Dense Nonaqueous Phase Liquids (DNAPLs)

Halogenated Alkanes

1,1,2,2- Tetrachloroethane

Human Health Toxicity

1,1,2,2-Tetrachloroethane (1,1,2,2-TetCE), a synthetic chemical, is probably no longer manufactured in the United States. It formerly was used as an industrial solvent and extractant and as a pesticide component, but is now employed as a feedstock in the production of other chlorinated organic compounds. Current releases of 1,1,2,2-TetCE to the environment likely occur from fugitive emissions during chemical processing.

It is unlikely that the general population is extensively exposed to 1,1,2,2-TetCE, and in general it can be surmised that exposure is likely limited to individuals working at or residing in areas where chemical processing plants or hazardous waste sites are located. In these instances, exposure might occur via inhalation of contaminated ambient air, ingestion of contaminated drinking water, or direct dermal contact with contaminated soil. Any workplace exposure to 1,1,2,2-TetCE likely would be via inhalation and dermal contact.

1,1,2,2-TetCE is well absorbed from the lungs and gastrointestinal tract of humans and laboratory animals. Studies indicate that it is absorbed through the skin of laboratory animals. Once absorbed, 1,1,2,2-TetCE is metabolized by both oxidative and reductive pathways, and its metabolites are excreted in exhaled air and urine. It is possible that reactive radicals and metabolites formed by the metabolic transformation of 1,1,2,2-TetCE are responsible for the compound's toxicity, but its mode of action is not fully characterized.

1,1,2,2-TetCE is acutely poisonous to humans in high doses, as evidenced by case reports of suicides and accidental poisonings. The target organs for acute toxicity in humans are the central nervous system (CNS), liver, and mucous membranes. Laboratory animal studies support the observation that the CNS and liver are target organs for 1,1,2,2-TetCE toxicity. Occupational inhalation exposure to the compound has been reported to be associated with an enlarged liver and the onset of jaundice (ATSDR 2008).

The summary in EPA's Integrated Risk Information System (IRIS) classifies 1,1,2,2-TetCE as "C; possible human carcinogen" on the basis of studies reporting an increased incidence of liver cancer in laboratory mice.

No studies were found that describe the reproductive and developmental toxicity of 1,1,2,2-TetCE in humans, and these aspects of the compound's toxicity have not been fully evaluated in animals (ATSDR 2008).

1,1,2,2-TetCE is weakly genotoxic, with most in vitro assays reporting negative results, with the exceptions of sister chromatid exchange and cell transformation studies (ATSDR 2008).

As of 2010, EPA has not developed a maximum contaminant level (MCL) for 1,1,2,2-TetCE in drinking water.

The Regional Screening Levels (formerly Preliminary Remediation Goals) posted by EPA Region 9 identify risk-based concentrations for chloroform for the following common exposure pathways:

Residential soil	5.6 E-01 mg/kg
Industrial soil	2.8 E-00 mg/kg
Residential air	4.2 E-02 ug/m3
Industrial air	2.1 E-01 ug/m3
Tapwater	6.7 E-02 ug/L

References

1,1,2,2-Tetrachloroethane (CASRN 79-34-5)
U.S. EPA, Integrated Risk Information System (IRIS)

Toxicological Profile for 1,1,2,2-Tetrachloroethane
Agency for Toxic Substances and Disease Registry (ATSDR),258 pp, 2008

Ecological Toxicity

No studies were found that describe the toxicity of 1,1,2,2-TetCE to terrestrial ecological receptors. The existing investigations of ecological toxicity generally are limited to aquatic species and usually are acute toxicity studies, such as LC₅₀s. These studies have been performed using aquatic invertebrates, such as daphnia and various species of fish. Hughes and Meek (1998) reported the results from these tests.

References

1,1,2,2-Tetrachloroethane
Hughes, K. and M.E. Meek.
World Health Organization, Geneva. Concise International Chemical Assessment Document No. 3, 1998