Dehalogenation of Pesticides by Anaerobic Microorganisms in Soils and Groundwater—A Review

This chapter concentrates on the primary degradative reactions associated with halogenated pesticides in anoxic soils and groundwaters. It introduces the various reaction mechanisms established for halogenated aromatic and nonaromatic chemicals. Many such pesticides seem to be more amenable to anaerobic biotransformation processes. Thus, the chapter is a summary of the various mechanisms associated with anaerobic dehalogenation of aromatic and aliphatic pesticides. Transition metal complexes are integral parts of many proteins involved in methyl group or electron transfer processes. In aerobic, NO3 - and SO4 2- reducing bacteria, cytochromes containing porphyrins function in establishing transmembrane redox potentials. Cytochrome P-450 is the terminal oxidase of the mixed function oxidase complex in aerobic bacteria. The chapter describes the effect of porphyrin and cytochrome P-450 on halogenated nonaromatic compounds. An interesting type of dehalogenation is involved in the biodegradation of phosalone in flooded soil. Phosalone is an organophosphate chemical used for pest control on potato, cotton, and orchards.