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Carbon tetrachloride

Report

To read the report please click here.

This marine risk assessment was also published in a peer-reviewed journal: Thompson, R.C. et al., 2004. Carbon Tetrachloride Marine Risk Assessment with Special Reference to the OSPARCOM region: North Sea. Environmental Monitoring and Assessment, Vol. 97, (1-3), 23-38.

Summary

Current usage of carbon tetrachloride does not represent a risk to the marine environment. This conclusion is based on 27 laboratory toxicity studies, plus 1991-1995 monitoring results from the North Sea, rivers and estuaries.

Applications of carbon tetrachloride

In 1986, carbon tetrachloride was identified as a compound which may deplete the stratospheric ozone layer. It is not listed as a greenhouse gas under the Kyoto Protocol, and has a negligible tropospheric ozone creation potential

A phase-out was scheduled under the Montreal Protocol, with the exception of some essential and feedstock uses. In the EU, use was phased out by end 1994 except for small authorised quantities (EU Regulation 3093/94). Feedstock, process agent and "essential" uses of carbon tetrachloride are still allowed. EU production of this compound was 59,691 tonnes in 1996 [European Chlorinated Solvent Association (ECSA), 1998]. Its main use is as a feedstock for production of CFC 11 and 12, which are in turn used as intermediates for other chemicals.

Process agent uses of carbon tetrachloride include extraction of nitrogen trichloride from liquid chlorine, recovery of chlorine from tail gas, chlorinated rubber manufacture and pharmaceutical processing. These account for less than 20 tonnes. In most of these applications, carbon tetrachloride is completely converted or destroyed, for example in incineration units complying with the UNEP requirements and recovering hydrochloric acid.

Emissions to air were estimated as 243 tonnes/year in 1995 from some 67 European sites using or manufacturing carbon tetrachloride as a feedstock or process agent, or producing it inadvertently. In water, emissions amounted to about 7 tonnes/year for the same period. These figures are very likely to have been reduced since production of CFC 11 and 12 has been largely reduced.

Evaluation of environmental risk

Toxicity

For carbon tetrachloride (CTC) 15 sets of data for fish, 7 sets of data for invertebrates and 5 sets of data for algae were evaluated according to the quality criteria recommended by the European authorities. Both acute and chronic toxicity studies were taken into account and the appropriate assessment factors were used to define a final PNEC value of 7 µg/l.

Monitoring data

Most monitoring data for carbon tetrachloride apply to rivers and estuary waters. Measurements were taken in the Elbe, Weser and Rhine estuaries (Germany); the Schelde and Meuse (Belgium/Netherlands border); UK river estuaries; the Seine estuary (France); and a range of coastal waters (Ostsee-Baltic See (Sweden), Skagerrak (Denmark), Nordsee (Germany), English Channel and the Dutch coast).

The most recent data (1990-95) support a typical PEC lower than 0.003 to 0.02 µg/l and a worst case PEC of 0.10 to 0.31 µg/l. Data on persistence indicate a half-life in water of days or a maximum of one month, and bioaccumulation in marine organisms is very limited.

Risk assessment conclusion

When the environmental concentration of carbon tetrachloride is compared with the probable no-effect level to give the PEC/PNEC ratio, there is a safety factor of 25-2500 between actual exposure and the predicted no effect concentration. This calculation takes no account of any further dilution within the sea, which would increase these safety margins. EU production and use of carbon tetrachloride have been very restricted since 1994, due to its persistence in the atmosphere and significant ozone depletion potential. This will contribute to further decreases in environmental concentration in future. This risk assessment shows that current, restricted use of carbon tetrachloride should not represent a risk to the aquatic environment.

North Sea monitoring data on carbon tetrachloride