Occupational cohort study of current and former workers exposed to chrysotile in mine and processing facilities in Asbest, the Russian Federation: Cohort profile of the Asbest Chrysotile Cohort study

Our plain-English summary of Occupational cohort study of current and former workers exposed to chrysotile in mine and processing facilities in Asbest, the Russian Federation: Cohort profile of the Asbest Chrysotile Cohort study, by J. Schüz, I. Bukhtiyarov, A. Olsson, et al (PloS One, 2020).

The study

• Authors: J. Schüz, I. Bukhtiyarov, A. Olsson, M. Moissonnier, E. Ostroumova, E. Feletto, S.J. Schonfeld, G. Byrnes, I. Tskhomariia, V. McCormack, K. Straif, S. Kashanskiy, T. Morozova, H. Kromhout, E. Kovalevskiy
• Journal: PloS One
• Published: 2020;15(7):e0236475
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

A historical cohort study in workers occupationally exposed to chrysotile was set up in the town of Asbest, the Russian Federation, to study their cause-specific mortality, with a focus on cancer. Chrysotile has different chemical and physical properties compared with other asbestos fibres; therefore it is important to conduct studies specifically of chrysotile and in different geographical regions to improve the knowledge about its carcinogenicity. Setting was the town of Asbest, Sverdlovsk oblast, the Russian Federation. Participants were all current and former employees with at least one year of employment between 1/1/1975 and 31/12/2010 in the mine, enrichment factories, auto-transport and external rail transportation departments, the central laboratory, and the explosives unit of the company. Of the 35,837 cohort members, 12,729 (35.5%) had died (2,373 of them of cancer, including 10 of mesothelioma), 18,799 (52.5%) were known to be alive at the end of the observation period (2015), and 4,309 (12.0%) were censored before the end of 2015. Mean follow-up duration was 21.7 years in men and 25.9 years in women. The mean age at death was 59.4 years in men and 66.5 years in women. This is the largest occupational cohort of chrysotile workers to date, and the only one with a large proportion of exposed female workers.

In plain English

This article was a cohort profile. It described how the Asbest Chrysotile Cohort was assembled and followed. It did not yet report cancer risks by level of exposure; those analyses were planned. The cohort was 35,837 current and former employees, 13,374 of them women, with at least one year of work between 1975 and 2010 at the chrysotile mine, enrichment factories and related units of JSC Uralasbest in Asbest, the Russian Federation. Each worker's cumulative dust exposure was estimated from more than 90,000 workplace dust measurements. Fibre exposure was modelled from the dust figures. By the end of 2015, 12,729 cohort members had died and 18,799 were known to be alive. Circulatory system diseases were the most frequent cause of death. There were 2,373 cancer deaths, including 679 from lung cancer and 10 from mesothelioma (8 men and 2 women, aged 48 to 76 at death). The mean age at death was 59.4 years in men and 66.5 years in women. The authors noted that individual smoking data were not available, that fibre estimates for early years were uncertain, and that the study counted cancer deaths, not new cancer cases.

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: Historical (retrospective) cohort study based on company records and death-record linkage. This article is a cohort profile describing methods and descriptive data; exposure-risk analyses are planned for later.
• Who was studied: 35,837 current and former employees (22,463 men, 13,374 women) with at least one cumulative year of employment between 1 January 1975 and 31 December 2010 in the mine, factories, auto-transport and external rail transportation departments, central laboratory and explosives unit of JSC Uralasbest, Asbest, Sverdlovsk oblast, Russian Federation. They were followed for mortality from 1976 to 2015.
• Exposure: Occupational exposure to chrysotile in mining and enrichment (dry milling). Cumulative dust exposure (mg/m3-years) was estimated from a job-exposure matrix built on more than 90,000 dust measurements. Cumulative fibre years were estimated using dust-to-fibre conversion factors from parallel measurements taken in 1995, 2007 and 2013 to 2014. Dust is the primary exposure metric and fibre years the second.
• Main results:
  • Of the 35,837 cohort members, 12,729 (35.5%) had died and 18,799 (52.5%) were known to be alive at the end of follow-up in 2015.
  • 4,137 (11.5%) cohort members were censored before the end of 2015. A further 172 (0.5%) could not be matched in any record linkage and were also censored.
  • Median duration of employment at JSC Uralasbest was 11 years (mean 14.4 years).
  • Circulatory system diseases were the most frequent cause of death. In men they were followed by external causes and then cancer; in women, by cancer and then external causes.
  • There were 2,373 cancer deaths (1,662 in men, 711 in women). Lung cancer accounted for 679 deaths (622 men, 57 women). Cancer mortality was dominated by lung cancer in men and breast cancer in women.
  • Ten workers died of mesothelioma (ICD-10 C38.4, C45), 8 men and 2 women, aged 48 to 76 years at death.
  • Mean age at death was 59.4 years in men and 66.5 years in women.
  • The study's manual cause-of-death coding agreed with independent coding by the regional registry (MIAC) for 96.4% of 1,009 cancer deaths.
• The authors' conclusion: The authors described the cohort as distinct among chrysotile mine and mill cohorts in its size and as the first in which cancer risk can be investigated in female workers. Risk analyses are to follow.
• Limitations the authors state:
  • No individual smoking data were available, which is a weakness for tobacco-related cancers.
  • Fibre conversion factors came only from 1995 onward. Fibre exposure in earlier, higher-exposure periods therefore had to be modelled.
  • Exposure may be underestimated for workers who worked elsewhere before or after their employment at the eligible enterprises.
  • About 12% of the cohort were censored before 2015, mostly because they moved away from the oblast. The authors found no strong evidence that this group was highly selective.
  • The outcome is cancer mortality, not cancer incidence.
  • Deaths occurred at relatively young ages, so competing causes of death, especially external causes, may affect the results.

Topics

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

Medical terms in this study, explained in our Lexicon: Cohort Study, Chrysotile, Mesothelioma.

Related studies

• Cancer mortality in chrysotile miners and millers, Russian Federation: main results (Asbest Chrysotile Cohort-Study) — J. Schüz, E. Kovalevskiy, et al. (2024)
• Comparison of Two Information Sources for Cause-of-Death Follow-up in the Russian Federation: The Asbest Chrysotile Cohort Study — J. Schüz, E. Kovalevskiy, et al. (2020)
• Tobacco smoking among chrysotile asbestos workers in Asbest in the Russian Federation — A. Olsson, E.V. Kovalevskiy, et al. (2020)
• A comparison of parallel dust and fibre measurements of airborne chrysotile asbestos in a large mine and processing factories in the Russian Federation — E. Feletto, S.J. Schonfeld, et al. (2017)
• A retrospective cohort study of cancer mortality in employees of a Russian chrysotile asbestos mine and mills: study rationale and key features — J. Schüz, S.J. Schonfeld, et al. (2013)
• Developing a company-specific job exposure matrix for the Asbest Chrysotile Cohort Study — E. Feletto, E.V. Kovalevskiy, et al. (2022)

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