Trichloroethylene
Encyclopedia
The chemical compound
trichloroethylene is a chlorinated
hydrocarbon
commonly used as an industrial solvent
. It is a clear non-flammable liquid with a sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.
The IUPAC
name is trichloroethene. Industrial abbreviations include TCE, trichlor, Trike, Tricky and tri. It has been sold under a variety of trade names. Under the trade names Trimar and Trilene, trichloroethylene was used as a volatile anesthetic and as an inhaled obstetrical analgesic
in millions of patients.
in Britain, its development was hailed as an anesthetic revolution. Originally thought to possess less hepatotoxicity
than chloroform
, and without the unpleasant pungency and flammability of ether
, TCE use was nonetheless soon found to have several pitfalls. These included promotion of cardiac arrhythmias, too low a volatility for quick anesthetic induction, reactions with soda lime
used in carbon dioxide absorbing systems, prolonged neurologic dysfunction when used with soda lime, and evidence of hepatotoxicity as had been found with chloroform.
The introduction of halothane
in 1956 greatly diminished the use of TCE as a general anesthetic. TCE was still used as an inhalation analgesic in childbirth given by self-administration. Fetal toxicity and concerns for carcinogenic potential of TCE led to its abandonment in the 1980s.
Due to concerns about its toxicity, the use of trichloroethylene in the food and pharmaceutical industries has been banned in much of the world since the 1970s. Legislation has forced the substitution of trichloroethylene in many processes in Europe as the chemical was classified as a carcinogen carrying an R45 risk phrase. Many degreasing chemical alternatives are being promoted such as Ensolv and Leksol; however, each of these is based on n-propyl bromide
which carries an R60 risk phrase and they would not be a legally acceptable substitute.
Groundwater
contamination by TCE has become an important environmental concern. Seepage of the compound into groundwater has raised health concerns in many locations.
Recently it was announced by the USEPA (the United States Environmental Protection Agency) that the agency had completed its Final Health Assessment for Trichloroethylene and released a list of new TCE toxicity values. The results of the study have formally characterized the chemical as a human carcinogen and a non-carcinogenic health hazard.
. First, acetylene was treated with chlorine using a ferric chloride
catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane
according to the chemical equation
The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can either be accomplished with an aqueous solution of calcium hydroxide
or in the vapor phase by heating it to 300-500°C on a barium chloride
or calcium chloride
catalyst
Today, however, most trichloroethylene is produced from ethylene
. First, ethylene is chlorinated over a ferric chloride
catalyst to produce 1,2-dichloroethane
.
When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene
This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride
and aluminum chloride
. However, various forms of porous carbon
can also be used. This reaction produces tetrachloroethylene
as a byproduct, and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation
.
for a variety of organic
materials.
When it was first widely produced in the 1920s, trichloroethylene's major use was to extract vegetable oils from plant materials such as soy, coconut
, and palm. Other uses in the food industry included coffee
decaffeination
and the preparation of flavoring extracts from hops
and spice
s. It has also been used for drying out the last bit of water for production of 100% ethanol.
From the 1930s through the 1970s, both in Europe and North America, trichloroethylene was used as a volatile gas anesthetic. TCE was used in place of the earlier anesthetics chloroform
and ether
in the 1940s, but was itself replaced in the 1950s by the newer halothane
, which allowed much faster induction and recovery times. Marketed in the UK by ICI under the trade name Trilene it was coloured blue (with a dye called waxolene blue) to avoid confusion with the similar smelling chloroform.
It has also been used as a dry cleaning
solvent, although replaced in the 1950s by tetrachloroethylene
(also known as perchloroethylene).
Trichloroethylene was marketed as 'Ecco 1500 Anti-Static Film Cleaner and Conditioner' until 2009, for use in automatic movie film cleaning machines, and for manual cleaning with lint-free wipes.
Perhaps the greatest use of TCE has been as a degreaser for metal parts. The demand for TCE as a degreaser began to decline in the 1950s in favor of the less toxic 1,1,1-trichloroethane
. However, 1,1,1-trichloroethane production has been phased out in most of the world under the terms of the Montreal Protocol
, and as a result trichloroethylene has experienced some resurgence in use as a degreaser.
TCE has also been used in the United States to clean kerosene-fueled rocket engines (TCE was not used to clean hydrogen-fueled engines such as the Space Shuttle Main Engine
). During static firing, the RP-1 fuel would leave hydrocarbon deposits and vapors in the engine. These deposits had to be flushed from the engine to avoid the possibility of explosion during engine handling and future firing. TCE was used to flush the engine's fuel system immediately before and after each test firing. The flushing procedure involved pumping TCE through the engine's fuel system and letting the solvent overflow for a period ranging from several seconds to 30–35 minutes, depending upon the engine. For some engines, the engine's gas generator and LOX dome were also flushed with TCE prior to test firing. The F-1 rocket engine had its LOX dome, gas generator, and thrust chamber fuel jacket flushed with TCE during launch preparations.
TCE is also used in the manufacture of a range of fluorocarbon refrigerants such as 1,1,1,2-Tetrafluoroethane
more commonly known as HFC 134a
and could not be used by other manufacturers. Considerable research took place in the 1960s to develop alternative stabilizers for trichloroethylene. Other chemical stabilizers include ketone
s such as methyl ethyl ketone.
depression resulting in general anesthesia
. Its high blood solubility results in a less desirable slower induction of anesthesia. At low concentrations it is relatively non-irritating to the respiratory tract. Higher concentrations result in tachypnea
. Many types of cardiac arrhythmias can occur and are exacerbated by epinephrine
(adrenaline). It was noted in the 1940s that TCE reacted with carbon dioxide (CO2) absorbing systems (soda lime
) to produce dichloroacetylene and phosgene
. Cranial nerve dysfunction (especially the fifth cranial nerve) was not uncommon when TCE anesthesia was given using CO2 absorbing systems. These nerve deficits could last for months. Occasionally facial numbness was permanent. Muscle relaxation with TCE anesthesia sufficient for surgery was poor. For these reasons as well as problems with hepatotoxicity
, TCE lost popularity in North America and Europe to more potent anesthestics such as halothane
by the 1960s.
The symptoms of acute non-medical exposure are similar to those of alcohol intoxication, beginning with headache, dizziness, and confusion and progressing with increasing exposure to unconsciousness. Respiratory and circulatory depression can result in death.
