Evaluation of tremolite asbestos exposures associated with the use of commercial products

Our plain-English summary of Evaluation of tremolite asbestos exposures associated with the use of commercial products, by B.L. Finley, J.S. Pierce, A.D. Phelka, et al (Critical Reviews in Toxicology, 2012).

The study

• Authors: B.L. Finley, J.S. Pierce, A.D. Phelka, R.E. Adams, D.J. Paustenbach, K.A. Thuett, C.A. Barlow
• Journal: Critical Reviews in Toxicology
• Published: 2012;42(2):119-46
• Type of article: Review
• Cited by: 24 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Tremolite is a noncommercial form of amphibole mineral that is present in some chrysotile, talc, and vermiculite deposits. Inhalation of asbestiform tremolite is suspected to have caused or contributed to an increased incidence of mesothelioma in certain mining settings; however, very little is known about the magnitude of tremolite exposure that occurred at these locations, and even less is known regarding tremolite exposures that might have occurred during consumer use of chrysotile, talc, and vermiculite containing products. The purpose of this analysis is to evaluate the exposure-response relationship for tremolite asbestos and mesothelioma in high exposure settings (mining) and to develop estimates of tremolite asbestos exposure for various product use scenarios. Our interpretation of the tremolite asbestos exposure metrics reported for the Thetford chrysotile mines and the Libby vermiculite deposits suggests a lowest-observed-adverse-effect level (LOAEL) for mesothelioma of 35-73 f/cc-year. Using measured and estimated airborne tremolite asbestos concentrations for simulated and actual product use, we conservatively estimated the following cumulative tremolite asbestos exposures: career auto mechanic: 0.028 f/cc-year; non-occupational use of joint compound: 0.0006 f/cc-year; non-occupational use of vermiculite-containing gardening products: 0.034 f/cc-year; home-owner removal of Zonolite insulation: 0.0002 f/cc-year. While the estimated consumer tremolite exposures are far below the tremolite LOAELs derived herein, this analysis examines only a few of the hundreds of chrysotile- and talc-containing products.

In plain English

This article reviewed information on tremolite asbestos in chrysotile, talc, vermiculite and products made from them, adding the authors' own exposure calculations. For 12 "high probability" mesothelioma cases among Thetford Mines (Quebec) chrysotile workers, the authors assumed tremolite made up 1% of the chrysotile. From this they estimated cumulative tremolite exposures of 35–73 f/cc-year, which they proposed as an approximate "lowest-observed-adverse-effect level": the lowest bounded exposure estimate with a statistically significant increased mesothelioma risk. From published Libby, Montana vermiculite worker data they derived 0.05–2.6 f/cc-year as a range with no statistically significant increase in mesothelioma. They stated that this does not mean such exposures cannot cause mesothelioma. Their product-use estimates were 0.028 f/cc-year for a career auto mechanic, 0.0006 f/cc-year for home joint compound use, 0.034 f/cc-year for vermiculite gardening products, and 0.0002 f/cc-year for one-time homeowner removal of Zonolite insulation. The authors concluded these were several orders of magnitude below the exposures at which increased mesothelioma risks were observed in the Thetford Mines and Libby cohorts. They noted uncertainties, including the assumed tremolite content and dust-to-fiber conversion, and that only a few of hundreds of products were examined.

