A case-referent study of cancer mortality among sulfate mill workers in Sweden

Our plain-English summary of A case-referent study of cancer mortality among sulfate mill workers in Sweden, by E. Andersson, S. Hagberg, T. Nilsson, et al (Occupational and Environmental Medicine, 2001).

The study

• Authors: E. Andersson, S. Hagberg, T. Nilsson, B. Persson, G. Wingren, K. Torén
• Journal: Occupational and Environmental Medicine
• Published: 2001;58(5):321-4
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Objectives: To investigate whether workers in Swedish sulfate mills have an increased risk of death from certain malignancies that have previously been linked to the pulping process.

Methods: Subjects of the study (n=2480) were men aged 40-75 at death during 1960-89 in the parishes surrounding four sulfate mills. Exposure assessment was based on information from the personnel files in the mills- 35% of the subjects were recognised there, and work categories were created.

Results: Among all sulfate mill workers, the odds ratio (OR) (90% confidence interval (90% CI)) for death from lung cancer was 1.6 (1.1 to 2.3), pleural mesotheliomas 9.5 (1.9 to 48), brain tumours 2.6 (1.2 to 5.3), and liver or biliary tract cancer 2.3 (1.0 to 5.2). There was an increased mortality from leukaemia among workers in the soda recovery plant (5.9 (2.6 to 13)) and bleaching plant and digester house (2.8 (1.0 to 7.5)).

Conclusions: Sulfate mill workers were at increased risk of dying from lung cancer and pleural mesotheliomas, probably due to exposure to asbestos. Increased risks of brain tumours and cancers of the liver or biliary tract were also found but the aetiology is not obvious.

In plain English

This Swedish case-referent study looked at causes of death among 2,480 men aged 40 to 75 who died between 1960 and 1989 in parishes around four sulfate (Kraft) pulp mills. Using mill personnel files, the authors classified 859 men (35%) as exposed if they had worked there as blue-collar workers for at least one year. The files held no information on exposure to specific agents. Compared with unexposed men, mill workers had higher odds of death from lung cancer (odds ratio 1.6, 90% confidence interval 1.1 to 2.3), pleural mesothelioma (9.5, 1.9 to 48, from 5 exposed and 1 unexposed case), brain tumours, and liver or biliary tract cancer. Four of the five exposed mesothelioma cases had worked in building and maintenance. Leukaemia deaths were raised among soda recovery plant workers and among bleaching plant and digester house workers, but not among all workers combined. Smoking habits were unknown. The authors concluded that the raised lung cancer and pleural mesothelioma risks were probably due to asbestos exposure. They said the cause of the brain and liver or biliary tract findings was not obvious.

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: Case-referent (case-control) study of deaths, using parish death registers and mill personnel files
• Who was studied: 2480 men aged 40 to 75 who died in 1960 to 1989 in five parishes surrounding four sulfate mills in rural Sweden. 859 (35%) were classified as exposed mill workers and 1621 as unexposed.
• Exposure: Employment for at least 1 year as a blue-collar worker in a sulfate (Kraft) pulp mill, taken from mill personnel files. Workers were also grouped by work category: maintenance, wood room, sawmill, bleaching plant and digester house, soda recovery plant, and others. Asbestos was not measured and no fiber type is named. The authors suggest asbestos as the probable cause of the lung cancer and pleural mesothelioma excess.
• Main results:
  • All exposed mill workers had an odds ratio of 1.6 (90% CI 1.1 to 2.3) for death from lung cancer. This was based on 32 exposed and 41 unexposed cases.
  • Pleural mesothelioma: 1 unexposed case and 5 exposed cases. The crude odds ratio was 9.5 (90% CI 1.9 to 48) for all exposed workers and 12.8 (90% CI 2.5 to 65) for workers employed more than 10 years.
  • Four of the five exposed mesothelioma cases had worked in the building and maintenance department.
  • All exposed mill workers had an odds ratio of 2.6 (90% CI 1.2 to 5.3) for brain tumours and 2.3 (90% CI 1.0 to 5.2) for liver or biliary tract cancer.
  • Unspecified abdominal cancer was increased among mill workers (n=10, OR 4.4, 90% CI 1.5 to 13). The authors said this may be due to peritoneal mesotheliomas.
  • Leukaemia was not increased among all mill workers (OR 0.7, 90% CI 0.4 to 1.4). It was increased among bleaching plant and digester house workers (OR 2.8, 90% CI 1.0 to 7.5) and soda recovery plant workers (OR 5.9, 90% CI 2.6 to 13).
• The authors' conclusion: The authors concluded that sulfate mill workers were at increased risk of dying from lung cancer and pleural mesotheliomas, probably due to asbestos exposure. They also found increased risks of brain tumours and liver or biliary tract cancers but said the cause was not obvious.
• Limitations the authors state:
  • The personnel files lacked information on exposure to specific agents and had incomplete employment periods. The authors said this would bias results toward no effect.
  • Using deceased people as the source population could affect the risk estimates.
  • Smoking habits were not known. Using assumed smoking rates from a similar mill town, the authors estimated the lung cancer relative risk would fall from 1.6 to 1.3.
  • The study population was too small to adjust for several possible confounders at once.

Topics

Medical terms in this study, explained in our Lexicon: Odds Ratio, confidence interval, Lung Cancer, Pleural Mesothelioma.

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)
• Mortality and cancer morbidity in cohorts of asbestos cement workers and referents — M. Albin, K. Jakobsson, et al. (1990)
• Cohort mortality study of pulp and paper mill workers in British Columbia, Canada — P.R. Band, N.D. Le, et al. (1997)
• Low-dose exposure to asbestos and lung cancer: dose-response relations and interaction with smoking in a population-based case-referent study in Stockholm, Sweden — P. Gustavsson, F. Nyberg, et al. (2002)
• Health effects of working in pulp and paper mills: malignant diseases — K. Torén, B. Persson, et al. (1996)
• Occupational exposure and lung cancer risk: a population-based case-referent study in Sweden — P. Gustavsson, R. Jakobsson, et al. (2000)

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