Carbon and Hydrogen Isotope Fractionation during Anaerobic Toluene Oxidation by Geobacter metallireducens with Different Fe(III) Phases as Terminal Electron Acceptors

Abstract

Microbial oxidation of BTEX compounds under iron-reducing conditions is an important attenuation process for fuel-contaminated sites. We evaluated the use of compound-specific isotope analysis for the identification and quantification of anaerobic toluene oxidation by Geobacter metallireducens. 13C and 2H enrichment of toluene was measured in laboratory batch systems and varied significantly for a solid vs a dissolved Fe(III) phase provided as terminal electron acceptor. 13C enrichment factors (epsilonC) in suspensions of a solid Fe(III) phase were between -1.0 and -1.3% per hundred, whereas epsilonC-values were significantly higher in solutions of Fe(lll) citrate (-2.9 to -3.6% per hundred. The same trend was observed for 2H fractionation. Solid phase reduction resulted in an epsilonH-value of -34.6 +/- 0.9% per hundred, compared to -98.4 +/- 3.0% per hundred for the reduction of dissolved Fe(lll). The linear correlation of delta(2)H vs. delta(13)C during toluene oxidation resulted in nearly identical slopes for both systems, confirming that the reaction mechanism, that is enzymatic methyl-group oxidation, was the same. We hypothesize that smaller 2H and 13C fractionation in suspensions is due to toluene transport limitations to cells of G. metallireducens at surfaces of solid Fe(III) phases. Enrichment factors determined in Fe(III) mineral suspensions should be more representative for anaerobic toluene degradation owing to the abundance of solid Fe(III) in soils and aquifers.

Carbon and Hydrogen Isotope Fractionation of Benzene, Toluene, and o‐Xylene during Chemical Oxidation by Persulfate

“…Carbon and hydrogen enrichment factors for benzene biodegradation have been extensively reported in the literature with significant variation, for example, ϵ C from −1.4‰ to −3.5‰ and ϵ H from no significant fractionation to −13‰, for aerobic conditions (Hunkeler et al ), and from −0.6‰ to −4.3‰ and −11‰ to −75‰ for anaerobic conditions (Mancini et al , ; Fischer et al , ; Bergmann et al ). Reported enrichment factors for toluene are less constrained with respect to aerobic and anaerobic conditions, with variations from −0.4‰ to −5.6‰ for carbon and from −2‰ to −159‰ for hydrogen (Mancini et al ; Ahad and Slater ; Tobler et al ; Vogt et al ; Herrmann et al ). The reported carbon and hydrogen enrichment under anaerobic (sulfate reducing) conditions for o ‐xylene vary from −0.7‰ to −8.1‰ and from −25‰ to −41‰, respectively (Richnow et al ; Steinbach et al ; Herrmann et al ).…”

“…In situations where dissolved PHC plumes are of interest, CSIA data can be used to estimate the extent of in situ biodegradation that has occurred by applying the Rayleigh model (Hunkeler et al ; Aelion et al ) and to assess remedial system effectiveness. Moreover the use of CSIA on two elements of a molecule, the so‐called dual isotope approach (2D–CSIA), can be used to distinguish between processes which can potentially co‐occur during treatment (Fischer et al , ; Palau et al ; Tobler et al ; Vogt et al ). For example, Palau et al () showed significant differences for 2D–CSIA carbon and chlorine fractionation during 1,1,1‐trichloroethane (1,1,1‐TCA) transformation by heat activated persulfate, hydrolysis/dehydrohalogenation, and zero valent iron.…”

Assessing transformation processes of organic contaminants by compound-specific stable isotope analysis

“…This behavior is reflected in distinct bulk toluene 13 C enrichment factors, C . While C -values of toluene for methyl group oxidations vary between -2 and -6 , they are much smaller for reactions at the aromatic ring (-0.4 to -1 ) [15,16].…”

Carbon and hydrogen stable isotope fractionation associated with the anaerobic degradation of propane and butane by marine sulfate‐reducing bacteria

“…In such environments, sulfate reduction rates that could not be accounted for by anaerobic oxidation of methane have been proposed to be the result of degradation of other hydrocarbons, including gaseous alkanes Orcutt et al, 2005;2010;Niemann et al, 2006;Bowles et al, 2011;Kleindienst et al, 2012). The isotope-sensitive step can be masked by several factors, for example high microbial cell densities (Templeton et al, 2006;Kampara et al, 2009), low substrate or electron acceptor bioavailability Thullner et al, 2008;Tobler et al, 2008;Aeppli et al, 2009;Rosell et al, 2009) or substrate transport across cellular membranes (Nijenhuis et al, 2005;Cichocka et al, 2007). CSIA is based upon kinetic isotope effects (KIEs) of biochemical reactions, leading to an enrichment of heavy isotopologues in the residual substrate pool.…”