Template:Short description Template:Redirect Template:Chembox Trichloroethylene (TCE) is an organochloride with the formula C2HCl3, commonly used as an industrial metal-degreasing solvent. It is a clear, colourless, non-flammable, volatile liquid with a chloroform-like pleasant mild smell<ref name=PGCH/> and sweet taste.<ref name=atsdr>Trichloroethylene (TCE) on ATSDR</ref> Its IUPAC name is trichloroethene. Trichloroethylene has been sold under a variety of trade names. Industrial abbreviations include trichlor, Trike, Tricky and tri. Under the trade names Trimar and Trilene, it was used as a volatile anesthetic and as an inhaled obstetrical analgesic. It should not be confused with the similar 1,1,1-trichloroethane, which was commonly known as chlorothene.
HistoryEdit
The earliest record of trichloroethylene synthesis dates back to 1836. It was obtained from the action of potassium hydroxide on 1,1,2,2-tetrachloroethane and 1,1,1,2-tetrachloroethane by Auguste Laurent and notated as Template:Chem2 (then the atomic weight of carbon was thought to be half of what it really is). Laurent named it chlorétherise but did not investigate the compound further.<ref>Essai sur l'Action du Chlore sur la Liqueur des Hollandais et sur quelques Ethers in Annales de Chimie, LXIII. (1836) page 379</ref><ref>The so-called Perchloride of Formyl, Gmelin, L. (translated in 1855). Hand-book of Chemistry: Organic chemistry. UK: Cavendish Society. pages 200–201</ref>
Trichloroethylene's discovery is widely attributed to E. Fischer who made it in 1864 via the reduction of hexachloroethane with hydrogen. Fischer investigated trichloroethylene and noted its boiling point as between 87 and 90 degrees Celsius.<ref>Ueber die Einwirkung von Wasserstoff auf Einfach-Chlorkohlenstoff, Fischer, E. (1864) in Zeitschrift für Chemie. page 268</ref><ref>Template:Cite journal</ref><ref>Hardie DWF (1964). Chlorocarbons and chlorohydrocarbons. 1,1,2,2-Tetrachloroethane. In: Encyclopedia of Chemical Technology. Kirk RE, Othmer DF, editors. New York: John Wiley & Sons, pp. 159–164</ref> Commercial production began in Germany, in 1920 and in the US in 1925.<ref>Mertens JA (1993). Chlorocarbons and chlorohydrocarbons. In: Kirk-Othmer Encyclopedia of Chemical Technology, 4th Ed. Kroschwitz JI, Howe-Grant M, editors. New York: John Wiley & Sons, pp. 40–50.</ref>
The use of trichloroethylene in the food and pharmaceutical industries has been banned in some parts of the world since the 1970s<ref name="FDA 1977 ban on cosmetic, food and medical use of trichloroethylne">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> due to concerns about its toxicity. Legislation has forced the replacement of trichloroethylene in many processes in Europe as the chemical was classified as a carcinogen carrying an R45 risk phrase, May cause cancer. 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 of May impair fertility, and would not be a legally acceptable substitute.
AnaesthesiaEdit
Trichloroethylene is a good analgesic at 0.35 to 0.5% concentrations.<ref name="textbook">Textbook of Obstetric Anaesthesia. (2002). UK: Greenwich Medical Media. Pages 64-65</ref> Trichloroethylene was used in the treatment of trigeminal neuralgia beginning in 1916.<ref name="forensic">Template:Cite book</ref>
Pioneered by Imperial Chemical Industries in Britain, under the trade name "Trilene" (from trichloroethylene), its development was hailed as an anesthetic revolution. It was mostly known as "Trimar" in the United States. The –mar suffix indicates study and development at the University of Maryland, e.g., "Fluoromar" for fluroxene and "Vinamar" for ethyl vinyl ether".<ref>Template:Cite book</ref> From the 1940s through the 1980s, both in Europe and North America, trichloroethylene was used as a volatile anesthetic almost invariably administered with nitrous oxide. Marketed in the UK by Imperial Chemical Industries under the trade name Trilene it was coloured blue (with a dye called waxoline blue in 1:200,000 concentration)<ref name="current">Current Researches in Anesthesia & Analgesia. (1951). USA: International Anesthesia Research Society. p.278</ref> to avoid confusion with the similar-smelling chloroform. Trilene was stabilised with 0.01% thymol.<ref name=current/>
Originally thought to possess less hepatotoxicity than chloroform, and without the unpleasant pungency and flammability of ether, TCE replaced earlier anesthetics chloroform and ether in the 1940s. TCE use was nonetheless soon found to have several pitfalls. These included promotion of cardiac arrhythmias, low volatility and high solubility preventing 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. Alkali components of carbon dioxide absorbers reacted with trichloroethylene and released dichloroacetylene, a neurotoxin.
