Contents - Previous - Next

Trichloroethene

DESIGNATIONS

CAS No.: 79-01-6
Registry name: Trichloroethene
Chemical name: Ethene, trichloro
Synonyms, Trade names: Tri, ethene trichloride, trichloroethene, Chlorylen, Algylen, Benzinol, Circosolv, Lanadin, Perm-a-chlor, Triasol, Trichloran, Triclene, Trimar, Vitran and many others
Chemical name (German): Trichlorethen
Chemical name (French): Trichloroéthène, éthène trichloré
Appearance: colourless, volatile liquid with sweet odour reminiscent of chloroform, the gas is much denser than air.

BASIC CHEMICAL AND PHYSICAL DATA

ORIGIN AND USE

Usage:
Trichloroethene is used for a wide range of applications. 75-80% of the worldwide trichloroethene production is used for degreasing in the metal and glass industry (DVGW, 1985). Because of its good solvent properties, it was formerly used in dry-cleaning facilities and for the extraction of natural substances (e.g. for decaffeinated coffee and for fruit juice extracts). It is also used as an intermediate product in the manufacture of chloroacetic acid and as a solvent for greases, oils, waxes, resins, rubber, paints, lacquers, cellulose ester and cellulose ether.

Origin/derivation:
Trichloroethene is an artificial compound; it is produced synthetically from 1,2-dichloroethane. Stabilisers are added to the marketed product.

Production figures:

with a common annual decline of 5 - 7 % worldwide

Toxicity

Characteristic effects:

Humans/mammals: Trichlorethene irritates the eyes and skin as well as having a narcotic effect; loss of consciousness occurs on inhaling an amount of more than 3 mg/kg weight. Loss of weight and nervous phenomena such as headaches, disturbance of consciousness, agitation and frenzy are the consequences of chronic absorption which damages the central nervous system (with female employees from more than 200 vppm; RIPPEN, 1989).

Trichloroethene likewise affects the heart, liver and kidneys. For a long time the substance was considered carcinogenic, but the current opinion is that the pure substance is not. The enhanced tumour rates in animal experiments were the result of stabilisers added to trichloroethene such as epichlorohydrin or epoxybutane. Experiments performed in the USA with pure trichloroethene have, however, revealed an increase in the number of tumours in two types of animal (UBA, 1986).

A direct degradation product has likewise proven to be injurious to humans: trichloroacetyldehydride forms in the body and has a mutagenic effect.

Plants: Trichloroethene inhibits cell reproduction and stunts growth. Slight yellowing of leaves is sometimes encountered.

ENVIRONMENTAL BEHAVIOUR

Water:
Trichloroethene is denser than water and sinks gradually to the bottom even in groundwater. Groundwater contamination may last for many decades. It is listed in water hazard class 3 (extremely hazardous) in Germany.

Air:
Because of its volatility, large quantities of the substance produced (an estimated 50,000 t in 1979; DVGW, 1985) evaporate and are uniformly distributed in the atmosphere (ubiquitous). Exchange takes place between air and water. According to RIPPEN (1989), the substance makes a minor contribution to the formation of smog. It is washed out by precipitation and thus ingresses into surface water or groundwater.

Soil:
The substance accumulates in sediment; in sewage sludge, sometimes even to an extent which damages anaerobes.

Half-life:
The estimated dwell time in the atmosphere is roughly 1 week. If not evaporated, trichloroethene is persistent for 2-18 months in water-unsaturated soils. The half-life in seawater (pH 8 / 10°C) is 39 weeks and 2.5 - 6 years in freshwater (RIPPEN, 1989). The half-life in darkness is 11 months. Trichloroethene is stable under normal conditions (pH 7 / 25°C) (RIPPEN, 1989).

Degradation, decomposition products:
Trichloroethene is converted when exposed to light and heat in the atmosphere to phosgene, formyl chloride, acetyl chloride and finally to CO₂ and HCl. In water, it forms CHCl₂COCl. Hexachlorobenzene is formed at high temperatures; reaction with alkaline materials (e.g. mortar) to form dichloroacetylene. Anaerobic transformation to dichloroethene isomers and vinyl chloride takes place in contaminated groundwater, in anaerobic soil and on dumps. There is no transformation in sandy soils. There is degradation by adapted microorganisms.

Food chain:
Approx. 2-4% of the human intake of trichloroethene results from drinking water, 3-26% from foodstuffs and 70-95% from the air (UBA, 1986). Metabolism and accumulation take place in the bodily tissue.

ENVIRONMENTAL STANDARDS

Notes:

¹⁾ Provisional tolerance value (sum total of all chlorinated solvents)
²⁾ Sum total of 14 halogenated hydrocarbons
³⁾ Sum total of 14 halogenated hydrocarbons in less than 6 months
⁴⁾ Sum total of trichloroethane, trichloroethene, tetrachloroethene and dichloromethane
⁵⁾ Sum total of organic chlorine compounds except pesticides
⁶⁾ With chronic exposure
⁷⁾ Criterion for water quality
⁸⁾ Parameter, trichloroethanol in whole blood
⁹⁾ Parameter, trichloroacetic acid in urine
¹⁰⁾ Cumulative value for several solvents in one item of food

COMPARISON/REFERENCE VALUES

Assessment/comments

Because of the high toxicity in aquatic organisms, the US EPA recommends a general surface-water concentration of zero. As the risk of cancer due to the consumption of contaminated drinking water cannot be precluded, a quality value has been established for the sum of four similar chlorinated hydrocarbons. Despite an extremely broad span in various countries, this figure should not exceed 10 m g/l for drinking water.

As trichloroethene is a typical contaminant for sewage water from cities and communities, it must be handled carefully to minimise emissions.

In the Nineties, several countries restricted the use of trichloroethene by law, so that gradually a replacement is taking place.

Contents - Previous - Next