Detection and identification of asbestos by microscopical dispersion staining

Our plain-English summary of Detection and identification of asbestos by microscopical dispersion staining, by W.C. McCrone (Environmental Health Perspectives, 1974).

The study

• Author: W.C. McCrone
• Journal: Environmental Health Perspectives
• Published: 1974;9:57-62
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos fibers as small as 1 mum in diameter can be uniquely identified by light microscopy by employing dispersion staining methods. The technique described herein involves suspension of fibers in liquids of known refractive indices and observation of color display by means of a dispersion staining objective. Wavelengths or indices of refraction may be determined at right angles to and parallel to fiber axes. This method is rapid and sensitive for identification purposes.

In plain English

This article described a light-microscopy method, dispersion staining, for detecting and identifying asbestos fibers. It was a methods paper, not a study of people or disease. Particles are placed in liquids of known refractive index and viewed through a special objective, so that asbestos shows characteristic colors against a black background. The author wrote that these colors can be seen on particles well below 1 micrometer in diameter. The article listed matching wavelengths for more than 30 asbestos samples from different parts of the world. There was some variation between samples, but all fell in the chrysotile region, with no overlap with the fibrous amphiboles. Amosite and crocidolite might overlap partly, which the author said should not cause confusion. Quartz and lizardite can give colors resembling chrysotile but, according to the author, are told apart by particle shape. The author noted that the technique requires skill. The author concluded that particle shape plus optical properties uniquely identifies any fibrous asbestos and that, properly carried out, the method is capable of sensitivity in the parts-per-million (ppm) range.

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: Technical methods paper describing a light-microscopy identification technique (dispersion staining), with reference measurements on mineral samples; no human subjects
• Who was studied: Asbestos mineral samples, not people. Table 1 lists 31 samples, described in the text as 'more than 30', from Canada, the United States, Venezuela, Rhodesia, Cyprus, Greece, Yugoslavia, Italy, Russia and Australia. Anthophyllite from Maryland and North Carolina is also shown.
• Exposure: Not a human exposure study. The fiber types examined were chrysotile, anthophyllite, amosite and crocidolite, mounted in Cargille refractive index liquids. Quartz, lizardite, talc, paper fibers and mineral wool were discussed as possible look-alikes.
• Main results:
  • Across the 30-plus asbestos samples, matching wavelengths varied somewhat from sample to sample, which the author attributed to composition differences. All values fell in the characteristic chrysotile region, with no overlap with the fibrous amphiboles.
  • Most asbestos minerals had distinctive refractive indices without overlap. Amosite and crocidolite may overlap partially, but the author stated there should be no confusion because only one index of amosite overlaps one index of crocidolite.
  • For chrysotile, the observed matching wavelengths were 500 nm parallel to the fiber length and 570 nm crosswise in Cargille liquid nD 1.550, and 610 nm and 640 nm in liquid nD 1.560.
  • Quartz and lizardite can give dispersion staining colors that at first glance are confused with chrysotile. The author stated that both are easily distinguished from fibrous asbestos by particle shape.
  • The author stated that the colors can be observed on particles well below 1 micrometer in diameter, and that the lower limit of detection depends on light intensity and contrast.
  • A centered, nearly closed field diaphragm was reported to eliminate well over 90% of the glare that makes very fine asbestos fibers hard to see.
• The authors' conclusion: The author concluded that particle shape combined with optical properties uniquely identifies any of the fibrous asbestos compounds, and that dispersion staining is the most rapid way to obtain this information. The author also concluded that, properly carried out, the method is capable of sensitivity in the ppm range.
• Limitations the authors state:
  • The author described dispersion staining as a relatively new technique that requires skill, both in reading the colors and in adjusting the microscope.
  • Some substances, such as quartz and lizardite, give colors that can be confused with chrysotile and must be told apart by shape.
  • Non-stained particles close to or overlapping asbestos can hide it, so particles must be well separated in the mounting liquid.

Mines named here

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

• Bell Asbestos mine, Thetford Mines, Quebec
• Cassiar mine, British Columbia
• Clinton Creek property, northwest of Dawson, Yukon
• Copperopolis property, California
• Jeffrey mine, Asbestos, Quebec
• Lake Asbestos of Quebec, Black Lake, Quebec
• Woodsreef mine, near Barraba, New South Wales

All asbestos mines

Topics

Medical terms in this study, explained in our Lexicon: dispersion staining.

Related studies

• Techniques for the detection, identification and analysis of fibers — R.G. Keenan, J.R. Lynch (1970)
• Electron diffraction patterns of U.I.C.C. asbestos samples — M.I. Skikne, J.H. Talbot, et al. (1971)
• Procedure for the detection and identification of asbestos and other fibres in fibrous inorganic materials — L.J. Monkman (1979)
• Strategies in lung cancer detection. Achieving early identification in patients at high risk — J.J. Bechtel, T.L. Petty (2003)
• Approaches and constraints to identification and quantitation of asbestos fibers — A.M. Langer (1974)
• Identification and quantitation of asbestos in talc — A.N. Rohl, A.M. Langer (1974)

Browse more research in Environmental Health Perspectives, or return to medical research.