New evaluation scheme for two-dimensional isotope analysis to decipher biodegradation processes: application to...

Area of Science:

• Environmental Science
• Geochemistry
• Microbiology

Background:

• Methyl tert-butyl ether (MTBE) is a common gasoline additive and groundwater contaminant.
• Assessing MTBE biodegradation in complex environments is challenging due to multiple sources and co-contaminants.
• Traditional mass balance approaches are often insufficient for evaluating contaminant fate at contaminated sites.

Purpose of the Study:

• To investigate the fate of MTBE and its degradation product tert-butyl alcohol (TBA) in a contaminated groundwater plume.
• To present a novel approach using two-dimensional compound-specific isotope data to identify reaction mechanisms and quantify biodegradation.
• To determine the extent and nature of in-situ MTBE biodegradation under complex site conditions.

Main Methods:

• Compound-specific stable carbon and hydrogen isotope analysis of MTBE and TBA.
• Evaluation of two-dimensional isotope data to identify reaction pathways and biodegradation extent.
• Calculation of intrinsic kinetic isotope effects (KIE) for carbon and hydrogen to infer reaction mechanisms.

Main Results:

• Isotopic shifts in MTBE indicate substantial biodegradation along the contaminant plume.
• Constant isotopic signatures of TBA suggest no significant degradation.
• Analysis indicates anaerobic biodegradation of MTBE, likely following an SN2-type reaction mechanism.
• Evaporation may also contribute to MTBE removal, especially in warmer climates.

Conclusions:

• Two-dimensional compound-specific isotope analysis provides a robust method for evaluating MTBE biodegradation at complex field sites.
• Anaerobic biodegradation is the primary mechanism for MTBE removal in the studied groundwater plume.
• The findings highlight the importance of considering multiple removal processes and environmental factors in contaminant fate assessments.