C-13/C-12 isotope fractionation of aromatic hydrocarbons during microbial degradation

The influence of microbial degradation on the C-13/C-12 isotope composition of aromatic hydrocarbons is presented using toluene as a model compound. F our different toluene-degrading bacterial strains grown in batch culture wi th oxygen, nitrate, ferric iron or sulphate as electron accepters were stud ied as representatives of different environmental redox conditions potentia lly prevailing in contaminated aquifers. The biological degradation induced isotope shifts in the residual, non-degraded toluene fraction and the kine tic isotope fractionation factors (alpha C for toluene degradation by Pseud omonas putida (1.0026+/-0.00017), Thauera aromatica (1.0017+/-0.00015), Geo bacter metal-lireducens (1.0018+/-0.00029) and the sulphate-reducing strain TRM1 (1.0017+/-0.00016) were in the same range for all four species, altho ugh they use at least two different degradation pathways. A similar C-13/C- 12 isotope fractionation factor (alpha C=1.0015+/-0.000155 was observed in situ in a non-sterile soil column in which toluene was degraded under sulph ate-reducing conditions. No carbon isotope shifts resulting from soil-hydro carbon interactions were observed in a non-degrading soil column control wi th aquifer material under the same conditions. The results imply that micro bial degradation of toluene can produce a C-13/C-12 isotope fractionation i n the residual hydrocarbon fraction under different environmental condition s.