Document G6z3XR0yw7zO1eyXdqY8N9a67

Km' science far a changing world Some Facts About Asbestos This Fact Sheet briefly reviews what asbestos is, how it is identified, where it is found, and how it is used. The U.S. Geological Survey (USGS) provides information on asbestos geolo gy, mineralogy, and mining; other agen cies listed on page 4 provide informa tion on regulations and health effects of asbestos exposure. What is asbestos? Asbestos is a generic name given to the fibrous variety of six naturally occurring minerals that have been used in commercial products. Asbestos is made up of fiber bundles. These bun dles, in turn, are composed of extremely long and thin fibers that can be easily separated from one another. The bundles have splaying ends and are extremely flexible. The term "asbestos" is not a miner. alogical definition. It is a commercial designation for mineral products that possess high tensile strength, flexibility, resistance to chemical and thermal degradation, and high electrical resist ance and that can be woven. What minerals occur as asbestos? The minerals that can crystallize as asbestos belong to two groups: serpen tine (chrysotile) and amphibole (crocidolite, amosite, anthophyllite asbestos, tremolite asbestos, and actinolite asbestos). Amphiboles are distinguished from one another by the amount of sodi um, calcium, magnesium, and iron that they containTSerpentine and amphibole} minerals can nave fibrous or nonfibrous structures (fig. 1); the fibrous type is called asbestos (see sidebar on Serpen tine and Amphibole Crystal Structure and Shape). Asbestiform varieties of several other amphiboles have been identified. Other minerals are similar to asbestos in their particle shape, but they do not pos sess the characteristics required to clas sify them as asbestos (see definition of asbestos above). Figure 1. A, Chrysotile asbestos, a member of the serpentine group of minerals. B, Antigorite and lizardite, nonasbestiform serpentine minerals. C, Tremolite asbestos, a member of the amphibole group. D, Tremolite having a nonasbestiform habit. Serpentine and amphi bole minerals can have fibrous or nonfibrous structures; the fibrous type is called asbestos. Photographs by Garrett Hyde from U.S. Bureau of Mines Information Circular 8751,1977. How is asbestos identified in a mineral sample or product? The best way to identify asbestos is to use a microscope to examine samples that have not been ground. Even with finely ground samples, there is no prob lem identifying chrysotile because its particle shape is distinct from the nonasbestiform varieties of serpentine. With amphiboles, however, the dis tinction between asbestiform and nonasbestiform varieties is much less clear when examining samples through a microscope. The reason is that amphi bole particles have a spectrum of shapes from blocky to prismatic to acicular to asbestiform. Also, amphiboles break (or cleave) into smaller fragments when finely ground. Long, thin cleavage frag ments resemble asbestos fibers. To resolve this problem, the ana- . lyst can compare the shapes of several hundred amphibole particles in the sample with those of asbestos reference materials and determine whether a sample is asbestiform with a fair degree of certainty. However, unless a fiber bundle has splaying ends, it is impossible to determine if a single long, thin particle grew that way (as asbestos) or is a cleavage fragment (nonasbestiform). U.S. Department of the Interior U.S. Geological Survey USGS Fact Sheet FS-O12-01 March 2001 HWBUI0005028 SERPENTINE AND AMPHIBOLE CRYSTAL STRUCTURE AND SHAPE The frameworks of silicate miner als are composed of oxygen and sili con. These elements are arranged in the shape of a pyramid or tetrahedron, with silicon in the center and oxygen at the four comers. For many silicate minerals, these tetrahedra are arranged in rows, and the rows are repeated to form the crystal structure. 4. _ A that is, they have one short dimension and two longer, approximately equal dimensions, like a saucer. In the asbestiform variety of serpen tine, chrysotile, sheets are rolled up tightly to form fibers. In serpentine, the element magne sium is coordinated with the oxygen atoms in the tetrahedra. The tetrahedra are arranged to form sheets. Serpen tine is a sheet silicate. With amphiboles, the distinction is not so clear. When short double chains are arranged side by side, blocky or equant crystals form. If growth is along the length of the double chains, rather than across their width, the amphibole crystals will be longer relative to their width. Slightly elongated crystals are prismatic. The framework for all amphi boles is a double chain composed of two rows of tetrahedra aligned side by side. Attached to these tetrahedra are elements such as aluminum, calci um, iron, magnesium, potassium, and sodium. A A. A. A A. A As the length increases relative to the width, the crystals are called acicular. When the length is extremely long compared with the width, the crystals are called asbestiform or fibrous. Among the .three principal serpen tine .minerals, the distinction between asbestos and nonasbestiform varieties is apparent. In the nonasbestiform antigorite and lizardite, the silica tetra hedra are arranged to form a sheet structure, and the crystals are platy; Unlike serpentine, which is either nonasbestiform (platy) or