Electron microscopical investigation of asbestos fibers

Our plain-English summary of Electron microscopical investigation of asbestos fibers, by A.M. Langer, A.D. Mackler, F.D. Pooley (Environmental Health Perspectives, 1974).

The study

• Authors: A.M. Langer, A.D. Mackler, F.D. Pooley
• Journal: Environmental Health Perspectives
• Published: 1974;9:63-80
• Cited by: 34 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Examination of asbestos fibers by electron microscopical techniques enables the observer to distinguish among the fiber types by morphological and structural characteristics. Chrysotile asbestos fibers are composed of bundles of fibrils. Fibers are often curvilinear with splayed ends. Individual fibrils consist of a central capillary defined by an electron dense crystalline wall. With increasing time of electron bombardment, the capillary wall decreases in thickness, deforms, and is encapsulated in an electron translucent material. The change in electron opacity is considered to be a product of structural disruption brought about by dehydroxylation due to electron radiation. A well recognized sequential deformation pattern may be used for identification purposes.Amphibole fibers tend to be straight, splintery, and electron-opaque, although curved fibers are occasionally observed. Diffraction contrast figures are visible as dark bands moving parallel and at right angles to the fiber axis. Crocidolite forms the shortest and thinnest fibers, followed in size by amosite and anthophyllite. Size distribution characteristics of the amphibole fiber types are different. The selected area electron diffraction pattern for chrysotile is unique. Reflections range in forms from streaked to arcuate. Reflection intensity and shape are related to the degree of openness of the fiber bundle and the extent of physical degradation of the fiber. The amphibole asbestos fibers possess diffraction patterns having similar characteristics prohibiting individual identification. Microchemical analysis is required for identification in such cases.A discussion of the industrial hygiene threshold limit values for ampliphibole asbestos fibers is presented. The discussion is based on their differing size distribution characteristics.

In plain English

This was a laboratory study that used transmission electron microscopy to describe features that could help identify very small asbestos fibers, even single fibers. The authors examined UICC standard reference samples of crocidolite, amosite and anthophyllite, tremolite from the vermiculite mining operation at Libby, Montana, and chrysotile from the Jeffrey mine in Quebec. The amphibole fibers differed in size. More than 50% of crocidolite fibers were under 0.16 micrometers wide, compared with 40% of amosite, 29% of tremolite and 20% of anthophyllite fibers. Almost 98% of crocidolite fibers were under 5 micrometers long, compared with 84% of amosite and 61% of anthophyllite fibers. Chrysotile fibers changed shape in a recognizable sequence under the electron beam. Chrysotile gave a distinctive electron diffraction pattern, but the amphibole patterns could not be told apart, so chemical analysis was needed. The authors argued that a single fiber-count limit corresponds to very different dust masses for different amphiboles. They concluded that the emphasis on crocidolite appeared premature.

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 of mineral samples using transmission electron microscopy and selected area electron diffraction; no human subjects
• Who was studied: Mineral samples, not people: UICC standard reference anthophyllite, amosite and crocidolite; tremolite from the vermiculite pit mining operation at Libby, Montana; chrysotile from the Jeffrey mine, Asbestos, Quebec
• Exposure: Fiber types examined: amphiboles (crocidolite, amosite, anthophyllite, tremolite) and chrysotile. Chrysotile was also examined after heating, Waring Blendor beating and ball milling.
• Main results:
  • Fiber widths: more than 50% of crocidolite fibers were under 0.16 micrometers wide, compared with 40% of amosite, 29% of tremolite and 20% of anthophyllite fibers. Widths measured: crocidolite 552, amosite 192, anthophyllite 261, tremolite 144.
  • Fiber lengths: almost 98% of crocidolite fibers were under 5 micrometers long, compared with 84% of amosite and 61% of anthophyllite fibers. Lengths measured: crocidolite 386, amosite 202, anthophyllite 212.
  • Chrysotile fibrils deformed in a recognizable sequence under prolonged electron bombardment, which the authors said may be used for identification
  • Chrysotile gave a unique selected area electron diffraction pattern
  • Selected area electron diffraction could not distinguish one amphibole type from another; the amosite and crocidolite patterns were indistinguishable
  • In the authors' discussion, the same mass of dust would give 39 countable fibers for anthophyllite but only two for crocidolite
  • The authors computed that Great Britain's limit of 0.1 fibers/ml for crocidolite corresponds to an equivalent mass exposure for anthophyllite of 2.0 fibers/ml
• The authors' conclusion: The authors concluded that, while the absolute carcinogenicity of the different fibers is unknown, the present emphasis on crocidolite appeared premature. They also stated that a single threshold limit value for all fibers rests on limited data.
• Limitations the authors state:
  • Widths above 1.0 micrometer were excluded from the mean calculation, so the mean width for anthophyllite is much lower than the real value
  • Tremolite was left out of the length analysis
  • The anthophyllite sample was contaminated with talc
  • Obtaining diffraction patterns accurate enough for spacing measurements was very difficult

Mines named here

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

• Jeffrey mine, Asbestos, Quebec
• Libby vermiculite mine, Montana

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: Chrysotile, Fibril, Crystalline, Dehydroxylation, Amphibole Group, Crocidolite, Amosite, Anthophyllite.

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