Much of what is known about the human health effects of trichloroethylene is based on occupational exposures. Beyond the effects to the central nervous system, workplace exposure to trichloroethylene has been associated with toxic effects in the liver and kidney. Over time, occupational exposure limits on trichloroethylene have tightened, resulting in more stringent ventilation controls and personal protective equipment use by workers.
Research from Cancer bioassays performed by the National Cancer Institute
(later the National Toxicology Program
) showed that exposure to trichloroethylene is carcinogenic in animals, producing liver cancer in mice, and kidney cancer in rats. Research published in 1994 examined the incidence of leukemia
and non-Hodgkin lymphoma
in populations exposed to TCE in their drinking water.
The National Toxicology Program’s 11th Report on Carcinogens categorizes trichloroethylene as “reasonably anticipated to be a human carcinogen”, based on limited evidence of carcinogenicity from studies in humans and sufficient evidence of carcinogenicity from studies in experimental animals.
One recent review of the epidemiology of kidney cancer
rated cigarette smoking and obesity as more important risk factors for kidney cancer than exposure to solvents such as trichloroethylene. In contrast, the most recent overall assessment of human health risks associated with trichloroethylene states, "[t]here is concordance between animal and human studies, which supports the conclusion that trichloroethylene is a potential kidney carcinogen". The evidence appears to be less certain at this time regarding the relationship between humans and liver cancer observed in mice, with the NAS suggesting that low-level exposure might not represent a significant liver cancer risk in the general population.
Recent studies in laboratory animals and observations in human populations suggest that exposure to trichloroethylene might be associated with congenital heart defects While it is not clear what levels of exposure are associated with cardiac defects in humans, there is consistency between the cardiac defects observed in studies of communities exposed to trichloroethylene contamination in groundwater, and the effects observed in laboratory animals. A study published in August 2008, has demonstrated effects of TCE on human mitochondria. The article questions whether this might impact female reproductive function.
The health risks of trichloroethylene have been studied extensively. The U.S. Environmental Protection Agency (EPA) sponsored a "state of the science" review of the health effects associated with exposure to trichloroethylene. The National Academy of Sciences
concluded that evidence on the carcinogenic risk and other potential health hazards from exposure to TCE has strengthened since EPA released their toxicological assessment of TCE, and encourages federal agencies to finalize the risk assessment for TCE using currently available information, so that risk management decisions for this chemical can be expedited.
In Europe, the Scientific Committee on Occupational Exposure Limits (SCOEL) recommends for trichloroethylene an occupational exposure limit
(8h time-weighted average) of 10 ppm and a short-term exposure limit (15 min) of 30 ppm.
if sufficient quantities are spilled in the environment. Another significant source of vapor exposure in Superfund sites that had contaminated groundwater, such as the Twin Cities Army Ammunition Plant, was by showering. TCE readily volatilizes out of hot water and into the air. Long, hot showers would then volatilize more TCE into the air. In a home closed tightly to conserve the cost of heating and cooling, these vapors would then recirculate.
The first known report of TCE in groundwater was given in 1949 by two English public chemists who described two separate instances of well contamination by industrial releases of TCE. Based on available federal and state surveys, between 9% to 34% of the drinking water supply sources tested in the U.S. may have some TCE contamination, though EPA has reported that most water supplies are in compliance with the Maximum Contaminant Level (MCL) of 5 ppb. In addition, a growing concern in recent years at sites with TCE contamination in soil or groundwater has been vapor intrusion in buildings, which has resulted in indoor air exposures, such is in a recent case in the McCook Field Neighborhood of Dayton, Ohio. Trichloroethylene has been detected in 852 Superfund sites across the United States, according to the Agency for Toxic Substances and Disease Registry
(ATSDR). Under the Safe Drinking Water Act of 1974, and as amended
annual water quality testing is required for all public drinking water distributors. The EPA'S current guidelines for TCE can be found here. It should be noted that the EPA's table of "TCE Releases to Ground" is dated 1987 to 1993, thereby omitting one of the largest Superfund Cleanup sites in the nation, the NIBW in Scottsdale, Arizona. The TCE "released" here occurred prior to its appearance in the municipal drinking wells in 1982.
In 1998, the View-Master factory supply well in Beaverton, Oregon
was found to have been contaminated with high levels of TCE. It was estimated that 25,000 factory workers had been exposed to it from 1950–2001.
As of 2007, 57,000 pounds, or roughly 19 tons of TCE have been removed from the system of wells that once supplied drinking water to the residents of Scottsdale. One of the three drinking water wells previously owned by the City of Phoenix and ultimately sold to the City of Scottsdale, tested at 390 ppb TCE when it was closed in 1982.
(see East Valley Tribune, April 6, 2007, "Feds to Examine Superfund Site" by John Yantis) Some Scottsdale residents who received their water bills from the City of Phoenix throughout the 1960s and 70's were understandably confused as to whether they indeed had been consuming contaminated water when information about the Superfund site was first disseminated. The City of Scottsdale recently updated their website to clarify that the contaminated wells were "in the Scottsdale area" and to delete all references to the levels of TCE discovered when the wells were closed as "trace".
A spot was then ultimately chosen to receive and treat the contaminated drinking water known as the Central Groundwater Treatment Facility. Then 1989, as now, this treatment facility (CGTF) is situated on land adjacent to Pima Park and the Siemens facility documented as one of the Potentially Responsible Parties at the corner of Thomas and Pima roads. Close proximity to this park did not appear to enter into Motorola's calculations when asserting that it would save money to remove the carbon air filters in 2007. (See East Valley Tribune, October 5, 2007, "Motorola wants to axe filters at Superfund site" by Ari Cohn)
Marine Corps Base Camp Lejeune
in North Carolina may be the largest TCE contamination site in the country. Legislation could force the EPA to establish a health advisory and a national public drinking water regulation to limit trichloroethylene.
For over twenty years of operation, RCA Corporation had been pouring toxic wastewater into a well in its Taoyuan, Taiwan facility. The pollution from the plant was not revealed until 1994, when former workers brought it to light. Investigation by the Taiwan Environmental Protection Administration confirmed that RCA had been dumping chlorinated organic solvents into a secret well and caused contamination to the soil and groundwater surrounding the plant site. High levels of TCE and tetrachloroethylene
(PCE) can be found in groundwater drawn as far as two kilometers from the site. An organization of former RCA employees reports 1375 cancer cases, 216 cancer deaths, and 102 cases of various tumors among its members.
