Abstract :
Organochlorine compounds have attracted interest since the discovery of chloroform as an anaesthetic, chloral hydrate as a sedative and more recently DDT as an insecticide. The value of many industrial products such as PCBs depends on their chemical stability, and many compounds including agrochemicals contain chlorine. In addition, a large and structurally diverse group of organochlorine compounds is produced by a range of biota, while some are by-products from the bleaching of pulp by conventional procedures using molecular chlorine. The chemical stability of organochlorine compounds is reflected in their resistance to microbial degradation, and this fact coupled to their ubiquitous occurrence in environmental samples has aroused widespread concern. The mechanisms of microbial degradation of aliphatic and aromatic organochlorine compounds include hydrolytic, oxidative, reductive and elimination mechanisms. These are reviewed with reference to their limitations, the range of structures that have been studied, and attention drawn to the environmental consequences of biotransformation. Illustrative examples are drawn from studies with chloroalkanes, and a range of aromatic compounds including hydrocarbons, carboxylic acids, phenols and anilines. Attention is directed to important environmental constraints including anaerobic conditions and bioavailability, and brief mention is made of the degradation of organofluorine and organobromine compounds to highlight the differences from organochlorine compounds.
