Dichloroethenes: 1,1-dichloroethene (1,1-DCE), 1,2-dichloroethene (1,2-DCE)

(endorsed 1996)

Guideline

Based on health considerations, the concentrations of dichloroethenes in drinking water should not exceed the following values:

1,1-dichloroethene 0.03 mg/L

1,2-dichloroethene 0.06 mg/L

General description

Available data indicate that the dichloroethenes are rarely found in drinking water. Studies in the United States have very occasionally reported DCEs in groundwater, usually from wells heavily contaminated with other chlorinated solvents.

1,1-DCE is used as a chemical intermediate in the manufacture of chloroform and polyvinylidene (PVDE) polymers. 1,2-DCE is also used as an intermediate in the manufacture of chlorinated solvents, and as a solvent. It can occur as two isomers, the cis and trans forms.

Typical values in Australian drinking water

DCEs have not been found in Australian drinking waters. They are included here to provide guidance in the unlikely event of contamination, and because they have been detected occasionally in drinking water supplies overseas.

Treatment of drinking water

The DCEs can be removed from drinking water by 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 the dichloroethenes trapped on an adsorbent. The adsorbent is then heated and the dichloroethenes analysed using gas chromatography with electron capture detection. The limit of determination is approximately 0.0002 mg/L.

Health considerations

The DCEs can be readily absorbed through the lungs and the gastrointestinal tract. They are distributed primarily to the liver and kidneys, and are metabolised to chloroacetic acid, chloroacetyl chloride, dichloroacetaldehyde and reactive epoxides.

In humans, exposure to high concentrations in air can lead to central nervous system depression. The DCEs have been used as anaesthetics.

A long-term study where rats were exposed to 1,1-DCE in their drinking water for 2 years reported minimal swelling to liver cells but no other adverse effects. No changes were observed in tissues taken from dogs after 97 days of exposure. 1,1-DCE induced tumours in mice in one inhalation study, but was not carcinogenic in other studies, including one drinking water study. It has exhibited some mutagenic activity in tests with bacteria but not with cultured mammalian cells.

The International Agency for Research on Cancer has concluded that 1,1-DCE is not classifiable as to its carcinogenicity (Group 3, evidence inadequate in humans and limited in animals) (IARC 1987).

No long-term data are available for 1,2-DCE; however, a 90-day immunotoxicity study with mice using the trans isomer reported increases in glutathione levels and aniline hydroxylase activity. No data are available on carcinogenicity bioassays with animals. The cis isomer, but not the trans isomer, has exhibited some mutagenic activity in vivo in tests with bacteria. Neither isomer induced chromosomal aberrations in hamster lung cells in vitro.

Derivation of guideline

The assessment of the toxicological data of these compounds by the World Health Organization (WHO) has been used without review. The guideline values were determined as follows:

i) 1,1-dichloroethene

$$\text{ 0.03 mg/L } = \dfrac{\text{ 9 mg/kg body weight per day x 70 kg x 0.1 }}{\text{ 2 L/day x 1000 }}$$

where:

• 9 mg/kg body weight per day is the lowest effect level based on a 2-year drinking water study using rats (Quast et al. 1983).

• 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.

• 1000 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 and 10 because a lowest effect level was used instead of a no-effect level).

ii) 1,2-dichloroethene

$$\text{ 0.06 mg/L } = \dfrac{\text{ 17 mg/kg body weight per day x 70 kg x 0.1 }}{\text{ 2 L/day x 1000 }}$$

where:

• 17 mg/kg body weight per day is the no-effect level based on a 90-day drinking water study using mice (Barnes et al. 1985).

• 1000 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 and 10 for the less than lifetime study).

• other factors apply as above.

The WHO guideline value of 0.05 mg/L was based on an adult body weight of 60 kg. The difference in guideline values is not significant.

References

Barnes DW, Sanders VM, White KL, Shopp GM, Munson AE (1985). Toxicology of trans-1,2-dichloroethylene in the mouse. Drug and Chemical Toxicology, 8:373–392.

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.

Quast JF, Humiston CG, Wade CE, Ballard J, Beyer JE, Schwetz RW, Norris JM (1983). A chronic toxicity and oncogenicity study in rats and subchronic toxicity study in dogs on ingested vinylidene chloride. Fundamental and Applied Toxicology, 3:55–62.

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.