Railways and asbestos in Japan (1928-1987)--epidemiology of pleural plaques, malignancies and pneumoconioses-

Our plain-English summary of Railways and asbestos in Japan (1928-1987)--epidemiology of pleural plaques, malignancies and pneumoconioses-, by Y. Hosoda, Y. Hiraga, S. Sasagawa (Journal of Occupational Health, 2008).

The study

• Authors: Y. Hosoda, Y. Hiraga, S. Sasagawa
• Journal: Journal of Occupational Health
• Published: 2008;50(4):297-307
• Type of article: Review
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos has been an indispensable insulating material for railway industries, especially steam locomotives (SLs). This review (1928-1987) consists of three parts. 1) Pleural plaques: Since the 1970s, pleural plaques have been regarded as evidence of past asbestos inhalation, and more recently recognized as a risk factor of asbestos-related malignancies. For diagnostic criteria on plain radiographs, the modified ILO 1980 International Classification of Radiographs of Pneumoconioses was used. Most cases had pleural plaques with normal lungs. Large plant workers showed a significantly higher rate of plaques than workers in smaller plants. Bilateral plaques were dominant followed by the left, then the right lung, and chest wall plaques were dominant over the diaphragm. The manifestation of pleural plaques was more correlated to years since the onset of the asbestos exposure than the sum of asbestos work years, although the result was not significant. The boilermen of railway ferry steamers had a significantly higher plaque rate than other seamen. CT studies on plaques started in 1978. 2) Asbestos-related malignancies: Five retrospective cohort studies 1960-1970 were made on primary lung cancer incidence and mortality among 350,000 active railway men with smoking information. The follow-up period was 20 yr at the longest. Almost all plant workers showed a tendency of higher incidence or mortality than the controls. Two cases of mesothelioma were reported in 1980. 3) Pneumoconioses: Most studies (1928-1975) had relatively low prevalence rates among SL-related workers.

In plain English

This article was a review of epidemiological studies, mostly by railway physicians, of asbestos-related disease among Japanese National Railways (JNR) workers from 1928 to 1987. Exposure came mainly from dismantling steam locomotives, whose boiler lagging at JNR was made of amosite. In a 1983 X-ray study of 4,150 workers over age 50 at 10 steam locomotive plants, pleural plaques were found in 15.5% of workers at large plants and 4.9% at small plants. Among 287 railway ferry crew members over age 50 examined in 1978, plaques were found in 10% of 90 engine room seamen and 1.5% of 197 other seamen. In a lung cancer incidence cohort of 355,145 JNR employees, the relative risks for plant workers and steam locomotive department workers were not statistically significant. In a cohort of 1,142 asbestos-exposed workers at the N plant, the observed-to-expected ratio for lung cancer was 1.45, also not statistically significant. Two mesothelioma cases were reported in the JNR cohort study. The authors suggested that plaque prevalence is a surrogate of asbestos exposure dose. They noted a possible healthy worker effect.

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: Review of epidemiological studies (X-ray surveys, CT studies and retrospective cohort studies) of Japanese railway workers
• Who was studied: Japanese National Railways (JNR) employees, including railway plant workers, steam locomotive department workers, railway ferry crew and trackmen, studied between 1928 and 1987. The JNR workforce was about 400,000 employees, 97% male.
• Exposure: Intermittent asbestos exposure, mainly during the dismantling of steam locomotives. Boiler lagging at JNR was made of amosite. Ferry boilermen were exposed through asbestos insulation on steam ships.
• Main results:
  • Among 4,150 workers over age 50 in 10 steam locomotive plants (1983), the average pleural plaque rate was 15.5% in large plants (2,126 workers) and 4.9% in small plants (2,024 workers), with p less than 0.001.
  • In 1970 miniature films of N plant workers, pleural plaque rates by job section were 20.5% in the boiler section, 12.3% in locomotive, 2.4% in inspection and 2.1% in engines.
  • Among 287 railway ferry crew members over age 50 examined in 1978, pleural plaques were found in 10% of 90 engine room seamen and 1.5% of 197 seamen in other jobs (p less than 0.05).
  • In the lung cancer incidence cohort of 355,145 JNR employees, 259 lung cancer cases were found (26 in plant workers, 27 in steam locomotive department workers, 206 in others). Relative risks by birth cohort were not statistically significant.
  • In a mortality study of 15,260 workers at 17 plants, the lung cancer observed-to-expected (O/E) ratio ranged from 0.7 to 1.0 and the stomach cancer O/E from 0.6 to 0.8.
  • In the N plant cohort of 1,142 asbestos-exposed workers followed from 1970 to 1990, the O/E was 0.72 for all causes, 0.76 for all cancers, 1.45 for lung cancer, 1.34 for esophagus cancer and 1.26 for stomach cancer. None of these was statistically significant.
  • Among N plant workers followed for 21 years, the all-cause relative risk was 1.04 in 98 workers with pleural plaques and 0.92 in 1,027 workers without plaques. The difference was not significant.
  • Only two mesothelioma cases were included in the JNR cohort study.
  • Of 77 ex-JNR men qualified for asbestos labor compensation as of May 2007, 42 (54.5%) had pleural mesothelioma, 19 (24.7%) had lung cancer and 16 had other conditions.
  • Among 96 asbestos workers over age 40, calcified pleural plaques were significantly correlated with both years since first exposure and the sum of asbestos work years. The authors suggested that years since onset of exposure might be the more important factor.
• The authors' conclusion: The authors suggested that steam locomotive work was a main source of asbestos exposure and that the prevalence rate of pleural plaques is a surrogate of asbestos exposure dose.
• Limitations the authors state:
  • Low O/E ratios suggested a healthy worker effect in the cohort populations.
  • About 12% of participants dropped out during follow-up in the cohort studies.
  • Railway plant workers were also exposed to other carcinogenic dusts besides asbestos.
  • Differences in CT findings between studies may reflect diagnostic criteria, selection bias, small numbers and the CT equipment used.
  • Plaque definitions differed between studies, so the authors said reported frequencies depend on the criteria used.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Pleural plaques and thickening, Railroads.

Medical terms in this study, explained in our Lexicon: Epidemiology, Pleural Plaques, Bilateral, Diaphragm, Asbestos Exposure, Lung Cancer, Mesothelioma.

Related studies

• Asbestos-related pleural plaques and lung function — L.C. Oliver, E.A. Eisen, et al. (1988)
• Railroad workers with pleural plaques: I. Spirometric and nitrogen washout investigation on smoking and nonsmoking asbestos-exposed workers — U. Hjortsberg, P. Orbaek, et al. (1988)
• Railroad workers with pleural plaques: II. Small airway dysfunction among asbestos-exposed workers — U. Hjortsberg, P. Orbaek, et al. (1988)
• The prevalence of pleural plaques and/or pulmonary changes among construction workers in Okayama, Japan — T. Kishimoto, K. Morinaga, et al. (2000)
• Pathologica, physiological, and radiological correlations in the pneumoconioses — E.A. Gaensler, C.B. Carrington, et al. (1972)
• Between- and within-reader variability in the assessment of pleural abnormality using the ILO 1980 international classification of pneumoconioses — J. Bourbeau, P. Ernst (1988)

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