Tetrachloroethylene

Tetrachloroethylene is a manufactured chemical used for dry cleaning and metal degreasing. It is also used in the manufacture of other chemicals and for textile finishing and dyeing. Tetrachloroethylene has been produced commercially since the early 1900s. At room temperature, tetrachloroethylene is a nonflammable colorless liquid. It evaporates easily and has a sharp, sweet odor similar to chloroform, which most people can smell at a level of about one part per million (ppm). Other names for tetrachloroethylene are perchloroethylene, PCE, tetrachloroethene, and "perc".

Results of animal studies using high levels of tetrachloroethylene indicated that it can cause liver and kidney damage. Exposure to very high levels of tetrachloroethylene was toxic to the unborn pups of pregnant rats and mice. The offspring of rats exposed to high levels of tetrachloroethylene during pregnancy exhibited changes in behavior. Since tetrachloroethylene has been shown to cause liver tumors in mice and kidney tumors in male rats, it is considered to be a potential human carcinogen .

Exposure to high concentrations of tetrachloroethylene, especially in poorly ventilated areas, can cause nose and throat irritation and dizziness, headache, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and death. Severe skin irritation may result from repeated or extended skin contact with tetrachloroethylene.

The Occupational Safety and Health Administration (OSHA) has set a limit of 100 ppm for an eight-hour workday over a 40-hour workweek. The National Institute for Occupational Safety and Health (NIOSH) recommends that because tetrachloroethylene is a potential carcinogen, levels in the workplace should be kept as low as possible. Since tetrachloroethylene is considered a hazardous air pollutant under the U.S. Clean Air Act , a federal rule went into effect in 1996 for dry cleaning establishments that regulates operating procedures and equipment type and use, with the goal of reducing tetrachloroethylene emissions from those facilities. However, tetrachloroethylene does not contribute to stratospheric ozone depletion and has been approved by the U.S. Environmental Protection Agency (EPA) for use as a replacement for ozone-depleting solvents.

Tetrachloroethylene can be released into air and water through dry cleaning and industrial metal cleaning or finishing activities. Water pollution can result from tetrachloroethylene leaching from vinyl pipe liners. Tetrachloroethylene released into soil will readily evaporate or may leach slowly to groundwater, for it biodegrades slowly in soil. When released into water bodies, tetrachloroethylene will primarily evaporate and has little potential for accumulating in aquatic life.

The Maximum Contaminant Level (MCL), which is an enforceable standard for tetrachloroethylene in drinking water, has been set at 5 parts per billion (ppb) by the EPA. This is the lowest level of tetrachloroethylene, given present technologies and resources, that a water treatment system can be expected to achieve. In contrast to the enforceable level of tetrachloroethylene is the desired level in drinking water, which is referred to as the Maximum Contaminant Level Goal (MCLG). This been set at zero because of possible health risks. If levels of tetrachloroethylene are too high in a drinking water source, it can be removed through the use of granular activated carbon filters and packed tower aeration , which is a way to remove chemicals from ground water by increasing the surface area of the contaminated water that is exposed to air. Tetrachloroethylene wastes are classified as hazardous under the Resource Conservation and Recovery Act (RCRA) and must be stored, transported, and disposed of according to RCRA requirements.

[Judith L. Sims ]

RESOURCES

BOOKS

Leeds, Michelle S. Perchloroethylene (Carbon Dichloride, Tetrachloroethylene, Drycleaner, Fumigant): Effects on Health and Work. Washington, DC: Abbe Publishing Association, 1995.

OTHER

Halogenated Solvents Industry Alliance. Perchloroethylene: White Paper. November 1999 [cited June 22, 2002]. <http://www.hsia.org/white_papers/perc.htm>.

U.S. Environmental Protection Agency. Consumer Factsheet on: Tetrachloroethylene. May 22, 2002 [cited June 22, 2002]. <http://www.epa.gov/safewater/dwh/c-voc/tetrachl.html>.

U.S. Environmental Protection Agency. Rule and Implementation Information for Perchloroethylene Dry Cleaning Facilities. June 10, 2002 [cited June 23, 2002]. <http://www.epa.gov/ttn/atw/dryperc/dryclpg.html>.

TETRACHLOROETHYLENE

Tetrachloroethylene is a dry-cleaning agent and industrial degreaser that often goes under the name perchloroethylene (PERC). The National Institute of Occupational Safety and Health estimates that 650,000 U.S. workers are exposed to PERC annually. PERC enters the environment through evaporation or through transport into groundwater and drinking water supplies. Through widespread use it has become a frequent drinking water contaminant, and it is present in approximately half of the nation's Superfund sites.

PERC has a low odor threshold and its smell is that associated with a dry-cleaning establishment. High levels of PERC released in workplace accidents can produce loss of consciousness and death. There is some evidence that longer-term exposures to lower levels at the workplace can lead to kidney and liver damage, cancer, neurological impairment, including changes in memory and learning, and to problems with visual perception. Reproductive and developmental effects have been suggested.

Whether any of these effects occur at the much lower levels present in the general environment is controversial. There is increased pressure to regulate PERC because of particular concern for children living in apartment buildings above dry-cleaning establishments, and because as a chlorinated compound it can be a precursor of dioxins.

Bernard D. Goldstein

(see also: Dioxins; Toxicology )

Bibliography

New York State Department of Health (1997). Tetrachloroethylene (PERC) in Indoor and Outdoor Air: Fact Sheet. Albany, NY: Author.

U.S. Health Department of Health and Human Services (1997). Toxicological Profile for Tetrachloroethylene. Washington, DC: Public Health Service, Agency for Toxic Substances and Disease Registry.