Isotope fractionation associated with sorption of polar and ionogenic pesticides to soil horizon A and B components - Fundamental studies and modelling
Subproject: Isotope fractionation associated with natural reactions and sorption of pesticides: Analytical development and initial process studies

Principle investigators: Dr. M. Elsner, Prof. Dr. P. Maloszewski

Co-workers: S. Reinnicke, A. Meyer


Methodological approach
Compound specific isotope analysis (CSIA) can be used to investigate and monitor the fate of organic contaminants in groundwater and soil systems. CSIA measures the isotope composition of a compound at natural abundance. The ratio of the isotopes (13C/12C, 2H/1H, 15N/14N, 18O/16O) is given relative to the international standard (Peedee Belemnite for carbon). On the one hand, different isotopic compositions of the same chemical substance can be used as fingerprints to determine the source of contamination. On the other hand, it may serve to verify that biological degradation occurs. It is well established that during chemical reactions and biodegradation, the heavier isotopes become enriched within the remaining substrate and the light isotope becomes enriched on the site of the products.
But it is not well established to what extend sorption of pesticides at soil components leads to similar isotope fractionation in the pesticides. CSIA as a tool to verify biodegradation might also serve as tool to investigate natural reactions as well as sorption associated with isotope fractionation.

Objectives and hypotheses
- Pioneer Compound Specific Isotope Analysis (CSIA) as a novel approach to investi-gate pesticide sorption and natural reactions in soil.
The isotope enrichment factor for C and N during transformation processes such as sorption to different model soil compartments will be investigated. Both reversible and irreversible sorption processes will be investigated with respect to the question whether these different sorption mechanisms contribute to significantly different isotope shifts. In addition to batch experiments HPLC column experiments will be performed, because the larger number of theoretical plates allows more precise measurements of isotope fractionation.
- Develop carbon and nitrogen stable isotope analysis for bentazone, atrazine and other pesticides (test derivatization agents, ensure accuracy of isotope measurement)
For nitrogen isotope measurements derivatization does not introduce artefacts as long as it occurs qualitatively. For carbon measurements one or more carbon atoms are added to the substances and therefore the isotope composition changes. Goal of the derivatization is to find a simple method to derivatise the substance, to add if possible only one carbon atom and to be able to correct for the isotope signature of the carbon which is added to the substance. As alternative to GC/C-IRMS, little volatile substances may instead be analysed by HPLC/IRMS. To this end, it is another major objective to develop carbon isotope analysis by HPLC/IRMS methods as alternative to GC/C-IRMS.

Cooperation within the priority programme
Prof. Dr. S. Haderlein, Prof. Dr. M.H. Gerzabek

Elsner1
Poster Elsner

Publications

Reinnicke, S., Bernstein, A., Elsner, M. 2010. Small and reproducible isotope effects during methylation with trimethylsulfonium hydroxide (TMSH): A convenient derivatization method for isotope analysis of negatively charged molecules. Anal. Chem. 82, 2013-2019.