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Dense Nonaqueous Phase Liquids (DNAPLs)

Chemistry and Behavior

Halogenated Alkenes


tetrachloroethyleneTetrachloroethene (PCE, CAS # 127-18-4) is a highly volatile compound with an ethereal odor. Howard (1991) estimated the Kow at 3.40 and the Koc at 209 to 238 (different reference sources). The Henry's constant is moderately high at 1.49 x 10-2 atm-m3/mole at 25° C, while water solubility and vapor pressure are 150 mg/L at 25° C and 18.49 mm Hg, respectively.

The low Kow indicates that PCE will not accumulate significantly in terrestrial or aquatic plants and animals.

PCE's movement through soil is dependent on its Koc value, which is an indication that it is sensitive to soil properties and reacts chemically in soil. The Koc value is moderately low, denoting an aversion to adsorption onto particles and a high to medium mobility through soil and ground water. PCE is leached more readily through sandy soil, and, due to its vapor pressure, it is volatilized more rapidly in dry soil. Slow degradation by soil microorganisms occurs more quickly in anaerobic conditions when an appropriate microbial consortium is present. If the consortium is not present there may be no degradation or stalling at 1,2-dichloroethene.

The high Henry's constant signifies that PCE will volatilize from surface waters. Howard (1991) found the half-life of this compound in surface waters to range from three hours to several weeks. This range is due to differences in the water body properties. The chemical and physical properties of the water, such as temperature, width, depth, season, and energy, also contribute to this range.

In air, PCE exists as a vapor, as indicated by its high vapor pressure, and is subject to photooxidation. Due to its solubility in water, it is subject to some washout in rain. PCE degrades in air by reacting with hydroxyl radicals. Degradation rates range from complete degradation in one hour to a half life of two months (Howard 1991). Half-life estimates reported in PubChem range to 96 days. The longer half-life estimates are supported by the fact that PCE is present in the atmosphere world-wide and at locations far removed from anthropogenic emission sources (ATSDR 1997). Atmospheric breakdown products of PCE include phosgene, chloroacetylchlorides, formic acid, carbon monoxide, carbon tetrachloride, and hydrochloric acid.

For Further Information

Concise International Chemical Assessment Document 68 Tetrachloroethene
International Programme on Chemical Safety II.Series
World Health Organization

This document is a comprehensive review of the physical and chemistry properties, fate and transport, human and ecological health effects, and occurrence of PCE.

Handbook of Environmental Fate and Exposure Data for Organic Chemicals, Volume II Solvents
Howard, P. (ed.)
Lewis Publishers, Chelsea, MI, 1991, 546 pp

This book provides physical and chemical properties and fate and transport information for 82 chemical solvents.

NIOSH Pocket Guide to Hazardous Chemicals
National Institute of Occupational Safety and Health

This guide contains information on the chemical physical properties of PCE and their physical hazards.

Adobe PDF LogoToxicological Profile for Tetrachloroethylene
Agency for Toxic Substances and Disease Registry
U.S. Department of Health and Human Services, 1997, 318 pp

This profile provides information on human health effects, fate and transport, production, and uses of PCE.