Dense Nonaqueous Phase Liquids (DNAPLs)

Halogenated Alkanes

1,1-Dichloroethane

Human Health Toxicity

1,1-Dichloroethane (1,1-DCA) is a synthetic organic chemical that has industrial use as a degreaser and solvent and as a feedstock for the production of other organochlorine compounds, particularly vinyl chloride. In addition to its industrial use, 1,1-DCA was formerly used as an inhalation anesthetic (ATSDR 1990).

The general population might be exposed to 1,1-DCA via inhalation of air contaminated by fugitive emissions from chemical plants that manufacture or process the chemical, or by the ingestion of contaminated drinking water. 1,1-DCA is not thought to be present in food. Any occupational exposure likely would occur via inhalation and/or dermal contact (Butler 2003).

Considering 1,1-DCA's former use as an inhalation anesthetic, it can be assumed that it is readily absorbed by the lungs. Animal studies suggest that it is also well absorbed from the gastrointestinal tract. Little information is available regarding the dermal absorption of this compound, but one study suggests that it might be absorbed through the skin of rabbits. An animal study suggests that once absorbed, 1,1-DCA is rapidly distributed to the liver, lung, stomach, and kidney. It can be assumed that 1,1-DCA is readily distributed to the human central nervous system (CNS) as it exerts general anesthesia by CNS depression. Studies of laboratory animals indicate that most absorbed 1,1-DCA is excreted unchanged in exhaled air, but some metabolism of the compound takes place, and acetic acid is the predominant end product of the process (Butler 2003).

Fewer toxicological studies are found for 1,1-DCA than for other chlorinated solvents; however, one study reports that 1,1-DCA can cause weight loss and kidney damage in cats (ATSDR 1990). No studies were found that describe the long-term effects of 1,1-DCA on humans. EPA's Integrated Risk Information System (IRIS) has classified 1,1-DCA as "C; possible human carcinogen." This classification was based on the limited evidence of carcinogenicity in two animal species rather than on human data.

The reproductive and developmental effects of 1,1-DCA in humans are unknown. One laboratory rodent study reported delayed ossification of bones comprising the sternum in the offspring of pregnant rats exposed to 1,1-DCA via inhalation. In this instance, the dose of 1,1-DCA was not deemed to be maternally toxic (ATSDR 1990).

1,1-DCA gives both positive and negative results for both in vitro and in vivo genotoxicity assays, and cannot be categorized as genotoxic or epigenetic (Butler 2003).

As of 2010, EPA has no maximum contaminant level (MCL) listed for 1,1-DCA in drinking water.

The Regional Screening Levels (formerly Preliminary Remediation Goals) posted by EPA Region 9 identify risk-based concentrations for 1,1-DCA for the following common exposure pathways:

Residential soil	3.3 E-00 mg/kg
Industrial soil	1.7 E+01 mg/kg
Residential air	1.5 E-00 ug/m3
Industrial air	7.7 E-00 ug/m3
Tapwater	2.4 E-00 ug/L

References

1,1-Dichloroethane (CASRN 75-34-3)
U.S. EPA, Integrated Risk Information System (IRIS).

Public Health Goal for 1,1,-Dichloroethane In Drinking Water
Butler, N.
California EPA, Office of Environmental Health Hazard Assessment, 32 pp, 2003

Regional Screening Levels
U.S. EPA Region 9, 2009

Toxicological Profile for 1,1-Dichloroethane
Agency for Toxic Substances and Disease Registry (ATSDR), 116 pp, 1990

For Further Information

1,1-Dichloroethane in Drinking-Water (Background document for development of WHO Guidelines for Drinking-water Quality)
World Health Organization (WHO), WHO/SDE/WSH/03.04/19, 10 pp, 2003

Ecological Toxicity

No readily available studies describe the toxicity of 1,1-DCA to aquatic receptors, but toxicity reference values (TRVs) for the compound in surface water have been calculated and are presented in Aquatic Toxicity Reference Values (TRVs) (DOE 1999).

Very little information is available regarding the toxicity of 1,1-DCA to terrestrial wildlife receptors; however, an ecological screening level (ESL) calculated to be protective of burrowing terrestrial animals is provided in Roy et al. (2009).

References

Aquatic Toxicity Reference Values
U.S. Department of Energy (DOE).
Manual ERD-AG-003 Revision 0, 1999

A 10-page Department of Energy document with toxicity reference value tables for surface water organisms.

Evaluating Vapor Intrusion in Ecological Risk Assessment
Roy, M., S. Smith, and B. Eklund.
2009 DoD Environmental Monitoring & Data Quality Workshop, March 30 - April 3, San Antonio, Texas. 31 slides, 2009