The risk of mesothelioma from exposure to chrysotile asbestos

Our plain-English summary of The risk of mesothelioma from exposure to chrysotile asbestos, by C.M. Yarborough (Current Opinion in Pulmonary Medicine, 2007).

The study

• Author: C.M. Yarborough
• Journal: Current Opinion in Pulmonary Medicine
• Published: 2007;13(4):334-8
• Type of article: Review
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Purpose Of Review: This review assesses the risk of developing diffuse malignant mesothelioma of the pleura from exposures to chrysotile fibers and contrasts it with the known risk of amphibole asbestos.

Recent Findings: Although a rare cancer, the mortality rates of pleural mesothelioma continue to be significantly elevated because of past occupational exposures to airborne asbestos fibers. New analyses of occupational epidemiologic studies for highly exposed workers show a substantially lower potency and suggest an empiric threshold for chrysotile compared with amphibole asbestos. Important kinetic and pathological differences between chrysotile and amphiboles have been substantiated that support chrysotile's impotency in causing pleural mesothelioma.

Summary: Excess risk of pleural mesothelioma from past exposures to asbestos, as evidenced by a trend of high incidence rates during the last half century, appears to be the result of nonchrysotile asbestiform fibers. Although scientific efforts and legal arguments continue, the risk of pleural mesothelioma in human populations is probably negligible for exposures to airborne chrysotile asbestos that is not known to be contaminated by amphibole. This distinction for asbestos fiber types is pivotal for understanding hazards and characterizing risks of continued use of natural chrysotile asbestos today and also new nanofibers.

In plain English

This 2007 review by a single author assessed the risk of pleural mesothelioma from chrysotile asbestos and contrasted it with amphibole asbestos. It drew on epidemiology, fiber-clearance, pathology and laboratory studies. The author restated results of the author's earlier assessment, which grouped 71 published occupational cohorts by the type of asbestos fiber processed. In those cohorts, 404 mesothelioma cases were reported among approximately 32853 amphibole-exposed people (1.23%), 994 among 147384 people with mixed chrysotile and amphibole exposure (0.67%), and at most seven among 32039 chrysotile-exposed people. No pleural case in the chrysotile-only cohorts could be confirmed. The review also described other studies. One was a meta-analysis of motor vehicle mechanics whose authors found no association with mesothelioma. Another was a meta-analysis that reported excess mesothelioma among chrysotile workers; the author questioned it because 12 of its studies reported amphibole or similar exposures. The author noted that past chrysotile fiber counts were of questionable validity and that the difference seen in people was not evident in animal studies. The author concluded that the claim that chrysotile alone is a risk factor for pleural mesothelioma is disputable.

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: Narrative review of published literature (epidemiology, fiber biopersistence, pathology, laboratory and dose-response studies), single author
• Who was studied: Published studies. The central epidemiologic data come from the author's earlier assessment of 71 occupational cohorts in the scientific literature, 14 of which had chrysotile exposure without identified amphibole exposure
• Exposure: Airborne chrysotile asbestos, contrasted with amphibole asbestos (crocidolite, amosite, tremolite, anthophyllite, actinolite) and with mixed chrysotile and amphibole exposure
• Main results:
  • In the author's earlier classification of cohorts, 404 mesothelioma cases (1.23%) were reported among approximately 32853 amphibole-exposed individuals
  • Cohorts with mixed fiber exposure had 994 cases among 147384 individuals (0.67%)
  • Chrysotile-exposed cohorts had at most seven cases among 32039 individuals. The article prints this as 0.04%, but that does not match its own counts: seven of 32039 is about 0.02%
  • Seven mesothelioma cases were reported in the 14 chrysotile-only cohorts, but no pleural mesothelioma case in those cohorts could be confirmed
  • A reviewed meta-analysis of motor vehicle mechanics (four proportionate mortality, eight case-control and four cohort studies) concluded there was no association between work as a mechanic and mesothelioma
  • A reviewed meta-analysis of 26 cohort studies of chrysotile-exposed workers by Li et al. concluded there was excess mesothelioma mortality. The author disputed this because 12 of the included studies reported amphibole or similar exposures
  • A reviewed meta-analysis of environmental (not job-related) exposures found the combined relative risk for chrysotile was not statistically elevated for neighborhood or household exposures
  • In a reviewed South African case-control study of 123 mesothelioma patients, no case had a history of chrysotile mining
• The authors' conclusion: The author concluded that the contention that airborne exposure to chrysotile fibers alone is a risk factor for pleural mesothelioma is disputable. The author also concluded that results from cohorts with high cumulative chrysotile exposure not known to be contaminated with amphiboles do not justify a conclusion of causation.
• Limitations the authors state:
  • The author stated that past count estimates of chrysotile fibers are of questionable validity because fibers were neither directly measured nor analyzed
  • The author noted that the lower risk from chrysotile seen in human epidemiology is not evident in animal studies, which show chrysotile as having mesotheliogenic potency
  • The author noted that the pleural fiber findings cited contradict those of several other researchers

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelioma, Chrysotile, Pleura, Amphibole Asbestos, Pleural Mesothelioma, Occupational Exposure, Amphibole Group, Incidence.

Related studies

• Analysis of mortality in chrysotile asbestos miners in China — L. Du, X. Wang, et al. (2012)
• Evaluation of take-home exposure and risk associated with the handling of clothing contaminated with chrysotile asbestos — J. Sahmel, C.A. Barlow, et al. (2014)
• Electricians' chrysotile asbestos exposure from electrical products and risks of mesothelioma and lung cancer — J.E. Goodman, M.K. Peterson, et al. (2014)
• Malignant mesothelioma, airborne asbestos, and the need for accuracy in chrysotile risk assessments — C. Meisenkothen (2013)
• Comparative Risks of Cancer from Drywall Finishing Based on Stochastic Modeling of Cumulative Exposures to Respirable Dusts and Chrysotile Asbestos Fibers — F.W. Boelter, Y. Xia, et al. (2015)
• An epidemiological study of the role of chrysotile asbestos fibre dimensions in determining respiratory disease risk in exposed workers — L. Stayner, E. Kuempel, et al. (2008)

Browse more research in Current Opinion in Pulmonary Medicine, or return to medical research.