Byproducts of Anaerobic Alkyibenzene Metabolism Useful as Indicators of in Situ Bioremediation

Based on the concordance of laboratory studies of anaerobic bacteria and field observations from an aquifer in Seal Beach, CA, a group of compounds including benzylsuccinic acid, benzylfumaric acid (or a closely related isomer), and the o-, m-, and p-methyl homologs of these compounds are proposed as biogeochemical indicators of in situ anaerobic alkylbenzene metabolism in gasoline-contaminated aquifers. Under the controlled conditions of the field study, a strong correspondence was observed between the disappearance of alkylbenzenes from groundwater overtime and the appearance of associated metabolic byproducts. This correspondence was both qualitative (i.e., only products specific to the metabolism of toluene, o-xylene, and m-xylene were observed, and only these three hydrocarbons were depleted) and quantitative (i.e., metabolic byproduct concentrations tended to increase as the associated alkytbenzene concentrations decreased). These metabolites may prove useful for distinguishing biotic losses of BTEX (benzene, toluene, ethylbenzene, and xylenes) from abiotic losses when monitoring gasoline-contaminated, typically anaerobic, aquifers that are not being actively remediated or that are being remediated by stimulation of anaerobic bacteria.