Cause-specific mortality among male chemical workers

Our plain-English summary of Cause-specific mortality among male chemical workers, by G.G. Bond, E.A. McLaren, J.B. Cartmill, et al (American Journal of Industrial Medicine, 1987).

The study

• Authors: G.G. Bond, E.A. McLaren, J.B. Cartmill, K.T. Wymer, W. Sobel, T.E. Lipps, R.R. Cook
• Journal: American Journal of Industrial Medicine
• Published: 1987;12(4):353-83
• Cited by: 36 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Cause specific mortality was surveyed among 37,682 male employees with three or more days of service between 1940 and 1982 at the Midland or Bay City, Michigan, locations of Dow Chemical USA. Vital status was ascertained through 1982 for 97.5% of the cohort members, and death certificates were obtained for 97.1% of the 7,751 decedents. Comparisons of observed mortality with expected levels based on any of three general population groups (US, Michigan, or seven local counties) consistently demonstrated lower mortality in the cohort from each of the major causes of death, including total malignant neoplasms. Unique among hourly employees was significant excess mortality in the categories of cancer of other lymphatic tissue, and motor vehicle accidents, and both hourly and salaried nonexempt employees experienced significantly higher mortality from other and ill-defined cancers. The influence of duration of employment and age at and period of hire were explored with the Mantel-Haenszel method as adapted for a cohort study. Results were evaluated both including and excluding the mortality experience of subsets of employees with past exposure to known human carcinogens (arsenic, asbestos, bis-chloromethyl ether, benzene, organic dyes, and vinyl chloride). The use of the general mortality survey in monitoring whether or not there are major health problems among the employees and in setting research priorities is emphasized.

In plain English

This mortality survey covered 37,682 men who worked at least three days between 1940 and 1982 at Dow Chemical's Midland or Bay City, Michigan, locations. The authors compared deaths with those expected from US, Michigan, and seven-county rates. Compared with US white men, deaths from all causes were lower than expected (SMR 85). So were deaths from all cancers (SMR 92) and lung cancer (SMR 91). The only cancer category significantly above expected was cancer of 'other and unspecified sites' (SMR 135). Among hourly workers' deaths in that category, six were mesotheliomas, and 12 more mesotheliomas were noted elsewhere in the cohort. The authors said this number, although of occupational interest, did not account for the excess. Among hourly workers, lung cancer deaths showed a marginally significant upward trend with length of employment. That trend disappeared after the authors removed workers exposed to arsenic, pipecoverers exposed to asbestos, and workers with high vinyl chloride exposure. The authors concluded that major undiscovered hazards were unlikely. They noted the study was not designed to link deaths to specific exposures.

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 (general mortality survey) using standardized mortality ratios against three general populations, plus Mantel-Haenszel internal comparisons
• Who was studied: 37,682 male employees with three or more days of service between 1940 and 1982 at the Midland or Bay City, Michigan, locations of Dow Chemical USA, followed through 1982
• Exposure: Employment at chemical manufacturing and research facilities in general. Results were also examined with and without subsets of employees with past exposure to known human carcinogens, including asbestos (pipecoverers)
• Main results:
  • Compared with US white males, mortality from all causes in the whole cohort was lower than expected (SMR 85), significantly below 100
  • Whole cohort compared with US white males: significant deficit for all malignant neoplasms (SMR 92) and for lung cancer (SMR 91)
  • Within cancers, the only significant excess in the whole cohort was for cancer of other and unspecified sites (SMR 135)
  • Significant excess mortality from cancer of other lymphatic tissue and from motor vehicle accidents was found only among hourly employees
  • Six of the hourly employees' death certificates in the other and unspecified cancer category were mesotheliomas. Twelve additional mesotheliomas were noted in the cohort: six among hourly employees coded to cancer of the pleura or unspecified neoplasms, four among salaried exempt workers and two among nonexempt workers
  • The authors stated that the number of mesotheliomas did not account for the excess of ill-defined cancer in the cohort
  • Among hourly employees, those employed 20 or more years had higher mortality from all cancers combined than those employed fewer than five years (RR 1.19, 95% CL 1.04 to 1.35)
  • Among hourly employees, the authors described a marginally significant increasing trend in lung cancer mortality with duration of employment
  • Among hourly employees, the trend of increasing lung cancer risk with duration disappeared after removing those exposed to arsenic, pipecoverers exposed to asbestos, and workers with high vinyl chloride exposure. The lung cancer SMR for those with 20 or more years of service fell from 118 (95% CL 101 to 137) to 103 (95% CL 86 to 122)
  • Increasing trends with duration of employment for stomach and large intestine cancer persisted after removing the asbestos-exposed and organic dye-exposed subgroups
• The authors' conclusion: The authors concluded that the generally favorable mortality experience of the cohort suggested major undiscovered hazards were unlikely. They noted that isolated excesses linked to specific exposures, such as asbestos, may exist
• Limitations the authors state:
  • Deaths without a death certificate were not assigned a cause, so cause-specific SMRs are underestimated by 2.0% on average
  • Employees lost to follow-up were concentrated among short-term employees
  • The study was not designed to link causes of death to particular exposures
  • Trends among salaried nonexempt employees did not reach statistical significance because there were too few deaths in this subgroup
  • The extent to which findings reflect higher risks among mechanics, machinists or welders is unknown without further study

Topics

Medical terms in this study, explained in our Lexicon: Death Certificate, Neoplasm, Cohort Study.

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