Chlorinated ethylenes are produced in large quantities and widely used in industry in the production of food packaging, synthetic fibres and industrial solvents.

The major route by which chlorinated ethylenes enter the environment is by volatilisation during production and use. Their presence in water may result from a direct discharge or atmospheric deposition. They may also be formed during the chlorination of water. In addition, diffuse inputs chlorinated ethylenes used in food packaging from land fill sites could occur.

Some information on concentrations in UK marine water is available. Pearson and McConnell (1975) reported concentrations in Liverpool Bay of up to 2.6 µg l^-1 (and average of 0.38 µg l^-1). A mean concentration in the range 1-100 ng l^-1 (highest concentration of 43 microg l^-1) has also been reported for river and estuarine samples of 80 sites in the UK (SAC Scientific 1987).

Marine sediment samples form Liverpool Bay taken in 1972 contained tetrachloroethylene at concentrations of 0.02 - 4.8 microg/kg (Pearson and McConnel, 1975).

Monitoring data from the National Rivers Authority and the National Monitoring Programme Survey of the Quality of UK Coastal Waters are presented in Appendix D. Water column concentrations for trichloroethylene and tetrachloroethylene were all found to be below the EQS values (see Appendix D). Monitoring data were not available for sediments or biota.

The available data suggest that concentrations of chloroethylenes in UK coastal and estuarine waters appear unlikely to exceed relevant quality standards derived for the protection of saltwater life.

Chlorinated ethylenes are unsaturated, low-molecular weight C₂ compounds in which one or more hydrogen atoms have been replaced with chlorine. With the exception of monochloroethylene, all chlorinated ethylenes are low-boiling liquids that have high vapour pressures and are moderately soluble in water. Vapour pressures and water solubility decrease with increasing chlorine substitution (CCME 1992).

Volatilisation is considered to be the main removal process from water. For example, the major sink tetrachloroethylene appears to be to the atmosphere, where it undergoes oxidation by reaction with hydroxyl radicals (half-life < 0.4 year). The half-life is sufficiently long, however, to allow a small proportion of the tetrachloroethylene released into the atmosphere to reach the stratosphere (Brooke et al 1993).

In addition, evaporative half-lives below 1 hour for chloroethylenes at an aqueous concentration of approximately 1 mg l^-1 have been reported (Dilling et al 1975).

Direct photolysis oxidation and hydrolysis are not considered to be important removal processes. Few data have been found on the degradation of chloroethylenes in the aquatic environment, and what are available suggest that, while some degradation may occur, in general, chlorinated ethylenes are fairly resistant to biodegradation (CCME 1992). In addition, limited sorption capacity has been reported for chlorinated ethylenes (CCME 1992).

For example, Brooke et al (1993) reviewed the environmental fate and behaviour of tetrachloroethylene. The authors concluded that the major removal process from aquatic systems appeared to be volatilisation to the atmosphere, with half-lives ranging from a few minutes to a few days, depending on the conditions. Degradation of tetrachloroethylene appears to occur under anaerobic conditions when a suitable carbon source is present. There is less conclusive evidence for degradation of tetrachloroethylene under aerobic conditions.

An exhaustive literature review on the toxicity of chlorinated ethylenes to marine organisms has not been carried out for the purposes of this profile. The information provided in this section is taken from existing review documents (CCME 1992, Brooke et al 1993). The most sensitive groups of organisms have been identified.

CCME (1992) reported that there appeared to be a degree of correlation between the degree of chlorination of ethylenes and toxicity, with tetrachloroethylene more toxic than dichloroethylene. The toxicity of trichloroethylene is intermediate between the toxicities of the dichloroethylenes and tetrachloroethylene.

Data for tetrachloroethylene suggest moderate toxicity to marine plants, invertebrates and fish.

For the marine alga Skeletonema costatum , 96 hour EC50s value of 509 mg l^-1 for chlorophyll-A content and 504 mg l^-1 for cell numbers have been reported (US EPA 1978). Greater sensitivity has been exhibited by Phaeodactylum tricorntum, with a 50% reduction in carbon uptake from CO₂ in photosynthesis occurring at a concentration of 10.5 mg l^-1.

Pearson and McConnel (1975) reported a 48 hour LC50 of 3.5 mg l^-1 for barnacle larvae Eliminius modestus. For the mysid shrimp Mysidopsis bahia, a 96 hour LC50 of 10.2 mg l^-1 and a chronic value (tested over a whole life stage) of 0.45 mg l^-1 (US EPA 1980).

For fish, 95 hour LC50 of 5 and >29-<52 mg l^-1 have been reported for dab and sheepshead minnow respectively.

No data could be located for sediment-dwelling organisms.

Brooke et al (1993) reviewed data on the bioaccumulation of tetrachloroethylene in aquatic organisms and found low to moderate (generally <100) bioconcentration factors in a variety of aquatic species.

Since most of the chloroethylenes have small octanol/water coefficients, bioaccumulation can be expected to be low.

Potential effects include:

• toxicity of tri- and tetrachloroethylene to algae, invertebrates and fish at concentrations above the EQS of 10 &micro;g l^-1 (annual average) in the water column.

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