Dichloromethane (methylene chloride)

(endorsed 1996)

Guideline

Based on health considerations, the concentration of dichloromethane in drinking water should not exceed 0.004 mg/L.

General description

Dichloromethane releases into the environment are substantial and widely dispersed. In overseas studies it has been found in the parts-per-trillion range in air and is a common contaminant of ground and surface waters, with higher concentrations found in groundwater. In surface waters it can volatilise into air and will degrade in the atmosphere.

Dichloromethane is a widely used organic solvent. It can be found in paints, insecticides, degreasing agents, cleaning fluids and paint strippers.

Typical values in Australian drinking water

Dichloromethane has not been found in Australian drinking waters. It is included here to provide guidance in the unlikely event of contamination, and because it has been detected occasionally in drinking water supplies overseas.

Treatment of drinking water

Dichloromethane concentrations in drinking water can be reduced using aeration, or by adsorption onto granular activated carbon.

Measurement

A purge and trap gas chromatographic procedure can be used for analysis (USEPA Draft Method 502.1 1986). An inert gas is bubbled through the sample and dichloromethane trapped on an adsorbent. The adsorbent is then heated and dichloromethane analysed using gas chromatography with electron capture detection. The limit of determination is approximately 0.0003 mg/L.

Health considerations

Studies indicate that dichloromethane is completely absorbed after ingestion and distributed primarily to the liver. It is metabolised to carbon monoxide, carbon dioxide and formic acid.

An extensive review and summary of the human and animal toxicity data for dichloromethane is available (IPCS 1984).

Inhalation of high doses has induced narcosis in humans, and acute exposure has caused impairment of sensory and motor functions.

In animals, a 2-year drinking water study on rats reported some changes to the liver at doses from 52 mg/kg body weight per day. Studies have shown mice to be less sensitive than rats to the toxic effects of dichloromethane.

Epidemiological investigations have failed to demonstrate a correlation between dichloromethane exposure and increased cancer incidence.

Overall, carcinogenicity of dichloromethane given in water to rodents is borderline and not conclusive. By inhalation there is clear evidence of carcinogenicity in rodents (IARC 1987).

The International Agency for Research on Cancer has concluded that dichloromethane is possibly carcinogenic to humans (Group 2B, inadequate evidence in humans but sufficient evidence in animals) (IARC 1987).

Derivation of guideline

The guideline value for dichloromethane in drinking water of 0.004 mg/L was determined as follows:

$$\text{ 0.004 mg/L } = \dfrac{\text{ 6 mg/kg body weight per day x 70 kg x 0.1 }}{\text{ 2 L/day x 5000 }}$$

where:

• 6 mg/kg body weight per day is the lowest effect level based on a 2-year drinking water study using rats (Serota et al. 1986).

• 70 kg is the average weight of an adult.

• 0.1 is the proportion of total daily intake attributable to the consumption of water.

• 2 L/day is the average amount of water consumed by an adult.

• 5000 is the safety factor in using the results of an animal study as a basis for human exposure (10 for interspecies variations, 10 for intraspecies variations, 10 for genotoxicity and 5 for lowest effect level).

The World Health Organization guideline of 0.02 mg/L did not include a safety factor for the use of a lowest effect level. The need to use this additional factor arose after a statistical evaluation of the data in the referenced study indicating that the end point was a lowest effect level, not a no-effect level.

References

IARC (International Agency for Research on Cancer) (1987). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans: Overall Evaluations of Carcinogenicity. An updating of IARC monographs volumes 1 to 42. World Health Organization, IARC, Supplement 7.

IPCS (International Programme on Chemical Safety) (1984). Methylene chloride. Environmental Health Criteria, 32. World Health Organization, IPCS.

Serota DG, Thakur AK, Ulland BM, Kirschman JC, Brown NM, Coots RH, Morgareidge K (1986). A two-year drinking water study of dichloromethane in rodents: I. Rats. Food and Chemical Toxicology, 24:951–958.

USEPA Draft Method 502.1 (1986). Volatile halogenated organic compounds in water by purge and trap gas chromatography. United States Environmental Protection Agency, Environmental Monitoring and Support Laboratory (ESML), Cincinnati, Ohio.