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Dichloromethane

Report

To read the report please click here.

This marine risk assessment was also published in a peer-reviewed journal: De Rooij, C. et al., 2004. Dichloromethane Marine Risk Assessment with Special Reference to the OSPARCOM region: North Sea. Environmental Monitoring and Assessment, Vol. 97, (1-3), 3-22.

Summary

Current usage of dichloromethane does not represent a risk to the marine environment. This conclusion is based on 46 laboratory toxicity studies, plus 1983-1995 monitoring results from the North Sea, rivers and estuaries.

Applications of dichloromethane

Dichloromethane is mainly produced together with other chloromethanes such as methyl chloride and chloroform. The raw materials are methanol and chlorine or, less frequently, methane and chlorine.

In the methanol hydrochlorination process, hydrogen chloride reacts with methanol to form methyl chloride. This is used to make heavier chloromethanes through thermal, catalytic or photolytic chlorination. Direct chlorination of methane is also used. The methanol hydrochlorination process (which generates no net hydrogen chloride) is usually preferred, except when HCl can be used locally, for example in vinyl chloride production.

European sales of dichloromethane totalled about 138,000 tonnes in 1996, down from 200,000 tonnes in 1984. This decrease is due to more efficient use, increased recycling and replacement in some applications. Dichloromethane is produced at eight plants in Germany, France, Italy, Spain, the Netherlands and the UK. European exports are estimated at 100,000 tonnes per year (ECSA, 1997).

The main uses of dichloromethane are:

• Pharmaceutical industry (30%), where it is used as solvent for chemical reactions, purification and isolation of intermediates or products. Its advantages are:
  • low miscibility with water (2% weight)
  • non flammable, high auto-ignition temperature (556°C)
  • easy to remove from products
  • low freezing point (-97°C)
• Paint stripping (19%): Dichloromethane-based paint strippers usually contain 70-90% dichloromethane plus other organic solvents (such as ethanol), surfactants, emulsifiers and alkaline and/or acid activators. These have several key advantages over other coating removal methods, such as non-flammability, reasonable price, universal suitability for all types of coatings, and fast action at room temperature.
• Aerosols (9%): This application began in the mid-1970s, as a CFC replacement. Dichloromethane is not itself a propellant, but contributes to package homogeneity and reduced flammability.
• Adhesives (10%): Dichloromethane is used as a solvent to replace for 1,1,1-trichloroethane.
• Other applications (32%): These include uses in metal degreasing, foam blowing, chemical processing (polyurethanes, polycarbonates), and as a secondary refrigerant medium.

Emissions of dichloromethane during manufacturing, processing and use are mainly to the atmosphere and to a lesser extent to water. Total emissions to water from about 77 sites using or manufacturing dichloromethane in 1995 was estimated at 45 tonnes/year.

Evaluation of environmental risk

Toxicity

For dichloromethane, 23 data for fish, 17 data for invertebrates and 6 data for algae were evaluated using the quality criteria recommended by EU authorities. Both acute and chronic toxicity studies were taken into account and appropriate assessment factors were used to define a final PNEC value of 830 µg/l.

Monitoring data

Most of the available monitoring data apply to rivers and estuaries. The most recent data (1983-1995) support a typical PEC for dichloromethane lower than 0.1 µg/l and a worst case PEC of
13.6 µg /l. Data came from the Solent and Tees estuaries (UK); North Sea (Germany); the Seine, Meuse and Rhine rivers and other adjacent rivers passing through industrial areas.

Available data on persistence of dichloromethane indicate a half-life in water of a few hours or days and negligible bioaccumulation in marine organisms. Current use of dichloromethane does not therefore represent a risk to the aquatic environment.

Risk assessment conclusion

The calculated PEC/PNEC ratios give a safety margin of 60 to 4000 between the predicted no effect concentration and the exposure concentration. Dilution within the sea would increase these safety margins.

North Sea monitoring data on dichloromethane