There are reports associating exposure to TCE with amyotrophic lateral sclerosis
and also with a neurologic syndrome resembling Parkinson's disease
. An international study published in 2011 has found a six-fold increase in the risk of developing Parkinson's in individuals exposed in the workplace to TCE. The study found a lag time of up to 40 years between exposure to TCE and the onset of Parkinson's. No statistical link was found with the other solvents examined in the study (toluene
, xylene
, n-hexane
).
—that is, it acted in concert with other substances to promote the formation of tumors.
Half a dozen state, federal, and international agencies now classify trichloroethylene as a probable carcinogen. The International Agency for Research on Cancer
considers trichloroethylene a Group 2A carcinogen, indicating that it considers it is probably carcinogenic to humans.
California EPA regulators consider it a known carcinogen and issued a risk assessment in 1999 that concluded that it was far more toxic than previous scientific studies had shown.
(DoD), the Department of Energy
, and NASA
, who appealed directly to the White House. They argued that the EPA had produced junk science, its assumptions were badly flawed, and that evidence exonerating the chemical was ignored.
The DoD has about 1,400 military properties nationwide that are contaminated with trichloroethylene. Many of these sites are detailed and updated by www.cpeo.org and include a former ammunition plant in the Twin Cities area. Twenty three sites in the Energy Department's nuclear weapons complex — including Lawrence Livermore National Laboratory
in the San Francisco Bay area, and NASA centers, including the Jet Propulsion Laboratory
in La Cañada Flintridge are reported to have TCE contamination.
Political appointees in the EPA sided with the Pentagon and agreed to pull back the risk assessment. In 2004, the National Academy of Sciences
was given a $680,000 contract to study the matter, releasing its report in the summer of 2006. The report has raised more concerns about the health effects of TCE.
In response to the heightened awareness of environmental toxins such as TCE and the role they may be playing in childhood disease, Sen. Obama proposed S1068, cosponsored by Hillary Clinton and others. This legislation aims to inform and protect communities that are threatened with environmental contamination. Sen. Clinton's own bill, S1911, is known as the TCE Reduction Act. This bill was co-sponsored by Sen. Elizabeth Dole (R-North Carolina).
The U.S. military has virtually eliminated its use of the chemical, purchasing only 11 gallons in 2005. About 100 tons of it is used annually in the U.S. as of 2006.
Recent research has focused on the in-place remediation of trichloroethylene in soil and ground water instead of removal for off-site treatment and disposal. Naturally-occurring bacteria have been identified with the ability to degrade or completely mineralize TCE. Dehalococcoide sp. degrade trichloroethylene by reductive dechlorination under anaerobic conditions. Under aerobic conditions, Pseudomonas fluorescence can co-metabolize TCE. Soil and ground water contamination by TCE has also been successfully remediated by chemical treatment and extraction.
, the case of a TCE-contaminated tannery and town water supply is covered in detail.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
trichloroethylene is a chlorinated
Chlorine
Chlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
hydrocarbon
Hydrocarbon
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons from which one hydrogen atom has been removed are functional groups, called hydrocarbyls....
commonly used as an industrial solvent
Solvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
. It is a clear non-flammable liquid with a sweet smell. It should not be confused with the similar 1,1,1-trichloroethane, which is commonly known as chlorothene.
The IUPAC
International Union of Pure and Applied Chemistry
The International Union of Pure and Applied Chemistry is an international federation of National Adhering Organizations that represents chemists in individual countries. It is a member of the International Council for Science . The international headquarters of IUPAC is located in Zürich,...
name is trichloroethene. Industrial abbreviations include TCE, trichlor, Trike, Tricky and tri. It has been sold under a variety of trade names. Under the trade names Trimar and Trilene, trichloroethylene was used as a volatile anesthetic and as an inhaled obstetrical analgesic
Analgesic
An analgesic is any member of the group of drugs used to relieve pain . The word analgesic derives from Greek an- and algos ....
in millions of patients.
History
Pioneered by Imperial Chemical IndustriesImperial Chemical Industries
Imperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...
in Britain, its development was hailed as an anesthetic revolution. Originally thought to possess less hepatotoxicity
Hepatotoxicity
Hepatotoxicity implies chemical-driven liver damage.The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure...
than chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
, and without the unpleasant pungency and flammability of ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
, TCE use was nonetheless soon found to have several pitfalls. These included promotion of cardiac arrhythmias, too low a volatility for quick anesthetic induction, reactions with soda lime
Soda lime
Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning.It is made by treating...
used in carbon dioxide absorbing systems, prolonged neurologic dysfunction when used with soda lime, and evidence of hepatotoxicity as had been found with chloroform.
The introduction of halothane
Halothane
Halothane is an inhalational general anesthetic. Its IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane. It is the only inhalational anesthetic agent containing a bromine atom; there are several other halogenated anesthesia agents which lack the bromine atom and do contain the fluorine and...
in 1956 greatly diminished the use of TCE as a general anesthetic. TCE was still used as an inhalation analgesic in childbirth given by self-administration. Fetal toxicity and concerns for carcinogenic potential of TCE led to its abandonment in the 1980s.
Due to concerns about its toxicity, the use of trichloroethylene in the food and pharmaceutical industries has been banned in much of the world since the 1970s. Legislation has forced the substitution of trichloroethylene in many processes in Europe as the chemical was classified as a carcinogen carrying an R45 risk phrase. Many degreasing chemical alternatives are being promoted such as Ensolv and Leksol; however, each of these is based on n-propyl bromide
N-Propyl bromide
n-Propyl bromide is a colorless to off-white, non-flammable chemical compound. It has the chemical formula C3H7Br. It is an organic solvent used for the cleaning of metal surfaces, removal of soldering residues from electronic circuit boards, and as an adhesive solvent...
which carries an R60 risk phrase and they would not be a legally acceptable substitute.
Groundwater
Groundwater
Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...
contamination by TCE has become an important environmental concern. Seepage of the compound into groundwater has raised health concerns in many locations.
Recently it was announced by the USEPA (the United States Environmental Protection Agency) that the agency had completed its Final Health Assessment for Trichloroethylene and released a list of new TCE toxicity values. The results of the study have formally characterized the chemical as a human carcinogen and a non-carcinogenic health hazard.
