Trihalomethanes (THMs) are organic chemicals composed of three halogen atoms (primarily chlorine and bromine) and one hydrogen atom bound to a single carbon atom. They are commonly used as solvents in a variety of applications, and trichloromethane (or chloroform) was once used by medical doctors as an anesthetic. In 1974, Johannes Rook of the Netherlands discovered the presence of THMs in chlorinated drinking water. He and other researchers subsequently demonstrated that minute quantities of THMs are formed during water treatment. Chlorine, when added to disinfect the water, reacts with naturally occurring organic matter present in the water. Groundwater can also be contaminated with THMs if people use them improperly, release them accidentally, or dispose of them unsuitably. Since high dosages of chloroform had been found to produce cancer in mice and rats, the United States Environmental Protection Agency (EPA) amended the drinking water standards in 1979 to limit the concentration of THMs to a sum total of 100 parts ber billion, or 0.1 mg/l. In 1998, a more stringent limit of 0.08 mg/l was introduced.

See Also

Carcinogen; Drinking-Water Supply; Water Quality Standards