Quantifying MTBE biodegradation in the Vandenberg Air Force Base ethanol release study using stable carbon isotopes

Role of back diffusion and biodegradation reactions in sustaining an MTBE/TBA plume in alluvial media

“…First-order kinetics were applied with the rate constant estimated by Mackay et al (2007) for anaerobic transformation of MTBE to TBA. The TBA production rate is $\frac{d{C}_2}{dt}=-\frac{1}{\beta }\frac{d{C}_1}{dt}$, where C 2 is TBA concentration [ML −3 ] and β is the mass ratio of MTBE consumed to TBA produced [-] calculated to be 1.19 assuming the following reaction stoichiometry: $$C_5{H}_{12}O\left(\mathit{MTBE}\right)+H_{2}O\to C_4{H}_{10}O\left(\mathit{TBA}\right)+{\mathrm{italicCH}}_3\mathit{OH}$$ The model assumes no anaerobic degradation of TBA, consistent with field results at VAFB (Mackay et al, 2007; McKelvie et al, 2007). …”

“…Acetogenic bacteria, members of methanogenic food webs, are hypothesized to be responsible for ether cleavage of the MTBE molecule and use the released methyl group as a carbon source; however, the pathway and particular organisms responsible are yet to be defined (Youngster et al, 2010a; Youngster et al, 2010b). Field experiments at VAFB have shown that MTBE transforms to TBA under strongly anaerobic conditions induced by experimental ethanol addition (Mackay et al, 2007; McKelvie et al, 2007), with an estimated pseudo-first-order reaction rate constant of 0.046 day −1 (after a lag period of about two months). Other lab and field evidence of in situ transformation of MTBE under anaerobic conditions is summarized by Wilson et al (2005).…”

Linking Low-Level Stable Isotope Fractionation to Expression of the Cytochrome P450 Monooxygenase-Encoding ethB Gene for Elucidation of Methyl tert -Butyl Ether Biodegradation in Aerated Treatment Pond Systems

“…Some of these MTBE-contaminated sites have been characterized recently by compound-specific stable isotope analysis (CSIA) (19,22,26,27,32,34,57). This tool allows for a qualitative and/or quantitative integrative assessment of biological transformation of organic contaminants over a flow path in environmental systems (36,46), thanks to the reaction-dependent compound-specific isotope enrichment factors (ε) obtained under different controlled laboratory conditions employing a modified form of the Rayleigh distillation equation.…”

Applications of Stable Isotopes in Hydrocarbon Exploration and Environmental Forensics

“…The rule of thumb is that observable biodegradation isotope effects are limited to small molecules, readily permeating cell membranes of degraders. So in environmental studies this would include chlorinated ethenes and ethanes, MTBE and mono-aromatic compounds that have been widely studied and where isotope fractionation has been typically observed McKelvie et al 2007). In exploration studies, fractionation has been observed to occur in the lighter hydrocarbons in the C 5 to C 10 range (George et al 2002).…”