Determination of in situ biodegradation rates using 13C-labelled aniline

A concept was developed that allowed the quantification of contaminant biodegradation in complex systems employing C-13-labelled compounds. Sediment groundwater microcosms with contaminated aquifer material were spiked with C-13-labelled mono-aromatic model substrates and their fate was studied over time. First-order biodegradation rate constants were generated from the apparent concentration decrease in the water phase, where HgCl2-amended controls accounted for abiotic contaminant loss. Secondly, rate constants were calculated from the increase of C-13-CO2 in the headspace of the microcosms upon substrate utilization. The model compound aniline proved that both C-13-based approaches were suitable to demonstrate the intrinsic mineralization potential. Moreover, rate constants based on the C-13 recovery in the CO2 of the headspace were unaffected by sorption compared to rate constants derived from concentration measurements in the water phase.