Contrasting carbon isotope fractionation during biodegradation of trichloroethylene and toluene: Implications for intrinsic bioremediation

In experiments involving anaerobic biodegradation of trichloroethylene (TCE), δ13C values for residual TCE changed from −30.4‰ to values more enriched than −16‰. All data exhibit a consistent correlation between δ13C value of the residual TCE and the extent of biodegradation of TCE, described by a fractionation factor (α) of 0.9929. In contrast, during aerobic biodegradation of toluene by two separate mixed consortia, no change in δ13C value of the residual toluene was observed within analytical uncertainty (0.5‰). Stable carbon isotopes have the potential to be a useful indicator for identification and monitoring of intrinsic bioremediation of chlorinated hydrocarbons such as TCE. Conversely, for aromatic hydrocarbons such as toluene, more conservative isotopic values may instead be more applicable as a means of source differentiation at sites with a history of multiple spills.