Trichloroethylene has been widely used as a degreaser for metal parts. In the late s, the demand for trichloroethylene as a degreaser began to decline in favor of the less toxic 1,1,1-trichloroethane. Another problem with trichloroethylene is that it's just too good a solvent in many mechanical applications, as it easily will strip many paints almost instantly and dissolves some plastics. 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 a resurgence in use.
Trichloroethylene Trimar and Trilene was used as a volatile gas anesthetic from the s through the s in Europe and North America. Supplanting chloroform and ether for a significant period of time, trichloroethylene demonstrated superior efficacy in induction times and cost-effectiveness. It retained use in other locations well into the s. It was known for its favorable analgesic properties. Equilibration would often result in patient levels of 0. Many patients were given Trilene inhalers to self administer analgesia, especially in obstetrical labor.
The number of patients exposed to these high levels of trichloroethylene is difficult to know, but is certainly well into the millions. Although it has proven useful as a metal degreaser, trichloroethylene itself is unstable in the presence of metal over prolonged exposure.
As early as , this phenomenon was clearly recognized by the manufacturing industry, since an additive was instilled in the commercial formulation of trichloroethylene. The reactive instability is accentuated by higher temperatures, so that the search for stabilizing additives is 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 Company and could not be used by other manufacturers. Considerable research took place in the s to develop alternative stabilizers for trichlorethylene. The principal family of chemicals that showed promise was the ketone family, such as methyl ethyl ketone. Considerable research was conducted at Frontier Chemical Company, Wichita, Kansas on this class of ketones using reflux condensation experiments. When inhaled, trichloroethylene, as with any anesthetic gas, depresses the central nervous system.
Its symptoms are similar to those of alcohol intoxication , beginning with headache, dizziness, and confusion and progressing with increasing exposure to unconsciousness . Respiratory and circulatory depression from any anesthetic can result in death if administration is not carefully controlled. As mentioned above, cardiac sensitization to catecholamines such as epinephrine can result in dangerous cardiac arrhythmias.
Caution should be exercised anywhere a high concentration of trichloroethylene vapors may be present; the drug can desensitize the nose to its scent, and it is possible to unknowingly inhale harmful or lethal amounts of the vapor. 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.
The tightening of occupational exposure limits and increased need for worker protection in part contributed to the substitution of other lower toxicity chemicals for trichloroethylene in solvent cleaning and degreasing. The carcinogenicity of trichloroethylene was first evaluated in laboratory animals in the s. Numerous epidemiological studies have been conducted on trichloroethylene exposure in the workplace, with differing opinions regarding the strength of evidence between trichloroethylene and human cancer.
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. However the NAS also concluded that higher levels of exposure, such as workplace exposure, or locations with significant environmental contamination, might be associated with a liver cancer risk in humans. Recent studies in laboratory animals and observations in human populations suggest that exposure to trichloroethylene might be associated with congenital heart defects J Am Coll Cardiol.
While it is not clear what levels of exposure are associated with cardiac defects in humans, there is consistency between the cadiac defects observed in studies of communities exposed to trichloroethylene contamination in groundwater, and the effects observed in laboratory animals. Trichloroethylene can also affect the fertility of males and females in laboratory animals, but the relevance of these findings to humans is not clear.
The health risks of trichloroethylene have been studied extensively. The U. Environmental Protection Agency EPA sponsored a "state of the science" review of the health effects associated with exposure to trichloroethylene. Human exposure to trichloroethylene is potentially widespread. Others are potentially exposed through inhalation of vapor from contaminated soil or groundwater entering nearby buildings.
TCE was first detected in groundwater in , and is one of the most frequently detected contaminants in groundwater in the U. 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-carcinogen —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 as a Group 2A carcinogen, indicating that it considers it is probably carcinogenic to humans. In , a draft report of the Environmental Protection Agency EPA laid the groundwork for tough new standards to limit public exposure to trichloroethylene.
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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, military properties nationwide that are polluted with trichloroethylene.
High-level political appointees in the EPA — notably research director Paul Gilman — sided with the Pentagon and agreed to pull back the risk assessment. The report has raised greater concern about the adverse health effects of TCE, opening up the debate for better regulation. View All Life Sciences. Calibration Weights.
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