Production
Prior to the early 1970s, most trichloroethylene was produced in a two-step process from acetyleneAcetylene
Acetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
. First, acetylene was treated with chlorine using a ferric chloride
Iron(III) chloride
Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...
catalyst at 90 °C to produce 1,1,2,2-tetrachloroethane
1,1,2,2-Tetrachloroethane
1,1,2,2-Tetrachloroethane is a chlorinated derivative of ethane. It has the highest solvent power of any chlorinated hydrocarbon. As a refrigerant, it is used under the name R-130....
according to the chemical equation
Chemical equation
A chemical equation is the symbolic representation of a chemical reaction where the reactant entities are given on the left hand side and the product entities on the right hand side. The coefficients next to the symbols and formulae of entities are the absolute values of the stoichiometric numbers...
- HC≡CHAcetyleneAcetylene is the chemical compound with the formula C2H2. It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in pure form and thus is usually handled as a solution.As an alkyne, acetylene is unsaturated because...
+ 2 Cl2ChlorineChlorine is the chemical element with atomic number 17 and symbol Cl. It is the second lightest halogen, found in the periodic table in group 17. The element forms diatomic molecules under standard conditions, called dichlorine...
→ Cl2CHCHCl21,1,2,2-Tetrachloroethane1,1,2,2-Tetrachloroethane is a chlorinated derivative of ethane. It has the highest solvent power of any chlorinated hydrocarbon. As a refrigerant, it is used under the name R-130....
The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can either be accomplished with an aqueous solution of calcium hydroxide
Calcium hydroxide
Calcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
- 2 Cl2CHCHCl2 + Ca(OH)2Calcium hydroxideCalcium hydroxide, traditionally called slaked lime, is an inorganic compound with the chemical formula Ca2. It is a colourless crystal or white powder and is obtained when calcium oxide is mixed, or "slaked" with water. It has many names including hydrated lime, builders lime, slack lime, cal, or...
→ 2 ClCH=CCl2 + CaCl2Calcium chlorideCalcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...
+ 2 H2O
or in the vapor phase by heating it to 300-500°C on a barium chloride
Barium chloride
Barium chloride is the inorganic compound with the formula BaCl2. It is one of the most common water-soluble salts of barium. Like other barium salts, it is toxic and imparts a yellow-green coloration to a flame. It is also hygroscopic....
or calcium chloride
Calcium chloride
Calcium chloride, CaCl2, is a salt of calcium and chlorine. It behaves as a typical ionic halide, and is solid at room temperature. Common applications include brine for refrigeration plants, ice and dust control on roads, and desiccation...
catalyst
- Cl2CHCHCl2 → ClCH=CCl2 + HClHydrochloric acidHydrochloric acid is a solution of hydrogen chloride in water, that is a highly corrosive, strong mineral acid with many industrial uses. It is found naturally in gastric acid....
Today, however, most trichloroethylene is produced from ethylene
Ethylene
Ethylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
. First, ethylene is chlorinated over a ferric chloride
Iron(III) chloride
Iron chloride, also called ferric chloride, is an industrial scale commodity chemical compound, with the formula FeCl3. The colour of iron chloride crystals depends on the viewing angle: by reflected light the crystals appear dark green, but by transmitted light they appear purple-red...
catalyst to produce 1,2-dichloroethane
1,2-Dichloroethane
The chemical compound 1,2-dichloroethane, commonly known by its old name of ethylene dichloride , is a chlorinated hydrocarbon, mainly used to produce vinyl chloride monomer , the major precursor for PVC production. It is a colourless liquid with a chloroform-like odour...
.
- CH2=CH2EthyleneEthylene is a gaseous organic compound with the formula . It is the simplest alkene . Because it contains a carbon-carbon double bond, ethylene is classified as an unsaturated hydrocarbon. Ethylene is widely used in industry and is also a plant hormone...
+ Cl2 → ClCH2CH2Cl1,2-DichloroethaneThe chemical compound 1,2-dichloroethane, commonly known by its old name of ethylene dichloride , is a chlorinated hydrocarbon, mainly used to produce vinyl chloride monomer , the major precursor for PVC production. It is a colourless liquid with a chloroform-like odour...
When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene
- ClCH2CH2Cl1,2-DichloroethaneThe chemical compound 1,2-dichloroethane, commonly known by its old name of ethylene dichloride , is a chlorinated hydrocarbon, mainly used to produce vinyl chloride monomer , the major precursor for PVC production. It is a colourless liquid with a chloroform-like odour...
+ 2 Cl2 → ClCH=CCl2 + 3 HCl
This reaction can be catalyzed by a variety of substances. The most commonly used catalyst is a mixture of potassium chloride
Potassium chloride
The chemical compound potassium chloride is a metal halide salt composed of potassium and chlorine. In its pure state, it is odorless and has a white or colorless vitreous crystal appearance, with a crystal structure that cleaves easily in three directions. Potassium chloride crystals are...
and aluminum chloride
Aluminium chloride
Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...
. However, various forms of porous carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
can also be used. This reaction produces tetrachloroethylene
Tetrachloroethylene
Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...
as a byproduct, and depending on the amount of chlorine fed to the reaction, tetrachloroethylene can even be the major product. Typically, trichloroethylene and tetrachloroethylene are collected together and then separated by distillation
Distillation
Distillation is a method of separating mixtures based on differences in volatilities of components in a boiling liquid mixture. Distillation is a unit operation, or a physical separation process, and not a chemical reaction....
.
Uses
Trichloroethylene is an effective solventSolvent
A solvent is a liquid, solid, or gas that dissolves another solid, liquid, or gaseous solute, resulting in a solution that is soluble in a certain volume of solvent at a specified temperature...
for a variety of organic
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...
materials.
When it was first widely produced in the 1920s, trichloroethylene's major use was to extract vegetable oils from plant materials such as soy, coconut
Coconut
The coconut palm, Cocos nucifera, is a member of the family Arecaceae . It is the only accepted species in the genus Cocos. The term coconut can refer to the entire coconut palm, the seed, or the fruit, which is not a botanical nut. The spelling cocoanut is an old-fashioned form of the word...
