U.S. EPA Contaminated Site Cleanup Information (CLU-IN)


U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Toxicology

Halogenated Alkenes

Human Health Toxicity

The halogenated alkenes, 1,1-dicloroethene (1,1-DCE), 1,2-dichloroethene (1,2-DCE), trichloroethene (TCE), and tetrachloroethene (PCE) have similar industrial uses as metal degreasers, dry cleaning agents, and intermediates in the synthesis of other chemicals. They are also used in the electrical industry and as solvents for a wide variety of paints, varnishes, and other products for the home and office. Several of these compounds, such as TCE, PCE, and 1,2-dichloroethene, have formerly been used as inhalation anesthetics, either alone or in combination with other compounds. TCE and PCE have had pharmaceutical uses as antihelminthics, such as those used to control parasitic worms in mammals. 1,3-Dichloropropene (1,3-DCP) is used as a soil fumigant to alleviate crop damage from small nematode worms that attack root systems.

In general, the halogenated alkenes are lipophilic, which is the key property that makes these compounds useful as solvents and degreasers. Furthermore, their lipophilic behavior enables them to rapidly penetrate absorption barriers, such as the respiratory and gastrointestinal tracts. They penetrate the skin more slowly. Once absorbed, they are distributed by the blood to body fat and fatty tissues, such as the brain. If absorbed in sufficient amount, compounds such as TCE, PCE, and 1,2-DCE, quickly exert the effects associated with their use as inhalational anesthetics, including depression of the central nervous system, which results in hypoactivity, ataxia, and anesthesia. Metabolism of the halogenated alkenes generally occurs in the liver, and their metabolites are excreted in urine. In some instances, the metabolites may exert their own toxic effects beyond those of the parent compound. A portion of the absorbed dose of TCE, PCE, and other compounds is exhaled unchanged.

Animal studies show that there are toxic effects associated with exposure to the halogenated alkenes that include damage to target organs, such as the liver and kidney, damage to the central nervous system, and development of benign and malignant tumors. Long-term animal studies and some epidemiological surveys suggest that some of the halogenated alkenes may be human carcinogens. Seven epidemiological studies involving well characterized exposures to TCE indicate that occupational exposure to the compound is associated with excess incidences of cancer in the liver and kidney, and non-Hodgkin's lymphoma. Additional evidence from these studies suggests an excess incidence of prostate cancer and multiple myeloma. Smaller studies have shown an increased risk of death from Hodgkin's disease and cervical cancer. An elevation in cancer mortality from cancers of the esophagus and cervix has been seen in workers exposed to PCE in dry cleaning operations. There also is some evidence to suggest an excess of kidney cancers.

No information is available on the potential developmental or reproductive toxicity of 1,2-DCE or 1,3-DCP, but studies in laboratory animals indicate that 1,1-DCE, TCE, and PCE may cause developmental abnormalities in the offspring of pregnant animals exposed to these compounds. Some epidemiological studies suggest that exposure to PCE causes an increased rate of spontaneous abortion in women, and that cardiac abnormalities are more frequently seen in the babies of women exposed to TCE in pregnancy.

Ecological Toxicity

Despite their lipophilic properties, minimal evidence exists to indicate that halogenated alkenes bioaccumulate. These compounds are volatile, and their volatility together with their limited potential for bioaccumulation may suggest that these compounds do not present a substantial toxic hazard to most ecological receptors. However, studies indicate that 1,3-DCP, which is used to control soil nematodes, is highly toxic to some species of zooplankton and juvenile sheepshead minnows. 1,3-DCP is moderately toxic to other fish species, such as largemouth bass, adult sheepshead minnows, and bluegill, and to invertebrates, such as the water flea and ramshorn snail. Fish appear to be sensitive to PCE, and this compound has been shown to cause reduced hatching, abnormal heart development, hemorrhage, and scoliosis in the Japanese medaka at low concentrations. Although some acute toxicity studies have been performed in some fish species, and in some plants and algae, minimal information exists on the effects of halogenated alkenes on terrestrial ecological receptors.



Other DNAPLs Toxicology Topics: