Mortality among employees of an Ontario asbestos-cement factory

Our plain-English summary of Mortality among employees of an Ontario asbestos-cement factory, by M.M. Finkelstein (The American Review of Respiratory Disease, 1984).

The study

• Author: M.M. Finkelstein
• Journal: The American Review of Respiratory Disease
• Published: 1984;129(5):754-61
• Cited by: 69 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. 000534).

Abstract

Mortality among 535 asbestos-exposed and 205 nonexposed employees of an asbestos-cement factory was investigated. In the period beyond 20 yr from first exposure, the exposed workers had standardized mortality ratios of 175 for all causes of death, 370 for all malignancies, 480 for lung cancer, 240 for gastrointestinal cancers, and 17 deaths from mesothelioma; the factory control subjects had mortality rates similar to the general population. The cell-type distribution of the lung cancers was similar to that occurring in middle-aged smokers. Cumulative fiber exposures were calculated for the production workers, and mortality rates for the asbestos-associated malignancies were found to have significant trends with exposure. Exposure-related lung cancer risks were noted, with a large margin of uncertainty, to be similar to those observed in an American study of manmade mineral fiber workers.

In plain English

This cohort study looked at deaths among men who worked at least one year at an Ontario asbestos-cement factory and were hired before 1960. The factory used chrysotile and crocidolite asbestos to make pipe, and chrysotile alone to make board. Death rates for 535 asbestos-exposed workers and 205 unexposed or minimally exposed factory control subjects were compared with those of Ontario men. More than 20 years after first exposure, exposed workers had standardized mortality ratios of 175 for all causes, 370 for all malignancies, 480 for lung cancer and 240 for gastrointestinal cancers. The control subjects' death rates were similar to the general population's, except for more blood and lymphatic cancers than expected. The whole cohort had 21 mesothelioma deaths (12 pleural, 9 peritoneal), 17 of them among production workers. Among production workers, death rates from lung cancer, mesothelioma and gastrointestinal cancer showed statistically significant trends with estimated cumulative fiber exposure. The author noted three limits: the exposure estimates were accurate only to within a factor of 3 to 5, smoking could not be adjusted for, and the results should be generalized only with great caution.

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 comparing exposed workers with Ontario death rates (standardized mortality ratios) and comparing exposure groups within the cohort
• Who was studied: Men employed at least 1 year and hired before 1960 at an Ontario asbestos-cement factory that opened in 1948: 535 asbestos-exposed employees and 205 nonexposed factory control subjects. At 10 years from hire the cohort was 428 production workers, 107 maintenance workers and 205 control subjects (740 in total). Deaths were traced through a national mortality database to 1977 and the Ontario Death Registry to 1981.
• Exposure: Asbestos-cement manufacturing. The pipe process used both chrysotile and crocidolite; the board operation (1955 to 1970) used chrysotile only. For production workers, 18-year cumulative fiber exposures (fibers/ml times years) were estimated from air sampling data and work histories.
• Main results:
  • More than 20 years after first exposure, exposed workers had standardized mortality ratios of 175 for all causes of death and 370 for all malignancies
  • In the same period, exposed workers had a standardized mortality ratio of 480 for lung cancer and 240 for gastrointestinal cancers, with 17 deaths from mesothelioma
  • The factory control subjects had death rates similar to the general population
  • The factory control subjects had more cancer deaths than expected, attributed to blood and lymphatic malignancies (3 myelogenous leukemia, 1 Hodgkin's disease, 2 lymphoma)
  • The expected number of lymphatic and hematopoietic cancers among control subjects more than 10 years after hire was 0.86. The author suggested this cluster may be a random fluctuation.
  • There were 21 mesothelioma deaths in the whole cohort: 17 among production workers and 2 each among maintenance and control workers. Of these, 12 were pleural and 9 peritoneal.
  • Among men with asbestos exposure, those who died of peritoneal mesothelioma had significantly greater cumulative exposures than those who died of pleural mesothelioma
  • All of the asbestos-exposed men who died of mesothelioma had been exposed to both chrysotile and crocidolite
  • One control-group man with no recorded work in an asbestos area died of peritoneal mesothelioma. The author noted he may have been exposed during brief clean-up duties in the pipe shop.
  • 18 of the 21 mesothelioma deaths occurred in men younger than 65
  • For the 23 lung cancers with pathology data, the mix of cell types did not differ significantly from that in a series of middle-aged smokers or in British men with asbestosis (chi-square 9.3, p greater than 0.1)
  • Exposed workers had 9 gastrointestinal cancer deaths against 3.7 expected (p less than 0.05)
  • Among production workers more than 20 years after first exposure, tests for trend rejected the hypothesis of no increase in death rates with cumulative exposure for every cause listed except ischemic heart disease. Lung cancer rates did not rise steadily across exposure categories.
  • At the production workers' average cumulative exposure of about 60 f-y/ml, 20 to 34 years after first exposure, the mesothelioma death rate was 4.9 per 1,000 man-years (95% confidence limits 2.5 to 7.6)
  • At that average exposure and time period, lung cancer death rates were raised fivefold (95% confidence limits 3.2- to 7.8-fold)
  • At that average exposure and time period, gastrointestinal cancer death rates were raised threefold (95% confidence limits 1.2- to 5.6-fold)
  • The author estimated that lung cancer relative risk rose by about 7% per fiber-year/ml at this factory
• The authors' conclusion: The author concluded that asbestos-exposed employees of the factory had substantially increased death rates from nonmalignant respiratory diseases, lung cancer, mesothelioma and gastrointestinal cancers. The author called the gastrointestinal findings suggestive of a cause-effect relationship.
• Limitations the authors state:
  • Cumulative exposures came from a crude model and were estimated to be accurate only to within a factor of 3 to 5
  • Exposures could not be calculated for maintenance workers because of inadequate data
  • Smoking data were available for less than half the cohort, so results could not be adjusted for smoking
  • 16% of the cohort could not be located and were withdrawn from the analysis at the end of 1977
  • Small numbers of deaths in each exposure category gave broad confidence intervals
  • Too few men had chrysotile-only exposure to judge whether chrysotile alone is less toxic than the mixture
  • Past exposure conditions no longer occur regularly, so the risk estimates may be generalized only with great caution, if at all

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: Asbestos-Cement, standardized mortality ratio (SMR), Lung Cancer, Mesothelioma, Mineral Fiber.

Related studies

• Mortality among long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1983)
• Mortality among employees of an Ontario factory manufacturing insulation materials from amosite asbestos — M.M. Finkelstein (1989)
• Asbestosis in long-term employees of an Ontario asbestos-cement factory — M.M. Finkelstein (1982)
• Radiographic asbestosis is not a prerequisite for asbestos-associated lung cancer in Ontario asbestos-cement workers — M.M. Finkelstein (1997)
• Mortality of workers in a French asbestos cement factory 1940-82 — A.M. Alies-Patin, A.J. Valleron (1985)
• Mortality rates among employees potentially exposed to chrysotile asbestos at two automotive parts factories — M.M. Finkelstein (1989)

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