Identification and quantitation of asbestos in talc

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. ImagesFIGURE 1.FIGURE 3.FIGURE 6.FIGURE 7.FIGURE 8.

Consumer talcums and powders: Mineral and chemical characterization

“…The application of X-ray diffraction analysis in step-scan mode for quantitative determination of asbestos in talc has been described in detail (Rohl and Langer, 1974), including the selection of talc and asbestos reference materials, the preparation of standard dilutions of asbestos minerals in talc to ensure sensitivity and reproducibility, the selection of characteristic X-ray reflections to be scanned, and instrumental technique.…”

“…The residue forms a flat cake of about 0.5 mm uniform thickness on the membrane filter. When dried, the sample is affixed to a glass slide for X-ray diffraction analysis (Rohl and Langer, 1974).…”

“…The intensity of a reflection is proportional to, but not necessarily a linear function of, its concentration. Other factors that may influence reflection intensities include instrumental conditions, particle size, degree of preferred orientation, sample thickness and flatness, and absorption characteristics (Klug and Alexander, 1954;Rohl and Langer, 1974). Figure 2 shows calibration curves obtained for chrysotile, anthophyllite, tremolite, and quartz using the step-scan technique.…”

Analysis of an Authentic Historical Italian Cosmetic Talc Sample – Further Evidence for the Lack of Cancer Risk

“…Paoletti, Caiazza, Donelli & Pocchiari (1984) reported "tremolite asbestos" in two of five Italian cosmetic talc samples but neither was identified as coming from the Fontane mine. IARC (2010) as well as Hildrick-Smith (1976) and Price (2010) seriously questioned all the claims of historical (pre-1976) contamination (Cralley, Key, Groth, Lainhart & Ligo, 1968;Rohl & Langer 1974;Rohl, Langer & Selikoff. 1976;Longo & Young, 1979).…”

Quantification of Silicate Fiber Concentrations in Rock Products and Dusts by Electron Microscopy

“…(11)(12)(13)(14) Amphiboles can be separated from talc by heavy liquids and from limestone or dolomite by hydrochloric acid dissolution. (l5-16) Other rock materials like olivine products have been analyzed after sieving into grain size fractions.I!"…”