An updated evaluation of reported no-observed adverse effect levels for chrysotile asbestos for lung cancer and mesothelioma

Our plain-English summary of An updated evaluation of reported no-observed adverse effect levels for chrysotile asbestos for lung cancer and mesothelioma, by J.S. Pierce, P.S. Ruestow, B.L. Finley (Critical Reviews in Toxicology, 2016).

The study

• Authors: J.S. Pierce, P.S. Ruestow, B.L. Finley
• Journal: Critical Reviews in Toxicology
• Published: 2016;46(7):561-86
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Although consumption of chrysotile asbestos has decreased since the 1970s, the latency period of asbestos-related cancers is thought to be at least 20-30 years, and therefore the potential health risks associated with historical exposures is still actively researched. This analysis represents an update to a previous paper in which we evaluated the exposure-response relationships for lung cancer and mesothelioma in chrysotile-exposed cohorts. Here, we review several recently published studies as well as updated information from previous studies. For each of the 14 studies considered, we identified the "no-observed adverse effect level" (NOAEL) for lung cancer and/or mesothelioma. NOAEL values for lung cancer ranged from 1.1 to <20 f/cc-years to 1600-3200 f/cc-years, and for mesothelioma ranged from 100-400 f/cc-years to 800-1599 f/cc-years. The range of "best estimate" NOAELs was estimated to be 89-168 f/cc-years for lung cancer and 208-415 f/cc-years for mesothelioma. None of the six cohorts of cement or friction product manufacturing workers exhibited an increased lung cancer risk at any exposure level, while all of the five studies of textile workers reported an increased risk at one or more exposure levels. This is likely because friction and cement workers were exposed to much shorter chrysotile fibers. Of the seven cases of peritoneal mesothelioma reported in the included studies, none were observed in the analyses of cement or friction product manufacturing workers in the absence of crocidolite exposure. These findings will help characterize potential worker and consumer health risks associated with historical and current chrysotile exposures.

In plain English

This review updated the authors' 2008 analysis of workers exposed mainly to chrysotile asbestos, with less than 10% amphiboles. Across 14 studies of cement, friction product, textile, and mining and milling workers, the authors identified each study's "no-observed adverse effect level" (NOAEL): the highest cumulative exposure group, in f/cc-years, at and below which there was no statistically significant increase in lung cancer or mesothelioma. Lung cancer NOAELs ranged from 1.1 to under 20 f/cc-years up to 1600 to 3200 f/cc-years, with a best-estimate range of 89 to 168 f/cc-years. Only three studies reported mesothelioma risk by level of cumulative exposure; their best-estimate range was 208 to 415 f/cc-years. None of six cement or friction cohorts showed increased lung cancer risk at any exposure level, while all five textile studies did at one or more levels. The authors suggested that shorter fibers in cement and friction work may explain this. Seven peritoneal mesothelioma cases were reported among over 66 000 workers, two with known or suspected crocidolite exposure. The authors noted uncertain exposure estimates, limited adjustment for smoking, and likely some amphibole exposure in most cohorts.

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: an update of the authors' 2008 review. The authors searched the literature and took no-observed adverse effect levels (NOAELs) from published cohort studies of chrysotile-exposed workers that reported risk by cumulative exposure. The studies were not weighted.
• Who was studied: 14 published studies of occupational cohorts exposed predominantly to chrysotile, with less than 10% amphiboles. The cohorts worked in cement and friction product manufacturing, textiles, and mining and milling in Europe, North America and China. All 14 studies gave lung cancer exposure-response data and 3 gave mesothelioma exposure-response data. Together the cohorts included over 66 000 individuals.
• Exposure: Estimated cumulative chrysotile exposure in f/cc-years (fibers per cubic centimeter multiplied by years). For each study, the NOAEL was the highest exposure group at and below which there was no statistically significant increase in lung cancer or mesothelioma.
• Main results:
  • Across the studies, lung cancer NOAELs ranged from 1.1 to under 20 f/cc-years up to 1600 to 3200 f/cc-years. The best-estimate range was 89 to 168 f/cc-years for lung cancer and 208 to 415 f/cc-years for mesothelioma.
  • Nine of the studies did not observe an increased lung cancer risk even at the highest chrysotile exposures.
  • None of the six cohorts of cement or friction product manufacturing workers showed an increased lung cancer risk at any exposure level. All five studies of textile workers reported an increased risk at one or more exposure levels.
  • Only three cohorts had mesothelioma risk stratified by cumulative chrysotile exposure. Mesothelioma NOAELs ranged from 100 to under 400 f/cc-years up to 800 to 1599 f/cc-years. In the Connecticut friction products cohort, no mesotheliomas were observed and the NOAEL was 112 f/cc-years.
  • In the Balangero (Italy) mining cohort, pleural and peritoneal mesothelioma were combined. A statistically significant increase was seen only in the highest exposure group (400 f/cc-years): SMR 6.80, 95% CI 1.85 to 17.41.
  • For the South Carolina textile cohort, the updated lung cancer NOAEL was 15 to under 60 f/cc-years. This was 10- to 20-fold higher than the earlier NOAEL of 1.4 to 2.7 f/cc-years.
  • Seven cases of peritoneal mesothelioma were reported among over 66 000 individuals in all studies combined. Four were in textile workers, two in miners or millers and one in a cement manufacturing worker.
  • Of the seven peritoneal mesothelioma cases, two had known or suspected crocidolite exposure. For the other five, no information was given on possible amphibole exposure.
  • In a sensitivity analysis leaving out the Deng et al. (2012) study, the best-estimate lung cancer NOAEL range was 94 to 182 f/cc-years, compared with 89 to 168 f/cc-years.
• The authors' conclusion: The authors concluded that the difference between the cement and friction cohorts and the textile cohorts may be due to the much shorter chrysotile fibers in cement and friction work. They stated that, in their view, the weight of evidence indicates short-fiber chrysotile is not associated with cancer risk regardless of exposure level.
• Limitations the authors state:
  • The authors described possible misclassification in the cumulative exposure estimates as perhaps the greatest source of uncertainty.
  • Smoking-adjusted risk estimates were reported for only four of the sixteen lung cancer cohorts.
  • Some exposure to amphiboles, both commercial (amosite, crocidolite) and non-commercial (tremolite), likely occurred in most if not all cohorts.
  • The NOAELs and LOAELs largely reflect the exposure categories each study's authors chose.
  • Lack of statistical power, such as small sample size, could make a NOAEL artificially high.
  • The studies were not weighted differently, even though they differed in industries, sampling methods, follow-up and cohort size.

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: Chrysotile, Lung Cancer, Mesothelioma, Latency, NOAEL, Peritoneal Mesothelioma, Crocidolite.

Related studies

• An evaluation of reported no-effect chrysotile asbestos exposures for lung cancer and mesothelioma — J.S. Pierce, M.A. McKinley, et al. (2008)
• Malignant pleural mesothelioma in US automotive mechanics: reported vs expected number of cases from 1975 to 2007 — B.L. Finley, J.S. Pierce, 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)
• Exposures from chrysotile-containing joint compound: evaluation of new model relating respirable dust to fiber concentrations — G.P. Brorby, P.J. Sheehan, et al. (2013)
• Evaluation of tremolite asbestos exposures associated with the use of commercial products — B.L. Finley, J.S. Pierce, et al. (2012)
• Potential artifacts associated with historical preparation of joint compound samples and reported airborne asbestos concentrations — G.P. Brorby, P.J. Sheehan, et al. (2011)

Browse more research in Critical Reviews in Toxicology, or return to medical research.