Effect of H2 and Redox Condition on Biotic and Abiotic MTBE Transformation

Abstract

Laboratory studies conducted with surface water sediment from a methyl tert-butyl ether (MTBE)-contaminated site in South Carolina demonstrated that, under methanogenic conditions, [U-¹⁴C] MTBE was transformed to ¹⁴C tert-butyl alcohol (TBA) with no measurable production of ¹⁴CO₂. Production of TBA was not attributed to the activity of methanogenic microorganisms, however, because comparable transformation of [U-¹⁴C] MTBE to ¹⁴C-TBA also was observed in heat-sterilized controls with dissolved H₂ concentrations > 5 nM. The results suggest that the transformation of MTBE to TBA may be an abiotic process that is driven by biologically produced H₂ under in situ conditions. In contrast, mineralization of [U-¹⁴C] MTBE to ¹⁴CO₂ was completely inhibited by heat sterilization and only observed in treatments characterized by dissolved H₂ concentrations < 2 nM. These results suggest that the pathway of MTBE transformation is influenced by in situ H₂ concentrations and that in situ H₂ concentrations may be an useful indicator of MTBE transformation pathways in ground water systems.