Monitoring stable carbon isotopes during biodegradation of toluene: Implications for contaminated site assessment

The potential for using compound-specific isotope analysis (CSIA) as a tool for monitoring the biodegradation of toluene was evaluated in laboratory experiments under anaerobic and aerobic conditions and at a contaminated field site. Within the +/-0.5‰ accuracy and reproducibility associated with CSIA, there was no significant change in the isotopic composition of the residual toluene despite greater than 85% aerobic biodegradation using two populations of mixed consortia and two different strains of Pseudomonas putida. The lack of a discernible isotopic fractionation signal produced during aerobic biodegradation in these laboratory experiments was also observed at the contaminated field site. In contrast, the anaerobic biodegradation of toluene, carried out under both methanogenic and sulfate-reducing conditions, produced a small (∼2‰), yet resolvable 13C-enrichment in the residual toluene at advanced stages of degradation. This thesis demonstrates that relating carbon isotope fractionation effects to intrinsic bioremediation of BTEX compounds will pose a challenge.