asbestiform (fibrous), amphiboles have a grada tional transition from blocky to pris matic to acicular to asbestiform. This gradational change makes it difficult to distinguish between asbestiform and nonasbestiform amphibole particles under the microscope. Does it matter whether an amphibole is asbestiform when it comes to health risk? Yes, the Occupational Safety and Health Administration (OSHA) conduct ed a review of the health effects of inhalation of nonasbestiform amphi boles. The agency determined (Federal Register, v. 57, no. 10, June 8, 1992, p, 24310)'that "available evidence supports a conclusion that exposure to non asbestiform cleavage fragments is not likely to produce a significant risk of developing asbestos-related disease." , Breathing high levels of asbestos fibers for a long time can lead to an increased risk of asbestosis, lung can cer, and mesothelioma. Asbestosis is a noncancerous lung disease related to scarring of the lungs. This disease occurs in people heavily exposed to asbestos in the workplace and in house hold contacts of asbestos workers. Lung cancer is a relatively common form of cancer, which has been linked to smok ing and a variety of occupational expo sures. Cigarette smoking significantly increases the risk of lung cancer for people exposed to asbestos. Mesothe lioma is a rare cancer of the membranes lining the lungs, chest, and abdominal cavity. Almost all cases are linked to occupational asbestos exposure. The symptoms of these diseases do not usu ally appear until 20 to 30 years after the first exposure to asbestos. Particle shape, particle solubility, and duration of exposure are reported to be the three most important factors that determine lung damage. Many researchers believe that amphibole asbestos particles pose a greater risk than chrysotile particles because they are less soluble and more rigid than chrysotile, allowing the amphibole asbestos particles to penetrate lung tis sue and remain longer. What is the most common type of asbestos? Chrysotile is the most common type of asbestos in the United States and the world. HWBUI0005029 What types of asbestos are mined? Currently, chrysotile is the only type of asbestos mined on a large scale. It makes up over 99 percent of presentday production in the world. Only chrysotile is mined in the United States. In 1999, one firm in California account ed for all U.S. chrysotile production. Small amounts of tremolite asbestos are mined in India and possibly a few other countries, but production is very limited. Commercial production of crocidolite and amosite ended about '4 years ago in South Africa. Anthophyllite asbestos has not been mined for an even longer period of time in the United States. Where does U.S. asbestos occur? Asbestos has been identified in 20 States (fig. 2) and mined in 17 States over the past 100 years. It is found in many common rocks. Serpentinite, the most widely occurring host rock for chrysotile, is present throughout the Appalachians, Cascades, Coast Ranges of California and Oregon, and other mountain belts. In general, chrysotile and amphibole asbestos varieties occur in areas where the original rock, under elevated . temperatures and pressures, has been changed by heated fluids (a process referred to as metamorphism). This type of altered rock occurs predominantly along the eastern seaboard from Alabama to Vermont, along the western seaboard from California to Washington, and in the upper Midwest in Minnesota and Michigan. Small occurrences of asbestos are in other areas, such as Arizona, Idaho, and Montana. Although asbestos can be present in most of the metamorphic rocks described above, the bulk of the rock mass does not contain asbestos. In fact, most commercial asbestos deposits con tain less than 6 percent asbestos by vol ume. Only a few deposits contain 50 percent or more asbestos (such as chrysotile deposits near Coalinga, Calif.). Is asbestos still used in the United States? Yes, about 15,000 metric tons (t) of asbestos was used in the United States in 1999; most was imported from Cana da. Major manufacturing uses in the United States are as follows: asphaltic roofing compounds used on commercial buildings, 61 percent; gaskets, 19 per cent; and friction products, such as brake shoes and clutches, 13 percent. Most of these products are installed on a commercial basis under conditions regu lated by OSHA. Although very few asbestos products have been banned in Figure 2. Occurrences of asbestos in the contiguous United States. Major asbestos-bearing deposits occur in the mountain belts in the Eastern and Western United States. Data from ISGS Digital Data Series DDS-52 (E.J. McFaul and others, 2000, U.S. Geological Survey Mineral Databases--MRDS and MAS/MILS). the United States, there are almost no asbestos-containing products manufac tured specifically for use by the general public. Is 15,000 metric tons a lot of asbestos? Relatively speaking, no. The peak year of asbestos use in the United States was 1973, when approximately 719,000 t of asbestos was used for manufacturing friction products, flooring, caulks, gas kets, packings, electrical and heat insu lation, plastics, roofing, textiles, and a host of other consumer and commercial products. There have been thousands of appli cations for asbestos. Most were viewed as practical solutions to difficult prob lems. For