1 BIOREMEDIATION OF CONTAMINATED SITES*

Bioremediation is a process in which microorganisms metabolize contaminants either through oxidative or reductive processes. Under favorable conditions, microorganisms can oxidatively degrade organic contaminants completely into non-toxic by-products such as carbon dioxide and water or organic acids and methane. Highly electrophilic compounds such as halogenated aliphatics and explosives typically are bioremediated through reductive processes that remove the electrophilic halogens or nitro groups. Bioremediation processes may be directed towards accomplishing: (1) complete oxidation of organic contaminants (termed mineralization) , (2) biotransformation of organic chemicals into smaller less toxic metabolites, or (3) reduction of highly electrophilic halo- and nitro- groups by transferring electrons from an electron donor (typically a sugar or fatty acid) to the contaminant, resulting in a less toxic compound. With increasing numbers of successfully demonstrated cleanups, biological remediation alone or in combination with other methods, has gained an established place as a soil restoration technology