Water Quality Standards

Summary information extracted from: Guidelines for drinking-water quality, 2nd ed. - Vol. 1. Recommendations. - Geneva, World Health Organization, 1993. pp. 61-62.

1,2-Dichlorethene exists in a cis and a trans form. The cis form is more frequently found as a water contaminant. The presence of these two isomers, which are metabolites of other unsaturated halogenated hydrocarbons in wastewater and anaerobic ground water, may indicate the simultaneous presence of more toxic organochlorine chemicals, such as vinyl chloride. Accordingly, their presence indicates that more intensive monitoring should be conducted. There are no data on exposure from food. Concentrations in air are low, with higher concentrations, in the microgram per cubic metre range, near production sites. The cis-isomer was previously used as an anaesthetic.

There is little information on the absorption, distribution, and excretion of 1,2-dichloroethene. However, by analogy with 1,1-dichloroethene, it would be expected to be readily absorbed, distributed mainly to the liver, kidneys, and lungs, and rapidly excreted. The cis-isomer is more rapidly metabolized than the trans-isomer in in vitro systems.

Both isomers have been reported to cause increased serum alkaline phosphatase levels in rodents. In a 3-month study in mice given the trans-isomer in drinking-water, there was a reported increase in serum alkaline phosphatase and reduced thymus and lung weights. Transient immunological effects were also reported, the toxicological significance of which is unclear. Trans-1,2-dichloroethene also caused reduced kidney weights in rats, but at higher doses. Only one rat toxicity study is available for the cis-isomer, which produced toxic effects in rats similar in magnitude to those induced by the trans-isomer in mice, but at higher doses.

There are limited data to suggest that both isomers may possess some genotoxic activity. There is no information on carcinogenicity.

Data on the trans-isomer were used to calculate a joint guideline value for both isomers because toxicity for the trans-isomer occurred at a lower dose than for the cis-isomer and because data suggest that the mouse is a more sensitive species than the rat. Accordingly, the NOAEL of 17 mg/kg of body weight per day from the trans-isomer toxicity study in mice was used to calculate a guideline value. An uncertainty factor of 1000 (100 for intra- and interspecies variation and 10 for the short duration of the study) was applied to derive a TDI of 17 µg/kg of body weight, giving a guideline value of 50 µg/litre (rounded figure) for an allocation of 10% of the TDI to drinking-water.