Cohort mortality study of pulp and paper mill workers in British Columbia, Canada

Our plain-English summary of Cohort mortality study of pulp and paper mill workers in British Columbia, Canada, by P.R. Band, N.D. Le, R. Fang, et al (American Journal of Epidemiology, 1997).

The study

• Authors: P.R. Band, N.D. Le, R. Fang, W.J. Threlfall, G. Astrakianakis, J.T. Anderson, A. Keefe, D. Krewski
• Journal: American Journal of Epidemiology
• Published: 1997;146(2):186-94
• Cited by: 39 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The authors studied a cohort of 30,157 male pulp and paper workers in British Columbia, Canada. Of these, 20,373 worked in kraft mills only, 5,249 in sulfite mills only, and 4,535 in both kraft and sulfite mills. All workers with at least 1 year of employment on January 1, 1950, or thereafter until December 31, 1992, were studied. Standardized mortality ratios (SMRs) were used to compare the mortality rates of the cohort with those of the Canadian male population. Ninety percent confidence intervals (CIs) for the SMRs were obtained. Cancer risks significantly associated with work duration and time from first employment of 15 years or more were observed: 1) total cohort: pleura (SMR = 3.61, 90% CI 1.42-7.58); kidney (SMR = 1.69, 90% CI 1.13-2.43); brain (SMR = 1.51, 90% CI 1.03-2.16); 2) workers in kraft mills only: kidney (SMR = 1.92, 90% CI 1.04-3.26); 3) workers in sulfite mills only: Hodgkin's disease (SMR = 4.79, 90% CI 1.29-12.37); 4) workers ever employed in both kraft and sulfite mills: esophagus (SMR = 1.91, 90% CI 1.00-3.33). These malignancies have been associated with the following known or suspected carcinogens to which pulp and paper workers may have been exposed: asbestos (pleura), biocides (kidney), formaldehyde (kidney, brain, Hodgkin's disease), hypochlorite (esophagus). A nested case-control study with detailed exposure assessment is under way to help determine whether excess risks for specific cancers reflect exposure among subsets of workers.

In plain English

This retrospective cohort study followed 30,157 men who worked at least 1 year between 1950 and 1992 at 14 pulp and paper mills in British Columbia, Canada. Of these, 20,373 worked in kraft mills only, 5,249 in sulfite mills only, and 4,535 in both. Their death rates were compared with Canadian men's using standardized mortality ratios (SMRs) with 90 percent confidence intervals (CI). There were 4,074 deaths, 1,052 of them from cancer. In the whole cohort, deaths from cancer of the pleura were higher than expected (SMR 2.65, CI 1.32-4.78). The excess was larger among men who had worked 15 years or more (SMR 3.61, CI 1.42-7.58). Among kraft-only workers, the pleural cancer SMR was 2.51, but its interval (0.85-5.74) included 1. Long-term workers also had raised deaths from kidney cancer (SMR 1.69, CI 1.13-2.43) and brain cancer (SMR 1.51, CI 1.03-2.16). The study collected no exposure data. The authors suggested that asbestos exposure in the mills may explain the pleural cancer excess. They noted that smoking was not recorded and that tissue diagnoses were lacking for pleural cancer.

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 comparing the cohort with the Canadian male population using standardized mortality ratios (SMRs) and 90 percent confidence intervals
• Who was studied: 30,157 male workers with at least 1 year of employment between January 1, 1950 and December 31, 1992 at 14 pulp and paper mills in British Columbia, Canada: 20,373 in the kraft process only, 5,249 in the sulfite process only, and 4,535 in both
• Exposure: Employment in pulp and paper mills, grouped by kraft process, sulfite process, or both, and by work duration and time since first employment. No exposure measurements were made and workers were not classified by department. Asbestos was not measured; the authors raised it only as a possible explanation for the pleural cancer excess.
• Main results:
  • Total cohort: 4,074 deaths from all causes, including 1,052 cancer deaths. The all-cause SMR was 0.92 (90 percent CI 0.89-0.94), which the authors attributed to the healthy worker effect.
  • Total cohort: cancer of the pleura SMR 2.65 (90 percent CI 1.32-4.78)
  • Total cohort, workers with work duration of 15 years or more: cancer of the pleura SMR 3.61 (90 percent CI 1.42-7.58)
  • Kraft-only workers: cancer of the pleura SMR 2.51 (90 percent CI 0.85-5.74); the interval includes 1
  • Total cohort, work duration of 15 years or more: kidney cancer SMR 1.69 (90 percent CI 1.13-2.43)
  • Total cohort, work duration of 15 years or more: brain cancer SMR 1.51 (90 percent CI 1.03-2.16)
  • Total cohort, work duration of 15 years or more: lung cancer SMR was low at 0.84 (90 percent CI 0.72-0.97)
  • Kraft-only workers with work duration over 15 years: kidney cancer SMR 1.92 (90 percent CI 1.04-3.26)
  • Sulfite-only workers with work duration over 15 years: Hodgkin's disease SMR 4.79 (90 percent CI 1.29-12.37)
  • Workers ever employed in both kraft and sulfite mills, work duration of 15 years or more: esophagus cancer SMR 1.91 (90 percent CI 1.00-3.33)
• The authors' conclusion: The authors suggested that exposure to asbestos in British Columbia pulp mills may explain the significantly increased risk of pleural cancer seen in the study. They planned a nested case-control study with detailed exposure assessment.
• Limitations the authors state:
  • No information on tobacco smoking or other lifestyle cancer risk factors was collected
  • For cancer of the pleura and of the eye, agreement between microscopically confirmed diagnoses and the death-certificate cause of death is less than 50 percent
  • Lack of histologic information prevents definitive conclusions for pleural, bone, eye, and kidney cancers
  • No exposure data were obtained and workers were not classified by department
  • 20 percent of sulfite-only workers were lost to follow-up; after further analysis the authors judged this unlikely to have substantially biased the results

Topics

Medical terms in this study, explained in our Lexicon: standardized mortality ratio (SMR), confidence interval, Pleura, nested case-control study.

Related studies

• Cancer incidence among Swedish pulp and paper mill workers: a cohort study of sulphate and sulphite mills — E. Andersson, H. Westberg, et al. (2013)
• Health effects of working in pulp and paper mills: malignant diseases — K. Torén, B. Persson, et al. (1996)
• Exposure to asbestos and lung and pleural cancer mortality among pulp and paper industry workers — R. Carel, P. Boffetta, et al. (2002)
• Pleural mesotheliomas and asbestos exposure in the pulp and paper industries: a new risk group identified by linkage of official registers — B. Järvholm, H. Malker, et al. (1988)
• Surveillance of mesothelioma and workers' compensation in British Columbia, Canada — T.L. Kirkham, M.W. Koehoorn, et al. (2011)
• Identification of occupational cancer risks in British Columbia, Canada: a population-based case-control study of 1,155 cases of colon cancer — R. Fang, N. Le, et al. (2011)

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