 |
Also see:
|
Asbestos
Description: Asbestos (C.A.S. 1332-21-4) is a generic term for a group of six naturally occurring fibrous minerals: amosite (C.A.S. 12172-73-5), chrysotile (C.A.S. 12001-29-5), crocidolite (C.A.S. 12001-28-4), and the fibrous varieties of tremolite (C.A.S. 14567-73-8), actinolite (C.A.S. 13768-00-8), and anthophyllite (C.A.S. 17068-78-9). The most common mineral type is chrysotile. These minerals are made of fibers that vary in length and may be straight or curled. Asbestos can be found naturally in soil and rocks in some areas. Because asbestos fibers are resistant to heat and most chemicals, they have been mined for use in at least 5,000 products, mostly in building materials and heat-resistant fabrics. The main uses have been in roofing products, paper products, cement products, thermal and electrical insulation, flooring, pharmaceutical and beverage filters, friction products, textiles, packings and gaskets, coatings, and asbestos-reinforced plastics. Because asbestos fibers are considered to be carcinogenic and may produce adverse health effects in exposed persons, all new uses of asbestos have been banned in the United States by the EPA. In October 1991, a U.S. federal court overturned an EPA regulation that banned most uses of asbestos by 1997. Only asbestos-containing products that were not being manufactured, imported, or processed on July 12, 1989, remain subject to the prohibition requirements of the EPA regulation. Chemical properties: The basic chemical structure of asbestos is (SiO4). Chemical formulae for the asbestos types are amosite ([Mg,FE]7Si8O22[OH]2)n; chrysotile Mg3Si2O5[OH]4); crocidolite ([NaFe32+Fe23+Si8O22(OH)2]n); tremolite ([Ca2Mg5Si8O22(OH)2]n; actinolite ([Ca2(Mg,Fe)5Si8O22(OH)2]n; and anthophyllite ([(Mg,Fe)7Si8O22(OH)2]n. Amosite is a brown, gray, or greenish color; chrysotile is white, gray, green, or yellowish; crocidolite is lavender, blue, or green; tremolite is white to light green; actinolite’s color is not known; and anthophyllite is gray, white, brown-gray, or green. Asbestos fibers do not evaporate into air or dissolve in water, and do not have any detectable odor or taste. They cannot move through soil, and are not broken down to other compounds in the environment. All asbestos fibers are solids, are insoluble in water and organic solvents, and are nonflammable. Chrysotile is soluble in acid. Amosite, crocidolite and anthophyllite are fairly resistant to acids. Synonyms for asbestos include 4T04, 7N04, 7R-F9, 7RF10, actinolite, actinolite asbesto, amosite (cummingtonite-grunerite), anthophyllite, anthophyllite asbestos, asbestos (friable), asbestos fiber, AT 7-1, BK 6-20, BP 3-50, calidria HPP, calidra R-G 244, carey 4T, chlorobestos 25, chrysotile, crocidolite (riebeckite), FAPM 410-120, ferodo C3C, fibers (mineral, asbestos), HPO (mineral), K 6-20, litaflex, M 3-60, M4-5, M5-60, M6-40, mountain cork, mountain leather, mountain wood, MTM, P 5-50, PRZH 2-30, sepiolex 3, sepiolex 5, SM 1 (mineral), SM 2 (mineral, T 135, tremolite, and tremolite asbestos. Identification: Health effects: Asbestos is classified as a substance known to be carcinogenic by the Seventh Annual Report on Carcinogens, 1994, published by the National Toxicology Program, U.S. Department of Health and Human Services. It is also listed in the EPA’s Toxic Release Inventory (TRI) as an "OSHA carcinogen." Inhalation is the principal route of exposure to asbestos. Other routes are dermal contact and ingestion. Workers who breathe in asbestos may develop a slow buildup of scar-like tissue in the lung and membrane that surrounds the lungs, a disease called asbestosis. It may make breathing difficult, decrease blood flow to the lung, and cause the heart to enlarge. It is often associated with a dry cough. Asbestos workers have increased chances of getting two types of cancer: cancer of the lung itself, and mesothelioma, a cancer of the thin membrane that surrounds the lung and other internal organs. Inhalation of asbestos increases the risk of cancer at other sites, especially the gastrointestinal tract. Prolonged inhalation of asbestos can cause cancer of the pleura, peritoneum, intestine, bronchus, and oropharynx. For lung cancer, the magnitude of the risk appears to be a complex function of a number of factors, including the level and duration of exposure; the time since exposure occurred; the age at which exposure occurred; the tobacco-smoking history of the exposed person; and the type and size distribution of the asbestos fibers. Both cigarette smoking and occupational exposure to asbestos fibers increase lung cancer incidence independently. When present together, they act multiplicatively. Asbestos exposure can also produce adverse effects in the upper airways, including