Dehalogenation of Organohalide Pollutants by Bacterial Enzymes and Coenzymes

Abstract

Organohalides are widespread environmental pollutants which typically contain a carbon-halogen bond. The halogen substituent can be fluorine, chlorine, bromine, or iodine but chlorine is most common. The environmental fate of organohalides is dominated by the chemistry of the carbon-halogen bond of particular compounds. For example, fluorocarbons are particularly inert. This is due in large measure to the high bond dissociation energy of the carbon-fluorine bond which ranges from 106–115 Kcal/mol (Reinecke, 1984). Chlorinated compounds differ markedly in their environmental persistence. Generally, aryl and alkenyl chlorides decompose much more slowly than alkyl chlorides. The former compounds undergo hydrolytic and photolytic cleavage of the carbon-halogen bond much less readily. Environmental organohalides often derive from industrial sources, but many halogenated organic natural products are known as well. Commodity organic chemicals that contain chlorine include vinyl chloride, trichloroethylene, dichloromethane, 1, 2-dichloroethane, and chlorobenzene. Each of these compounds are used by United States industries at levels exceeding ten million pounds annually (Hutzinger & Veerkamp, 1981). Several natural products such as methyl chloride (Wuosmaa & Hager, 1990) and tribromomethane (Gschwend, et al., 1985) are released into the environment at comparable levels on a global scale by fungi and algae, respectively. As an illustration of the complexity of this group of compounds, over 700 halogenated natural products have been identified (Neidleman & Geigert, 1986).