USE OF STABLE OXYGEN AND CARBON-ISOTOPE ANALYSES FOR MONITORING THE PATHWAYS AND RATES OF INTRINSIC AND ENHANCED IN-SITU BIODEGRADATION

Significant challenges remain in developing reliable techniques to mon itor in situ biodegradation. Stable carbon and oxygen isotope analyses of the contaminants, products of degradation, and electron acceptor(s ) may provide robust means for monitoring the occurrence, pathways, an d rates of intrinsic or enhanced in situ biodegradation. Results of a laboratory study using diesel fuel and a mixed microbial culture show that combined stable carbon isotope analyses of carbon dioxide and sta ble oxygen isotope analyses of molecular oxygen allow monitoring of th e occurrence and pathways of degradation. The first-order rate constan ts far contaminant degradation (about -0.04 day(-1)) obtained from oxy gen and contaminant concentrations are in excellent agreement with tho se obtained from isotopic data for oxygen (-0.04 to -0.05 day(-1)), in dicating that oxygen isotope analyses of molecular oxygen can be used for quantifying the rate of contaminant degradation. Based on our resu lts and a review of the published literature on oxygen isotope systema tics of molecular oxygen and other common electron accepters (nitrate and sulfate), it is suggested that combined carbon and oxygen isotope analyses of carbon dioxide and the electron accepters provide effectiv e toots far monitoring intrinsic and enhanced in situ biodegradation o f fuel or chlorinated hydrocarbons under aerobic and anaerobic conditi ons.