ANAEROBIC BENZENE OXIDATION IN THE FE(III) REDUCTION ZONE OF PETROLEUM-CONTAMINATED AQUIFERS

The potential for anaerobic benzene oxidation in the Fe(III)-reduction zone of petroleum-contaminated aquifers was evaluated. Sediments were incubated under strict anaerobic conditions without any amendments in order to simulate in situ conditions. [C-14]Benzene was not oxidized to (CO2)-C-14 at most sites examined, which is consistent with previou s studies that have found that benzene tends to persist in unamended, anaerobic aquifer materials and/or long periods of time are required i n order to adapt the microbial population for benzene degradation. How ever, at one site located in Bemidji, MN, [C-14]benzene was oxidized t o (CO2)-C-14 in unamended sediments without an apparent lag, suggestin g that benzene was anaerobically degraded in situ. Benzene was not sig nificantly oxidized in sediments from nearby Fe(III)-reducing sites no r in sediments collected from an uncontaminated background site in the same aquifer. Culturing and 16S rRNA-based molecular studies of the B emidji aquifer demonstrated that while all sites contained similar num bers of Fe(III)-reducing microorganisms closely related to Geothrix fe rmentens, the site at which anaerobic benzene degradation was observed was greatly enriched with microorganisms in the family Geobacteraceae . This study provides the first data consistent with in situ anaerobic oxidation of benzene to carbon dioxide in the Fe(III)-reducing zone o f a petroleum-contaminated aquifer and suggests that comparative studi es on the size of the Geobacteraceae community in petroleum-contaminat ed aquifers might aid in the location of zones in which benzene degrad ation coupled to Fe(III) reduction is taking place.