Carbon tetrachloride is a volatile, clear, colourless, heavy liquid. This substance is an ozone-depleting substance and, as a result, its production and use (except for essential uses) within the European Community was due to be phased out by 1st January 1995. Carbon tetrachloride production in the United Kingdom has recently ceased and the major use for carbon tetrachloride (production of CFC-11 and CFC-12) is now in decline. The majority of the reported levels of carbon tetrachloride in the environment were measured before these controls were introduced and therefore may not accurately reflect the present situation.

A Coopers Lybrand and Deloitte report for the Department of Trade and Industry (DTI) states that the United Kingdom consumption of carbon tetrachloride was 40,000-50,000 tonnes per annum in 1990 (DTI, 1990). Willis et al (1994) estimated that to be far less in 1994 due to the reduction in the production of CFC-11 and CFC-12, which was a major use of carbon tetrachloride.

Most carbon tetrachloride produced is used in the manufacture of chlorofluorocarbons (CFCs). Other recorded uses of carbon tetrachloride include in fire extinguishers, as a grain fumigant, flammability suppressant, solvent, metal degreaser and various roles in the production of paint, plastics, semi-conductors and petrol additives (CEC, 1986). Carbon tetrachloride is used as a chemical intermediate in the manufacture of pharmaceutical and pesticide products. It is widely used as a reagent in laboratories (RSC, 1981).

Carbon tetrachloride is ubiquitous in the global atmospheric and aquatic environments and numerous measurements of carbon tetrachloride levels have been made and reported.

Willis et al (1998) found that carbon tetrachloride levels in the atmosphere had been measured extensively (as the atmosphere is acknowledged to be the major sink for carbon tetrachloride). The authors estimated the global background level of carbon tetrachloride to be around 0.7-1.0 µg m^-3.

For UK freshwaters, the authors reported concentrations in the range 0.3-24 &micro;g l^-1 (the higher levels generally having been measured near to source dominated areas). Typical levels away from sources of carbon tetrachloride were <l&micro;g l^-1.

For UK marine waters, Willis et al (1994) reported levels to be between <0.1 - 44 &micro;g l^-1. Again, higher levels were found in source dominated areas. Levels measured in the open ocean were generally much lower, at around 0.5 ng l^-1.

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. Only one water column concentration was found to approach the EQS value (see Appendix D). Monitoring data were not available for sediments or biota.

The available data suggest that concentrations of carbon tetrachloride in UK coastal and estuarine waters do not, generally exceed relevant quality standards derived for the protection of saltwater life.

Willis et al (1994) reviewed the environmental fate and behaviour of carbon tetrachloride. The authors concluded that the major removal process from water bodies was volatilisation to the atmosphere. Laboratory tests have suggested a volatilisation lifetime from water between 29 minutes and a few hours, depending on the degree of agitation (Dilling et al, 1975; Versar Inc., 1979). Zoeteman et al (1980) calculated half-life values for carbon tetrachloride in rivers and lakes, and groundwaters of 0.3-3 days and 30-300 days respectively.

Adsorption of carbon tetrachloride onto soil and sediment may occur to a small extent (Organic carbon-water partition coefficient (Koc) of 439 (log 2.6) (Eastwood et al 1991)) have been reported for carbon tetrachloride, but carbon tetrachloride is likely to be mobile in such media.

Carbon tetrachloride is highly resistant to photolysis and photo-oxidation reactions in the troposphere. The major removal process for carbon tetrachloride in the troposphere is transfer to the stratosphere. Once in the stratosphere, carbon tetrachloride is photodegraded by short wavelength radiation and contributes to ozone depleting processes. The overall atmospheric lifetime for carbon tetrachloride is around 50 years, the lifetime being dominated by the troposphere to stratosphere turnover time.

Carbon tetrachloride does not appear to biodegrade under aerobic conditions. Many bacteria have been shown to dehalogenate carbon tetrachloride under anaerobic conditions.

An exhaustive literature review on the toxicity of carbon tetrachloride 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 (Willis et al 1994). The most sensitive groups of organisms have been identified.

Willis et al (1994) reviewed data on the aquatic toxicity of carbon tetrachloride. No toxicity data appear to be available for marine species of algae. However, for freshwater algae, the lowest toxic concentration of carbon tetrachloride was 105 mg 1^-1 which caused a reduction in cell multiplication in the freshwater algae Microcystis aeruginosa.

For invertebrates, Willis et al (1994) only found data for the freshwater crustacean Daphnia magna with the lowest acute LC50 reported being 35 mg l^-1.

For marine fish, the lowest acute LC50 found was 50 mg l^-1 for dab Limanda limanda. In comparison, for freshwater species, an LC50 of 1.97 mg l^-1 was reported for the embryo-larval stages of rainbow trout Oncorhynchus mykiss. However, the results of this test have been criticised as they are an order of magnitude lower than reported in other studies.

No data could be located for sediment-dwelling organisms.

The log octanol-water partition coefficient of carbon tetrachloride is 2.64. This indicates a moderate potential for bioaccumulation under conditions of constant exposure. However, studies cited in Willis et al (1994) have shown that the compound's short tissue lifetime reduces this tendency. Barrows et al (1980) reported a tissue half-life of less than 1 day for the bluegill sunfish, and a bioconcentration factor of 30. A similar tissue half-life of <l day has been reported for trout muscle (Niimi, 1987) and a steady state bioconcentration factor for rainbow trout of 17.7 has been measured (Neely et al, 1974). No significant bioaccumulation in marine food chains was found in an extensive study by Pearson and McConnell (1975).

A slightly higher bioconcentration factor of 300 (on a wet weight basis) has been measured for carbon tetrachloride in the green alga Chlorella fusco exposed to 50 &micro;g l^-1 of carbon tetrachloride for at least 24 hours (Geyer et al 1984).

Potential effects include:

• toxicity to algae, invertebrates and fish at concentrations above the EQS of 12 &micro;g l^-1 (annual average) in the water column.

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