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)


Halogenated Monoaromatics

Human Health Toxicity

The chlorobenzenes are a subset of the group of compounds termed halogenated monoaromatics. Chlorobenzenes can contain between one and six carbon atoms, and the dichloro-, trichloro-, and tetrachlorobenzenes can exist in several isomeric states. Although the physical chemistry of the chlorinated compounds varies considerably, there is some commonality in the toxic actions they exert.

Few studies describe the toxicity of the chlorinated benzenes to humans; however, animal studies suggest that the liver is the primary target organ for chlorobenzene toxicity. Laboratory animals exposed to monochloro-, dichloro-, trichloro-, and tetrachlorobenzenes can develop lesions of the liver. Kidney damage has also been reported in exposed animals. Monochlorobenzene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, and 1,2,4-trichlorobenzene are classified "D; not classifiable as to human carcinogenicity," in EPA's Integrated Risk Information System (IRIS). Very few studies are available of the developmental and reproductive toxicity of the chlorinated benzenes to laboratory animals. Available studies do not indicate that these compounds exert adverse effects on reproduction or fetal development.

Monochlorobenzene has given mainly negative results on standard genotoxicity assays, but the dichloro- and trichloro-substituted compounds have given both positive and negative results.

Ecological Toxicity

There also are few studies of ecological toxicity of the chlorinated benzenes, and the existing investigations generally are limited to acute toxicity studies using aquatic environmental receptors as test subjects. In the aquatic environment, it might be generalized that the bioaccumulation and bioconcentration of chlorobenzenes increases with an increasing level of chlorine substitution. Similarly, acute aquatic toxicity studies suggest that for most aquatic species the toxicity of the chlorobenzenes also increases with increasing chlorination.

For Further Information

Toxicological Profile for Dichlorobenzenes
Agency for Toxic Substances and Disease Control, 493 pp, 2006

Chlorobenzenes Other Than Hexachlorobenzene: Environmental Aspects
Malcolm, H.M., P.D. Howe, and S. Dobson.
World Health Organization, Concise International Chemical Assessment Document 60, 2004

Other DNAPLs Toxicology Topics: