Anaerobic biodegradation of MTBE in a field site above the Israeli Coastal Aquifer: Evidence from δ¹³C compound-specific isotope analysis

BACKGROUND: The fuel additive, methyl tert-butyl ether (MTBE), is one of the most frequently occurring groundwater pollutants worldwide. The present study focused on assessing microbial degradation of MTBE in groundwater below a gasoline station situated above the Israeli Coastal Aquifer. Groundwater was monitored in six monitoring wells over a time period of 2.5years. RESULTS: The site water geochemistry indicated that anaerobic conditions prevailed in two of the most contaminated wells. During a year MTBE concentrations declined from 81 to 4.2mgL^-1, concurrently, with a significant change in δ¹³C from -31.4 to -11.8 ‰ in a source area monitoring well. MTBE biodegradation during microcosm experiments under sulfate reducing and methanogenic conditions resulted in carbon isotopic enrichment factors (ε) of -17.2±1.1 ‰. CONCLUSION: Significant decrease in MTBE concentrations, along with pronounced changes in carbon isotope composition, indicates in situ degradation of MTBE occurring at the site. This evidence was supported by a microcosm experiment with indigenous microbial cultures. The estimated rate of biodegradation is 0.7year^-1, which is about 70% of the total natural attenuation (NA) processes.