Detection of anaerobic metabolites of saturated and aromatic hydrocarbons in petroleum-contaminated aquifers.

Recent investigations have demonstrated that several classes of petroleum hydrocarbons are susceptible to anaerobic decay, including alkanes and mono- and polycyclic aromatic compounds. In previous work, benzylsuccinates were shown to be useful indicators of in situ anaerobic alkylbenzene metabolism. In the present study, we sought to determine whether metabolites of alkanes and naphthalenes could similarly be used as indicators of the intrinsic decomposition of these compounds in petroleum-contaminated aquifers. Such metabolites include succinate derivatives of n-alkanes, cyclic alkanes, and alkylaromatic hydrocarbons as well as naphthoic acids. Using gas chromatography-mass spectrometry (GC-MS), we analyzed trimethylsilyl-derivatized organic extracts from six hydrocarbon-contaminated groundwaters for MS fragment ions indicative of such anaerobic metabolites. Geochemical indicators in these aquifers suggested the prevalence of anaerobic processes. In the groundwaters of the contaminated sites, we found compounds whose MS profiles suggested that they were indeed alkylsuccinic acids, ranging from C3 to C11 succinates. Propyl-, hexyl-, octyl-, and decylsuccinic acids were positively identified in the groundwaters by GC-MS matches with chemical or biologically produced standards. In two of the aquifers, we also detected components whose MS profiles matched with authentic standards of naphthoic acids and tetrahydronaphthoic acids. Metabolites were detected in nanomolar concentrations. The finding of these putative anaerobic metabolites of alkanes and naphthalenes signifies the in situ biodegradation of these hydrocarbons and attests to their value as indicators of intrinsic bioremediation.