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

Abstract

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 2.5 years. 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 4.2 mg L −1 , concurrently, with a significant change in 13 C 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 ( ) 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 0.7 year −1 , which is about 70% of the total natural attenuation (NA) processes.Assessing the natural attenuation of MTBE at the field site Assuming that MTBE biodegradation within the groundwater follows first-order kinetics, a rate constant for the process can be calculated based on shifts in 13 C (Equation (2)). Alternatively, a rate constant can be assessed by measuring the concentration J Chem Technol Biotechnol 2016; 91: 1638-1645

In Situ Bioremediation of a Gasoline‐Contaminated Vadose Zone: Implications from Direct Observations

“…4). Field studies addressing the aerobic bioattenuation of MTBE in the saturated zone have suggested its inhibition by BTEX compounds due to either preferred utilization of the latter or depletion of electron acceptors and nutrients (Gafni et al, 2016). Indeed, aerobic MTBE degradation by the model bacterium Methylibium petroleiphilum PM1 was inhibited by BTEX (Joshi et al, 2016).…”

Tracking Degradation of Organic Pollutants in Israeli Groundwater by Stable Isotope Analysis

“…The studied sites were characterized by different geochemical parameters: anaerobic with a negative redox potential, low nitrate and sulfate concentrations and high concentrations of dissolved manganese and iron as well as aerobic with high concentration of dissolved oxygen and a positive redox potential. In the anaerobic zone, a decrease in MTBE concentrations during a year, was accompanied by a significant change in δ 13 C from −31.4 to −11.8‰ (Gafni et al 2016;Gelman et al 2014). Based on carbon isotopic enrichment factors (E) of −17.2‰, determined in the microcosm experiments under sulfate reducing and methanogenic conditions, a half-life value of~1 year was estimated (Gafni et al 2016).…”

“…In the anaerobic zone, a decrease in MTBE concentrations during a year, was accompanied by a significant change in δ 13 C from −31.4 to −11.8‰ (Gafni et al 2016;Gelman et al 2014). Based on carbon isotopic enrichment factors (E) of −17.2‰, determined in the microcosm experiments under sulfate reducing and methanogenic conditions, a half-life value of~1 year was estimated (Gafni et al 2016). In another study, where an active remediation by increasing oxygen level in groundwater was applied, significant decrease in MTBE concentrations was accompanied by small shifts in carbon isotope values.…”

“…However, a trend of decreasing MTBE concentrations, over the period 2004-2011, has been observed in~30% of the monitoring wells (Reshef and Zhuravel 2013). In order to assess biodegradation of MTBE in situ, compound-specific isotope analysis has been applied in the field (Gelman et al 2014;Gafni et al 2016). The studied sites were characterized by different geochemical parameters: anaerobic with a negative redox potential, low nitrate and sulfate concentrations and high concentrations of dissolved manganese and iron as well as aerobic with high concentration of dissolved oxygen and a positive redox potential.…”

Recent Advances in Bioremediation

“…According to their results, the use of Streptomyces strains as bioremediation agents seems very promising in terms of clofibric acid degradation. Gafni et al , investigated the in situ biodegradation of gasoline products in groundwater, in which these pollutants undergo processes of natural attenuation including volatilisation, dilution, sorption, and microbial degradation. Finally, the biodegradation of waste products from the poultry industry was the subject of work by Stiborová et al Specifically, they isolated keratin‐degrading bacteria from poultry, in order to study their role in processing keratin waste.…”