laryngitis. Worker exposure is a concern in the mining and milling of asbestos, during the manufacture of asbestos products, and in the construction and shipbuilding industries. Worker exposure also occurs in asbestos end-product use occupations such as asbestos insulation workers, brake repair and maintenance workers, building demolition workers, and asbestos abatement workers. Families of asbestos workers are potentially exposed to high fiber levels through contaminated clothing brought home for laundering. The general public may encounter low levels of asbestos by oral, inhalation, or dermal routes of exposure. Dermal contact with asbestos can cause small warts or corns. Exposure Values: Economics: U.S. manufacturer of asbestos International Commodities Export Corp, White Plains, NY. Regulation: NIOSH considers asbestos (i.e., actinolite, amosite, anthophyllite, chrysotile, crocidolite, and tremolite) to be a potential occupational carcinogen and recommends that exposures be reduced to the lowest possible concentration. For asbestos fibers >5 micrometers in length, NIOSH recommends a REL of 100,000 fibers per cubic meter of air (100,000 fibers/m3), which is equal to 0.1 fiber per cubic centimeter of air (0.1 fiber/cm3), as determined by a 400-liter air sample collected over 100 minutes and NIOSH Analytical Method #7400. As found in 29 CFR 1910.1001, the OSHA PEL for asbestos fibers (i.e., actinolite asbestos, amosite, anthophyllite asbestos, chrysotile, crocidolite, and tremolite asbestos) is an 8-hour TWA airborne concentration of 0.1 fiber (longer than 5 micrometers and having a length-to-diameter ratio of at least 3 to 1) per cubic centimeter of air (0.1 fiber/cm3), as determined by the membrane filter method at approximately 400X magnification with phase contrast illumination. No worker should be exposed in excess of 1 fiber/cm3 (excursion limit) as averaged over a sampling period of 30 minutes. EPA Offices regulating asbestos are Air Quality Planning and Standards; Water Resources and Standards; Drinking Water; Emergency and Remedial Response; and Toxic Substances. The Food and Drug Administration (FDA) regulates asbestos as a component of food packaging material. The Consumer Product Safety Commission has banned asbestos in patching compounds and in gas fireplaces. Manufacturers of hand-held hair dryers have cooperated with the CPSC by voluntarily ceasing to use asbestos liners in hair dryers. Asbestos is regulated under the Emergency Planning and Community Right-to-Know Act; Clean Air Act; Comprehensive Environmental Response, Compensation and Liability Act; Safe Drinking Water Act, under the National Primary Drinking Water Regulations; and Clean Water Act, as a priority pollutant. National Overview of 1998 Toxics Release Inventory See EPA's Toxic Release Inventory. Notations: The NIOSH recommended exposure limits (RELs) are time-weighted average (TWA) concentrations for up to a 10-hour workday during a 40-hour workweek. A short-term exposure limit (STEL) is designated by "ST" preceding the value; unless noted otherwise, the STEL is a 15-minute TWA exposure that should not be exceeded at any time during a workday. A ceiling REL is designated by "C" preceding the value. Any substance that NIOSH considers to be a potential occupational carcinogen is designated by the notation "Ca." The OSHA permissible exposure limits (PEL) are found in Tables Z-1, Z-2, and Z-3 of the OSHA General Industry Air Contaminants Standard (29 CFR 1910.1000). Unless noted otherwise, PEL are TWA concentrations that must not be exceeded during any 8-hour workshift of a 40-hour workweek. A STEL is designated by "ST" preceding the value and is measured over a 15-minute period unless noted otherwise. OSHA ceiling concentrations (designated by "C" preceding the value) must not be exceeded during any part of the workday; if instantaneous monitoring is not feasible, the ceiling must be assessed as a 15-minute TWA exposure. In addition, there are a number of substances from Table Z-2 (e.g., beryllium, ethylene dibromide, etc.) that have PEL ceiling values that must not be exceeded except for specified excursions. For example, a "5-minute maximum peak in any 2 hours" means that a 5-minute exposure above the ceiling value, but never above the maximum peak, is allowed in any 2 hours during an 8-hour workday. Information Sources:
Originally published in Environment Writer by the National Safety Council. Reprinted with permission. Environment Writer Metcalf Institute for Marine and Environmental Reporting University of Rhode Island Graduate School of Oceanography Office of Marine Programs Narragansett, RI 02882 Tel: 401-874-6211; Fax: 401-874-6485 Disclaimer * Copyright 2002-2006 * All rights reserved. * University of Rhode Island |