A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans

Our plain-English summary of A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans, by D.H. Garabrant, S.T. Pastula (Toxicology and Applied Pharmacology, 2018).

The study

• Authors: D.H. Garabrant, S.T. Pastula
• Journal: Toxicology and Applied Pharmacology
• Published: 2018;361:127-136
• Cited by: 48 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We analyzed the mesothelioma mortality in cohorts of workers exposed to crocidolite, amosite, and chrysotile to estimate asbestos fiber potency for mesothelioma, using the method of Hodgson and Darnton (2000). We relied on the original 17 cohort studies in their analysis, along with 3 updates of those studies and 3 new asbestos cohort studies published since 2000. We extended the analyses to examine the mesothelioma potency of tremolite in vermiculite from Libby, Montana, and for non-asbestiform elongate mineral particles (EMPs) in taconite iron ore, talc, and South Dakota gold mining. Mesothelioma potency (RMeso) was calculated as the percent of all expected deaths that were due to mesothelioma per fiber/cc-year of exposure.The RMeso was 0.0012 for chrysotile, 0.099 for amosite, and 0.451 for crocidolite: thus, the relative potency of chrysotile:amosite:crocidolite was 1:83:376, which was not appreciably different from the estimates by Hodgson and Darnton in 2000. The RMeso for taconite mining fibers was 0.069 which was slightly smaller than that for amosite. The RMeso for Libby fibers was 0.028 which was greater than that for chrysotile and less than that for amosite. Talc and gold mining EMPs were non-potent for mesothelioma. Although there are a number of methods for estimating fiber potency of asbestos and non-asbestiform EMPs, the method of Hodgson and Darnton provides a uniform method by which fiber potency can be compared across many fiber types. Our estimates of RMeso provide a useful addition to our knowledge of mesothelioma potency for different asbestos and non-asbestiform EMP fibers.

Copyright © 2018 Elsevier Inc. All rights reserved.

In plain English

The authors re-analyzed published studies of worker groups to estimate how strongly different mineral fibers were linked to mesothelioma deaths. They used a method introduced by Hodgson and Darnton in 2000, updated with longer follow-up and newer asbestos cohorts. They also applied it to workers exposed to Libby, Montana vermiculite, taconite iron ore, talc and South Dakota gold mining. Potency was expressed as mesothelioma deaths as a percent of all expected deaths, per fiber/cc-year of exposure. The combined estimates were 0.451 for crocidolite, 0.099 for amosite and 0.0012 for chrysotile. That is a ratio of 376:83:1, which the authors said varied only modestly from the earlier 500:100:1. Estimates were 0.069 for taconite mining fibers and 0.028 for Libby fibers. The authors judged talc and Homestake gold mining exposures non-potent for mesothelioma. No estimate was calculated for anthophyllite or South Carolina vermiculite. The authors noted that their confidence intervals are narrower than they would otherwise be, that the taconite exposure figures are rough approximations, and that some chrysotile cohorts may have had amphibole exposure.

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: Quantitative re-analysis (meta-regression) of published occupational cohort mortality studies, using the Hodgson and Darnton (2000) method
• Who was studied: Published occupationally exposed worker cohorts: the 17 asbestos cohorts used by Hodgson and Darnton, updates of three of them (Wittenoom crocidolite miners, South Carolina textile workers, Balangero chrysotile miners), and newer cohorts published since 2000. Also cohorts of Minnesota taconite miners, Homestake gold miners, talc miners and millers (New York, Vermont, Norway, Italy, France, Austria, Russia), and Libby, Montana and South Carolina vermiculite workers.
• Exposure: Crocidolite, amosite, chrysotile and anthophyllite asbestos; Libby vermiculite fibers (winchite, richterite, tremolite); and non-asbestiform elongate mineral particles (EMPs) in taconite iron ore, talc and gold mining. Exposure was measured as average cumulative exposure in fiber/cc-years.
• Main results:
  • Amosite cohorts combined (two cohorts): RMeso 0.099% (95% CI 0.062-0.147%)
  • Crocidolite cohorts combined (three cohorts): RMeso 0.451% (95% CI 0.397-0.510)
  • Chrysotile cohorts: individual estimates ranged from 0 to 0.0158%, with a combined RMeso of 0.0012% (0.0009-0.0016%). The chrysotile results were statistically heterogeneous; the amosite and crocidolite results were not.
  • Excluding the Chinese chrysotile textile and miner cohorts, which may have had tremolite exposure, changed the chrysotile RMeso from 0.0012 to 0.0011
  • Relative potency was 376:83:1 for crocidolite:amosite:chrysotile, compared with 500:100:1 in Hodgson and Darnton (2000)
  • Minnesota taconite miners: RMeso 0.069 (95% CI 0.047-0.099 in Table 4), based on 30 mesothelioma deaths, 8,765 expected deaths and an estimated 2.91 EMP/cc-years. This was 58 times the chrysotile value.
  • Libby vermiculite workers: RMeso 0.028 (95% CI 0.016-0.047 in Table 4), based on 15 mesothelioma deaths, 574.04 expected deaths and 91.4 f/cc-years. This was 23 times the chrysotile value.
  • Talc: of seven talc mining regions, only the New York cohort reported mesothelioma cases. The two cases in the Honda (2002) cohort were not attributed to talc, and talc mining EMP exposures were judged non-potent.
  • Homestake gold miners: a single mesothelioma case was identified across publications on this cohort and was judged unlikely to be caused by gold mine work. No RMeso was calculated, and the exposures were judged non-potent.
  • South Carolina vermiculite miners: no mesotheliomas among 51 decedents (43.74 expected deaths). No RMeso was calculated.
  • Finnish anthophyllite miners: four mesothelioma deaths, but RMeso could not be calculated because average cumulative exposure was not reported
• The authors' conclusion: The authors concluded that their updated potency estimates for chrysotile, amosite and crocidolite (1:83:376) varied only modestly from Hodgson and Darnton's (1:100:500). They also concluded that talc and gold mining were non-potent for mesothelioma.
• Limitations the authors state:
  • The confidence intervals account only for variability in mesothelioma deaths, not in expected mortality or exposure estimates, so they are narrower than they would otherwise be
  • RMeso values are valid only if all observed cases can be attributed to the measured exposures
  • The taconite exposure estimate was borrowed from a different, larger study population and is a rough approximation
  • Taconite exposure was measured as EMPs without distinguishing mineral habit, and any unaccounted-for commercial asbestos could be mixed into the estimate
  • Some chrysotile cohorts may also have had amphibole exposure, for example tremolite in the Chinese cohorts
  • The South Carolina vermiculite cohort was too small, with too low an exposure, to draw conclusions about potency

Topics

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

Medical terms in this study, explained in our Lexicon: Fiber Potency, elongate mineral particles (EMPs), Mesothelioma, Crocidolite, Amosite, Chrysotile, Tremolite, vermiculite.

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