Asbestos

CAS RN:1332-21-4

Exposure Summary

Asbestos is a term for six naturally occurring fibrous silicate minerals that have been mined, milled and used in many commercial products. Today, only one form of asbestos, chrysotile, is used in products in the United States. Due to its high tensile strength, low cost, resistence to heat, chemical attack, and biological attack, about 3,000 types of products were previously produced using asbestos. In most of these applications, asbestos fibers were bonded with some other material such as cement, plastics, pipes, or resins. Due to health concerns, asbestos is primarily used today in roofing products, gaskets and friction parts. The mining, milling and fabrication of asbestos containing products has resulted in its release to the environment through various waste streams. The last operating US asbestos mine closed in 2002. If released to air, asbestos fibers will eventually return to soil or water through gravitational settling and wet and dry deposition. Mean airborne concentrations of asbestos in US cities are roughly 2-4 ng/cu m, but much higher levels are typically observed near source dominated areas. Movement of asbestos fibers through soils only occur during runoff or erosion. Asbestos fibers will not volatilize or degrade in soils although they may be resuspended to the air by vehicular traffic or mining operations. Asbestos may be released to water from waste water in asbestos related industries, erosion of natural deposits or waste piles, corrosion of asbestos-cemented/asbestos-lined pipes, disintegration of asbestos containing roofing materials followed by subsequent runoff. Asbestos does not volatilize or degrade from water surfaces, nor does it appear to bioconcentrate in aquatic organisms. Occupational exposure occurs through inhalation and dermal contact in workplaces where asbestos is mined, milled, and products are manufactured or used. Monitoring data suggest that the general population is exposed to asbestos through inhalation of ambient air, ingestion of drinking water, and ingestion of food sources containing asbestos. In the past, filters made from asbestos were employed in the preparation of wines, beers, cigarette filters and other consumer products; however, these practices have been discontinued and intake of asbestos through foods and drugs is now unlikely. Low levels of asbestos are present in some talc powders and vermiculite, but the level of exposure from this source is considered low. (SRC)
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