Two-dimensional compound-specific isotope analysis as a site diagnostic tool to assess the fate of aromatic hydrocarbons
Résumé
Our study focuses on the possibility of how the Rayleigh concept of isotope fractionation can be applied to quantify the extent of in-situ biodegradation at complex field sites. To this end, the selection of appropriate isotope enrichment factors representative of the specific biogeochemical conditions at the site is crucial. Published carbon and hydrogen isotope enrichment factors for the biodegradation of benzene, toluene and naphthalene determined in controlled microcosm studies under aerobic and anaerobic conditions, respectively, will be presented and compared to the extent of isotope fractionation observed at our field site. The combined evaluation of carbon and hydrogen isotope composition of the fore-mentioned aromatic hydrocarbons allowed deciphering sulphate-reducing microbial activity as the predominant biodegradation process in the field and to select an appropriate isotope enrichment factor for this site. The calculation of the extent of benzene biodegradation at the site was consistent based on both, carbon and hydrogen fractionation data. In our contribution we will demonstrate the usefulness of the two-dimensional CSIA approach to determine both the nature and the extent of in-situ biodegradation of volatile organic contaminants in the field. In addition, we will present new developments with respect to analytical techniques and demonstrate, based on experience from field studies, how isotope signatures can help revealing different pollution sources. Limitations and challenging aspects of the multi-dimensional isotope approach will be critically addressed.