, and palm. Other uses in the food industry included coffee
Coffee
Coffee is a brewed beverage with a dark,init brooo acidic flavor prepared from the roasted seeds of the coffee plant, colloquially called coffee beans. The beans are found in coffee cherries, which grow on trees cultivated in over 70 countries, primarily in equatorial Latin America, Southeast Asia,...
decaffeination
Decaffeination
Decaffeination is the act of removing caffeine from coffee beans, cocoa, tea leaves and other caffeine-containing materials. Despite removal of caffeine, many decaffeinated drinks still have around 1-2% of the...
and the preparation of flavoring extracts from hops
Hops
Hops are the female flower clusters , of a hop species, Humulus lupulus. They are used primarily as a flavoring and stability agent in beer, to which they impart a bitter, tangy flavor, though hops are also used for various purposes in other beverages and herbal medicine...
and spice
Spice
A spice is a dried seed, fruit, root, bark, or vegetative substance used in nutritionally insignificant quantities as a food additive for flavor, color, or as a preservative that kills harmful bacteria or prevents their growth. It may be used to flavour a dish or to hide other flavours...
s. It has also been used for drying out the last bit of water for production of 100% ethanol.
From the 1930s through the 1970s, both in Europe and North America, trichloroethylene was used as a volatile gas anesthetic. TCE was used in place of the earlier anesthetics chloroform
Chloroform
Chloroform is an organic compound with formula CHCl3. It is one of the four chloromethanes. The colorless, sweet-smelling, dense liquid is a trihalomethane, and is considered somewhat hazardous...
and ether
Diethyl ether
Diethyl ether, also known as ethyl ether, simply ether, or ethoxyethane, is an organic compound in the ether class with the formula . It is a colorless, highly volatile flammable liquid with a characteristic odor...
in the 1940s, but was itself replaced in the 1950s by the newer halothane
Halothane
Halothane is an inhalational general anesthetic. Its IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane. It is the only inhalational anesthetic agent containing a bromine atom; there are several other halogenated anesthesia agents which lack the bromine atom and do contain the fluorine and...
, which allowed much faster induction and recovery times. Marketed in the UK by ICI under the trade name Trilene it was coloured blue (with a dye called waxolene blue) to avoid confusion with the similar smelling chloroform.
It has also been used as a dry cleaning
Dry cleaning
Dry cleaning is any cleaning process for clothing and textiles using a chemical solvent other than water. The solvent used is typically tetrachloroethylene , abbreviated "perc" in the industry and "dry-cleaning fluid" by the public...
solvent, although replaced in the 1950s by tetrachloroethylene
Tetrachloroethylene
Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...
(also known as perchloroethylene).
Trichloroethylene was marketed as 'Ecco 1500 Anti-Static Film Cleaner and Conditioner' until 2009, for use in automatic movie film cleaning machines, and for manual cleaning with lint-free wipes.
Perhaps the greatest use of TCE has been as a degreaser for metal parts. The demand for TCE as a degreaser began to decline in the 1950s in favor of the less toxic 1,1,1-trichloroethane
1,1,1-Trichloroethane
The organic compound 1,1,1-trichloroethane, also known as methyl chloroform, is a chloroalkane. This colourless, sweet-smelling liquid was once produced industrially in large quantities for use as a solvent...
. However, 1,1,1-trichloroethane production has been phased out in most of the world under the terms of the Montreal Protocol
Montreal Protocol
The Montreal Protocol on Substances That Deplete the Ozone Layer is an international treaty designed to protect the ozone layer by phasing out the production of numerous substances believed to be responsible for ozone depletion...
, and as a result trichloroethylene has experienced some resurgence in use as a degreaser.
TCE has also been used in the United States to clean kerosene-fueled rocket engines (TCE was not used to clean hydrogen-fueled engines such as the Space Shuttle Main Engine
Space Shuttle main engine
The RS-25, otherwise known as the Space Shuttle Main Engine , is a reusable liquid-fuel rocket engine built by Pratt & Whitney Rocketdyne for the Space Shuttle, running on liquid hydrogen and oxygen. Each Space Shuttle was propelled by three SSMEs mated to one powerhead...
). During static firing, the RP-1 fuel would leave hydrocarbon deposits and vapors in the engine. These deposits had to be flushed from the engine to avoid the possibility of explosion during engine handling and future firing. TCE was used to flush the engine's fuel system immediately before and after each test firing. The flushing procedure involved pumping TCE through the engine's fuel system and letting the solvent overflow for a period ranging from several seconds to 30–35 minutes, depending upon the engine. For some engines, the engine's gas generator and LOX dome were also flushed with TCE prior to test firing. The F-1 rocket engine had its LOX dome, gas generator, and thrust chamber fuel jacket flushed with TCE during launch preparations.
TCE is also used in the manufacture of a range of fluorocarbon refrigerants such as 1,1,1,2-Tetrafluoroethane
1,1,1,2-Tetrafluoroethane
1,1,1,2-Tetrafluoroethane, R-134a, Genetron 134a, Suva 134a or HFC-134a, is a haloalkane refrigerant with thermodynamic properties similar to R-12 , but with less ozone depletion potential...
more commonly known as HFC 134a
Chemical instability
Despite its widespread use as a metal degreaser, trichloroethylene itself is unstable in the presence of metal over prolonged exposure. As early as 1961 this phenomenon was recognized by the manufacturing industry, when stabilizing additives were added in the commercial formulation. Since the reactive instability is accentuated by higher temperatures, the search for stabilizing additives was conducted by heating trichloroethylene to its boiling point in a reflux condenser and observing decomposition. The first widely used stabilizing additive was dioxane; however, its use was patented by Dow Chemical CompanyDow Chemical Company
The Dow Chemical Company is a multinational corporation headquartered in Midland, Michigan, United States. As of 2007, it is the second largest chemical manufacturer in the world by revenue and as of February 2009, the third-largest chemical company in the world by market capitalization .Dow...
and could not be used by other manufacturers. Considerable research took place in the 1960s to develop alternative stabilizers for trichloroethylene. Other chemical stabilizers include ketone
Ketone
In organic chemistry, a ketone is an organic compound with the structure RCR', where R and R' can be a variety of atoms and groups of atoms. It features a carbonyl group bonded to two other carbon atoms. Many ketones are known and many are of great importance in industry and in biology...
s such as methyl ethyl ketone.
