Carbon isotope systematics of monoaromatic hydrocarbons: vaporization and adsorption experiments

This study investigates the carbon isotope systematics of benzene, toluene, ethylbenzene, and xylene monoaromatic hydrocarbons (BTEX) with regard to an improved understanding of the behavior of these compounds in the subsurface, particularly during remediation processes. We found that fractionation effects due to vaporization are small and positive for all compounds studied (Δ13Cvapor–liquid +0.2‰), and that fractionation effects due to soil adsorption are also likely to be small (13C-labeled compounds cannot be resolved from unlabeled compounds by HPLC). We also evaluated use of the isotopic composition of contaminants as tracers of source and migration in the subsurface by performing a survey of the bulk isotopic composition of commercially available sources of BTEX. The results indicate that a wide range of δ13C values exist (e.g., benzene, −23.87‰ to −29.40‰). Our work suggests that stable C isotope analysis has great potential for qualifying, and possibly quantifying, the subsurface processes affecting contaminant concentrations. In particular, stable isotope analysis may be especially beneficial for monitoring the efficacy of abiological and biological remediation efforts.