Hydration affected soil:water sorption processes of xenobiotics - experiments and modeling approaches

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SOM is not a passive sorbent but may be physically altered by the sorbate. This was already shown for water molecules and cations. Here it is hypothesized that sorption of organic xenobiotics takes part in the formation of SOM and induces changes in SOM physical structure and physicochemical properties. These changes feed back on sorption processes. Sorption and the (competitive) sorption of secondary sorbates have been shown to be sensitive measures enabling mechanistic (thermodynamic) modeling of processes. For that purpose, ten solutes offering a range of physicochemical properties and expected effects on SOM were selected and will be combined with three soil samples with different SOM quantity and composition and a polygalacturonic calcium network (Ca-PGA) as model SOM. Tested in batch trials and under varied conditions (cation crosslinking, temperature, solvent properties, organo-mineral association, aging time) data on sorption extent, nonlinearity, hysteresis, kinetics and competitiveness will be obtained. Correspondingly, SOM are thoroughly characterized before and after sorption induced changes and SOM-sorbate binding mechanisms are identified, using DRIFT, DSC, 1H-NMR, and methods for surface characterization. Data will be combined and modeled using mechanistic multisite and multiphase models and molecular mechanics computational modeling.