Signature metabolites attesting to the in situ attenuation of alkylbenzenes in anaerobic environments

Accurate assessment of the fate of hydrocarbons spilt in aquifers is essent ial far gauging associated health and ecological risks. Regulatory pressure to actively remediate such contaminated ecosystems can be substantially di minished 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 toluen e, ethylbenzene, xylene, and toluic acid isomers with stoichiometric amount s of sulfate consumed or methane produced. The activation of the alkylated aromatic contaminants involved conversion to their corresponding benzylsucc inic acid derivatives, a reaction known to occur for toluene and m-xylene d ecay, but one previously unrecognized for ethylbenzene, o- and p-xylene, an d m-toluate metabolism. Benzylsuccinates were further biodegraded to toluat es, 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 decr eased over time, suggesting that anaerobic microbial metabolism of these co ntaminants also occurs in situ. Our studies confirm the utility of the afor ementioned compounds as signature metabolites attesting to the natural atte nuation of aromatic hydrocarbons in anaerobic environments.