Dichloroethanes: 1,1-dichloroethane, 1,2-dichloroethane

(endorsed 1996)

Guideline

1,1-dichloroethane: data are inadequate to set a drinking water guideline value.

1,2-dichloroethane: based on health considerations, the concentration in drinking water should not exceed 0.003 mg/L.

General description

Dichloroethanes are present in some industrial effluent and have occasionally been found in drinking water supplies in the United States at concentrations below 0.006 mg/L.

The major use for 1,2-dichloroethane is in the production of vinyl chloride. It is also used in the production of other solvents, and can be used as a lead scavenger in petrol. 1,1-dichloroethane is used in the commercial production of 1,1,1-trichloroethane, as a solvent in paints, and as a varnish and finish remover.

Typical values in Australian drinking water

Dichloroethanes 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 dichloroethanes can be removed from drinking water using packed tower aeration, or by adsorption onto granular activated carbon.

Measurement

The dichloroethanes can be analysed by the purge and trap method (USEPA Method 502.1 1986). In this method an inert gas is bubbled through the sample and the dichloroethanes trapped on an adsorbent. The adsorbent is then heated and the dichloroethanes analysed using gas chromatography with electron capture detection. The limit of determination is approximately 0.0002 mg/L.

Health considerations

1,2-dichloroethane is absorbed through the lungs and gastrointestinal tract. Highest concentrations occur in the kidney and liver where it is metabolised to 2-chloroethanol. There are few data for 1,1-dichloroethane but it could be absorbed faster as it is more lipophilic (fat soluble).

An extensive review and summary of the human and animal toxicity data for 1,2-dichloroethane is available (IPCS 1987).

A number of cases of poisoning following consumption of high doses of 1,2-dichloroethane have been reported. While not all cases have been fatal, death is attributed to circulatory and respiratory failure.

1,1-dichloroethane has been used as an anaesthetic. Its use was discontinued because of problems associated with heart rhythm.

A 13-week inhalation study with 1,1-dichloroethane reported elevated blood-urea nitrogen concentrations in cats but not in rats, rabbits or guinea pigs. No other adverse effects were observed. A 78-week feeding study reported a marginally significant increase in the incidence of tumours of the mammary glands of female rats. No statistically significant increase in tumours was observed in male rats, or male and female mice. 1,1-dichloroethane has exhibited mutagenic activity in tests with bacteria and mammalian cells.

A 13-week feeding and drinking water study with 1,2-dichloroethane using rats and mice reported increased kidney and liver weights at high doses (4000 mg/L). No increase in the incidence of tumours or lesions was observed in mice or male rats, but female rats exhibited an increase in the incidence of kidney lesions.

A significant increase in tumours of the fore-stomach and circulatory system was reported in male rats fed 1,2-dichloroethane five times per week for 78 weeks. The same study reported tumours of the mammary glands in female rats. 1,2-dichloroethane has exhibited mutagenic activity in tests with different strains of bacteria, and metabolites are known to be strongly mutagenic.

The International Agency for Research on Cancer has concluded that 1,2-dichloroethane is possibly carcinogenic to humans (Group 2B, no data in humans but sufficient evidence in animals) (IARC 1987).

Derivation of guideline

The assessment of the toxicological data of these compounds by the World Health Organization (WHO) has been used without review; however, the guideline value has been adjusted to a risk level of one in one million.

i) 1,1-dichloroethane

There are insufficient long-term data to set a health-based guideline value for 1,1-dichloroethane in drinking water.

ii) 1,2-dichloroethane

The guideline value for 1,2-dichloroethane in drinking water has been set at 0.003 mg/L. The WHO has conservatively calculated, using an extrapolation model based on a 78 week study in rats (NCI 1978), that consumption of water containing 0.003 mg/L of 1,2-dichloroethane would pose a lifetime risk of one additional cancer per million people.

The guideline value should be reviewed when more data are available.

The WHO guideline value of 0.03 mg/L was based on a calculation that estimated an additional lifetime risk of one fatal cancer per 100,000 people.

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) (1987). 1,2-Dichloroethane. Environmental Health Criteria, 62. World Health Organization, IPCS.

NCI (National Cancer Institute) (1978). Bioassay of 1,2-dichloroethane for possible carcinogenicity. NCI, Department Health Education and Welfare, Washington DC, Report NCI-CG-TR-55.

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.