| Abstract
| - We examine sorption of pyridine by soil organic matter(SOM) from different organic media including n-hexadecane,acetonitrile, acetone, and n-hexadecane mixtures witheither acetonitrile or acetone and compare it with sorptionfrom water. By using an activity-based comparison, wedistinguish between solvent-assisted and solvent-competitivesorption behavior. Pyridine was selected because itforms strong complexes with phenolic and carboxylicgroups, such that site interactions should dominateinteractions in SOM. It is anticipated that pyridine sorptionwill be illustrative of the importance of disrupting stronginteractions in a condensed, shrunken SOM phase for manyorganic compounds. It was generally found that activity-normalized pyridine uptake was assisted by polar solventmolecules rather than suppressed due to competition.An explanation is tendered on the basis of our earlierhypothesis of water-assisted disruption of polar SOM contacts.Certain polar moieties of dry SOM are unavailable forcompound sorption due to strong interactions betweenthem. By penetrating SOM structure, solvent molecules (andwater) solvate (hydrate) polar moieties creating newsorption sites. Solvent molecules must solvate both moietiesof the polar contact, such that the driving force for solvent-assisted sorption is solvation of the partner of thedisrupted contact that does not directly interact with thesorbate.
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