The introduction of halothane in 1956 greatly diminished the use of TCE as a general anesthetic in the 1960s, as halothane allowed much faster induction and recovery times and was considerably easier to administer. Trichloroethylene has been used in the production of halothane.<ref>Template:Ref patent3</ref>
Trilene was also used as an inhaled analgesic, mainly during childbirth, often self-applied by the patient. Trichloroethylene was introduced for obstetrical anaesthesia in 1943, and used until the 1980s.<ref name=textbook/> Its anaesthetic use was banned in the United States in 1977 but the anaesthetic use in the United Kingdom remained until the late 1980s (especially for childbirth).<ref name=forensic/> Fetal toxicity and concerns about the carcinogenic potential of TCE led to its abandonment in developed countries by the 1980s. TCE was used with halothane in the tri-service field anaesthetic apparatus used by the UK armed forces under field conditions. Template:As of, TCE was still in use as an anesthetic in Africa.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>Template:Update inline
ProductionEdit
Today, most trichloroethylene is produced from ethylene. First, ethylene is chlorinated over a ferric chloride catalyst to produce 1,2-dichloroethane:<ref name=morrison2013/>
- CH2=CH2 + Cl2 → ClCH2CH2Cl
When heated to around 400 °C with additional chlorine, 1,2-dichloroethane is converted to trichloroethylene:
- ClCH2CH2Cl + 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 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.<ref name=morrison2013/>
Prior to the early 1970s, however, most trichloroethylene was produced in a two-step process from acetylene. 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:<ref name=morrison2013/>
- HC≡CH + 2 Cl2 → Cl2CHCHCl2
The 1,1,2,2-tetrachloroethane is then dehydrochlorinated to give trichloroethylene. This can be accomplished either with an aqueous solution of calcium hydroxide:<ref name=morrison2013/>
- 2 Cl2CHCHCl2 + Ca(OH)2 → 2 ClCH=CCl2 + CaCl2 + 2 H2O
or in the vapor phase by heating it to 300–500 °C on a barium chloride or calcium chloride catalyst:
- Cl2CHCHCl2 → ClCH=CCl2 + HCl
Common impurities in reagent and technical grade TCE are methyl chloroform, carbon tetrachloride, ethylene dichloride, tetrachloroethanes, benzene and phenol. However, these compounds are present in very small amounts and do not possess any risk.<ref name=forensic/>
UsesEdit
Trichloroethylene is an effective solvent for a variety of organic materials. It is mainly used for cleaning. Trichloroethylene is an active ingredient (solvent) in various printing ink, varnish and industrial paint formulations.<ref name="Subramanian 2023 t808">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name=forensic/> Other uses include dyeing and finishing operations, adhesive formulations, rubber processing, adhesives, lacquers, and paint strippers. It is applied before plating, anodizing, and painting.<ref name="Caudle Guillot Lazo Miller 2012 pp. 178–188">Template:Cite journal</ref>
When trichloroethylene was first widely produced in the 1920s, its 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 (removal of caffeine) and the preparation of flavoring extracts from hops and spices.<ref name=forensic/> TCE was used a freezing point depressant in carbon tetrachloride fire extinguishers.<ref name=forensic/>
Trichloroethylene is also a chain terminator for polyvinyl chloride.<ref name=forensic/> Chlorination gives pentachloroethane.
