Dense Nonaqueous Phase Liquids (DNAPLs)

Halogenated Alkenes

1,1-Dichloroethene

Human Health Toxicity

1,1-Dichloroethene (1,1-DCE) is not a naturally occurring compound. It is manufactured from 1,1,2-trichloroethane by dechlorination or by the thermal decomposition of 1,1,1-trichloroethane. 1,1-DCE is used as an intermediate in the production of solvents and agricultural chemicals. Polymerized forms of 1,1-DCE are in general use as food packaging products, such as Saran wrap. Other polymers derived from 1,1-DCE are used as flame retardants on fabrics, and are also components of carpet backing. Piping and coatings for steel pipes are made from the polymerized compound.

1,1-DCE is widely distributed in the environment. It is released to the air during its manufacture and use, and to soil, surface water, and ground water during waste disposal. Waste disposal practices have resulted in the presence of 1,1-DCE in soil and ground water at hazardous waste sites. Residual amounts of the compound are found in textiles treated with flame retardants containing 1,1-DCE and in food packaging products and the food packed in them.

The general public may be exposed to 1,1-DCE in drinking water, food packed in plastic film, and ambient air. Occupational exposure to 1,1-DCE is generally through ambient air.

1,1-DCE is rapidly absorbed by the stomach and intestines and is rapidly distributed to all tissues. The metabolism of 1,1-DCE has been thoroughly described (WHO). Much of the inhaled compound is exhaled in an unchanged form. However, residual amounts of the compound and its metabolites are found in the kidney and liver. Based on the physical chemistry of the compound, there is little expectation that 1,1-DCE bioaccumulates. In laboratory animals, the target organs affected by high-dose exposure to 1,1-DCE are the liver, the Clara cells of the lungs, and the kidney. These organs are affected whether the compound is administered by inhalation or ingestion. Severe damage and disruption to the structures of these organs has been observed.

Long-term, low-dose animal studies show species differences in the organs affected by 1,1-DCE. The liver is the major target organ of long-term toxicity in the rat following oral or inhalation exposure, but after long-term inhalation of the compound, the kidney is the target organ in mice. Based on both inhalation and oral exposure studies in rats, the critical effect of 1,1-DCE is on the liver and can be summarized as "minimal hepatocellular mid-zonal fatty changes." Based on the critical effects studies from oral and inhalation exposures to 1,1-DCE in the rat, a tolerable intake of 0.05 mg/kg body weight per day has been calculated, and a tolerable concentration of 0.2 mg/m³ (WHO).

Animal studies indicate that teratogenicity or reproductive toxicity are not critical effects for 1,1-DCE. At oral exposures that caused minimal hepatotoxicity in female rats, no reproductive or developmental toxicity was observed. One study indicated developmental variations in the heart after oral exposure of the dams, but it is unclear whether this effect was caused by 1,1-DCE. However, there is evidence of delayed ossification, an indicator of fetal toxicity, in the absence of maternal toxicity following inhalation exposure.

Only one epidemiological study addresses occupational exposure to 1,1-DCE, but this study is too limited to evaluate the health effects of the compound. Oral exposure studies of rats, mice, and trout have not provided significant evidence that 1,1-DCE is a carcinogen, although it is acknowledged that the studies have protocol limitations. The Integrated Risk Information System (IRIS) record for 1,1-DCE (IRIS 2002) states, "The data are inadequate for an assessment of human carcinogenic potential by the oral route" Inhalation studies performed on rats, mice, and hamsters also have protocol limitations. One mouse study reported an increase in the incidence of kidney tumors in male mice. However, the effect observed at a single exposure concentration was not part of a dose-related trend. EPA has concluded that "1,1-DCE exhibits suggestive evidence of carcinogenicity but not sufficient evidence to assess human carcinogenic potential following inhalation studies in rodents." Although 1,1-DCE can cause gene mutation in bacteria if metabolic activation is present, most studies indicate a lack of genotoxicity in mammalian cells.

Ecological Toxicity

Information is limited on the effects of 1,1-DCE on the aquatic environment. Data from existing plant and fish studies indicate that toxic effects are seen for this compound in the milligram per liter range. This suggests that 1,1-DCE has a minimal acute toxic effect on the aquatic environment. Limited data indicate that concentrations of this compound in surface water are in the microgram per liter range. The 96-hour LC₅₀ value (the concentration that kills 50 percent of treated animals) for bluegill is 74 mg/Liter. Rainbow trout dosed at 4 mg/kg body weight per day did not develop tumors or other effects related to chronic toxicity in an 18-month carcinogenicity study. The most sensitive end-point to the effect of 1,1-DCE was the inhibition of the growth of algae (72 hour EC₅₀ of 9.12 mg/liter).

The data are inadequate to evaluate the effects of 1,1-DCE on the terrestrial environment and insufficient to characterize risk to the marine environment.

Human Health References

Concise International Chemical Assessment Document (#51) for 1,1-Dichloroethene
International Programme on Chemical Safety (IPCS), 2003

This document is a comprehensive review of the physical/chemistry properties, fate and transport, human and ecological health effects, and occurrence of 1,1-DCE.

1,1-Dichloroethylene (CASRN 75-35-4)
Integrated Risk Information System (IRIS)
U.S. EPA, 2002

An EPA developed and maintained database that contains toxicological data and discussions of effects for a variety of chemicals of regulatory interest.

Public Health Goal for 1,1-Dichloroethylene in Drinking Water
Office of Environmental Health Hazard Assessment
California Environmental Protection Agency (CalEPA), 1999

A 31 page discussion of the health effects of 1,1-DCE for the purpose of providing the scientific basis for setting a maximum contaminant level in drinking water for California.

cis-1,1-Dichloroethylene*
U.S. EPA, Substance Registry Services.
*Check for updates using 75-35-4 as the search term.

A database maintained by EPA that provides synonyms and some physical chemical data but is mostly devoted to providing links to regulatory resources and toxicological databases.

Toxicological Profile for 1,1-Dichloroethene
Agency for Toxic Substances and Disease Registry (ATSDR)
Department of Health and Human Services, Atlanta, GA, 1994

This profile provides information on human health effects, fate and transport, production, and uses of 1,1-DCE.

Toxicological Review of 1,1-Dichloroethylene
U.S. EPA
Report: EPA/635/R-02/002, 2002

A 72 page report that provides Support of 1,1-DCE Summary Information on the Integrated Risk Information System (IRIS)

Ecological References

Concise International Chemical Assessment Document (#51) for 1,1-Dichloroethene
International Programme on Chemical Safety (IPCS), 2003

This document is a comprehensive review of the physical/chemistry properties, fate and transport, human and ecological health effects, and occurrence of 1,1-DCE.

Environmental Contaminants Encyclopedia. Dichloroethylene-1,1 (1,1-Dichloroethylene) Entry
Irwin, RJ, et al.
National Park Service, Water Resources Division, Fort Collins, CO, 1997

This web page provides information on human health effects, fate and transport, production, and uses of many chemicals including a 1,1-DCE section.

Toxicity reference values for inhalation of volatile organic compounds by terrestrial mammals
Lee, B and M. Roy
SETAC 26th Annual Meeting in North America, 2005