Crude oil is a complex mixture containing 10s of thousands of compounds. When a crude oil is released into the environment, the hydrocarbons begin to undergo biodegradation. During these biodegradation processes the constituents are transformed from the original hydrocarbons into oxygen-containing organic compounds (OCOCs). These OCOCs can be extracted from soil or groundwater samples with dichloromethane and quantified as total petroleum hydrocarbons (TPH) unless they are removed prior to analysis on the gas chromatograph (EPA Method 8015). Silica gel cleanup, EPA Method 3630, will effectively remove the polars from the extract, however, there is hesitancy accepting the use of silica gel cleanup because the unknown nature and toxicity of these OCOCs produced during the biodegradation process. Because of these questions, two research grade technologies, were used to comprehensively characterize the OCOCs.<br/>For this study, both GC×GC-TOFMS and Orbitrap ESI-MS were used to characterize the OCOCs present in groundwater at a site where a crude oil pipeline ruptured decades ago. The results from the advanced analytical characterization resulted in an updated hypothesis for the polar species extracted during the TPH analysis. Our initial biochemistry-focused hypothesis was that OCOCs are petroleum degradation intermediates. Recent findings suggest that the some of the compounds are not intermediates, but are typical products of microbial growth, secondary production, and carbon cycling. Based on this theory, dissolved organic carbon (DOC) in groundwater plumes may be consistent with that of other natural aquatic systems. The purpose of this presentation is to describe our characterization results, and present the hypothesis that OCOCs are consistent with organic matter resulting from biosynthesis or other processes found in natural water systems and are unlikely to be intermediates (metabolites) along petroleum biodegradation pathways.

Composition and nature of dissolved organic carbon in groundwater at petroleum release sites

ACS Fall 2021

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