Cleaning solventEdit
Perhaps the greatest use of TCE is as a degreaser for metal parts. It has been widely used in degreasing and cleaning since the 1920s because of its low cost, low flammability, low toxicity, and high effectivity as a solvent. 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 due to its contribution to the ozone depletion. As a result, trichloroethylene has experienced some resurgence in use as a degreaser.<ref name=forensic/>
Trichloroethylene has been used as a dry cleaning solvent, although mostly replaced by tetrachloroethylene, except for spot cleaning where it is still often used under various tradenames. Trichloroethylene is used to remove grease and lanolin from wool before weaving.<ref name=forensic/>
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 liquid oxygen (LOX) dome were also flushed with TCE before test firing.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref name="RocketdyneF1OperatingManual">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The F-1 rocket engine had its LOX dome, gas generator, and thrust chamber fuel jacket flushed with TCE during launch preparations.<ref name="RocketdyneF1OperatingManual"/>
RefrigerantsEdit
TCE is also used in the manufacture of a range of fluorocarbon refrigerants<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> such as 1,1,1,2-tetrafluoroethane more commonly known as HFC-134a.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- CHCl=CCl2 + 4 HF → CF3CH2F + 3 HCl
TCE was also used in industrial refrigeration applications due to its high heat transfer capabilities and its low-temperature specification.Template:Cn
SafetyEdit
Chemical instabilityEdit
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 to 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 under a reflux condenser and observing decomposition. Definitive documentation of 1,4-dioxane as a stabilizing agent for TCE is scant due to the lack of specificity in early patent literature describing TCE formulations.<ref>Template:Cite book</ref><ref>Template:Cite book</ref> Epichlorohydrin, butylene oxide, N-methylpyrrole and ethyl acetate are common stabilisers for TCE, with epichlorohydrin being the most persistent and effective.<ref name=morrison2013>Morrison, R. D., Murphy, B. L. (2013). Chlorinated Solvents: A Forensic Evaluation. UK Royal Society of Chemistry.</ref> Other chemical stabilizers include ketones such as methyl ethyl ketone. Template:Multiple image
Physiological effectsEdit
When inhaled, trichloroethylene produces central nervous system depression resulting in general anesthesia. These effects may be mediated by trichloroethylene acting as a positive allosteric modulator of inhibitory GABAA and glycine receptors.<ref>Template:Cite journal</ref><ref>Template:Cite journal</ref> 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 by dehydrochlorination and phosgene.<ref name=Orkin>Orkin, F. K. (1986) Anesthesia Systems (Chapter 5). In R. D. Miller (Ed.), Anesthesia (second edition). New York, NY: Churchill Livingstone.Template:Page needed</ref> Cranial nerve dysfunction (especially the fifth cranial nerve) was common when TCE anesthesia was given using CO2 absorbing systems. 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 anesthetics such as halothane by the 1960s.<ref name=Stevens>Stevens, W.C. and Kingston H. G. G. (1989) Inhalation Anesthesia (Chapter 11). In P. G. Barash et al. (Eds.) Clinical Anesthesia. Philadelphia, PA: Lippincott.Template:Page needed</ref>
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.<ref name="epa.gov">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Much of what is known about the chronic human health effects of trichloroethylene is based on occupational exposures. Besides the effects to the central nervous system, workplace exposure to trichloroethylene has been associated with toxic effects in the liver and kidney.<ref name="epa.gov"/> A history of long-term exposure to high concentrations of trichloroethylene is a suspected environmental risk of Parkinson's disease.<ref>Template:Cite journal</ref>
MetabolismEdit
Trichloroethylene is metabolised to trichloroepoxyethane (TCE oxide) which rapidly isomerises to trichloroacetaldehyde (chloral).<ref>Fishbein, L. (1977). Potential Industrial Carcinogens and Mutagens. Environmental Protection Agency, Office of Toxic Substances</ref> Chloral hydrates to chloral hydrate in the body. Chloral hydrate is either reduced to 2,2,2-trichloroethanol or oxidised to trichloroacetic acid. Monochloroacetic acid,<ref name=monitor/> dichloroacetic acid<ref>Biologically Based Methods for Cancer Risk Assessment. (2013). Springer US.</ref> and trichloromethane<ref name=monitor>21.4.25: Trichloroethylene in Biological Monitoring: An Introduction. (1993). UK: Wiley.</ref><ref>Toxicological Profile for Trichloroethylene: Draft. (1995). U.S. Department of Health and Human Services.</ref><ref>Mutagenesis. (1978). page 268</ref> were also detected as minor metabolites of TCE.
