Signature Metabolites Attesting to the In Situ Attenuation of Alkylbenzenes in Anaerobic Environments

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Abstract
Accurate assessment of the fate of hydrocarbons spilt in aquifers is essential for gauging associated health and ecological risks. Regulatory pressure to actively remediate such contaminated ecosystems can be substantially diminished if solid evidence for in situ microbial destruction of pollutants is obtained. In laboratory incubations, sediment-associated microorganisms from a gas condensate-contaminated aquifer anaerobically biodegraded toluene, ethylbenzene, xylene, and toluic acid isomers with stoichiometric amounts of sulfate consumed or methane produced. The activation of the alkylated aromatic contaminants involved conversion to their corresponding benzylsuccinic acid derivatives, a reaction known to occur for toluene and m-xylene decay, but one previously unrecognized for ethylbenzene, o- and p-xylene, and m-toluate metabolism. Benzylsuccinates were further biodegraded to toluates, phthalates, and benzoate. In laboratory incubations, these metabolites were transiently produced. Several of the metabolites were also detected in groundwater samples from an aquifer where alkylbenzene concentrations decreased over time, suggesting that anaerobic microbial metabolism of these contaminants also occurs in situ. Our studies confirm the utility of the aforementioned compounds as signature metabolites attesting to the natural attenuation of aromatic hydrocarbons in anaerobic environments.

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