REDUCTIVE TRANSFORMATIONS OF ANTHROPOGENIC CHEMICALS IN NATURAL AND TECHNICAL SYSTEMS

Reductive transformation reactions of chemical pollutants (e.g., polyh alogenated hydrocarbons, aromatic azo and nitro compounds, chromium(VI ) species) in the environment are important both from an ecotoxicologi cal and from an environmental technology point of view. Using well-def ined model reactors as well as more complex 'real world' systems, seve ral groups at EAWAG are trying to unravel compound-and system-specific factors that control the reduction of a variety of anthropogenic chem icals under different conditions in the environment. The examples pres ented in this article include the reduction of nitroaromatic compounds under iron- and sulfate-reducing conditions, the reductive dehalogena tion of chlorinated ethenes by cob(I)alamin and by a bacterium that us es such compounds as terminal electron accepters, and the reduction of chromium(VI) by various reduced iron species. The link between microb ial and abiotic (chemical) processes involved in reductive transformat ions of pollutants is emphasized. The major goal of this article is to illustrate the approaches taken to elucidate the mechanisms and kinet ics of environmentally relevant reduction reactions of pollutants, and to discuss how the results of such studies can be used 1) to gain ins ight into what is actually happening in the environment, and 2) to dev elop methods for the treatment of chemical wastes or contaminated site s.