Tetrachloroethylene Defined

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Highlights of Tetrachloroethylene
What is Tetrachloroethylene?
What happens to tetrachloroethylene when it enters the environment?
How might I be exposed to tetrachloroethylene?
How can tetrachloroethylene affect my health?
How likely is tetrachloroethylene to cause cancer?
Is there a medical test to show whether I’ve been exposed ?
Has the federal government made recommendations to protect human health?
Production
Uses
Historical applications
Health and safety
Testing for exposure
Environmental contamination


Highlights of Tetrachloroethylene

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.

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What is tetrachloroethylene?

Tetrachloroethylene is a manufactured chemical that is widely used for dry cleaning of fabrics and for metal-degreasing. 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.

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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.

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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

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 How can tetrachloroethylene affect my health?

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.

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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.

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 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.

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Glossary

Carcinogen: A substance with the ability to cause cancer.

CAS: Chemical Abstracts Service.

Milligram (mg): One thousandth of a gram.

Nonflammable: Will not burn.


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.

From Wikipedia, the free encyclopedia

Tetrachloroethylene
Tetrachloroethylene Tetrachloroethylene
Identifiers
CAS number 127-18-4 Yes
ChemSpider 13837281 Yes
UNII TJ904HH8SN Yes
EC number 204-825-9
UN number 1897
KEGG C06789 Yes
ChEBI CHEBI:17300 
ChEMBL CHEMBL114062 Yes
RTECS number KX3850000
Jmol-3D images Image 1
Properties
Molecular formula C2Cl4
Molar mass 165.83 g mol−1
Appearance Clear, colorless liquid
Density 1.622 g/cm3
Melting point −19 °C (−2 °F; 254 K)
Boiling point 121.1 °C (250.0 °F; 394.2 K)
Solubility in water 0.15 g/100 mL (20 °C)
Viscosity 0.89 cP at 25 °C
Hazards
MSDS External MSDS
R-phrases R40 R51/53
S-phrases S23 S36/37 S61
Main hazards Harmful (Xn), Dangerous for the environment (N)
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no code

NFPA 704 four-colored diamond

Flash point Not flammable
Related compounds
Related Related organohalides Tetrabromoethylene Tetraiodoethylene
Related compounds Trichloroethylene Dichloroethene Tetrachloroethane
Supplementary data page
Structure and properties n, εr, etc.
Thermodynamic data Phase behaviour Solid, liquid, gas
Spectral data UV, IR, NMR, MS

Tetrachloroethylene, also known under the systematic name tetrachloroethene, or perchloroethylene (“perc” or “PERC“), and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colorless liquid widely used for dry cleaning of fabrics, hence it is sometimes called “dry-cleaning fluid.” It has a sweet odor detectable by most people at a concentration of 1 part per million (1 ppm). Worldwide production was about one million metric tons in 1985.[1]


Production

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.[1] Side products include carbon tetrachloride, hydrogen chloride, and hexachlorobutadiene.

Several other methods have been developed. When 1,2-dichloroethane is heated to 400 °C with chlorine, tetrachloroethylene is produced by the chemical reaction: ClCH2CH2Cl + 3 Cl2 → Cl2C=CCl2 + 4 HCl

This reaction can be catalyzed by a mixture of potassium chloride and aluminium chloride or by activated carbon. Trichloroethylene is a major byproduct, which is separated by distillation.

According to an United States Environmental Protection Agency (EPA) report of 1976, the quantity of tetrachloroethylene produced in the United States in the 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).[3]

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Uses

Tetrachloroethylene is an excellent solvent for organic materials. Otherwise it is volatile, highly stable, and nonflammable. For these reasons, it is widely used in dry cleaning. Usually as a mixture with other chlorocarbons, it is also used to degrease metal parts in the automotive and other metalworking industries. It appears in a few consumer products including paint strippers and spot removers.

It is used in neutrino detectors where a neutrino interacts with a neutron in the chlorine atom and converts it to a proton to form argon.


Historical applications

Tetrachloroethylene was once extensively used as an intermediate in the manufacture of HFC-134a and related refrigerants. In the early 20th century, tetrachloroethene was used for the treatment for hookworm infestation.[4]


Health and safety

The International Agency for Research on Cancer has classified tetrachloroethylene as a Group 2A carcinogen, which means that it is probably carcinogenic to humans.[5] Like many chlorinated hydrocarbons, tetrachloroethylene is a central nervous system depressant and can enter the body through respiratory or dermal exposure.[6] Tetrachloroethylene dissolves fats from the skin, potentially resulting in skin irritation.

