Effect of H ₂ and Redox Condition on Biotic and Abiotic MTBE Transformation

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