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Xylenes
Description: Xylene (C.A.S. 1330-20-7) is a mixture of the three xylene isomers (ortho [o-xylene] (C.A.S. 95-47-6 ), meta [m-xylene] (C.A.S. 108-38-3), and para [p-xylene]) (C.A.S. 106-46-3), with possible trace amounts of ethylbenzene. It is also referred to as xylenes (mixed). It is a colorless liquid at room temperature, with an aromatic odor. Xylene is used as a solvent, to manufacture gasoline, as a raw material for the production of organic chemicals used to make polyester fibers, and to make dyes and insecticides. Other uses are in sterilizing catgut and in microscopy. The main source of xylenes has been from reforming petroleum fractions.
o-Xylene is used almost entirely as the feedstock for phthalic anhydride manufacture, and for the preparation of phthalonitrile which is converted to the copper phthalocyanine, a pigment.
m-Xylene is used for the manufacture of isophthalic acid and to a lesser extent, isophthalonitrile, which is the starting material of the fungicide tetrachloroisophthalonitrile.
p-Xylene, the most important commercial isomer, is primarily converted for use in fibers, films, or resins, including polyester fibers which are used for household fabrics, carpets, and clothing.
Chemical properties: Xylenes are flammable liquids and fire hazards. When heated to decomposition, xylenes emit acrid smoke and fumes. Xylene vapors may travel to a source of ignition and flash back. Xylenes are moderately soluble in water, and are incompatible with strong oxidizers.
Synonyms for xylene are dimethylbenzene and xylol. Synonyms for o-xylene are 1,2-dimethylbenzene and o-xylol. Synonyms for m-xylene are 1,3-dimethylbenzene and m-xylol. Synonyms for p- xylene are 1,4-dimethylbenzene and p-xylol.
Identification: Health effects: Xylenes can affect human health by being breathed in, being ingested, contacting skin or eyes, or passing through skin. High levels can cause dizziness, passing out, and death. Repeated exposure may damage bone marrow, causing low blood cell count. Xylene exposure may cause problems with memory and concentration, and may damage a developing fetus.
Xylenes may also irritate the eyes, nose, and throat. They may cause stomach problems, drowsiness, staggering gait, corneal vacuolization, nausea, vomiting, abdominal pain, dermatitis, lack of coordination, and anorexia.
Xylenes have high acute and chronic toxicity to aquatic life.
Exposure Values: Economics: U.S. manufacturers of xylenes are Amoco Oil Co, subsidiary, Texas City, TX; Amoco Chemicals Co, Whiting, IN; Ashland Oil, Inc, Ashland Chemical Co,
Div, Petrochemicals Div, Catlettsburg, KY; BP Oil, Alliance, LA; Chevron Corp, subsidiary, Chevron Chemical Co, Pascagoula, MS; Citgo Petroleum Corporation, Chorpus Christi, TX; Coastal Eagle Point Oil Company, Westville, NJ; Coastal Refining and Marketing Company, Chorpus Christi, TX; Exxon Corp, Baytown, TX; Fina Oil and Chemical Company, Port Arthur, TX; Hess Oil Virgin Islands Corp, St. Croix, Koch Industries, Inc, Corpus Christi, TX; Lyondell-Citgo Refining Company LTD, Houston, TX; Marathon Oil, Texas City, TX; Mobil Chemical Company, Petroleum Division, Beaumont, TX; Phillips Petroleum Co, Sweeny, TX; Guayama, Puerto Rico; Shell Oil Co, Deer Park, TX; Sun Company, Inc, Marcus Hook, PA; Toledo, OH; and The UNO-VEN Company, Lemont, IL.
Regulation: The Occupational Safety and Health Administration issues permissible exposure limits for xylenes. Xylene and the three xylene isomers are regulated by the U.S. Environmental Protection Agency as air toxics on the hazardous air pollutant list, and as volatile organic compounds.
Under the Emergency Planning and Community Right-to-Know Act of 1986, releases of more than one pound of xylene and the three xylene compounds into the air, water, and land must be reported annually and entered into the national Toxic Release Inventory (TRI).
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 |