Separation and characterization of respirable amphibole fibers from Libby, Montana

Our plain-English summary of Separation and characterization of respirable amphibole fibers from Libby, Montana, by J.S. Webber, D.J. Blake, T.J. Ward, et al (Inhalation Toxicology, 2008).

The study

• Authors: J.S. Webber, D.J. Blake, T.J. Ward, J.C. Pfau
• Journal: Inhalation Toxicology
• Published: 2008;20(8):733-40
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

The vermiculite mine in Libby, Montana, was in operation for over 70 yr and was contaminated with asbestos-like amphibole fibers. The mining, processing, and shipping of this vermiculite led to significant fiber inhalation exposure throughout the community, and residents of Libby have developed numerous pulmonary diseases such as lung cancer and mesothelioma. The present study describes the separation of Libby 6-mix into respirable and nonrespirable size fractions by means of aqueous elutriation. The elutriator, designed to separate fibers with aerodynamic diameters smaller than 2.5 microm (respirable) from larger fibers, used an upward flow rate of 3.4 x 10(- 4) cm s(-1). The resultant respirable fraction constituted only 13% of the raw Libby 6-mix mass, and less than 2% of the fibers in the elutriated fraction had aerodynamic diameters exceeding 2.5 microm. Surface area of the elutriated fibers was 5.3 m(- 2) g(-1), compared to 0.53 m(-2) g(-1) for the raw fibers. There were no detectable differences in chemical composition between the larger and smaller fibers. Such harvesting of respirable fractions will allow toxicological studies to be conducted within a controlled laboratory setting, utilizing fiber sizes that may more accurately simulate historical exposure of Libby residents' lungs. Importantly, this work describes a method that allows the use of material enriched in more uniform respirable material than raw Libby 6-mix, making comparisons with other known fiber preparations more valid on a mass basis.

In plain English

This was a laboratory study, not a study of people. The authors took Libby 6-mix, a U.S. Geological Survey sample of amphibole fibers including winchite, richterite and tremolite, and put it through a water-flow separation (aqueous elutriation). The separation was designed to keep only respirable particles, defined as an aerodynamic diameter of 2.5 micrometers or less. The separated portion made up only 13% of the original mass. Of 101 separated fibers measured by electron microscopy, 98% were at or below respirable diameters, while many fibers in the raw 6-mix were larger than respirable. The separated fibers averaged 2.7 micrometers long and 0.19 micrometers wide, with an aspect ratio of 16. Surface area was 5.3 square meters per gram for the separated fibers versus 0.53 square meters per gram for the raw 6-mix. The authors said this more closely approximated crocidolite (8.4 in their text, 8.1 in their table). The respirable fibers showed no size-related difference in elemental composition. The authors concluded that elutriation effectively separated respirable fibers from larger ones. They did not characterize nonfibrous particles or identify individual mineral species.

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: Laboratory study: separation of a reference amphibole sample into respirable and nonrespirable size fractions by aqueous elutriation, with electron-microscope characterization of fiber size and chemistry
• Who was studied: Libby 6-mix amphibole sample obtained from the U.S. Geological Survey. 101 elutriated fibers were characterized by TEM from 4 grid openings on three grids. Crocidolite from the Research Triangle Institute was analyzed for comparison but not elutriated.
• Exposure: Libby 6-mix amphibole fibers from Libby, Montana, containing six amphibole fiber types including winchite, richterite and tremolite. No human or animal exposure was studied.
• Main results:
  • The elutriated (respirable) fraction made up only 13% of the mass of the original Libby 6-mix placed in the elutriator.
  • In the elutriated fibers, 98% were at or below the respirable diameters.
  • Many of the fibers in the raw 6-mix were larger than respirable.
  • Mean dimensions of the elutriated fibers were 2.7 µm length, 0.19 µm width and aspect ratio 16.
  • Surface area was 0.53 square meters per gram for raw 6-mix fibers versus 5.3 square meters per gram for the elutriated fraction. The article prints the unit as m−2 g−1.
  • The authors stated that the elutriated fraction more closely approximated asbestiform materials. They cited a surface area of 8.4 square meters per gram for crocidolite in this study; Table 1 gives 8.1.
  • The respirable Libby amphibole fibers showed no size-selective difference in elemental composition.
  • Oxygen showed a significant negative correlation with fiber width (p = 3.1 × 10−6). The authors attributed this probably to self-absorption of oxygen x-rays.
  • Potassium showed a less significant positive correlation with fiber width (p = .047), with only a slight slope (0.033).
• The authors' conclusion: The authors concluded that elutriation was effective in separating respirable fibers from larger fibers in the stock Libby 6-mix.
• Limitations the authors state:
  • Nonfibrous particles in the Libby 6-mix were not characterized.
  • No attempt was made to identify specific amphibole mineral species fiber by fiber.
  • The authors stated it is uncertain, and beyond the scope of the article, how much the larger (nonrespirable) material would contribute to disease.

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Libby vermiculite mine, Montana

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Amphibole Group, vermiculite, Lung Cancer, Mesothelioma, Respirable Fraction.

Related studies

• Amphibole asbestos in tree bark--a review of findings for this inhalational exposure source in Libby, Montana — T.J. Ward, T.M. Spear, et al. (2012)
• Trees as reservoirs for amphibole fibers in Libby, Montana — T.J. Ward, T. Spear, et al. (2006)
• Where occupation and environment overlap: US Forest Service worker exposure to Libby Amphibole fibers — M. Harper, C. Butler, et al. (2015)
• Mortality in a cohort of vermiculite miners exposed to fibrous amphibole in Libby, Montana — J.C. McDonald, J. Harris, et al. (2004)
• A review of scientific literature examining the mining history, geology, mineralogy, and amphibole asbestos health effects of the Rainy Creek igneous complex, Libby, Montana, USA — B.R. Bandli, M.E. Gunter (2006)
• Exposure to airborne amphibole structures and health risks: Libby, Montana — B. Price (2008)

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