Exposure and regulationsEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}} With a specific gravity greater than 1 (denser than water), trichloroethylene can be present as a dense non-aqueous phase liquid (DNAPL) if sufficient quantities are spilt in the environment.
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.<ref>Lyne FA, McLachlan T (1949). "Contamination of water by trichloroethylene" p. 513 in Template:Cite journal</ref> Based on available federal and state surveys, between 9% and 34% of the drinking water supply sources tested in the US may have some TCE contamination, though EPA has reported that most water supplies comply with the maximum contaminant level (MCL) of 5 ppb.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Generally, atmospheric levels of TCE are highest in areas of concentrated industry and population. Atmospheric levels tend to be lowest in rural and remote regions. Average TCE concentrations measured in air across the United States are generally between 0.01 ppb and 0.3 ppb, although mean levels as high as 3.4 ppb have been reported.<ref name=":0a">{{#invoke:citation/CS1|citation |CitationClass=web }}Template:PD-notice</ref> TCE levels in the low parts per billion range have been measured in food; however, levels as high as 140 ppb were measured in a few samples of food.<ref name=":0a" /> TCE levels above backgroundTemplate:How have been found in homes undergoing renovation.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Existing regulationsEdit
State, federal, and international agencies classify trichloroethylene as a known or probable carcinogen for humans. In 2014, the International Agency for Research on Cancer updated its classification of trichloroethylene to Group 1, indicating that sufficient evidence exists that it can cause cancer of the kidney in humans as well as some evidence of cancer of the liver and non-Hodgkin's lymphoma.<ref>Template:Cite book</ref>
In the European Union, the Scientific Committee on Occupational Exposure Limit Values (SCOEL) recommends an exposure limit for workers exposed to trichloroethylene of 10 ppm (54.7 mg/m3) for 8-hour TWA and of 30 ppm (164.1 mg/m3) for STEL (15 minutes).<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
Existing EU legislation aimed at protection of workers against risks to their health (including Chemical Agents Directive 98/24/EC<ref>Template:CELEX</ref> and Carcinogens Directive 2004/37/EC<ref>
Template:CELEX</ref>) currently do not impose binding minimum requirements for controlling risks to workers' health during the use phase or throughout the life cycle of trichloroethylene.
In 2023, the United States United States Environmental Protection Agency (EPA) determined that trichloroethylene presents a risk of injury to human health in various uses, including during manufacturing, processing, mixing, recycling, vapor degreasing, as a lubricant, adhesive, sealant, cleaning product, and spray. It is dangerous from both inhalation and dermal exposure and was most strongly associated with immunosuppressive effects for acute exposure, as well as autoimmune effects for chronic exposures.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Chronic exposure to trichloroethylene has also been linked to an increased risk of Parkinson's disease.<ref name="Link to Parkinson's">Template:Cite journal</ref><ref>Template:Cite news</ref> As of June 1, 2023, two U.S. states (Minnesota and New York) have acted on the EPA's findings and banned trichloroethylene in all cases but research and development.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite act</ref> According to the US EPA, in October 2023 it "proposed to ban the manufacture (including import), processing, and distribution in commerce of TCE for all uses, with longer compliance time frames and workplace controls (including an exposure limit) for some processing and industrial and commercial uses until the prohibitions come into effect" to "protect everyone including bystanders from the harmful health effects of TCE".<ref name="US EPA h041">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Following the EPA's recommendation the Biden Administration announced a proposal to ban trichloroethylene later that month.<ref>Template:Cite news</ref> In December 2024 the EPA issued a final ruling on the regulation of trichloroethylene, with the rule taking effect on January 16, 2025.<ref name="EPA's trichloroethylene takes effect">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The rule bans the manufacture (including import), processing, and distribution in commerce of trichloroethylene for all uses, with longer compliance timeframes and stringent worker protections for some processing and industrial and commercial uses until the prohibitions come into effect.