trihalomethane

Trihalomethane (THM) is a class of chemical compounds with the general formula CHX3, in which three hydrogen atoms of methane are replaced by halogen atoms. Common members include chloroform (CHCl3), bromoform (CHBr3) and iodoform (CHI3). Mixed-halogen trihalomethanes such as CHCl2Br and CHClBr2 also belong to the group. THMs can be colorless liquids or gases at room temperature and are typically volatile; their physical properties vary with halogen composition.

In water treatment, THMs are notable as disinfection byproducts formed when chlorine or chlorinating agents react with natural organic matter and bromide present in source water. The amount and composition of THMs depend on precursor materials, bromide levels, pH, temperature, and contact time. Because of their toxicity and potential health risks, many countries regulate total THMs in drinking water and monitor representative compounds such as chloroform, bromodichloromethane, dibromochloromethane and bromoform.

Historically, some THMs have been used as solvents or reagents, and chloroform in particular was used as an anesthetic in the 19th and early 20th centuries; today their use is largely limited to specialized industrial applications and research.

Toxicology and safety: several THMs are considered to pose health risks, with chloroform and brominated THMs linked to organ toxicity and possible carcinogenic effects in humans at elevated exposures. Exposure in drinking water typically occurs via ingestion or inhalation of vapors during showering, which can be mitigated by treatment options such as activated carbon, aeration, or alternative disinfection strategies.