Cancer incidence among Swedish pulp and paper mill workers: a cohort study of sulphate and sulphite mills

Our plain-English summary of Cancer incidence among Swedish pulp and paper mill workers: a cohort study of sulphate and sulphite mills, by E. Andersson, H. Westberg, I.L. Bryngelsson, et al (International Archives of Occupational and Environmental Health, 2013).

The study

• Authors: E. Andersson, H. Westberg, I.L. Bryngelsson, A. Magnuson, B. Persson
• Journal: International Archives of Occupational and Environmental Health
• Published: 2013;86(5):529-40
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose: Associations between various malignancies and work in the pulp and paper industry have been reported but mostly in analyses of mortality rather than incidence. We aimed to study cancer incidence by main mill pulping process, department and gender in a Swedish cohort of pulp and paper mill workers.

Methods: The cohort (18,113 males and 2,292 females, enrolled from 1939 to 1999 with >1 year of employment) was followed up for cancer incidence from 1958 to 2001. Information on the workers' department and employment was obtained from the mills' personnel files, and standardized incidence ratios (SIRs) were calculated using the Swedish population as reference.

Results: Overall cancer incidence, in total 2,488 cases, was not increased by work in any department. However, risks of pleural mesothelioma were increased among males employed in sulphate pulping (SIR, 8.38; 95 % CI, 3.37-17) and maintenance (SIR, 6.35; 95 % CI, 3.47-11), with no corresponding increase of lung cancer. Testicular cancer risks were increased among males employed in sulphate pulping (SIR, 4.14; 95 % CI, 1.99-7.61) and sulphite pulping (SIR, 2.59; 95 % CI, 0.95-5.64). Female paper production workers showed increased risk of skin tumours other than malignant melanoma (SIR, 2.92; 95 % CI, 1.18-6.02).

Conclusions: Incidence of pleural mesothelioma was increased in the cohort, showing that asbestos exposure still has severe health consequences, and highlighting the exigency of strict asbestos regulations and elimination. Testicular cancer was increased among pulping department workers. Shift work and endocrine disruptors could be of interest in this context.

In plain English

This Swedish retrospective cohort study followed 20,405 workers (18,113 men, 2,292 women) employed more than a year at eight pulp and paper mills, enrolled 1939 to 1999, for cancer from 1958 to 2001. Department served as a stand-in for exposure; asbestos was not measured for individual workers. 2,305 workers developed 2,488 cancers; overall incidence was not raised. Men had excess pleural mesothelioma: 27 cases (standardized incidence ratio, SIR, 3.17; 95% CI 2.09 to 4.61), including 7 in sulphate pulping (SIR 8.38; 95% CI 3.37 to 17) and 14 in maintenance (SIR 6.35; 95% CI 3.47 to 11). Women had none. Lung cancer was not significantly increased in any department, though female paper production workers showed a non-significant rise (SIR 1.76; 95% CI 0.71 to 3.63). Testicular cancer was raised in male sulphate pulping workers (SIR 4.14; 95% CI 1.99 to 7.61), and non-melanoma skin cancer in female paper production workers (SIR 2.92; 95% CI 1.18 to 6.02). The authors concluded the mesotheliomas related to asbestos exposure. They noted department-only exposure assessment, scarce lifestyle data, and possible chance findings.

