U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Pathways of Methanogenic Biodegradation of Creosote-Derived Aromatic Compounds

Abstract

The fate of organic compounds in ground water is controlled by various transport and biotransformation processes. Possibly the most important, but currently the least understood, process affecting ground-water quality is biotransformation of organic compounds by indigenous microorganisms. In this study, the degradation pathways of benzothiophene, quinoline, and naphthalene are determined on the basis of intermediate compounds that appear before and just after the onset of methanogenesis. This study revealed that the biodegradation process consists of both a major and a minor pathway. The first transformation step of the major-pathway heterocyclic compounds is oxidation and cleavage of the heterocyclic ring. After cleavage of this ring, the substituent side chains and the remaining homocyclic ring are subjected to various reactions, including oxidation, decarboxylation, desul-furylation or ammonification, and O-methylation. These reactions are followed by the reduction of the homocyclic ring, cleavage of this ring, ß-oxidation, and mineralization. The major pathway intersects both the benzoic acid and phenol methanogenic-degradation pathways. A minor pathway for heterocyclic compounds starting with the oxidation of the homocyclic ring with subsequent ring reduction, ring cleavage, degradation of the remaining heterocyclic ring, and mineralization also was observed.