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Carbon Tetrachloride
Description: Carbon tetrachloride (C.A.S. 56-23-5) is a clear, heavy liquid with a strong, aromatic odor. It is not believed to occur naturally, but is produced in large quantities for use in the manufacturing of refrigerants and propellants for aerosol cans. It is also used as a feedstock in the synthesis of chlorofluorocarbons and other chemicals, in petroleum refining, pharmaceutical manufacturing, and general solvent use. Until the mid 1960s, it was also widely used as a cleaning fluid, both in industry, where it served as a degreasing agent, and in the home, where it was used as a spot remover and in fire extinguishers. Chemical properties: Carbon tetrachloride is a highly volatile liquid with a strong etherial odor similar to chloroform. It mixes sparingly with water and is not flammable. When heated to decomposition, it emits highly toxic fumes of phosgene and hydrogen chloride. There is strong evidence that the toxicity of carbon tetrachloride is dramatically increased by its interaction with alcohols, ketones, and a range of other chemicals. Carbon tetrachloride is known to deplete the ozone layer, where it is responsible for 17 percent of the ozone-destroying chlorine now in the stratosphere due to human activities. Carbon tetrachloride has a half-life of between 30 and 100 years. Synonyms for carbon tetrachloride are carbona; carbon chloride; carbon tet; methane tetrachloride; methane, tetrachloro-; perchloromethane; and tetrachloromethane. Identification: Health effects: Carbon tetrachloride is listed in the National Toxicology Program's Fifth Annual Report on Carcinogens as a "substance which may reasonably be anticipated to be carcinogen." Short-term exposure by inhalation or ingestion can cause death. Short and long-term exposure also affects the brain, the liver, and the kidneys, in some cases causing death. There is some evidence that exposure to carbon tetrachloride causes liver cancer in humans; there is limited evidence that exposure may damage the developing fetus. Repeated contact can cause thickening and cracking of the skin. Effects on the brain are usually quite rapid. The most common effects are dizziness, lightheadedness, nausea and vomiting, which can cause permanent damage to nerve cells. In severe cases, these effects can lead rapidly to stupor, coma, unconsciousness or death. Exposure can make the heart beat irregularly or stop. The chemical may irritate the eyes on contact. When carbon tetrachloride is emitted into the air, it rises to the atmosphere and depletes the ozone layer. Depletion of the ozone layer is believed to increase human exposure to ultraviolet rays, leading to increased skin cancer, eye diseases and disorders, and possible disruption of the immune system. Persons who are moderate to heavy drinkers are at greatly increased risk of liver and/or kidney injury following ingestion or inhalation of carbon tetrachloride. Substantial exposures to alcohols and ketones which increase the toxicity of carbon tetrachloride may occur in occupational settings, or in certain instances in the use of household products containing these chemicals. Exposure Values: Economics: U.S. manufacturers of carbon tetrachloride are Akzo America, Inc, Le Moyne, AL; Dow Chemical USA, Pittsburg, CA; Hanlin Group, Inc, Moundsville, WV; Occidental Petroleum Corp, Belle, WV; Vulcan Materials Company, Geismar, LA; Five U.S. companies manufacture carbon tetrachloride: Akzo-America, formerly Stauffer Chemical, Chicago, IL; Dow, Midland, MI; LCP Chemicals and Plastics, Edison, N.J.; Occidental, Dallas, TX; and Vulcan Chemical, Birmingham, AL. In 1988, 761 million pounds of carbon tetrachloride were produced in the United States. Regulation: It seems certain that when the nations which signed the Montreal Protocol meet in London this month, they will agree to phase out carbon tetrachloride in the industrial world by 2000, though differences may exist over how fast to phase out the chemical in the 1990s. A phase-out of carbon tetrachloride in the United States is included in both the Senate and House versions of the Clean Air Act currently being negotiated in the U.S. Congress. The specific date and schedule of the phase-out are being determined by a House-Senate conference committee finalizing the bill to be sent to President Bush. EPA offices overseeing regulations and guidelines applicable to carbon tetrachloride are Air Quality Planning and Standards, Water Regulations and Standards (for the National Pollutant Discharge Elimination System), Drinking Water, Emergency and Remedial Response, Solid Waste, and Pesticide Programs. The Occupational Safety and Health Administration (OSHA) has established permissible exposure limits for carbon tetrachloride. The Federal Drug Administration has listed it as a banned hazardous substance. Under Section 313 of the Emergency Planning and Community Right to Know Act of 1986, releases of more than one pound of carbon tetrachloride into the air, water, and land must be reported annually and entered into the 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 |