Mortality from occupational exposure to relatively pure chrysotile: a 39-year study

Our plain-English summary of Mortality from occupational exposure to relatively pure chrysotile: a 39-year study, by L. Sichletidis, D. Chloros, D. Spyratos, et al (Respiration; International Review of Thoracic Diseases, 2009).

The study

• Authors: L. Sichletidis, D. Chloros, D. Spyratos, A.B. Haidich, I. Fourkiotou, M. Kakoura, D. Patakas
• Journal: Respiration; International Review of Thoracic Diseases
• Published: 2009;78(1):63-8
• Cited by: 21 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Asbestos exposure is related to serious adverse health effects. However, there is disagreement about the relationship between chrysotile exposure and mesothelioma or lung cancer.

Objectives: Our aim was to investigate the mortality rate among workers exposed to relatively pure chrysotile in an asbestos cement factory.

Patients And Methods: In an asbestos cement plant opened in 1968, we prospectively studied all 317 workers. A quantity of 2,000 tons of chrysotile, with minimal amphibole contamination, was used annually until 1 January 2005. Asbestos fiber concentration was measured regularly. Date and cause of death were recorded among active and retired workers.

Results: Asbestos fiber concentration was always below permissible levels. Fifty-two workers died during the study. The cause was cancer in 28 subjects; lung cancer was diagnosed in 16 of them. No case of mesothelioma was reported. Death was attributed to cardiovascular diseases in 23 subjects and to liver cirrhosis in 1. Overall mortality rate was significantly lower than that of the Greek general population, standardized mortality ratio (SMR) was 0.71 (95% CI 0.53-0.93). Mortality due to cancer was increased (SMR 1.15, 95% CI 0.77-1.67), mainly due to lung cancer mortality (SMR 1.71, 95% CI 0.98-2.78), but not significantly.

Conclusions: Occupational exposure to relatively pure chrysotile within permissible levels was not associated with a significant increase in lung cancer or with mesothelioma. Decreased overall mortality of workers indicates a healthy worker effect, which--together with the relatively small cohort size--could have prevented small risks to be detected.

Copyright 2008 S. Karger AG, Basel.

In plain English

This prospective cohort study followed 317 workers employed for at least five years at an asbestos cement plant near Thessaloniki, Greece. Follow-up ran from the plant's opening in 1968 until 31 December 2006. The plant used only chrysotile, with average amphibole contamination of 0.5%. Measured airborne fiber levels fell from 6.49 to 1.7 fibers/cm3 between 1968 and 1983, and stayed below 1 fiber/cm3 after 1983. Fifty-two workers died: 28 from cancer (16 of them lung cancer), 23 from cardiovascular disease and 1 from cirrhosis. No mesothelioma was reported. Compared with the Greek male population, overall deaths were significantly lower (standardized mortality ratio, SMR, 0.71; 95% CI 0.53–0.93). Lung cancer deaths were higher (SMR 1.71, 95% CI 0.98–2.78), but the difference was not statistically significant. Smoking was the only significant independent predictor of death. Cumulative fiber exposure was not significantly associated with time to death. The authors concluded that exposure to relatively pure chrysotile under strict permissible levels did not increase the risk of mesothelioma or lung cancer. They noted that a healthy worker effect and the relatively small cohort could have kept small risks from being detected.

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: Prospective cohort mortality study, comparing deaths with expected numbers (standardized mortality ratios) and using Cox models to look at predictors of death
• Who was studied: 317 workers who worked at least 5 years at an asbestos cement products plant near Thessaloniki, Greece, followed from 1968 to 31 December 2006 (9,537 person-years). Mortality was compared with the Greek male population.
• Exposure: Chrysotile only: imported from Canada and Russia up to 1983, then from a mine in Zidani, Greece. Average amphibole contamination was 0.5%, rarely approaching 3%. About 2,000 tons of raw asbestos were used per year. Asbestos cement products contained about 8–12% chrysotile.
• Main results:
  • Measured airborne fiber concentration in the plant fell from 6.49 to 1.7 fibers/cm3 over 1968–1983, and was below 1 fiber/cm3 after 1983
  • 52 of the 317 workers died: 23 from cardiovascular diseases, 28 from malignant neoplasms (16 lung cancer) and 1 from liver cirrhosis
  • Of the 28 cancer deaths, 16 were lung cancer
  • No case of mesothelioma was reported among the workers
  • Overall mortality among the workers was significantly lower than in the Greek male population (SMR 0.71, 95% CI 0.53–0.93)
  • Cancer deaths among the workers were higher than in the Greek male population, but not significantly (SMR 1.15, 95% CI 0.77–1.67). This was mainly due to lung cancer (SMR 1.71, 95% CI 0.98–2.78).
  • Among the workers, each 10 pack-years of smoking was associated with a 1.28 times higher risk of lung cancer death. In multivariate models, smoking was the only significant independent predictor for all three outcomes (all-cause, cancer and lung cancer deaths).
  • Cumulative asbestos exposure (fibers/cm3 x years) was not significantly associated with time to death since first exposure, for all-cause, cancer or lung cancer deaths
  • More years of chrysotile exposure were associated with lower risk: lung cancer death risk was 10% lower per year of exposure. The authors called this difficult to explain and suggested falling fiber levels and more ex-smokers over time as possible reasons. They also noted that deceased workers had heavier asbestos exposure histories than living workers.
• The authors' conclusion: The authors concluded that occupational exposure to relatively pure chrysotile under strict permissible levels does not increase the relative risk for mesothelioma and lung cancer. They attributed the lung cancer SMR of 1.71 almost exclusively to smoking.
• Limitations the authors state:
  • The lower overall mortality indicates a healthy worker effect. Together with the relatively small cohort, this could have prevented small risks from being detected.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Chrysotile, Asbestos Exposure, Mesothelioma, Lung Cancer, Asbestos-Cement, Amphibole Group, standardized mortality ratio (SMR).

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