Exploring the Suitability of Compound-Specific Isotope Analysis to Study Degradation of Non-point Source Micropollutants on a Large Aquifer-Scale

• Applicants: Rani Bakkour, Ph.D.; Professor Dr. Martin Elsner
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Analytical Chemistry
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 456675267

Stable isotope fractionation is a well-established indicator for degradation of organic groundwater pollutants downstream of the source at contaminated sites (i.e. point source). Recently, attempts have addressed also diffuse contaminants (i.e. non-point source) such as pesticides at low μg/L to sub-μg/L concentrations. Here, compound-specific isotope analysis (CSIA) offers a powerful approach to demonstrate long-term turnover even over timescales otherwise inaccessible to investigations, or if fluctuating groundwater concentrations make assessments of degradation challenging. This is based on laboratory observations that isotope values change during biodegradation of typical micropollutants such as atrazine, providing an independent line of evidence of degradation. To facilitate field applications of micropollutant CSIA, however, critical methodological advances are needed at this stage. (1) Low micropollutant (sub-μg/L) concentrations in groundwater are dwarfed by comparatively high (mg/L) dissolved organic matter levels, which makes selective and sensitive CSIA of micropollutants challenging. Pillaring on Bakkour’s expertise in selective enrichment and cleanup techniques we, hence, aim for decisive further increases in the sensitivity of isotope analysis of groundwater samples. (2) Laboratory-derived isotope fractionation is usually determined at mg/L concentrations questioning the representativeness for field conditions. Pillaring on Elsner’s expertise in chemostat and fed-batch studies, we will revisit isotope fractionation of pesticide degradation in the low concentration regime to provide the basis for interpretations in the field. (3) To serve as indicator of contaminant breakdown, degradation-induced isotope shifts must exceed commercial products values. In a concerted German-Israeli effort we therefore take advantage of the Israeli coastal aquifer to conduct a survey of atrazine isotope values (δ13C, δ15N) in groundwater in a country where this notorious micropollutant is still applied, and to compare these isotope values to those analyzed in parallel in commercial atrazine products. (4) To critically evaluate our insight from isotope results, finally, Bernstein’s combined expertise in hydrology and the use of microbial tools will serve to provide additional lines of evidence for comparison. These combined advances will enable us to fundamentally explore the applicability of CSIA to micropollutant degradation at low concentrations in groundwater.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicant: Dr. Anat Bernstein