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IAQUK Resources - Tetrachlorethylene

Sources of Pollution

 

Michael Faraday, who also discovered Benzene, first synthesized Tetrachloroethene in 1821 by thermal decomposition (a chemical reaction in which a compound breaks up into at least two other substances when heated) of hexachloroethane into Tetrachloroethene and chlorine.

 

Most Tetrachloroethene is produced by high temperature chlorinolysis of light hydrocarbons. The method is related to Faraday's discovery since hexachloroethane is generated and thermally decomposes. Side products include carbon tetrachloride, hydrogen chloride, and hexachlorobutadiene.

 

This reaction can be catalyzed (rate of chemical reaction) by a mixture of potassium chloride and aluminium chloride, or by activated carbon.

 

Trichloroethylene is a major byproduct of the reaction, and since both are salable commercial chemicals, typical industrial practice is to collect both products and then separate them by distillation.

 

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

 

It appears in a few consumer products including contact adhesives, degreasing agents, wax removers, shoe polishes, garden pesticides, upholstery cleaners and carpet cleaners. In most products, Tetrachloroethene has been replaced by other less toxic solvents.

 

Tetrachloroethene was once extensively used as an intermediate in the manufacture of HFC-134a and related refrigerants. In the early 20th century, Tetrachloroethene was used for the treatment for hookworm infestation (parasitic worms).

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Health effects

The results of single or short-term human exposure to Tetrachloroethylene indicate that human beings are likely to begin to experience eye irritation at air concentrations of approximately 500 mg/m3, and depression of the central nervous system and nose and throat irritation at approximately 700 mg/m3. Such effects are reversible on cessation of exposure, but increase in severity with both increasing concentration and duration of exposure.

 

High concentrations of Tetrachloroethylene (particularly in closed, poorly ventilated areas) can cause dizziness, headache, sleepiness, confusion, nausea, difficulty in speaking and walking, unconsciousness, and death. Observations after repeated exposure to Tetrachloroethylene, over months or years, indicate that human beings inhaling Tetrachloroethylene are likely to begin to exhibit depression of the central nervous system at concentrations exceeding approximately 700 mg/m3.

 

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

 

The International Agency for Research on Cancer has classified Tetrachloroethylene as probably carcinogenic to humans. Prolonged exposure to high levels is believed to be necessary to cause cancer. Like many chlorinated hydrocarbons, Tetrachloroethene is a central nervous system depressant and can enter the body through inhalation.

 

Most Tetrachloroethylene is excreted unchanged via the lungs.   Removal of Tetrachloroethylene from blood and excretion in the breath are slow, the amount increasing with increasing exposure level. The concentrations of the compound in blood and breath can be used for estimating exposure levels.

 

One way of testing for Tetrachloroethylene exposure is to measure the amount of the chemical in the breath, much the same way breath-alcohol measurements are used to determine the amount of alcohol in the blood.  Because it is stored in the body's fat and slowly released into the bloodstream, Tetrachloroethylene can be detected in the breath for weeks following a heavy exposure.

 

Tetrachloroethylene and Trichloroacetic acid (TCA), a breakdown product of Tetrachloroethylene, can be detected in the blood. These tests are relatively simple to perform.

 

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

 

A study of 99 twins by Dr. Samuel Goldman and researchers at the Parkinson's Institute in Sunnyvale, California determined there is a "lot of circumstantial evidence" that exposure to Tetrachloroethlene increases the risk of developing Parkinson's disease ninefold. Larger population studies are planned.

 

Technical - Tetrachloroethylenee - Cl2C=CCl2.


  • Colourless liquid
  • Ether-like odour
  • Detectable in the air at 1ppm
  • CAS Number: 127-18-4
  • LTEL - 50ppm (345 mg/m³)
  • STEL - 100ppm (689mg/m³)
  • Risk Phrases: R40, 51, 53
  • Safety Phrases: S23, 36, 37, 61

Tetrachloroethylene is a manufactured chlorocarbon (chlorine-containing compound. The chlorocarbons have long been known for causing organ, genetic and reproductive damage), with the formula Cl2C=CCl2. It is a colourless liquid widely used fordry cleaning of fabrics, hence it is sometimes called dry-cleaning fluid.

 

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