Asbestos electron microscopy

Asbestos fiber identification can also be achieved through transmission or scanning electron microscopy (tern, sem) techniques which are especially usefiil with very short fibers, or with extremely small samples (see Microscopy). With appropriate peripheral instmmentation, these techniques can yield the elemental composition of the fibers using energy dispersive x-ray fluorescence, or the crystal stmcture from electron diffraction, selected area electron diffraction (saed). 

In order to define the extent of emissions from automotive brakes and clutches, a study was carried out in which specially designed wear debris collectors were built for the dmm brake, the disk brake, and the clutch of a popular U.S. vehicle (1). The vehicle was driven through various test cycles to determine the extent and type of brake emissions generated under all driving conditions. Typical original equipment and aftermarket friction materials were evaluated. Brake relines were made to simulate consumer practices. The wear debris was analyzed by a combination of optical and electron microscopy to ascertain the asbestos content and its particle size distribution. It was found that more than 99.7% of the asbestos was converted to a nonfibrous form and... 

BS ISO 10312 Asbestos Direct-transfer transmission Electron microscopy... 

Asbestos by Transmission Electron Microscopy Analytical Method for the Determination of Asbestos Fibers in Water (EPA/600/4-83-043)... 

Asbestos by Transmission Electron Microscopy Determination of Asbestos Structures Over 10 p,m in Length in Drinking Water (EPA/600R-94/134)... 

Standard Methods for the Examination of Water and Wastewater 2570B Transmission Electron Microscopy (Asbestos)... 

Asbestos can be determined by several analytical techniques, including optical microscopy, electron microscopy, X-ray diffraction (XRD), light scattering, laser microprobe mass analysis, and thermal analysis. It can also be characterized by chemical analysis of metals by atomic absorption, X-ray fluorescence, or neutron activation techniques. Electron microscopy methods are, however, commonly applied for the analysis of asbestos in environmental matrices. 

Yada, K. 1971 Study of microstructure of chrysotile asbestos by high resolution electron microscopy. Acta crystallogr. A 27, 659-664. 

Optical Microscopy is a powerful tool in industrial hygiene for the analysis of asbestos, quartz or other substances. Electron microscopy and specialized techniques in optical microscopy such as ultraviolet, infrared, and fluorescence, although important, will not be considered in this paper. 

Given the need and financial incentives for improved, faster asbestos analysis, studies are ongoing to improve these areas. Intense activity is underway in the areas of automation and computerization, especially with TEM and analytical electron microscopy. Another area of investigation is to identify the fiber types and sizes most closely identified with risk of lung cancer and mesothelioma and develop methodology that will give results that are most closely correlated with risk (Berman et al. 1995). 

Dodson RF, Hurst GA, Williams MG, et al. 1988. Comparison of light and electron microscopy for defining occupational asbestos exposure in transbronchial lung biopsies. Chest 94 366-370. 

Kaijalainen A, Taikina-Aho O, Anttila S, et al. 1994c. Asbestos exposure among Finnish lung cancer patients. Comparison of scanning and transmission electron microscopy in the analysis of lung burden. Ann Occup Hyg 38 657-663. 

Kauffer E, Vigneron JC, Fabrics JF, et al. 1996. The use of a new static device based on the collection of the thoracic fraction for the assessment of the airborne concentration of asbestos fibres by transmission electron microscopy. Arm Occup Hyg 40 311-319. 

Paoletti L, Caiazza S, Donnelli G, et al. 1984. Evaluation by electron microscopy techniques of asbestos contamination in industrial, cosmetic, and pharmaceutical talcs. Regul Toxicol Pharmacol 4 222-235. 

PreatB. 2000. Confusion about the precision of asbestos fibres counting by electron microscopy. Ann Occup Hyg 44(1) 75. 

Verma DK, Clark NE. 1995. Relationships between phase contrast microscopy and transmission electron microscopy results of samples from occupational exposure to airborne chrysotile asbestos. Am Ind Hyg Assoc J 56 866-873. 

Results of a survey of asbestos fibers in consumer cosmetic talc powders from Italian and international markets using electron microscopy, electron diffraction, and energy dispersive x-ray analysis showed that asbestos was detected in 6 of 14 talc samples from the European Pharmacopeia (Paoletti et al. 1984). Chrysotile was identified in 3 samples, 2 samples contained tremolite asbestos and anthophyllite asbestos, and 1 sample contained chrysotile and tremolite asbestos. The authors noted that, in all talc powders analyzed, fibrous talc particles frequently were present that were morphologically similar to amphibole asbestos fibers. Counting fibers as particles with aspect ratio >3 1 and width < 3 m, the percentages of particles that were asbestos fibers ranged from <0.03% to 0.13% for 4 samples, and were 18% to 22% for the other 2 samples. Paoletti et al. (1984) noted that the European Pharmacopeia, at that time, had not established analytical quality control of asbestos contamination. 

Conversion Factors Conversion factors are used to compare results from epidemiologic studies that used different methods to measure airborne asbestos levels. Early studies often measured air concentrations in units of mass per volume of air or number of particles per volume of air, whereas more recent studies measure air concentrations in units of number of fibers (particles with lengths 5 m and aspect ratio 3 1, determined by PCM or electron microscopy) per volume of air. 

Constantopoulos et al. (1985, 1987a, 1991) attributed the pleural calcifications to the domestic production and use of a tremolite-asbestos-containing whitewash ( luto ) made from a local soil. Analysis of samples of the whitewash material by light microscopy, transmission electron microscopy, and x-ray dispersion analysis indicated that it contained predominantly asbestiform tremolite (Langer et al. 1987). 

The combined use of light microscopy, electron microscopy (transmission and scanning), and x-ray dispersive methods in analyzing air and/or bulk material samples offers the most accurate approach to estimating airborne asbestos concentrations. 

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