Physiological effects
When inhaled, trichloroethylene produces central nervous systemCentral nervous system
The central nervous system is the part of the nervous system that integrates the information that it receives from, and coordinates the activity of, all parts of the bodies of bilaterian animals—that is, all multicellular animals except sponges and radially symmetric animals such as jellyfish...
depression resulting in general anesthesia
Anesthesia
Anesthesia, or anaesthesia , traditionally meant the condition of having sensation blocked or temporarily taken away...
. Its high blood solubility results in a less desirable slower induction of anesthesia. At low concentrations it is relatively non-irritating to the respiratory tract. Higher concentrations result in tachypnea
Tachypnea
Tachypnea means rapid breathing. Any rate between 12-20 breaths per minute is normal. Tachypnea is a respiration rate greater than 20 breaths per minute. - Distinction from other breathing terms :...
. Many types of cardiac arrhythmias can occur and are exacerbated by epinephrine
Epinephrine
Epinephrine is a hormone and a neurotransmitter. It increases heart rate, constricts blood vessels, dilates air passages and participates in the fight-or-flight response of the sympathetic nervous system. In chemical terms, adrenaline is one of a group of monoamines called the catecholamines...
(adrenaline). It was noted in the 1940s that TCE reacted with carbon dioxide (CO2) absorbing systems (soda lime
Soda lime
Soda lime is a mixture of chemicals, used in granular form in closed breathing environments, such as general anaesthesia, submarines, rebreathers and recompression chambers, to remove carbon dioxide from breathing gases to prevent CO2 retention and carbon dioxide poisoning.It is made by treating...
) to produce dichloroacetylene and phosgene
Phosgene
Phosgene is the chemical compound with the formula COCl2. This colorless gas gained infamy as a chemical weapon during World War I. It is also a valued industrial reagent and building block in synthesis of pharmaceuticals and other organic compounds. In low concentrations, its odor resembles...
. Cranial nerve dysfunction (especially the fifth cranial nerve) was not uncommon when TCE anesthesia was given using CO2 absorbing systems. These nerve deficits could last for months. Occasionally facial numbness was permanent. Muscle relaxation with TCE anesthesia sufficient for surgery was poor. For these reasons as well as problems with hepatotoxicity
Hepatotoxicity
Hepatotoxicity implies chemical-driven liver damage.The liver plays a central role in transforming and clearing chemicals and is susceptible to the toxicity from these agents. Certain medicinal agents, when taken in overdoses and sometimes even when introduced within therapeutic ranges, may injure...
, TCE lost popularity in North America and Europe to more potent anesthestics such as halothane
Halothane
Halothane is an inhalational general anesthetic. Its IUPAC name is 2-bromo-2-chloro-1,1,1-trifluoroethane. It is the only inhalational anesthetic agent containing a bromine atom; there are several other halogenated anesthesia agents which lack the bromine atom and do contain the fluorine and...
by the 1960s.
The symptoms of acute non-medical exposure are similar to those of alcohol intoxication, beginning with headache, dizziness, and confusion and progressing with increasing exposure to unconsciousness. Respiratory and circulatory depression can result in death.
Much of what is known about the human health effects of trichloroethylene is based on occupational exposures. Beyond the effects to the central nervous system, workplace exposure to trichloroethylene has been associated with toxic effects in the liver and kidney. Over time, occupational exposure limits on trichloroethylene have tightened, resulting in more stringent ventilation controls and personal protective equipment use by workers.
Research from Cancer bioassays performed by the National Cancer Institute
National Cancer Institute
The National Cancer Institute is part of the National Institutes of Health , which is one of 11 agencies that are part of the U.S. Department of Health and Human Services. The NCI coordinates the U.S...
(later the National Toxicology Program
National Toxicology Program
The National Toxicology Program is an inter-agency program run by the United States Department of Health and Human Services to coordinate, evaluate, and report on toxicology within public agencies....
) showed that exposure to trichloroethylene is carcinogenic in animals, producing liver cancer in mice, and kidney cancer in rats. Research published in 1994 examined the incidence of leukemia
Leukemia
Leukemia or leukaemia is a type of cancer of the blood or bone marrow characterized by an abnormal increase of immature white blood cells called "blasts". Leukemia is a broad term covering a spectrum of diseases...
and non-Hodgkin lymphoma
Non-Hodgkin lymphoma
The non-Hodgkin lymphomas are a diverse group of blood cancers that include any kind of lymphoma except Hodgkin's lymphomas. Types of NHL vary significantly in their severity, from indolent to very aggressive....
in populations exposed to TCE in their drinking water.
The National Toxicology Program’s 11th Report on Carcinogens categorizes trichloroethylene as “reasonably anticipated to be a human carcinogen”, based on limited evidence of carcinogenicity from studies in humans and sufficient evidence of carcinogenicity from studies in experimental animals.
One recent review of the epidemiology of kidney cancer
Renal cell carcinoma
Renal cell carcinoma is a kidney cancer that originates in the lining of the proximal convoluted tubule, the very small tubes in the kidney that filter the blood and remove waste products. RCC is the most common type of kidney cancer in adults, responsible for approximately 80% of cases...
rated cigarette smoking and obesity as more important risk factors for kidney cancer than exposure to solvents such as trichloroethylene. In contrast, the most recent overall assessment of human health risks associated with trichloroethylene states, "[t]here is concordance between animal and human studies, which supports the conclusion that trichloroethylene is a potential kidney carcinogen". The evidence appears to be less certain at this time regarding the relationship between humans and liver cancer observed in mice, with the NAS suggesting that low-level exposure might not represent a significant liver cancer risk in the general population.
Recent studies in laboratory animals and observations in human populations suggest that exposure to trichloroethylene might be associated with congenital heart defects While it is not clear what levels of exposure are associated with cardiac defects in humans, there is consistency between the cardiac defects observed in studies of communities exposed to trichloroethylene contamination in groundwater, and the effects observed in laboratory animals. A study published in August 2008, has demonstrated effects of TCE on human mitochondria. The article questions whether this might impact female reproductive function.
The health risks of trichloroethylene have been studied extensively. The U.S. Environmental Protection Agency (EPA) sponsored a "state of the science" review of the health effects associated with exposure to trichloroethylene. The National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
concluded that evidence on the carcinogenic risk and other potential health hazards from exposure to TCE has strengthened since EPA released their toxicological assessment of TCE, and encourages federal agencies to finalize the risk assessment for TCE using currently available information, so that risk management decisions for this chemical can be expedited.
