Tetrachloroethylene Overview

 

Tetrachloroethylene is a manufactured chemical used for dry cleaning and metal degreasing. Exposure to very high concentrations of tetrachloroethylene can cause dizziness, headaches, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and death. Tetrachloroethylene has been found in at least 771 of the 1,430 National Priorities List sites identified by the Environmental Protection Agency (EPA) and is a major drinking water contamination concern.

 

Michael Faraday first synthesized tetrachloroethylene in 1821 by thermal decomposition of hexachloroethane.  C2Cl6 → C2Cl4 + Cl2.  Most tetrachloroethylene is produced by high-temperature chlorinolysis of light hydrocarbons. The method is related to Faraday’s discovery since hexachloroethane is generated and thermally decomposes. Side products include carbon tetrachloride, hydrogen chloride, and hexachlorobutadiene.

 

 

 

What is Tetrachloroethylene?

 

Tetrachloroethylene is a manufactured chemical that is widely used for dry cleaning of fabrics.  Usually, as a mixture with other chlorocarbons, it is also used to degrease metal parts in the automotive and other metalworking industries.It is also used to make other chemicals and is used in some consumer products.

 

Other names for tetrachloroethylene include perchloroethylene, PCE, and tetrachloroethene. It is a nonflammable liquid at room temperature. It evaporates easily into the air and has a sharp, sweet odor. Most people can smell tetrachloroethylene when it is present in the air at a level of 1 part tetrachloroethylene per million parts of air (1 ppm) or more, although some can smell it at even lower levels.

 

According to the United States Environmental Protection Agency (EPA) report of 1976, the quantity of tetrachloroethylene produced in the United States in  1973 totaled 320,000 metric tons (706 million lb).[2] By 1993, the volume produced in the United States had dropped to 123,000 metric tons (271 million lb).

 

What Happens to Tetrachloroethylene When it Enters the Environment?

 

• Much of the tetrachloroethylene that gets into water or soil evaporates into the air.

• Microorganisms can break down some of the tetrachloroethylene in soil or underground water.

• In the air, it is broken down by sunlight into other chemicals or brought back to the soil and water by rain.

• It does not appear to collect in fish or other animals that live in water.

• Tetrachloroethylene is a common soil contaminant.

• With a specific gravity greater than 1, tetrachloroethylene will be present as a dense nonaqueous phase liquid (DNAPL) if sufficient quantities are released. Because of its mobility in groundwater, its toxicity at low levels, and its density (which causes it to sink below the water table), cleanup activities are more difficult than for oil spills (which has a specific gravity less than 1).

• Recent research has focused on the in place remediation of soil and groundwater pollution by tetrachloroethylene. Instead of excavation or extraction for above-ground treatment or disposal, tetrachloroethylene contamination has been successfully remediated by chemical treatment or bioremediation.

• Bioremediation has been successful under anaerobic conditions by reductive dechlorination by Dehalococcoides sp. and under aerobic conditions by cometabolism by Pseudomonas sp.

• Partial degradation daughter products include trichloroethylene, cis-1,2-dichloroethene and vinyl chloride; full degradation converts tetrachloroethylene to ethene and hydrogen chloride dissolved in water.

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How Might I Be Exposed to Tetrachloroethylene?

 

• When you bring clothes from the dry cleaners, they will release small amounts of tetrachloroethylene into the air.

• When you drink water containing tetrachloroethylene, you are exposed to it

 

How Can Tetrachloroethylene Affect My Health?

 

The International Agency for Research on Cancer has classified tetrachloroethylene as a Group 2A carcinogen, which means that it is probably carcinogenic to humans. Like many chlorinated hydrocarbons, tetrachloroethylene is a central nervous system depressant and can enter the body through respiratory or dermal exposure.

 

Drinking water contamination due to high concentrations of tetrachloroethylene (particularly in closed, poorly ventilated areas) can cause dizziness, headache, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and death.

Irritation may result from repeated or extended skin contact with it. These symptoms occur almost entirely in work (or hobby) environments when people have been accidentally exposed to high concentrations or have intentionally used tetrachloroethylene to get a “high.”

 

In industry, most workers are exposed to levels lower than those causing obvious nervous system effects. The health effects of breathing in air or drinking water with low levels of tetrachloroethylene are not known.

 

Results from some studies suggest that women who work in dry cleaning industries where exposures to tetrachloroethylene can be quite high may have more menstrual problems and spontaneous abortions than women who are not exposed. However, it is not known if tetrachloroethylene was responsible for these problems because other possible causes were not considered.

 

Results of animal studies, conducted with amounts much higher than those that most people are exposed to, show that tetrachloroethylene can cause liver and kidney damage. Exposure to very high levels of tetrachloroethylene can be toxic to the unborn pups of pregnant rats and mice. Changes in behavior were observed in the offspring of rats that breathed high levels of the chemical while they were pregnant.

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How Likely is Tetrachloroethylene to Cause Cancer?

 

The Department of Health and Human Services (DHHS) has determined that tetrachloroethylene may reasonably be anticipated to be a carcinogen. Tetrachloroethylene has been shown to cause liver tumors in mice and kidney tumors in male rats.

 

Is There a Medical Test to Show Whether I’ve Been Exposed to Tetrachloroethylene?

 

One way of testing for drinking water contamination due to tetrachloroethylene exposure is to measure the amount of the chemical in the breath, much the same way breath-alcohol measurements are used to determine the amount of alcohol in the blood.

 

Because it is stored in the body’s fat and slowly released into the bloodstream, tetrachloroethylene can be detected in the breath for weeks following a heavy exposure.

 

Tetrachloroethylene and trichloroacetic acid (TCA), a breakdown product of tetrachloroethylene, can be detected in the blood. These tests are relatively simple to perform. These tests aren’t available at most doctors’ offices, but can be performed at special laboratories that have the right equipment.

 

Because exposure to other chemicals can produce the same breakdown products in the urine and blood, the tests for breakdown products cannot determine if you have been exposed to tetrachloroethylene or the other chemicals.

 

Has the Federal Government Made Recommendations to Protect Human Health?

 

The EPA maximum contaminant level for the amount of tetrachloroethylene that can be in drinking water is 0.005 milligrams tetrachloroethylene per liter of water (0.005 mg/L).

 

The Occupational Safety and Health Administration (OSHA) has set a limit of 100 ppm for an 8-hour workday over a 40-hour workweek.

 

The National Institute for Occupational Safety and Health (NIOSH) recommends that tetrachloroethylene be handled as a potential carcinogen and recommends that levels in workplace air should be as low as possible.

 

References

 

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

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