Tetrachloroethene and Trichloroethane in Drinking Water Information:

Properties:

Tetrachloroethene and trichloroethane (TCE) are similar molecules composed of only carbon, hydrogen, and chlorine atoms. Tetrachloroethene has a chemical formula of C2Cl4 and is a symmetric molecule with a central double bond. It is colourless, evaporates into its gas phase easily, and is used as a solvent for dry-cleaning and a degreasing agent in metal industries.1 TCE has a chemical formula of C2H3Cl3 and is also known as methyl chloroform. It is colourless, sweet-smelling, useful for solvating grease and oil, and an intermediate in the production of chemicals like vinyl chloride and insecticides.2

Sources:

Both chemicals have industrial applications and can therefore enter raw water sources if contaminated effluent is discharged. Dry cleaning and degreasing applications often produce liquid waste that can make its way downstream and contaminate raw water supplies.2 Although tetrachloroethene is highly volatile, it can persist in ground water or be converted into TCE. TCE is not only released in industrial effluents, but in landfills with inadequate storage or disposal practices.3

Regulations:

The limit for tetrachloroethene and TCE in drinking water is 10 micrograms per litre (µg/L). This is a combined limit; so the total amount of both tetrachloroethene and TCE cannot exceed 10 µg/L.

Health/Environmental Concerns:

Tetrachloroethene is a toxin that can cause damage to the nervous system, kidneys, and reproductive system.2 When tetrachloroethene is present in raw water sources, it can also be broken down into more toxic compounds like vinyl chloride the pose additional health risks. Short-term health impacts of TCE reflect those of tetrachloroethene, and long-term exposure has been linked to cancer. TCE has been determined by the Department of Human Health Services to be carcinogenic.

Action:

Exceedances of tetrachloroethene and TCE limits are rare. The tendency of the tetrachloroethene to evaporate reduces the concentration that ultimately reaches drinking water. However, if high levels of these compounds are present, they can be removed through aeration or adsorption onto granular activated carbon.4 Contact your Water Service Authority if you are concerned that your water may be contaminated. If drinking water makes you ill, contact a doctor right away.

1 Guidelines for Drinking Water Quality. Tetrachloroethene in Drinking Water; Vol. 2; World Health Organisation: Switzerland, 1996.

2 Toxicological Profile for Tetrachloroethene; Agency for Toxic Substances and Disease Registry, U.S. Department of Health and Human Services: Atlanta, GA, 2006. 

3 Guidelines for Drinking Water Quality. Trichloroethane in Drinking Water; Vol. 2; World Health Organisation: Switzerland, 1996.

4 Guide to the Parameters in the European Communities. What’s in your water?; S. I. No. 278 of 2007; National Federation of Group Water Schemes: Ireland.