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 cancer incidence. Cancer cases were found by linking the cohort to the Swedish Cancer Registry, and standardized incidence ratios were calculated against the Swedish population.
• Who was studied: 20,405 workers (18,113 males and 2,292 females) employed more than 1 year at eight Swedish pulp and paper mills (four sulphate, four sulphite). They were enrolled from 1939 to 1999 and followed for cancer incidence from 1958 to 31 December 2001.
• Exposure: Work in mill departments, used as a proxy for exposure: wood preparation, sulphite pulping, sulphate pulping, paper production, maintenance, steam and power generation, office, and other or unknown. Asbestos is named among several carcinogens present in the industry. No asbestos fiber type is named, and there was no individual asbestos measurement. The authors note that the few asbestos measurements made in Swedish mills, reported in their earlier study, all indicated very low levels.
• Main results:
  • Over 1958 to 2001, 2,305 workers developed 2,488 diagnosed cancers.
  • Overall cancer incidence among male workers was lower than in the reference population (SIR 0.93; 95% CI 0.89 to 0.97). There was no difference among females (SIR 1.00; 95% CI 0.89 to 1.13).
  • Pleural mesothelioma was increased among males in sulphate pulping (7 cases; SIR 8.38; 95% CI 3.37 to 17) and in maintenance (14 cases; SIR 6.35; 95% CI 3.47 to 11).
  • Among all male workers there were 27 pleural mesothelioma cases (SIR 3.17; 95% CI 2.09 to 4.61).
  • Among male sulphite pulping workers, pleural mesothelioma was raised but not statistically significant (3 cases; SIR 2.92; 95% CI 0.60 to 8.53).
  • Among male steam and power generation workers there were 2 pleural mesothelioma cases, against 0.11 expected.
  • By mill process, pleural mesothelioma was increased among male sulphate mill workers employed 10 years or more (15 cases; SIR 5.17; 95% CI 2.89 to 8.52) and among male sulphite mill workers employed 10 years or more (7 cases; SIR 2.59; 95% CI 1.04 to 5.33). For sulphate mill males employed under 10 years the figure was 5 cases (SIR 3.00; 95% CI 0.98 to 7.01).
  • No cases of pleural mesothelioma were reported among female workers.
  • Lung cancer incidence was not increased in any department. It was decreased among all male workers (192 cases; SIR 0.85; 95% CI 0.73 to 0.97). Using the Swedish population outside the three largest cities as reference raised the estimates only marginally.
  • Lung cancer was slightly, but not significantly, increased among female paper production workers (7 cases; SIR 1.76; 95% CI 0.71 to 3.63).
  • Comparing 1958 to 1979 with 1980 to 2001 showed no significant trends or changes, including for pleural mesothelioma.
  • Testicular cancer was increased among male sulphate pulping workers (10 cases; SIR 4.14; 95% CI 1.99 to 7.61). The authors said it tended to be more common among male sulphite pulping workers (6 cases; SIR 2.59; 95% CI 0.95 to 5.64).
  • Female paper production workers had an increased risk of skin tumours other than malignant melanoma (7 cases; SIR 2.92; 95% CI 1.18 to 6.02). The authors said this could be a random finding.
  • Lip cancer was increased among male sulphite pulping workers (7 cases; SIR 2.77; 95% CI 1.11 to 5.70).
• The authors' conclusion: The authors concluded that the study showed known effects of pulp and paper mill exposures, such as pleural mesotheliomas related to asbestos exposure. They also saw indications of other cancers, such as hormone-related ones, where the cause is unclear and shift work and endocrine-disrupting compounds might be involved.
• Limitations the authors state:
  • Information on potential lifestyle confounders was rare.
  • Occupational exposure was assessed only by department, not by specific agents, so misclassification can occur.
  • Departments may have been misclassified, and changes in department may not have been recorded.
  • With many outcomes analysed, some reported results may have been due to chance.

Topics

Medical terms in this study, explained in our Lexicon: Cohort Study, Standardized Incidence Ratio (SIR), Pleural Mesothelioma, Lung Cancer, Asbestos Exposure.

Related studies

• Cohort mortality study of pulp and paper mill workers in British Columbia, Canada — P.R. Band, N.D. Le, et al. (1997)
• Health effects of working in pulp and paper mills: malignant diseases — K. Torén, B. Persson, et al. (1996)
• A case-referent study of cancer mortality among sulfate mill workers in Sweden — E. Andersson, S. Hagberg, et al. (2001)
• 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)
• Cancer morbidity and quartz exposure in Swedish iron foundries — H. Westberg, L. Andersson, et al. (2013)

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