Rapporteur's Report Session 6: risk assessment of asbestos and other fibrous mineral particulates

Our plain-English summary of Rapporteur's Report Session 6: risk assessment of asbestos and other fibrous mineral particulates, by R.P. Nolan, A.M. Langer (Regulatory Toxicology and Pharmacology, 2008).

The study

• Authors: R.P. Nolan, A.M. Langer
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S246-8
• Read it: PubMed · Publisher

In plain English

This was a rapporteur's report, not an original study. It summarized four papers presented at a conference session on risk assessment of asbestos and other fibrous mineral particulates, with the rapporteurs' own comments. A review of meta-analyses reported the cumulative exposure that doubled lung cancer risk: 4000 fiber/ml-years in chrysotile mining and milling and 130 in chrysotile manufacturing and textiles. A paper on mesothelioma reported that 2 of 2907 deaths in taconite worker cohorts (0.07%) were from mesothelioma, compared with 0.17% of deaths among US males in the general population. The rapporteurs compared two studies of Libby, Montana vermiculite miners: 12 mesotheliomas in 286 deaths (4.2%) in the earlier one and 15 in 767 (2%) in the later one. A fourth paper made a worst-case estimate that treated airborne fibers in Silver Bay, Minnesota, as asbestos. It found one excess cancer in 28,500 lifetimes, and less than 0.77 per million lifetimes when chrysotile data were used. The rapporteurs wrote that averaging fiber potencies, as the US EPA has done, overestimates the risk of chrysotile-only 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: Rapporteur's report summarizing four papers presented at a conference session, with the rapporteurs' commentary; no new data
• Who was studied: Four session papers: Langer on identifying and counting asbestos fibers in mining; Berry and Gibbs on lung cancer and asbestos and taconite miners; Gibbs and Berry on mesothelioma and asbestos; Wilson, McConnell, Ross, Axten and Nolan on environmental exposure to fibrous particulates from taconite ore in Silver Bay, Minnesota. The rapporteurs (Nolan and Langer) were among the authors of papers 1 and 4.
• Exposure: Asbestos (chrysotile, crocidolite, amosite, anthophyllite, tremolite-actinolite asbestos) and other fibrous mineral particulates, including amphiboles of the cummingtonite-grunerite and tremolite-actinolite series associated with taconite ore
• Main results:
  • Paper 1 (as reported): the US permissible exposure limit for asbestos was cut by more than 120-fold from 12 fiber/ml in 1969. It is now 0.1 fiber/ml as an 8-hour time-weighted average in both mining and manufacturing workplaces.
  • Paper 2 (as reported): the cumulative exposure that doubled lung cancer risk was 130 fiber/ml-years in chrysotile manufacturing and textiles, compared with 4000 fiber/ml-years in chrysotile mining and milling. It was 24 fiber/ml-years for crocidolite versus 1613 for chrysotile.
  • Paper 2 (as reported): the US EPA lung cancer model predicted twice the number of lung cancers actually observed among women in the asbestos mining towns of Quebec.
  • Paper 2 (as reported): in three cohorts of taconite miners and millers in Minnesota and South Dakota, no convincing evidence of increased lung cancer risk was identified.
  • Paper 3 (as reported): among workers in three taconite-related cohorts, 2 of 2907 deaths (0.07%) were from mesothelioma. Among US males in the general population, 0.17% of deaths are from mesothelioma.
  • Rapporteurs' comparison for Libby, Montana vermiculite miners: 12 mesotheliomas among 286 deaths (4.2%) in McDonald et al. (2004), and 15 among 767 deaths (2%) in Sullivan (2007). Of these, 14 were pleural and one was peritoneal.
  • Rapporteurs' comment: in four major crocidolite mining and manufacturing cohorts, mesothelioma mortality ranged from 2.3% to 17.8% (overall about 8.2%).
  • Paper 4 (as reported): Silver Bay town air had a mean of 0.00014 f/ml, giving a lifetime cumulative exposure of 0.0479 f/cc-years. Treating the fibers as amphibole asbestos gave one excess cancer (lung and mesothelioma) in 28,500 lifetimes, or 35 per million.
  • Paper 4 (as reported): using chrysotile data, the estimated excess cancer risk was less than 0.77 deaths per million lifetimes. The calculated Silver Bay relative risk for lung cancer was 1.007.
• The authors' conclusion: The rapporteurs wrote that Gibbs and Berry made a convincing argument that asbestos fiber type matters in mesothelioma risk assessment. They added that the US EPA's averaging of fiber-type potencies overestimates the risk of chrysotile-only exposure.
• Limitations the authors state:
  • Paper 4's risk estimate was described as worst-case, because it assumed the Silver Bay fibers were as potent as asbestos. The report adds that a mineralogical survey of the source pit found no asbestos.
  • Paper 3 developed no mathematical model for anthophyllite asbestos and mesothelioma, because there were only four cases.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis.

Related studies

• Risk assessment due to environmental exposures to fibrous particulates associated with taconite ore — R. Wilson, E.E. McConnell, et al. (2008)
• Rapporteur's Report Session 2: characterization of fibrous minerals — A.M. Langer (2008)
• The relationship between various exposure metrics for elongate mineral particles (EMP) in the taconite mining and processing industry — J. Hwang, G. Ramachandran, et al. (2014)
• A comparison of asbestos fiber potency and elongate mineral particle (EMP) potency for mesothelioma in humans — D.H. Garabrant, S.T. Pastula (2018)
• An overview of the risk of lung cancer in relation to exposure to asbestos and of taconite miners — G. Berry, G.W. Gibbs (2008)
• Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry — J. Hwang, G. Ramachandran, et al. (2013)

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