Identification and enumeration of asbestos fibers in the mining environment: mission and modification to the Federal Asbestos Standard

Our plain-English summary of Identification and enumeration of asbestos fibers in the mining environment: mission and modification to the Federal Asbestos Standard, by A.M. Langer (Regulatory Toxicology and Pharmacology, 2008).

The study

• Author: A.M. Langer
• Journal: Regulatory Toxicology and Pharmacology
• Published: 2008;52(1 Suppl):S207-17
• Cited by: 10 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Since the promulgation of the first Federal Asbestos Standard by the Occupational Safety and Health Administration in 1972, other federal agencies have modified the standard to better carry on their own unique missions. The instruments used to identify and measure asbestos, the sampling protocol, and the criteria used to define asbestos, have been modified to some degree. The Mine Safety and Health Administration regulates and controls asbestos dust in the mining and mineral commodity industries. However, crushed stone and processed ores contain mineral fragments that are frequently difficult to distinguish from asbestos. Mineral nomenclature, instruments for particle analysis, and sampling strategy must be accommodated to some degree to make asbestos control workable and meaningful. Precedent in other agencies has made consideration of these changes possible. Newly identified amphibole asbestos minerals have further complicated the agency's regulatory charge. Changes in its Asbestos Standard are now being considered. Crushed taconite ore in the Eastern Mesabi highlights many of these issues.

In plain English

This article is a review and commentary presented at a symposium. It reported no new study of workers or disease. It traced how US agencies adapted the 1972 Federal Asbestos Standard. It also described how hard it is, in mines and mills, to tell asbestos fibers from 'cleavage fragments', formed when non-asbestos forms of the same minerals are crushed. Citing Wylie (1988), it reported that 88% of tremolite from the Libby, Montana vermiculite deposit had a length-to-width ratio greater than 10:1, against 8% of tremolite from talc in Gouverneur, New York. Polarized light microscopy indicated that only the Libby tremolite occurred as asbestos. A 1979 analysis by the author's laboratory of crushed Eastern Mesabi taconite ore concluded that grunerite particles indistinguishable from amosite were only a very small fraction of the amphibole particles. The author noted MSHA's 2005 proposal to lower its eight-hour time-weighted average limit from 2.0 to 0.1 fibers per milliliter, and its 30-minute excursion limit to 1.0. The author judged analytical transmission electron microscopy no universal solution and suggested starting with geological field surveys.

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 and commentary on US asbestos regulation and on telling asbestos apart from cleavage fragments; a symposium paper with no new data
• Who was studied: No study population. The article covers US federal asbestos standards (OSHA, EPA, FDA, MSHA), mining and mineral-processing environments, Libby, Montana vermiculite, and crushed taconite ore of the Eastern Mesabi Range, Minnesota
• Exposure: The six regulated asbestos minerals (chrysotile, actinolite, amosite/grunerite asbestos, anthophyllite, crocidolite/riebeckite asbestos, tremolite). Newly described amphibole asbestos types (winchite, richterite, fluor-edenite, arfvedsonite). Non-asbestiform cleavage fragments of amphiboles in crushed ores
• Main results:
  • From Wylie (1988), as cited: 88% of Libby tremolite had an aspect ratio greater than 10:1, versus 8% of Gouverneur (talc) tremolite. 52% of Libby tremolite and 4% of Gouverneur tremolite had an aspect ratio of 20:1 or greater
  • Polarized light microscopy comparison indicated that only the Libby tremolite occurs as asbestos
  • Earlier analysis of Eastern Mesabi taconite (Langer et al., 1979) concluded that grunerite particles indistinguishable from amosite were only a very small fraction of all amphibole particles
  • MSHA's existing limit was 2 f/ml of air as an 8-hour time-weighted average
  • In 2005 MSHA proposed lowering its permissible exposure limit from 2.0 f/ml to the current OSHA level of 0.1 f/ml of air (OSHA's level being an 8-hour time-weighted average). It also proposed lowering its excursion level to 1.0 f/ml of air over 30 minutes
  • OSHA removed cleavage fragments from its Asbestos Standard in 1994
  • The author stated that analytical transmission electron microscopy (ATEM) is not a universal answer to identification
• The authors' conclusion: The author suggested that MSHA consider a tiered analysis, with field survey by MSHA geology staff as a reasonable first step

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Asbestos, Taconite.

Related studies

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• Double standards: the multinational asbestos industry and asbestos-related disease in South Africa — J. McCulloch, G. Tweedale (2004)
• Comprehensive assessment of exposures to elongate mineral particles in the taconite mining industry — J. Hwang, G. Ramachandran, et al. (2013)
• Asbestos risks: Manville tries to pass the buck — S. Budiansky (1983)
• The effect of a proposed change to fiber-counting rules in ASTM International Standard D7200-06 — M. Harper, E.G. Lee, et al. (2007)
• Occupational exposures and lung cancer risk among Minnesota taconite mining workers — E.M. Allen, B.H. Alexander, et al. (2015)

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