Hydrogen and carbon isotope fractionation during aerobic biodegradation ofbenzene

The main aim of the study was to evaluate hydrogen and carbon isotope fract ionation during biodegradation of benzene as a possible tool to trace the p rocess in contaminated environments. Aerobic biodegradation of benzene by t wo bacterial isolates, Acinetobacter sp. and Burkholderia sp., was accompan ied by significant hydrogen and carbon isotope fractionation with hydrogen isotope enrichment factors of -12.8 0.7 parts per thousand and -11.2 1.8 pa rts per thousand respectively, and average carbon isotope enrichment factor s of -1.46 +/- 0.06 parts per thousand and -3.53 +/- 0.26 parts per thousan d, respectively. Inorganic carbon produced by Acinetobacter sp. was deplete d in C-13 by 3.6-6.2 parts per thousand as compared to the initial delta C- 13 of benzene, while the produced biomass was enriched in C-13 by 3.8 parts per thousand. The secondary aim was to determine isotope ratios of benzene s from different manufacturers with regard to the use of isotopes for sourc e differentiation. While two of the four analyzed benzenes had similar delt a C-13 values, each of them had a distinct,delta H-2-delta C-13 pair and de lta H-2 values spread over a range of 66.5 parts per thousand. Thus, combin ed analyses of hydrogen and carbon isotopes may be a more promising approac h to trace sources and/or biodegradation of benzene than measuring carbon i sotopes only.