SOIL MICROBIAL RESPONSE TO BENZENE CONTAMINATION: NEW ON-SITE GAS ANALYSIS TECHNIQUE REVEALS RESPIRATION AND BIODEGRADATION KINETICS

Soil and groundwater contamination with benzene can cause serious environmental damages. However, many soil microorganisms are capable to adapt and are known to strongly control the fate of organic contamination. Innovative cavity enhanced Raman multi-gas spectroscopy (CERS) was applied to investigate the short-term response of soil bacteria to a sudden surface contamination with benzene regarding the temporal variations of gas products and their exchange rates with the adjacent atmosphere. ¹³C-labeled benzene was spiked on a silty-loamy soil column in order to track and separate the changes in heterotrophic soil respiration - involving ¹²CO₂ and O₂ - from the microbial process of benzene degradation, which ultimately forms ¹³CO₂. The respiratory quotient (RQ) decreased from value 0.98 to 0.46 directly after the spiking and increased again within 33 hours to a value of 0.72. This coincided with maximum ¹³CO₂ concentration rates (0.63 µmol m^-2 s^-1), indicating highest benzene degradation at 33 hours after the spiking event. The diffusion of benzene in the headspace and the biodegradation into ¹³CO₂ were simultaneously monitored and 12 days after the benzene spiking no measurable degradation was detected anymore. The RQ finally returned to a value of 0.96 demonstrating the reestablished pure aerobic respiration. In summary, this study shows the potential of Raman spectroscopy as versatile sensor technique to follow microbial biodegradation dynamics while simultaneously monitoring the underlying respiration behavior.