Chrysotile and amphibole asbestos

Short-fiber asbestos A trade name for asbestos with relatively short fibers. Both chrysotile and amphibole asbestos may occur in short fibers. 

Most attention has focused on occupational exposures to chrysotile and amphibole asbestos as it has been mined, processed, and used commercially or industrially. However, there has been some renewed attention to potential occupational, residential, and environmental exposures to asbestos that occur as an accessory mineral in rocks such as serpentinite (Renner, 2000), and to deposits of other industrial minerals such as vermiculite (e.g., Libby, Montana Lybarger et al., 2001 Dearwent et al., 2000 McDonald et al., 1986 Wright et al., 2002 Van Gosen et al., 2002 Meeker et al., in press Wylie and Verkouteren, 2000). Environmental exposures to erionite have also been well documented as... 

The different chemical composition and structures of chrysotile and amphibole asbestos have a considerable influence on their physical properties. 

Workplace exposure is usually assessed by personal sampling in which a known volume of air is sucked through a membrane filter which is subsequently prepared for examination by phase-contrast optical microscopy, and respirable fibres counted using predetermined rules (HSE, 1990). 0.5 0.2 f/ml control limits for chrysotile and amphibole asbestos exposure respectively has been introduced in the UK, and a 2f/ml maximum exposure to MMMF has been agreed, running in parallel with a 5mg/m gravimetric limit. 

The two main amphibole asbestos fibers are amosite and crocidoHte, and both are hydrated siHcates of iron, magnesium, and sodium. The appearance of these fibers and of the corresponding nonfibrous amphiboles is shown in Figure 1. Although the macroscopic visual aspect of clusters of various types of asbestos fibers is similar, significant differences between chrysotile and amphiboles appear at the microscopic level. Under the electron microscope, chrysotile fibers are seen as clusters of fibrils, often entangled, suggesting loosely bonded, flexible fibrils (Fig. 2a). Amphibole fibers, on the other hand, usually appear as individual needles with a crystalline aspect (Fig. 2b). 

The friction coefficients of asbestos fibers are also different for chrysotile and amphiboles (when measured against the same material). Compared to glass fibers, the friction coefficients decrease in the order chrysotile, amphiboles, glass fibers. 

Along these same lines, further work would be helpful in defining other fiber characteristics that are important determinants of carcinogenicity. It is suspected, for example, that amphiboles, such as crocidolite and tremolite asbestos, are more likely to cause mesothelioma than chrysotile, but it is not certain if this is attributable to differences in fiber length alone or to differences in chemical properties (e g., fiber morphometry, iron content, durability in biological fluids and tissues). Consequently, additional animal studies of the relative carcinogenic potency of airborne asbestos fibers of different types (e.g., chrysotile versus amphibole asbestos), carefully matched with regard to fiber size distribution, may be valuable. 

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. 

Bonneau, L., Suquet, H., Malard, C., and Pezerat, H. (1986b). Studies on surface properties of asbestos. I. Active sites on surface of chrysotile and amphiboles. Environ Res 41, 251-267. 

Malignant Mesothelioma As is true of carcinoma of the lung, the exact relationship of malignant mesothelioma and asbestos exposure is complicated (reviewed in Churg and Green 1998 EPA 2003 Churg et al. 2005a,b). The important issue of differences between chrysotile and amphiboles has been mentioned above. 

The word asbestos is a collective term that refers to a family of fibrous hydrous silicate minerals, including a serpentine (chrysotile) and amphiboles (crocidolite, amosite, tremolite). Because of its heat resistance and insulating properties, asbestos has been extensively used in most industrialized countries. The health effects of asbestos were described early in the 20th century, but it was only in the last few decades of this century that an intense medical and political debate was started, resulting in the ban of the use of these minerals in many countries and increasing restrictions in others. Even if the use of asbestos has dramatically decreased, leading to a virtual disappearance of severe cases of asbestosis (lung fibrosis), pleural manifestations are and will... 

In accordance with demonstrated differences between the various asbestos fiber types, the workplace regulation in many countries specifies different exposure limits for chrysotile and the amphiboles (45). Moreover, to alleviate estabHshed, or apprehended, risk from substitute fibers, the regulation often specifies maximum exposure limits for synthetic fibers (46) values of exposure limits adopted in leading industrial countries are coUected in Table 8. 

Cover the prohibition of the importation, supply or new use of amphibole asbestos or products containing it. Also prohibit the supply and use of a range of products containing chrysotile asbestos. 

ASBESTOS. The tenn asbestos is a generic designation referring usually to six types of naturally occurring mineral fibers which are or have been commercially exploited, These fibers are extracted from certain varieties of hydrated alkaline silicate minerals comprising two families seipe.ntin.es and amphiboles. The serpentine group contains a single fibrous variety chrysotile five fibrous forms of amphiboles are known anthophyllite, amosite, crocidolite. tremolite, and actinolite... 

Two molecular types of silicates are referred to as asbestos. Chrysotile is a magnesium silicate built upon a layered structure of silicate rings and Mg(OH)2. The layered structure causes the sheets to roll into cylinders approximately 200A in diameter. Amphibole asbestos may contain a variety of cations but is built upon a double chain silicate structure. The chrysotile asbestos is always found as an asbestiform crystal while the amphiboles may be either acicular or asbestiform. 

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