Compound-Specific Isotope Analysis for Monitoring Degradation of Organic Contaminants

Anat Bernstein, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel

Quantifying degradation extents of contaminants in the subsurface is a desired goal for management of water resources. Nevertheless, solving this task using spatial and temporal shifts in the contaminants concentration is often not sensitive enough. In the last ca. 15 years, compound specific isotope analyses (CSIA) was introduced as complementary approach that can provide better insight on in-situ degradation processes.

The application of the CSIA concept will be demonstrated in my talk by two different case studies: The first case study attempted in quantifying the degradation extent of the explosive compound RDX along a contamination plume within the Israeli Coastal Aquifer. In this study, controlled laboratory experiments have shown that RDX degradation is accompanied by ¹⁵N enrichment. These experiments enabled to determine the specific enrichment factors (ε) for the reaction. Further on, field survey has shown that RDX composition becomes enriched in ¹⁵N along the contamination plume, where δ¹⁵N composition of RDX was up to ca. 10‰ more enriched in downstream samples than its composition at the source. Using the enrichment factors obtained in the laboratory study, it was possible to estimate RDX degradation extent in-situ, along this plume. The second case study attempted in quantifying the degradation extent of the flame retardant TBNPA in Neot Hovav industrial site. In this case study, groundwater samples showed similar δ¹³C composition of TBNPA, indicating that biodegradation is not a significant process.  These findings are of great importance for choosing the proper remediation scheme for the site.