instance, asbestos helped make the braking systems in automo biles much more dependable, it enabled the production of inexpensive cementbased water-supply pipes, and despite the dire consequences to the installers, asbestos insulation made the warships of World War II much safer. In the late 1960's and early 1970's, the consumption of asbestos increased at the rate of 3 to 4 percent annually. In the 1980's and 1990's, consumption declined 5 percent annually (fig. 3). What caused the decline in asbestos use? Concerns over health risks posed by high exposures to airborne asbestos brought on much of the decline. From the I970's onward, public pressure to reduce exposure to asbestos resulted in lowered exposure standards and spurred the quest for alternatives to asbestos. Exposure standards were reduced from 5 fibers per cubic centimeter (f/cc) of air over an 8-hour time period to 0.1 f/cc in the workplace. Also, spraying of asbestos insulation onto steel girders and consumer sales of raw asbestos and artificial fireplace logs containing asbestos were banned. Commercial products such as asbestos-containing insulations, plasters, ceiling tiles, cement products, and caulks were slow ly phased out. Many companies ceased production of asbestos products because of liability issues. As a result, asbestos consumption in the United States declined rapidly. HWBUI0005030 5.000 EXPLANATION :;\i' A ' 4,500 A ' Hill U.S; consumption-. AA A,''-'' A'.A 4.000 0Q3 A;-'mu Worfd'produ'ctibri AA AA 19 ? 3,500 12 j O 3,000 "-It 'fc: r ' XH CJ --2' HLU 2,500 O 2 2,000 K* in O & 1,500 in < 1,000 QH HiSlI jlliS Ilf'.' iSo ||fl11 BfIS IS ;.;G 500 sll: 0 1940 'Hi 1950 'fllEgHEiiSH 1960 1 IWWM-- , | 1970 inr --MB | 1980 m-./' - Bin --, 1990 S;i '-- 1999 Figure 3. Asbestos consumption in the United States and world production of asbestos, which is used as a guide to world consumption. Peak U.S. consumption of asbestos was 719,000 met ric tons in 1973. Peak world production was 5.09 million metric tons in 1975. Data from Minerals Yearbook, v. I (published by the U.S. Bureau of Mines until 1995 and by the U.S. Geological Sur vey after 1995). "What about worldwide use of asbestos? Worldwide, the use of asbestos has declined, particularly in Western Europe. Asbestos production is used as a rough guide for consumption (fig. 3). Production declined from 5.09 million metric tons (Mt) in 1975 to about 1.93 \Mt in 1999. Several Western European . countries have banned some or all asbestos products. In other regions of the world, there is a continued demand for inexpensive, durable construction materials. Conse quently, markets remain strong for asbestos-cement (A/C) products, such as A/C panels for construction of buildings and A/C pipe for water-supply lines. What is the connection between asbestos and vermiculite? The connection between asbestos and vermiculite was first brought to public attention recently because of a vermiculite mine near Libby, Mont. Ver miculite consists of clay minerals that expand when heated to form wormlike particles. Vermiculite is used in concrete aggregate, fertilizer carriers, insulation, potting soil, and soil conditioners.. The Libby mine opened in 1921 and once accounted for almost 80 per cent of the world's vermiculite produc tion. The Libby deposit is unique among commercial U.S. .Vermiculite deposits in having an average amphibole asbestos content of 4 to 6 percent. Miners and millers were, at times, exposed to high levels of asbestos-containing dusts. Many workers developed health prob lems as a result of those exposures. Some residents of Libby who were exposed to high levels of asbestos also have been diagnosed with asbestosrelated symptoms. Officials are concerned about the asbestos content of the soils around Libby, about workers who processed the Libby vermiculite ore in manufacturing plants scattered throughout the United States, and about the customers of those plants. USGS scientists are using a hyperspectral remote-sensing survey of Libby to help map the distributions of the asbestiform amphiboles in Soils. Is this vermiculite still being sold? The Libby vermiculite mine closed in 1990, and shipments of vermiculite from the Libby mill site ended in 1992. However, products made from the Libby vermiculite may still be available from retailers who sell from old stocks. The only certain way to know whether ver miculite came from the Libby mine is to ask the manufacturer. Is more information available on asbestos? Yes. For questions concerning geol ogy, mineralogy, and the asbestos indus try, contact the U.S. Geological Survey online at http://minerals.usgs.gov/minerals or by fax from Mines FaxBack at (703) 648-4999. For information on regulations and health effects of asbestos exposure, con tact these agencies online: Consumer Product Safety Commis sion (www.cpsc.gov) U.S. Environmental Protection Agency (www.epa.gov) Mine Safety and Health Administra tion (www.msha.gov) Occupational Safety and Health Administration (www.osha.gov) National Institute for Occupational Safety and Health (www.cdc.gov/niosh/) National Institutes of Health (www.nih.gov) For information on this Fact Sheet, please contact: Robert L. Virta U.S. Geological Survey 983 National Center Reston, VA 20192 Telephone: (703) 648-7726 Fax: (703) 648-7722 E-mail: rvirta@usgs.gov Printed on recycled paper HWBUI0005031