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Tracking the Fate of Petroleum Hydrocarbons in Groundwater

Silvia A. Mancini, University of Toronto, Department of Geology, Toronto, Canada, [email protected]


This research will develop stable carbon and hydrogen isotope analysis and quantitative Polymerase Chain Reaction (qPCR) analysis as techniques to quantify the extent to which in-situ biodegradation processes are contributing to the attenuation of petroleum hydrocarbons in contaminated groundwater. Benzene and toluene will be the focus of this project - the most soluble and toxic components of petroleum derivatives.

It is known that processes, such as sorption and volatilization, do not significantly alter the isotopic signature of benzene and toluene, whereas biodegradation is known to cause isotopic enrichment in the remaining contaminant pool. This makes it possible to use isotope analysis to distinguish between biodegradation and non-degradative processes. qPCR analysis is increasingly being used as a “biomarker” method of enumerating bacterial genes, cells and their potential functions in nature. Demonstration of both of these techniques in the field has remained limited. The combined use of isotope analysis and qPCR analysis is particularly valuable given the challenge of verifying and quantifying biodegradation at sites where biodegradation rates can be slow and traditional geochemical indicators may not be significantly affected.

This project will involve measuring the isotopic behavior of benzene and toluene in anaerobic cultures characterized for gene sequences from different organisms involved in the biodegradation process.  The predictability of bioremediation performance will be tested in soil filled columns inoculated with the benzene and toluene cultures.  By modeling the isotope data and relating the qPCR data to the consumption of contaminant, it will be determined whether these methods can quantitatively assess biodegradation.