Mortality rates among employees potentially exposed to chrysotile asbestos at two automotive parts factories

Our plain-English summary of Mortality rates among employees potentially exposed to chrysotile asbestos at two automotive parts factories, by M.M. Finkelstein (CMAJ, 1989).

The study

• Author: M.M. Finkelstein
• Journal: CMAJ
• Published: 1989;141(2):125-30
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 000078).

Abstract

A study of the mortality rates among 1657 employees at two Ontario automotive parts factories that manufactured friction materials containing chrysotile asbestos was initiated in response to the workers' concerns about the effects of asbestos on their health. A total of 1194 men and 258 women had had their first potential exposure at least 10 years before the end of the study period; 563 of the men and 138 of the women had had such an exposure at least 20 years before the end of the study period. A significantly increased rate of death from laryngeal cancer and an elevated rate of death from lung cancer were observed in a cohort analysis. One or two deaths might have been due to pleural mesothelioma. There was no increase in the rate of death from gastrointestinal cancer or from nonmalignant respiratory disease. Case-control analysis showed no association between the risk of laryngeal or lung cancer and the total duration of employment (a surrogate for the extent of ambient exposure to asbestos or other workplace toxic substances) or employment in departments where asbestos had been used. An association between risk of death and occupational exposure is uncertain.

In plain English

The author studied deaths among 1657 workers (1314 men) employed at least 12 months since 1950 at two Ontario automotive parts factories using brake linings containing 25% to 50% chrysotile asbestos. Deaths through 1985 were compared with Ontario rates, and a case-control analysis examined work histories. Among men 20 or more years after first potential exposure, laryngeal cancer deaths were significantly raised (3; standardized mortality ratio 854), and lung cancer deaths were elevated (11; ratio 140). Among women 20 or more years after first potential exposure, all-cause deaths were significantly raised (20; ratio 181). Two deaths recorded as lung cancer were possibly pleural mesothelioma, but neither was confirmed. Deaths from gastrointestinal cancer and non-cancer respiratory disease were not increased, and no asbestosis was diagnosed. None of the four men who died of laryngeal cancer had worked in an asbestos department, though two (a millwright and a cleaning-crew head) may have had direct contact with asbestos dust. The case-control analysis found no association of lung or laryngeal cancer with employment length or asbestos-department work. Smoking data were fragmentary. The author concluded it could not be determined whether workplace factors caused the excess deaths.

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 (person-years analysis comparing deaths with the general population of Ontario) with a matched case-control analysis within the cohort
• Who was studied: 1657 workers (1314 men) at two automotive parts factories in Ontario, employed on or after January 1, 1950, for at least 12 months. Follow-up ran to December 31, 1985. 1194 men and 258 women were hired at least 10 years before the end of the study period, and 563 men and 138 women at least 20 years before.
• Exposure: Chrysotile asbestos in brake linings (25% to 50% chrysotile), with possible exposure to dust from drilling, grinding and riveting from 1940. Only a small part of the workforce worked directly with friction materials: 88 of 778 workers in 1976. Air sampling from 1975 until closure showed less than 2 fibres per ml of air; levels before 1975 were unknown and may have been higher. The author also noted exposures to cutting fluids and abrasives.
• Main results:
  • Men 20 or more years after first potential exposure: 3 laryngeal cancer deaths, standardized mortality ratio (SMR) 854, statistically significant (p less than 0.05). Counting a fourth death that occurred 15 years after hire, there were four laryngeal cancer deaths, against 0.51 expected 10 or more years after first exposure.
  • Men 20 or more years after first potential exposure: lung cancer 11 deaths, SMR 140, not marked as statistically significant. All causes: 104 deaths, SMR 109.
  • Among men, laryngeal cancer was the only disease with a significantly increased SMR, and SMRs did not rise with longer employment.
  • Women 20 or more years after first potential exposure: all-cause mortality 20 deaths, SMR 181, statistically significant. There were 6 cancer deaths (SMR 146), due to lung, skin, breast and ovarian tumours, lymphoma and leukemia.
  • Two deaths recorded as lung cancer were suspected pleural mesothelioma. One diagnosis could not be confirmed because the slides were lost. In the other, metastatic carcinoma could not be excluded.
  • Men employed 10 years or more: all-cause mortality was significantly higher 30 or more years after first exposure than before, due to cancer and circulatory disease. Excess cancers in this period included laryngeal cancer (3 cases, 0.19 expected), renal tumour (2, 0.29 expected) and prostatic cancer (3, 0.95 expected).
  • Case-control analysis of the 18 lung cancer deaths: 2 (11%) of cases had never worked in an asbestos department, compared with 12 (23%) of controls. No association was found between lung cancer and asbestos-department employment or duration of employment.
  • None of the four men who died of laryngeal cancer had worked in an asbestos department. The author noted that two, a millwright and the head of the cleaning crew, may have had direct contact with asbestos dust in those roles. There was no significant association between duration of employment and laryngeal cancer risk.
  • There was no increase in deaths from gastrointestinal cancer or nonmalignant respiratory disease, and no cases of asbestosis were diagnosed.
• The authors' conclusion: The author concluded that mortality rates were increased among employees and that potentially toxic exposures to chrysotile asbestos, cutting fluids and abrasives occurred. It was not possible to determine whether occupational factors were responsible. Given the small number of laryngeal cancer cases and the diversity of jobs, no firm conclusions could be drawn about an occupational cause.
• Limitations the authors state:
  • There was little quantitative exposure information, and asbestos concentrations before 1975 were unknown.
  • Detailed personnel records were unavailable for workers who left before 1968. Records for some controls were missing or incomplete.
  • Probabilistic record linkage may have missed some deaths. SMRs were estimated to be underestimated by less than 10%.
  • Smoking data were fragmentary and came from a 1981 telephone survey answered by 426 (26%) of subjects, which is subject to selection bias. Smoking and alcohol information was generally unavailable for the laryngeal cancer cases.
  • The small number of laryngeal cancer cases and the diversity of their jobs prevented firm conclusions.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Auto mechanics and brake work, Chrysotile.

Medical terms in this study, explained in our Lexicon: Chrysotile, Laryngeal Cancer, Lung Cancer, Pleural Mesothelioma, Occupational Exposure.

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