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 the literature on tremolite asbestos, combined with the authors' own exposure-response analysis of mining cohort data and their own estimates of cumulative tremolite exposure from product use
• Who was studied: Published data on Thetford Mines (Quebec) chrysotile miners and millers, specifically 12 'high probability' mesothelioma cases from McDonald et al. (1997), and Libby, Montana vermiculite workers (Amandus and Wheeler 1987; Larson et al. 2010). The authors also used published and simulated air measurements for product-use scenarios.
• Exposure: Tremolite asbestos in Thetford chrysotile and Libby vermiculite (Libby amphibole, assumed to be 6% tremolite). Product scenarios were automotive friction products (brake repair), joint compound, vermiculite-containing garden products, and Zonolite attic insulation.
• Main results:
  • For the 12 high-probability Thetford Mines mesothelioma cases, the estimated cumulative tremolite asbestos exposure was 35–73 f/cc-year.
  • The authors proposed 35–73 f/cc-year as a reasonable approximation of the LOAEL for tremolite asbestos. They defined the LOAEL as the lowest bounded exposure estimate for which there was a statistically significant increased risk of mesothelioma.
  • For two Libby mesothelioma cases reported by Amandus and Wheeler, whose cumulative amphibole exposure exceeded 300 f/cc-years, the authors derived a tremolite-equivalent exposure of more than 18 f/cc-year.
  • Larson et al. reported a rate ratio of 17.1 (95% CI 3.7–78.1) at 44.0 f/cc-year or more of Libby amphibole. From this the authors derived a tremolite-equivalent exposure of 2.6 f/cc-year or more associated with a statistically significantly increased rate ratio.
  • Based on Larson et al. (2010), the authors put the NOAEL (the highest exposure group with no statistically significant increase in mesothelioma risk) at between 0.05 and 2.6 f/cc-year tremolite-equivalent. The rate ratio for that group was 4.5 (95% CI 0.8–24.6).
  • Career auto mechanic: 95th percentile cumulative tremolite asbestos exposure of 0.028 f/cc-year. This figure assumed that tremolite made up 1% of all automotive friction products, an assumption the authors called implausible.
  • Non-occupational joint compound use: maximum cumulative tremolite asbestos exposure of 0.0006 f/cc-year.
  • Non-occupational use of vermiculite-containing garden products: cumulative tremolite asbestos exposure of 0.034 f/cc-year.
  • One-time homeowner removal of Zonolite insulation: maximum cumulative tremolite asbestos exposure of 0.0002 f/cc-year.
  • The authors stated that all the consumer-use estimates were well below the NOAELs (0.05–2.6 f/cc-year) and LOAELs (35–73 f/cc-year) derived from the mining cohorts.
• The authors' conclusion: The authors concluded that even implausibly high estimates of tremolite asbestos exposure from consumer product use (automotive friction products, joint compound, and vermiculite) are several orders of magnitude lower than the estimated cumulative exposures at which increased mesothelioma risks were observed in the Thetford Mines and Libby worker cohorts.
• Limitations the authors state:
  • The authors stated that their NOAEL is not meant to imply that exposures at or below it cannot cause mesothelioma.
  • The authors listed uncertainties in converting dust counts to fiber concentrations and in their assumptions about the tremolite asbestos content of the airborne fibers.
  • The Libby cohort was not completely followed to death, so the Libby-derived NOAEL may be overestimated.
  • The authors assigned zero potency to winchite and richterite in Libby vermiculite. If these amphiboles have some potency, the Libby-derived tremolite estimates are underestimated.
  • For Thetford Mines, the authors assumed that pre-1949 dust levels equalled 1949 levels, which likely underestimated exposure.
  • For Thetford Mines, the authors used a single fiber-to-dust ratio instead of job- and task-specific ratios.
  • For Thetford Mines, the authors' assumption of a 40-hour work week likely underestimated cumulative exposure.
  • The 1% tremolite assumption for Thetford chrysotile is uncertain. If tremolite were 0.1% or 10% of the chrysotile, the LOAELs would be 3.5–7.3 or 350–730 f/cc-year, respectively.
  • The analysis examined only a few of potentially hundreds of tremolite-containing products.

Topics

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

Medical terms in this study, explained in our Lexicon: Tremolite, Asbestos Exposure, Amphibole Group, Chrysotile, Talc, vermiculite, Asbestiform Tremolite, Mesothelioma.

Related studies

• Evaluation of asbestos-containing products and released fibers in home appliances — S.H. Hwang, W.M. Park (2016)
• Health effects of tremolite. This official statement of the American Thoracic Society was adopted by the ATS Board of Directors, June 1990 — (1990)
• An evaluation of reported no-effect chrysotile asbestos exposures for lung cancer and mesothelioma — J.S. Pierce, M.A. McKinley, et al. (2008)
• Sumas Mountain chrysotile induces greater lung fibrosis in Fischer344 rats than Libby amphibole, El Dorado tremolite, and Ontario ferroactinolite — J.M. Cyphert, A. Nyska, et al. (2012)
• Evaluation of the presence of asbestos in cosmetic talcum products — J.S. Pierce, A.S. Riordan, et al. (2017)
• Cohort study of mortality of vermiculite miners exposed to tremolite — J.C. McDonald, A.D. McDonald, et al. (1986)

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