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Although the uniform initial hydroxylation of methyl tert-butyl ether (MTBE) and other oxygenates during aerobic biodegradation has already been proven by molecular tools, variations in carbon and hydrogen enrichment factors (ε C and ε H ) have still been associated with different reaction mechanisms (McKelvie et al. Environ. Sci. Technol. 2009, 43, 2793−2799. Here, we present new laboratory-derived ε C and ε H data on the initial degradation mechanisms of MTBE, ethyl tert-butyl ether (ETBE), and tert-amyl methyl ether (TAME) by chemical oxidation (permanganate, Fenton reagents), acid hydrolysis, and aerobic bacteria cultures (species of Aquincola, Methylibium, Gordonia, Mycobacterium, Pseudomonas, and Rhodococcus). Plotting of Δδ 2 H/ Δδ 13 C data from chemical oxidation and hydrolysis of ethers resulted in slopes (Λ values) of 22 ± 4 and between 6 and 12, respectively. With A. tertiaricarbonis L108, R. zopfii IFP 2005, and Gordonia sp. IFP 2009, ε C was low (<|−1|‰) and ε H was insignificant. Fractionation obtained with P. putida GPo1 was similar to acid hydrolysis and M. austroaf ricanum JOB5 and R. ruber DSM 7511 displayed Λ values previously only ascribed to anaerobic attack. The fractionation patterns rather correlate with the employment of different P450, AlkB, and other monooxygenases, likely catalyzing ether hydroxylation via different transition states. Our data questions the value of 2D-CSIA for a simple distinguishing of oxygenate biotransformation mechanisms, therefore caution and complementary tools are needed for proper interpretation of groundwater plumes at field sites.

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Hydroxylamine (NHOH) undergoes biotic and abiotic transformation processes in soil, producing nitrous oxide gas (NO(g)). Little is known about the magnitude of the abiotic chemical processes in the global N cycle, and the role of abiotic nitrification is still neglected in most current nitrogen trace gas studies. The abiotic fate of NHOH in soil systems is often focused on transition metals including manganese (Mn) and iron (Fe), and empirical correlations of nitrogen residual species including nitrite (NO), nitrate (NO), and NO(g). In this study, abiotic NHOH nitrification by well-characterized manganese (Mn)- and iron (Fe)-bearing minerals (pyrolusite, amorphous MnO(s), goethite, amorphous FeOOH(s)) was investigated. A nitrogen mass balance analysis involving NHOH, and the abiotic nitrification residuals, NO(g), NO(aq), NO, NO, was used, and specific reactions and mechanisms were investigated. Rapid and complete NHOH nitrification occurred (4-5 h) in the presence of pyrolusite and amorphous MnO(s), achieving a 95-96% mass balance of N byproducts. Conversely, NHOH nitrification was considerably slower by amorphous FeOOH(s) (14.5%) and goethite (1.1%). Direct reactions between the Mn- and Fe-bearing mineral species and NO and NO were not detected. Brunauer-Emmett-Teller surface area and energy dispersive X-ray measurements for elemental composition were used to determine the specific concentrations of Mn and Fe. Despite similar specific concentrations of Mn and Fe in crystalline and amorphous minerals, the rate of NHOH nitrification was much greater in the Mn-bearing minerals. Results underscore the intrinsically faster NHOH nitrification by Mn minerals than Fe minerals.