<ref name="EPA trichloroethylene ban">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The EPA is prohibiting most uses of trichloroethylene within one year of the rule taking effect including manufacture and processing for most commercial and all consumer products, with only a limited number of commercial uses being allowed after January 16, 2026.<ref name="EPA phasing out commercial trichloroethylene use">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> These uses will eventually be phased out as well, though an exact timeframe hasn't been determined yet, but until they have been phased out more stringent worker protections will be required with a lower inhalation exposure limit for airborne trichloroethylene being put in place.<ref name="EPA trichloroethylene ban" /> Many of the trichloroethylene uses that are continuing for longer than one year occur in highly industrialized settings with critical uses such as the cleaning of parts used in medical devices, aircraft & other transportation, security and defense systems and the manufacture of battery separators and refrigerants.<ref name="EPA trichloroethylene ban" /> These uses will ultimately be prohibited as well but are temporarily being allowed to continue in order to avoid negative impacts to national security or critical infrastructure, and to allow time to transition to alternative chemicals and methods.<ref name="EPA trichloroethylene ban" />
RemediationEdit
Recent research has focused on the in-place remediation of trichloroethylene in soil and groundwater using potassium permanganate instead of removal for off-site treatment and disposal. Naturally occurring bacteria have been identified with the ability to degrade TCE. Dehalococcoides sp. degrade trichloroethylene by reductive dechlorination under anaerobic conditions. Under aerobic conditions, Pseudomonas fluorescens can co-metabolize TCE. Soil and groundwater contamination by TCE has also been successfully remediated by chemical treatment and extraction. The bacteria Nitrosomonas europaea can degrade a variety of halogenated compounds including trichloroethylene.<ref name="genome">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Toluene dioxygenase has been reported to be involved in TCE degradation by Pseudomonas putida.<ref name="Irvine">Template:Cite book</ref> In some cases, Xanthobacter autotrophicus can convert up to 51% of TCE to CO and Template:CO2.<ref name="Irvine"/>
Society and cultureEdit
Groundwater and drinking water contamination from industrial discharge including trichloroethylene is a major concern for human health and has precipitated numerous incidents and lawsuits in the United States.
The 1995 non-fiction book A Civil Action was written about a lawsuit (Anderson v. Cryovac) following the increase in leukemia cases, blamed on trichloroethylene pollution. It was adapted to cinema in 1998.
TCE has been used as a recreational drug.<ref>Trichloroethylene in Neurology in Clinical Practice, Daroff, R. B., Fenichel, G. M., Jankovic, J., Mazziotta, J. C. (2012).</ref> Common methods of trichloroethylene abuse include inhalation and drinking.<ref name=abuse>Chapter 50: Trichloroethylene Medical Toxicology of Drug Abuse: Synthesized Chemicals and Psychoactive Plants.Barceloux, D. G. (2012).</ref> Most TCE abusers were young people and workers. The main reported reason for abuse is trichloroethylene's euphoriant and slight hallucinogenic effect.<ref name=abuse/> Some workers had become addicted to TCE.<ref>Trichlorethylene Addiction and its Effects (1972) Boleslaw Alapin M.D., M.R.C. Psych. British Journal of Addiction to Alcohol & Other DrugsVolume 68, Issue 4 p. 331-335 DOI</ref>
ReferencesEdit
Further readingEdit
- Agency for Toxic Substances and Disease Registry (ATSDR). 1997. Toxicological Profile for Trichloroethylene.
- Template:Cite journal
- Template:Cite journal
- {{#invoke:citation/CS1|citation
|CitationClass=web }}
- US Environmental Protection Agency (USEPA). 2011. Toxicological Review for Trichloroethylene
- US 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.
- US National Toxicology Program (NTP). 2021. Trichloroethylene, in the 15th Annual Report of Carcinogens.
External linksEdit
- US EPA: Trichloroethylene – TCE information website – US Environmental Protection Agency (EPA)
- chlorinated-solvents.eu – Sustainable uses and industry recommendations, European Chlorinated Solvents Association
- Case Studies in Environmental Medicine: Trichloroethylene Toxicity – Agency for Toxic Substances and Disease Registry (ATSDR), of the US Department of Health and Human Services (public domain)
- Assessing Human Health Risks of Trichloroethylene – Key Scientific Issues – US National Academy of Sciences (NAS)
- US NIH: Fifteenth Report on Carcinogens: Trichloroethylene Monograph – US National Institutes of Health (NIH)
- Workplace Safety and Health Topics: Trichloroethylene – TCE – US National Institute for Occupational Safety and Health (NIOSH)
Template:Pollution Template:General anesthetics Template:Navboxes Template:Authority control