Degradation isotope enrichment factor

For aerobic degradation by Pseudomonas sp. strain P51, which carried out degradation by dioxygenation, the valnes were not significant. In contrast, the isotope enrichment factor (e) for anaerobic dechlorination by Dehalococcoides sp. strain CDBl, which produced 1,3-dichlorobenzene from 1,2,3-trichlorobenzene, was -3.4 ppm, and for 1,2,4-trichlorobenzaene, which produced 1,4-dichlorobenzene, was -3.2 ppm. 

Laboratory Degradation Studies to Assess the Isotope Enrichment Factor 106... 

Abstract Isotope fractionation of fuel oxygenates has been employed as an indicator for monitoring in-situ degradation in the field. For quantification of in-situ degradation, the Rayleigh concept can be applied. The selection of an appropriate isotope enrichment factor (e) that is representative of the biogeochemical conditions governing the microbial... 

The purpose of this chapter is to provide a summary of the different isotope enrichment factors for MTBE and related fuel oxygenates from biotic and abiotic reactions, furthermore, the chapter shows how the current CSIA state of the art can help in the characterisation of MTBE degradation pathways and the quantification of in-situ degradation. 

Only limited information is available on isotope fractionation of TBA, which is a by-product of MTBE manufacturing or occurs as a major main metabolite of MTBE degradation. The carbon isotope fractionation of TBA (eC = -4.21 0.07%o) was studied in cometabolic aerobic microcosms [41], however, hydrogen isotope enrichment factors are not available yet. 

Investigation of the indigenous microbial consortiiun in the aquifer and the identification of the organisms by molecular biological methods in the environment might help to improve the selection of appropriate isotope enrichment factors suitable for the assessment of in-situ degradation at sites contaminated by fuel oxygenates. 

To date, anaerobic MTBE-degrading strains have not been isolated and the mechanisms of anaerobic MTBE degradation have not yet been elucidated. Moreover, only a limited number of enrichment cultures have been used to study isotope fractionation and, in particiflar, data to evaluate the variabihty in isotope fractionation under anoxic conditions are missing. The isotope enrichment factors for more microbial strains as well as for electron-accepting conditions, in particular for other fuel oxygenates, is needed. 

Results have been expressed in a number of ways. In the Raleigh model that has been extensively used, the fractionation factor a is given by R/Rq = when the fraction of remaining substrate is/and where R is the isotopic composition of the substrate during degradation and Rq is the initial value. The enrichment factor e where e = 1000 (a - 1) has also been used. There are certain conditions that must be fulfilled for the Raleigh model to be applicable ... 

Carbon isotope fractionation was examined during the aerobic degradation of TCE by Burkholderia cepacia strain G4 that possesses toluene monooxygenase activity (Barth et al. 2002). There were substantial differences in values of isotope shifts during degradation, from 57 to 17 ppm, and when the data were corrected to correspond to the same amount of substrate reduction the Releigh enrichment factor was 18.2. 

Hydrogen isotope fractionation analysis using Methylibium sp. PMl and R8 revealed enrichment factors for MTBE degradation between -33 and 42%o, respectively, which was in the order of previous studies (-29 to -66%o) using mixed consortia from VAFB [37]. Similar to carbon isotope fractionation of the -Proteobacterium L108 (-0.48 0.05%o) and Rhodococcus ruber IFF 2001 (-0.28 0.06%o) the hydrogen isotope fractionation was negligible (sH < -0.2%o) if present at all [40]. 

Table 2 Expected carbon and hydrogen isotopic shifts for increasing extents of biodegradation calculated by a modified Rayleigh equation (Eq. 3) and the different MTBE degradation patterns reported so far in the literature (carbon and hydrogen enrichment factors, eC and eH, respectively)...

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