Past exposure to asbestos and combustion products and incidence of cancer among Finnish locomotive drivers

Our plain-English summary of Past exposure to asbestos and combustion products and incidence of cancer among Finnish locomotive drivers, by P. Nokso-Koivisto, E. Pukkala (Occupational and Environmental Medicine, 1994).

The study

• Authors: P. Nokso-Koivisto, E. Pukkala
• Journal: Occupational and Environmental Medicine
• Published: 1994;51(5):330-4
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Locomotive drivers in the steam engine era were exposed to asbestos during their vocational training for two years while training in workshops. Later in their career they had exposure to coal and diesel combustion products. To assess the level of earlier exposure historical working conditions were reconstructed and hygienic conditions were measured. The average exposure to asbestos (mainly anthophylline) fibres > 5 microns was 5.0 fibres/cm3. Incidence of cancer in a cohort of 8391 members of the Finnish Locomotive Drivers' Association, 1953-91, was analysed. The incidence of lung cancer and also total cancer was below the national average, probably due to the low prevalence of smoking among the drivers in the steam engine era. A four-fold risk of mesothelioma was found, most likely caused by exposure to asbestos. Also the observed 1.5-fold incidence of non-melanoma skin cancer and 1.7-fold risk of cancer of the oral cavity and pharynx may be related to occupation.

In plain English

This Finnish study combined a workplace reconstruction with a cancer cohort study. Before the 1970s, trainee locomotive drivers spent two years in railway workshops. In a reconstruction of boiler insulation removal, eight air samples averaged 5.0 asbestos fibres longer than 5 µm per cm3. Anthophyllite was the main type in boiler insulation, and chrysotile was also found. The authors followed 8391 men in the Finnish Locomotive Drivers' Association from 1953 to 1991, comparing their cancer rates with Finland's. Drivers had 915 cancers against 962 expected, and 236 lung cancers against 274 expected. Mesothelioma occurred in 8 drivers against 2 expected (standardized incidence ratio 4.05, 95% confidence interval 1.75 to 7.97), all more than 30 years after first employment. Oral cavity and pharynx cancer (17 versus 10) and non-melanoma skin cancer excluding basal cell carcinomas (32 versus 21) were also raised. The authors concluded that short-term asbestos exposure likely triggered the mesothelioma excess and that the skin and oral cancers might be work related. They attributed the low lung cancer rate to little smoking in the steam engine era.

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, compared with the national Finnish population, combined with a reconstruction and air measurement of past workshop exposures
• Who was studied: 8391 men who were members of the Finnish Locomotive Drivers' Association, Finland, 1953 to 1991. Of 8693 members, 302 (3.5%) were excluded for inadequate identification data. They contributed 212 800 person-years, with a mean follow-up of 25.4 years.
• Exposure: Asbestos exposure during two years of workshop training in the steam engine era, mainly from dismantling boiler insulation. In the reconstruction, eight personal air samples averaged 5.0 fibres longer than 5 µm per cm3 (range 2.5 to 7.5), which the authors called medium exposure. The samples contained anthophyllite and chrysotile. Anthophyllite was the main type in boiler insulation, and chrysotile was found in woven strings around pipes and ventilators. Asbestos was undetectable (below 0.1 fibres/cm3) in diesel locomotive cabins. Later in their careers, drivers were also exposed to coal and diesel combustion products, benz(a)pyrene, lubricating oils and coal tar (creosote).
• Main results:
  • All cancers combined among the drivers: 915 observed versus 962 expected (standardized incidence ratio 0.95, 95% CI 0.89 to 1.01)
  • Mesothelioma among the drivers: 8 observed versus 2 expected (standardized incidence ratio 4.05, 95% CI 1.75 to 7.97)
  • No mesothelioma cases occurred in the first 30 years after first employment. After 30 years the risk was significantly increased (standardized incidence ratio 5.04, 95% CI 2.18 to 9.93).
  • Lung and trachea cancer among the drivers was below expectation: 236 observed versus 274 expected (standardized incidence ratio 0.86, 95% CI 0.75 to 0.97)
  • Cancer of the oral cavity and pharynx among the drivers: 17 observed versus 10 expected (standardized incidence ratio 1.75, 95% CI 1.02 to 2.80). The excess appeared after 15 years of follow-up.
  • Non-melanoma skin cancer (excluding basal cell carcinomas) among the drivers: 32 observed versus 21 expected (standardized incidence ratio 1.53, 95% CI 1.04 to 2.15). The excess appeared after 15 years of follow-up.
  • Stomach cancer among the drivers was below expectation: 86 observed versus 112 expected (standardized incidence ratio 0.77, 95% CI 0.61 to 0.94)
• The authors' conclusion: The authors concluded that the fourfold risk of mesothelioma in locomotive drivers is likely to have been triggered by short-term asbestos exposure, and that the increased non-melanoma skin cancer and oropharyngeal cancer might be work related. They attributed the below-average lung cancer risk to the low prevalence of smoking in the steam engine era.
• Limitations the authors state:
  • 302 members (3.5%) of the original cohort were excluded for inadequate identification data. The authors judged this loss likely to be non-systematic and not a source of bias.

Topics

Medical terms in this study, explained in our Lexicon: Lung Cancer, Mesothelioma.

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