Microbial metabolism of benzene and the oxidation of ferrous iron under anaerobic conditions: Implications for bioremediation

Benzene and toluene were biodegraded when chelated Fe(III) served as the te rminal electron acceptor in aquifer sediments contaminated by a petroleum r efinery. Benzene biodegradation ceased when Fe(III) was depleted but resume d upon reamendment. Microorganisms from the same sediments degraded toluene , but not benzene, under nitrate reducing conditions. However, the anaerobi c oxidation of Fe(II) to Fe(III) was also observed in toluene-degrading inc ubations. Fe(II) oxidation was dependent on the presence of nitrate and enh anced when organic electron donors were provided. Microbial nitrate-linked Fe(II) oxidation was also documented in other petroleum-contaminated aquife r sediments, sludge from an oil-water separator, a landfill leachate-impact ed aquifer and a garden soil. These observations suggest that some of the r eported effects of nitrate on hydrocarbon biodegradation may be indirect th rough the reoxidation of Fe(II). (C) 1999 Academic Press.