In Europe, the Scientific Committee on Occupational Exposure Limits (SCOEL) recommends for trichloroethylene an occupational exposure limit
Occupational exposure limit
An occupational exposure limit is an upper limit on the acceptable concentration of a hazardous substance in workplace air for a particular material or class of materials. It is typically set by competent national authorities and enforced by legislation to protect occupational safety and health...
(8h time-weighted average) of 10 ppm and a short-term exposure limit (15 min) of 30 ppm.
Human exposure
Some are exposed to TCE through contaminated drinking water. With a specific gravity greater than 1, trichloroethene can be present as a dense nonaqueous phase liquidDNAPL
A dense non-aqueous phase liquid or DNAPL is a liquid that is both denser than water and is immiscible in or does not dissolve in water.The term DNAPL is used primarily by environmental engineers and hydrogeologists to describe contaminants in groundwater, surface water and sediments...
if sufficient quantities are spilled in the environment. Another significant source of vapor exposure in Superfund sites that had contaminated groundwater, such as the Twin Cities Army Ammunition Plant, was by showering. TCE readily volatilizes out of hot water and into the air. Long, hot showers would then volatilize more TCE into the air. In a home closed tightly to conserve the cost of heating and cooling, these vapors would then recirculate.
The first known report of TCE in groundwater was given in 1949 by two English public chemists who described two separate instances of well contamination by industrial releases of TCE. Based on available federal and state surveys, between 9% to 34% of the drinking water supply sources tested in the U.S. may have some TCE contamination, though EPA has reported that most water supplies are in compliance with the Maximum Contaminant Level (MCL) of 5 ppb. In addition, a growing concern in recent years at sites with TCE contamination in soil or groundwater has been vapor intrusion in buildings, which has resulted in indoor air exposures, such is in a recent case in the McCook Field Neighborhood of Dayton, Ohio. Trichloroethylene has been detected in 852 Superfund sites across the United States, according to the Agency for Toxic Substances and Disease Registry
Agency for Toxic Substances and Disease Registry
The Agency for Toxic Substances and Disease Registry is a federal public health agency within the United States Department of Health and Human Services. The agency focuses on minimizing human health risks associated with exposure to hazardous substances...
(ATSDR). Under the Safe Drinking Water Act of 1974, and as amended
annual water quality testing is required for all public drinking water distributors. The EPA'S current guidelines for TCE can be found here. It should be noted that the EPA's table of "TCE Releases to Ground" is dated 1987 to 1993, thereby omitting one of the largest Superfund Cleanup sites in the nation, the NIBW in Scottsdale, Arizona. The TCE "released" here occurred prior to its appearance in the municipal drinking wells in 1982.
In 1998, the View-Master factory supply well in Beaverton, Oregon
Beaverton, Oregon
Beaverton is a city in Washington County, Oregon, United States, seven miles west of Portland in the Tualatin River Valley.As of the 2010 census, the population is 90,267. This makes it the second-largest city in the county and Oregon's sixth-largest city...
was found to have been contaminated with high levels of TCE. It was estimated that 25,000 factory workers had been exposed to it from 1950–2001.
As of 2007, 57,000 pounds, or roughly 19 tons of TCE have been removed from the system of wells that once supplied drinking water to the residents of Scottsdale. One of the three drinking water wells previously owned by the City of Phoenix and ultimately sold to the City of Scottsdale, tested at 390 ppb TCE when it was closed in 1982.
(see East Valley Tribune, April 6, 2007, "Feds to Examine Superfund Site" by John Yantis) Some Scottsdale residents who received their water bills from the City of Phoenix throughout the 1960s and 70's were understandably confused as to whether they indeed had been consuming contaminated water when information about the Superfund site was first disseminated. The City of Scottsdale recently updated their website to clarify that the contaminated wells were "in the Scottsdale area" and to delete all references to the levels of TCE discovered when the wells were closed as "trace".
A spot was then ultimately chosen to receive and treat the contaminated drinking water known as the Central Groundwater Treatment Facility. Then 1989, as now, this treatment facility (CGTF) is situated on land adjacent to Pima Park and the Siemens facility documented as one of the Potentially Responsible Parties at the corner of Thomas and Pima roads. Close proximity to this park did not appear to enter into Motorola's calculations when asserting that it would save money to remove the carbon air filters in 2007. (See East Valley Tribune, October 5, 2007, "Motorola wants to axe filters at Superfund site" by Ari Cohn)
Marine Corps Base Camp Lejeune
Marine Corps Base Camp Lejeune
Marine Corps Base Camp Lejeune is a United States military training facility in North Carolina. The base's of beaches make it a major area for amphibious assault training, and its location between two deep-water ports allows for fast deployments.The main base is supplemented by five satellite...
in North Carolina may be the largest TCE contamination site in the country. Legislation could force the EPA to establish a health advisory and a national public drinking water regulation to limit trichloroethylene.
For over twenty years of operation, RCA Corporation had been pouring toxic wastewater into a well in its Taoyuan, Taiwan facility. The pollution from the plant was not revealed until 1994, when former workers brought it to light. Investigation by the Taiwan Environmental Protection Administration confirmed that RCA had been dumping chlorinated organic solvents into a secret well and caused contamination to the soil and groundwater surrounding the plant site. High levels of TCE and tetrachloroethylene
Tetrachloroethylene
Tetrachloroethylene, also known under its systematic name tetrachloroethene and many other names, is a chlorocarbon with the formula Cl2C=CCl2. It is a colourless liquid widely used for dry cleaning of fabrics, hence it is sometimes called "dry-cleaning fluid." It has a sweet odor detectable by...
(PCE) can be found in groundwater drawn as far as two kilometers from the site. An organization of former RCA employees reports 1375 cancer cases, 216 cancer deaths, and 102 cases of various tumors among its members.
There are reports associating exposure to TCE with amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis , also referred to as Lou Gehrig's disease, is a form of motor neuron disease caused by the degeneration of upper and lower neurons, located in the ventral horn of the spinal cord and the cortical neurons that provide their efferent input...
and also with a neurologic syndrome resembling Parkinson's disease
Parkinson's disease
Parkinson's disease is a degenerative disorder of the central nervous system...
