Identification and quantitation of asbestos in talc

Our plain-English summary of Identification and quantitation of asbestos in talc, by A.N. Rohl, A.M. Langer (Environmental Health Perspectives, 1974).

The study

• Authors: A.N. Rohl, A.M. Langer
• Journal: Environmental Health Perspectives
• Published: 1974;9:95-109
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001285).

Abstract

The currently used analytical methods for identification, characterization and quantitation of asbestos fiber in consumer talcum products include polarized light microscopy, x-ray diffraction analysis, transmission electron microscopy with selected area electron diffraction and electron microprobe techniques. Light microscope methods have severe limitations imposed by the ultimate size resolution of the light-optical system. Small particles go unresolved; those marginally resolved may possess optical properties different from those properties cited in the literature; most optical properties, e.g., indices of refraction, are difficult to measure on small particles. In addition to these difficulties, talc fibers often possess optical properties different from those of talc plates, which further confound analysis. Light microscopy is recommended for use only as a preliminary tool on limited, large-sized, samples. Transmission electron microscopy is a good standard technique for visualization of contaminant asbestos fibers. Together with selected area electron diffraction, talc fibers may be easily differentiated from amphibole asbestos fibers on the basis of both morphological and structural characterization. Chrysotile fibers are easily distinguished on this basis as well. The amphibole asbestos minerals require chemical characterization to differentiate among the different fiber types. Probe analysis is mandatory for such fibers. The major drawbacks to electron beam instrumentation for the mineralogical characterization of talcum products are the time and effort required for data acquisition. These techniques do not lend themselves to routine study.X-ray diffraction analysis, utilizing the step-scan method, offers a relatively rapid, quantitative technique for gross fiber analysis. Based on comparison with standard specimens the fiber content of talcs may be quantitatively determined. It is essential to employ a specimen preparation technique which yields homogeneously dispersed particles. Tremolite may be determined at levels as low as 0.10% by weight, chrysotile 0.25%, and anthophyllite at 2.0% by weight occurrence in talc. The variance of these values depends upon many factors, including the mass absorption coefficient of the fiber types as compared to talc and selected diagnostic reflections and their relative intensities. Each of the above techniques is described in detail. A method for routine analysis of consumer talcum products is suggested.

In plain English

This 1974 laboratory methods paper described and compared ways of finding and measuring asbestos in talc, including consumer talcum products. It did not study people. The authors mixed known amounts of chrysotile, tremolite and anthophyllite into a talc that appeared free of asbestos. They then tested the smallest amount of each that x-ray diffraction, using a step-scan method, could detect. The lowest amounts detected were 0.1% by weight for tremolite, 0.25% for chrysotile and 2.0% for anthophyllite. By electron microscopy, a 0.25% chrysotile mixture was estimated to contain about one billion fibrils per milligram. The authors allowed that this calculation could be off by as much as one order of magnitude. Light microscopy missed many small fibers. Transmission electron microscopy with electron diffraction readily told talc fibers from asbestos but could not distinguish among amphiboles, which needed microprobe chemical analysis. The electron methods were too slow for routine use. The authors called x-ray diffraction at the chrysotile limit a crude and inaccurate measure. They recommended combining step-scan x-ray diffraction with transmission electron microscopy and electron diffraction for consumer talcs.

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 analytical methods study comparing light microscopy, x-ray diffraction, transmission electron microscopy with selected area electron diffraction, and electron microprobe analysis for detecting asbestos in talc
• Who was studied: No human subjects. The materials were laboratory-prepared two-mineral mixtures of chrysotile, tremolite or anthophyllite in a talc matrix that appeared free of asbestos. Consumer talcs (number not stated) were also examined by transmission electron microscopy, and talc samples from a mill containing anthophyllite and tremolite were examined by microprobe.
• Exposure: Asbestos fiber types added to talc at known weight percentages: UICC reference anthophyllite and tremolite, and a triple air jet milled chrysotile from the Jeffrey Mine, Quebec
• Main results:
  • Tremolite in talc was detected by step-scan x-ray diffraction down to 0.1% by weight; less than 0.1% was not detected
  • Chrysotile in talc was detected consistently by x-ray diffraction at a minimum of 0.25% by weight; lower levels could not be detected
  • Anthophyllite in talc was not detected by step-scan x-ray diffraction below 2.0%; the authors stated that as much as 2.0% anthophyllite may go undetected by this method
  • With continuous (rather than step) scanning, anthophyllite was not detected at or below 4.0%
  • Electron microscope counts of chrysotile fibrils tracked the chrysotile level. At 7100X magnification the average was 92 fibrils per field at 5% chrysotile, 22 at 1%, 8 at 0.5% and 6 at 0.25%, each plus or minus 10%.
  • The authors calculated about 4 billion chrysotile fibrils per milligram in a 1% mixture, and about 1 billion fibrils per milligram at 0.25%, the lowest level detectable by x-ray diffraction
  • Transmission electron microscopy with selected area electron diffraction distinguished fibrous talc from asbestos fibers easily
  • Transmission electron microscopy with electron diffraction could not distinguish among the amphiboles, which required microchemical analysis
  • By microprobe, tremolite was easily told apart from fibrous talc; anthophyllite, depending on its iron content, might not be
  • Light microscopy had severe limitations for asbestos in talc because many fibers were too small to see
• The authors' conclusion: The authors recommended using both step-scan x-ray diffraction and transmission electron microscopy with selected area electron diffraction to analyze consumer talcs for asbestos
• Limitations the authors state:
  • Preferred orientation of the platy and fibrous particles was described as the main factor limiting the accuracy of x-ray analysis
  • X-ray diffraction detection of chrysotile only at the 0.25% level was described as a crude and inaccurate measure of contamination and possible hazard
  • Electron beam methods take too much time and effort for routine use
  • The fibril-per-milligram calculation allowed for an error as large as one order of magnitude
  • Talcs with more than two mineral phases can be compared with the two-mineral standards only with limitations

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

All asbestos mines

Topics

The National Library of Medicine indexes this study under subjects our site covers: Talc and vermiculite.

Medical terms in this study, explained in our Lexicon: Talc, Polarized Light Microscopy (PLM), X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), Electron Microprobe Analysis, Amphibole Asbestos, Chrysotile.

Related studies

• Asbestos in talc — A.N. Rohl (1974)
• Approaches and constraints to identification and quantitation of asbestos fibers — A.M. Langer (1974)
• Identification of chlorite and serpentine in cosmetic or pharmaceutical talc — A.M. Blount, A.H. Vassiliou (1983)
• Mineralogical features associated with cytotoxic and proliferative effects of fibrous talc and asbestos on rodent tracheal epithelial and pleural mesothelial cells — A.G. Wylie, H.C. Skinner, et al. (1997)
• Characterization of talc and associated minerals — D.H. Hamer, F.R. Rolle, et al. (1976)
• Evaluation by electron microscopy techniques of asbestos contamination in industrial, cosmetic, and pharmaceutical talcs — L. Paoletti, S. Caiazza, et al. (1984)

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