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1,2,4-Trichlorobenzene

Report

To read the report please click here.

This marine risk assessment was also published in a peer-reviewed journal: Van Wijk, D. et al., 2006. 1,2,4-Trichlorobenzene marine risk assessment with special emphasis on the Osparcom region North Sea. Chemosphere 62, 1294-1310.

Summary

Current levels of 1,2,4-trichlorobenzene in the surface waters and sediments are unlikely to pose a risk to marine aquatic and sediment organisms living in the North Sea. This conclusion is based on 66 laboratory toxicity studies and monitoring data from the North Sea, rivers and estuaries.

Applications and emissions of 1,2,4-trichlorobenzene

Trichlorobenzenes are produced by direct chlorination of benzene. Today, commercial production of 1,2,4-trichlorobenzene is 99.8% pure. Historically, trichlorobenzenes were produced as a mixture of 1,2,4-trichlorobenzene and 1,2,3-trichlorobenzene.

1,2,4-Trichlorobenzene is only used as a chemical intermediate, specifically for the production of herbicides, pigments and dyes. Both 1,2,3- and 1,2,4-trichlorobenzene are used as process solvents, such as dye carriers. Europe has ceased using trichlorobenzenes in dielectric fluids - a main application in the past.

About 6,000 tonnes/year of trichlorobenzenes are produced in Europe in 1995, mainly in Belgium and Germany, and to a lesser extent in Spain and Italy. In Europe in 1995, 1,800 t of trichlorobenzene was used to produce pesticides; imports were around 2,000 t, and net exports 6,200 t. Estimated world trichlorobenzene production was 14,300 t in 1995.

Trichlorobenzene may enter the environment during manufacturing, processing and use of the chemical. A 1997 survey of 78 European sites producing or using trichlorobenzene showed emissions from water at 0.552 t/y and air at 0.351 t/y. Emissions in water were reduced by 97% between 1985 and 1997. Trichlorobenzene is also formed during various combustion processes and in the production of the wood preservative lindane.

Evaluation of environmental risk

Risks associated with the use of any substance are determined by the hazard properties of the substance and exposure to it. This risk assessment focuses on the aquatic marine environment, with special attention to North Sea conditions.

Hazard assessment

For 1,2,4-trichlorobenzene, a total of 27 data for fish, 29 data for invertebrates and ten data for algae are available. Some 14 each for fish and invertebrates, and one for algae were considered valid for risk assessment purposes. A further two for fish, three for invertebrates and one for algae were considered with care.

Based on acute and chronic toxicity studies a PNEC value of 3 µg/l has been calculated for the aquatic environment. A PNEC of 0.12-0.19 mg/kg d.w. is estimated for sediments.

Exposure assessment

1,2,4-Trichlorobenzene exposure assessments are based on data from analytical monitoring programmes. Specific isomers are not always mentioned, so data is given covering all trichlorobenzenes. A summary of the available monitoring data of trichlorobenzene levels in the marine environment and estuaries is presented (see map below).

The data indicates that in coastal waters and estuaries concentrations of trichlorobenzenes range from less than 0.0004 µg/l to 0.4 µg/l. Data from 1994-1996 suggests that typical marine and estuarine concentrations are below 0.1 µg/l and regional worst-case figures could be up to 0.1 µg/l.

Background levels of trichlorobenzenes in large German, Dutch, French and UK rivers are lower than 0.4 µg/l. Based on monitoring data, predicted environmental concentrations of trichlorobenzenes in marine environments are below detection levels of 0.1 µg/l. A mean value of 0.047 µg/l for river water is used as a typical PECmarine value.

The amount of trichlorobenzene adsorbed by sediment is considered. Concentrations have been measured in the freshwater sediment of rivers in Germany, Denmark, France and the Netherlands between 1994-1997. The values vary from <0.5 to 400 g/kg, with a mean value of 40 g/kg d.w. and a worst case of 90 g/kg d.w.

Risk assessment calculations

Using the values derived above, PEC/PNEC ratios for the marine environment are calculated at 0.016 for typical and 0.03 for worst case instances - or a safety margin of 33 to 63 between PNEC and PEC. Dilution within the sea will increase those safety margins.

The corresponding PEC/PNEC ratios for sediments give safety margins of 1.3-2.1 to 3-4.8 for the worst-case and typical PEC's, respectively. Based on these margins, risks for marine sediment organisms are unlikely from 1,2,4-trichlorobenzene.

North Sea Monitoring Data on 1,2,4-trichlorobenzene