. An international study published in 2011 has found a six-fold increase in the risk of developing Parkinson's in individuals exposed in the workplace to TCE. The study found a lag time of up to 40 years between exposure to TCE and the onset of Parkinson's. No statistical link was found with the other solvents examined in the study (toluene
Toluene
Toluene, formerly known as toluol, is a clear, water-insoluble liquid with the typical smell of paint thinners. It is a mono-substituted benzene derivative, i.e., one in which a single hydrogen atom from the benzene molecule has been replaced by a univalent group, in this case CH3.It is an aromatic...
, xylene
Xylene
Xylene encompasses three isomers of dimethylbenzene. The isomers are distinguished by the designations ortho- , meta- , and para- , which specify to which carbon atoms the two methyl groups are attached...
, n-hexane
Hexane
Hexane is a hydrocarbon with the chemical formula C6H14; that is, an alkane with six carbon atoms.The term may refer to any of four other structural isomers with that formula, or to a mixture of them. In the IUPAC nomenclature, however, hexane is the unbranched isomer ; the other four structures...
).
Existing regulation
Until recent years, the US Agency for Toxic Substances and Disease Registry (ATSDR) contended that trichloroethylene had little-to-no carcinogenic potential, and was probably a co-carcinogenCo-carcinogen
A Co-carcinogen is a chemical that promotes the effects of a carcinogen in the production of cancer. Usually, the term is used to refer to chemicals that are not carcinogenic on their own...
—that is, it acted in concert with other substances to promote the formation of tumors.
Half a dozen state, federal, and international agencies now classify trichloroethylene as a probable carcinogen. The International Agency for Research on Cancer
International Agency for Research on Cancer
The International Agency for Research on Cancer is an intergovernmental agency forming part of the World Health Organisation of the United Nations....
considers trichloroethylene a Group 2A carcinogen, indicating that it considers it is probably carcinogenic to humans.
California EPA regulators consider it a known carcinogen and issued a risk assessment in 1999 that concluded that it was far more toxic than previous scientific studies had shown.
Proposed U.S. federal regulation
In 2001, a draft report of the Environmental Protection Agency (EPA) laid the groundwork for tough new standards to limit public exposure to trichloroethylene. The assessment set off a fight between the EPA and the Department of DefenseUnited States Department of Defense
The United States Department of Defense is the U.S...
(DoD), the Department of Energy
United States Department of Energy
The United States Department of Energy is a Cabinet-level department of the United States government concerned with the United States' policies regarding energy and safety in handling nuclear material...
, and NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
, who appealed directly to the White House. They argued that the EPA had produced junk science, its assumptions were badly flawed, and that evidence exonerating the chemical was ignored.
The DoD has about 1,400 military properties nationwide that are contaminated with trichloroethylene. Many of these sites are detailed and updated by www.cpeo.org and include a former ammunition plant in the Twin Cities area. Twenty three sites in the Energy Department's nuclear weapons complex — including Lawrence Livermore National Laboratory
Lawrence Livermore National Laboratory
The Lawrence Livermore National Laboratory , just outside Livermore, California, is a Federally Funded Research and Development Center founded by the University of California in 1952...
in the San Francisco Bay area, and NASA centers, including the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
in La Cañada Flintridge are reported to have TCE contamination.
Political appointees in the EPA sided with the Pentagon and agreed to pull back the risk assessment. In 2004, the National Academy of Sciences
United States National Academy of Sciences
The National Academy of Sciences is a corporation in the United States whose members serve pro bono as "advisers to the nation on science, engineering, and medicine." As a national academy, new members of the organization are elected annually by current members, based on their distinguished and...
was given a $680,000 contract to study the matter, releasing its report in the summer of 2006. The report has raised more concerns about the health effects of TCE.
In response to the heightened awareness of environmental toxins such as TCE and the role they may be playing in childhood disease, Sen. Obama proposed S1068, cosponsored by Hillary Clinton and others. This legislation aims to inform and protect communities that are threatened with environmental contamination. Sen. Clinton's own bill, S1911, is known as the TCE Reduction Act. This bill was co-sponsored by Sen. Elizabeth Dole (R-North Carolina).
Reduced production and remediation
In recent times, there has been a substantial reduction in the production output of trichloroethylene; alternatives for use in metal degreasing abound, chlorinated aliphatic hydrocarbons being phased out in a large majority of industries due to the potential for irreversible health effects and the legal liability that ensues as a result.The U.S. military has virtually eliminated its use of the chemical, purchasing only 11 gallons in 2005. About 100 tons of it is used annually in the U.S. as of 2006.
Recent research has focused on the in-place remediation of trichloroethylene in soil and ground water instead of removal for off-site treatment and disposal. Naturally-occurring bacteria have been identified with the ability to degrade or completely mineralize TCE. Dehalococcoide sp. degrade trichloroethylene by reductive dechlorination under anaerobic conditions. Under aerobic conditions, Pseudomonas fluorescence can co-metabolize TCE. Soil and ground water contamination by TCE has also been successfully remediated by chemical treatment and extraction.
Media
In the John Travolta film A Civil ActionA Civil Action
A Civil Action is a 1998 American drama film starring John Travolta and Robert Duvall, based on the book of the same name by Jonathan Harr...
, the case of a TCE-contaminated tannery and town water supply is covered in detail.
Further reading
- Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Toxicological Profile for Trichloroethylene. link
- 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 2 - Trichloroethylene and 1,1,1-Trichloroethane. Journal of Environmental Forensics (2000) 1, 83-93. link
- U.S. Environmental Protection Agency (USEPA). 2001. Trichloroethylene Health Risk Assessment: Synthesis and Characterization (External Review Draft) link
- U.S. National Academy of Sciences (NAS). 2006. Assessing Human Health Risks of Trichloroethylene - Key Scientific Issues. Committee on Human Health Risks of Trichloroethylene, National Research Council. link
- U.S. National Toxicology Program (NTP). 2005. Trichloroethylene, in the 11th Annual Report of Carcinogens. link
- Comment on Voluntary Scheme for users of Trichloroethylene at http://www.ensolv-europe.com
External links
- Q&A on trichloroethylene from Euro Chlor - ECSA (European Chlorinated Solvent Association)
- ATSDR - Case Studies in Environmental Medicine: Trichloroethylene Toxicity U.S. Department of Health and Human Services (public domain)
- Assessing Human Health Risks of Trichloroethylene - Key Scientific Issues, National Academy of Sciences
- EPA's Trichloroethylene web site
- Eleventh Report on Carcinogens: Trichloroethylene Monograph
- NIOSH Safety and Health Topic: Trichloroethylene