Animal studies and a study of 99 twins showed there is a “lot of circumstantial evidence” that exposure to tetrachloroethylene increases the risk of developing Parkinson’s disease ninefold. Larger population studies are planned.[7]

At temperatures over 315 °C (599 °F), such as in welding, tetrachloroethylene can be oxidized into phosgene, an extremely poisonous gas.[8] Therefore, tetrachloroethylene should not be used near welding operations, flames, or hot surfaces.[9]

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Testing for exposure

Tetrachloroethylene exposure can be evaluated by a breath test, analogous to breath-alcohol measurements. 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.

In Europe, the Scientific Committee on Occupational Exposure Limits (SCOEL) recommends for tetrachloroethylene an occupational exposure limit (8 hour time-weighted average) of 20 ppm and a short-term exposure limit (15 min) of 40 ppm.[10]


Environmental contamination

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 ground water 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.[11][12] 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.

Estimates state that 85% of tetrachloroethylene produced is released into the atmosphere; while models from OECD assumed that 90% is released into the air and 10% to water. Based on these models, its distribution in the environment is estimated to be in the air (76.39% – 99.69%), water (0.23% – 23.2%), soil (0.06-7%), with the remainder in the sediment and biota. Estimates of lifetime in the atmosphere vary, but a 1987 survey estimated the lifetime in the air has been estimated at about 2 months in the Southern Hemisphere and 5–6 months in the Northern Hemisphere. Degradation products observed in a laboratory include phosgene, trichloroacetyl chloride, hydrogen chloride, carbon dioxide, and carbon monoxide. Tetrachloroethylene is degraded by hydrolysis, and is also persistent under aerobic conditions. This compound is degraded by reductive dechlorination with anaerobic conditions present, with the degradation products such as trichloroethylene, dichloroethylene, vinyl chloride, ethylene, and ethane.[13]

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References

  1. M. Rossberg et al. “Chlorinated Hydrocarbons” in Ullmann’s Encyclopedia of Industrial Chemistry, 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a06_233.pub2
  2. “Assessment of Hazardous Waste Practices: Organic Chemicals, Pesticides and Explosives Industries” prebpublication issue for EPA Libraries and Solid Waste Management Agencies under contract # 68-01-2919, USEPA 1976
  3. “Toxicological Profile For Tetrachloroethylene”. Atlanta, GA: Agency for Toxic Substances and Disease Registry. September 1997. p. 174. Retrieved 2012-09-16. citing C&EN, 1994, Facts and Figures for the Chemical Industry, Chemical and Engineering News, July 4, 1994.
  4. Young, M.D.; et al. (1960). “The Comparative Efficacy of Bephenium Hydroxynaphthoate and Tetrachloroethylene against Hookworm and other Parasites of Man”. American Journal of Tropical Medicine and Hygiene 9 (5): 488–491. PMID 13787477.
  5. IARC monograph. Tetrachloroethylene, Vol. 63, p. 159. Last Updated May 20, 1997. Last retrieved June 22, 2007.
  6. Control of Exposure to Perchloroethylene in Commercial Drycleaning. Hazard Controls: Publication 97-157. National Institute for Occupational Safety and Health.
  7. Industrial Solvent Linked to Increased Risk of Parkinson’s Disease
  8. Medical Management Guidelines for Tetrachloroethylene
  9. Working safely with tetrachloroethylene
  10. “SCOEL recommendations”. 2011-04-22. Retrieved 2011-04-22.
  11. Ryoo, D., Shim, H., Arenghi, F. L. G., Barbieri, P., Wood T. K. (2001). “Tetrachloroethylene, Trichloroethylene, and Chlorinated Phenols Induce Toluene-o-xylene Monooxoygenase Activity in Pseudomonas Stutzeri OX1”. Applied Microbiol Biotechnol 56 (3–4): 545–549. doi:10.1007/s002530100675.
  12. Deckard, L. A., Wills, J. C., Rivers, D. B. (1994). “Evidence for aerobic degradation of tetrachloroethylene by bacterial isolate”. Biotechnol. Lett. 16 (11): 1221–1224. doi:10.1007/BF01020855.
  13. Watts P. (2006). Concise International Chemical Assessment Document 68: TETRACHLOROETHENE, World Health Organization

Further reading

  • Doherty, R.E. (2000). “A History of the Production and Use of Carbon Tetrachloride, Tetrachloroethylene, Trichloroethylene and 1,1,1-Trichloroethane in the United States: Part 1 – Historical Background; Carbon Tetrachloride and Tetrachloroethylene”. Environmental Forensics 1 (2): 69–81. doi:10.1006/enfo.2000.0010.

External links

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