Hydration-facilitated sorption of specifically interacting organic compounds by model soil organic matter

Site-specific interactions between organic compounds and soil organic matter (SOM) may occur at surface sites or limited interior sites; limited sites can have either a specific force component (e.g., hydrogen bonding) or a nonspecific force component (van der Waals) or both. This research addresses sorption specificity to gain an understanding of SOM structure. Sorption of phenol, pyridine, and atrazine on Pahokee peat, a mineral-free SOM endmember, was measured as a function of so lute activity in hydrated and dehydrated conditions. Sorption of phenol and pyridine from water at low solute activities was the same as from n-hexadecane; sorption at high solute activities was much greater from water than from n-hexadecane. Uptake of atrazine at high activities was not influenced by peat hydration. Sorption isotherms measured in nonaqueous systems were more nonlinear than those measured in water. The increase in sorption on hydrated peat at high pyridine and phenol activities is attributed to an increase in sorption sites resulting from penetration of solute molecules between polar peat contacts which are either previously solvated by water or solvated during penetration of the solute. High solute activities are necessary for simultaneous disruption of multiple points of contact in the hydrated SOM macromolecular complex.