finkelstein
• Journal: The American Review of Respiratory Disease
• Published: 1982;125(5):496-501
• Cited by: 24 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. 000671).

Abstract

We studied the development of compensable (certified) asbestosis among the 201 workers at an asbestos-cement factory who were first exposed to asbestos dust prior to 1980 and who had been employed at least 15 yr. By July 1980, 39% of the production workers and 20% of the maintenance workers had developed a compensable chest disability; the "latent interval" generally exceeded 20 yr. Workers with asbestosis were found to have markedly elevated mortality rates with deaths caused by malignancies and respiratory disease being primarily responsible. We combined the limited air sampling data available with individual work histories to calculate 18-yr cumulative fiber exposures. The cumulative probability of certification was related to the cumulative exposures and the exposure-response relationship was found to be sigmoidal in form.

In plain English

This study followed 201 men at an Ontario asbestos-cement factory who were hired between 1948 and the end of 1959 and worked there at least 15 years. The pipe plant used chrysotile and crocidolite asbestos with silica and cement. The board plant used only chrysotile. The outcome was asbestosis certified as a compensable disability. By July 1, 1980, 61 of 157 production workers (39%) and 9 of 44 maintenance workers (20%) had been certified, mostly 22 to 28 years after first exposure. Using estimated exposures for production workers, the probability of certification by 32 years after first exposure ranged from 0.1 (10%) below 50 fiber-years/ml to 0.9 at 200 to 249 fiber-years/ml, an S-shaped relationship. Among the 61 certified production workers, 24 died against 5.1 expected from Ontario rates, including 12 cancer deaths against 1.3 expected. The authors said the exposure estimates were probably accurate only to within a factor of 3 to 5, and that excluding shorter-term workers could bias the results. They concluded that at lower exposures the main risk is likely cancer rather than asbestosis.

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 study of long-term factory workers. It used life-table analysis of certification for asbestosis in relation to estimated cumulative fiber exposure, and compared mortality among certified men with Ontario population rates.
• Who was studied: 201 men at an Ontario asbestos-cement factory (opened 1948) who had been exposed to asbestos dust in the pipe or board shops for at least 1 year before 1961 and had been employed at least 15 years. There were 157 production workers and 44 maintenance workers. Certification was followed to July 1, 1980, and mortality to October 1, 1980.
• Exposure: Asbestos-cement pipe production used chrysotile and crocidolite asbestos plus silica and cement. Asbestos-cement board production (1955 to 1970) used only chrysotile. Exposure was estimated as cumulative fiber exposure (fiber-years/ml) in the first 18 years from first exposure. These estimates were built from 1969/1970 personal membrane filter sampling, extrapolated back to 1948, and matched to individual job histories. Exposures were assigned for production workers only.
• Main results:
  • By July 1, 1980, 61 of the 157 production workers (39%) and 9 of the 44 maintenance workers (20%) had developed certified asbestosis.
  • By the maximal follow-up of 32 years from first exposure, the cumulative probability of certification was 68% for men with 15 or more years in dust exposure, 37% for 11 to 14 years, 13% for 6 to 10 years, and 28% for 5 years or less. The authors noted that small numbers in the shorter categories allow considerable statistical fluctuation.
  • Only 2 men were certified before the twentieth year from first exposure. Most certifications were made between 22 and 28 years after first exposure.
  • Among production workers, the average incidence rate of certified asbestosis increased steadily with increasing 18-year cumulative exposure. Per 100 person-years at risk it was 0.5 in the 0 to 49 fiber-years/ml group, 3.4 at 50 to 99, 6.5 at 100 to 149, 7.9 at 150 to 199, and 14.3 at 200 to 249.
  • Among production workers, the cumulative probability of certified asbestosis by the end of 32 years from first exposure ranged from 0.1 (10%) among men with less than 50 fiber-years/ml to 0.9 among men in the 200 to 249 fiber-years/ml category. Standard errors ranged from 0.07 to 0.15.
  • The exposure-response relationship was sigmoidal (S-shaped) and was fit by a log-normal curve.
  • Extrapolating along the log-normal curve, the authors estimated that accumulating 10 fiber-years/ml in the 18 years from first exposure would carry a 1% risk of certified asbestosis by the end of 32 years.
  • Among the 61 certified production workers (251 man-years of observation), there were 24 deaths from all causes against 5.1 expected (observed to expected ratio 4.7).
  • In the same 61 certified men there were 12 deaths from all malignancies against 1.3 expected (ratio 9.2). There were also 2 deaths from peritoneal mesothelioma, and 5 deaths from nonmalignant respiratory diseases against 0.3 expected.
• The authors' conclusion: The authors concluded that at lower exposures the major risk is likely to be cancer rather than asbestosis. They held that morbidity studies like this one should be only a secondary line of evidence when setting exposure standards. They also considered it probable that a linear extrapolation from high exposures would overestimate the risk of certified asbestosis at low exposures.
• Limitations the authors state:
  • The exposure estimates were crude extrapolations and were probably accurate only to within a factor of about 3 to 5.
  • Large peak exposures in the early years, from work practices and equipment breakdowns, could not be accurately assessed.
  • Exposures could not be assigned to maintenance workers, so the exposure-response analysis covered production workers only.
  • Selection bias was possible because workers with less than 15 years of employment were excluded. The authors said this could affect risk estimates at low to moderate exposures.
  • Small numbers of men in each exposure category caused considerable statistical uncertainty in the 32-year probabilities.
  • Certified asbestosis is a medico-legal end point rather than a biological one. The comparability of Ontario certification criteria with those of other jurisdictions could not be assessed.
  • The exposure was to mixed dust: at autopsy many of the men showed silicosis as well as asbestosis. The certifying committee called the condition mixed-dust pneumoconiosis.
  • The results are difficult to apply directly to risks under current, much lower exposure conditions.

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, Air Sampling, Cumulative Exposure.

Related studies

• Mortality among long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1983)
• 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)
• Radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer in Ontario asbestos-cement workers — M.M. Finkelstein (1997)
• Long-term follow-up mortality study of petroleum refinery and chemical plant employees — S.P. Tsai, E.L. Gilstrap, et al. (1996)
• Decreased lung function in long-term asbestos cement workers: a cross-sectional study — C.G. Ohlson, T. Rydman, et al. (1984)

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