TRIHALOMETHANES (THMS)

A group of low-molecular-weight, halogenated hydrocarbons, derivatives of methane, CH4, in which three halogen atoms (chlorine, bromine, or iodine) are substituted for three of the hydrogen atoms. The subsequent substances typically include the compounds of chloroform, bromodichloromethane, dibromochloromethane, and bromoform. The group includes suspect human Carcinogens. Small amounts of THMs have been detected in raw water collected from surface sources used as a public water supply, and concentrations have been shown to be increased during the chlorination phase of the water purification process. The most marked increase during chlorination of drinking water has been recorded in water containing suspended particles and/or humic substances.