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 Alkanes

Human Health Toxicity

Halogenated alkanes are alkane molecules with one or more hydrogen atoms replaced by either chlorine, fluorine, bromine, or iodine, or by a combination of those elements. For example, dibromochloromethane (bromine and chlorine), and 1,1,2-trichloro-1,2,2-trifluoroethane (chlorine and fluorine) are two of many examples of this class of compounds. Although halogenated alkanes differ in their physical chemistry and reactivity, there are some broad similarities in their toxicological effects and modes of action.

Many of the halogenated alkanes exert general anesthetic effects by depressing the functioning of the central nervous system. Some of these compounds, chloroform for example, formerly had clinical use as inhalational anesthetics; however, the use of chloroform and similar compounds as anesthetics was discontinued in part due to another common feature of halogenated alkane toxicity, the ability to cause liver damage. At sufficient levels of exposure, most of the 21 halogenated alkane compounds considered in the DNAPL web pages are capable of causing liver damage, a condition that varies from mild to severe depending on the compound concerned. In addition, some halogenated alkanes have been reported to cause damage to the kidney, thyroid, spleen, adrenal glands, and testis.

U.S. EPA's Integrated Risk Information System (IRIS) has classified 11 of the 21 compounds as probable or possible human carcinogens. Laboratory rodent studies have reported cancers of the liver, kidney, stomach, and intestine in exposed animals.

With two notable exceptions, 1,2-dibromoethane (EDB) and 1,2-dibromo-3-chloropropane (DBCP), the chlorinated alkanes do not appear to have adverse reproductive effects, and do not appear to be toxic to the developing fetus except at doses that cause maternal toxicity. EDB and DBCP are male reproductive toxins in humans and animals.

Halogenated alkanes have given both positive and negative results on standard genotoxicity assays. EDB, DBCP, 1,2-dichloroethane, and bromodichloromethane give mostly positive results in genotoxicity tests.

Ecological Toxicity

Few studies are available that describe the ecological toxicity of the halogenated alkanes. Those studies that are available usually are acute toxicity studies that use aquatic invertebrates and fish as test subjects. With the exceptions of a few highly sensitive species, these compounds generally exert slight toxicity to aquatic species. No data were found that describe the toxicity of halogenated alkanes to terrestrial species.

For Further Information

See references appended to individual compound toxicity sections.



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