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
by
E. Michael Godsy (U.S. Geological Survey, Menlo Park, Calif.),
Donald F. Goerlitz (U.S. Geological Survey, Menlo Park, Calif.), and Dunja
Grbic'-Galic' (Stanford University, Stanford, Calif.)
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.
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