Borisover, M., Institute of Soil, Water and Environmental Sciences, Volcani Center, ARO, Bet Dagan 50250, Israel
Graber, E.R., Institute of Soil, Water and Environmental Sciences, Volcani Center, ARO, Bet Dagan 50250, Israel

Interactions of a wide set of organic compounds with model natural organic matter (NOM, Pahokee peat) were examined using a new approach that converts aqueous sorption to compound transfer from n-hexadecane to the hydrated NOM. This conversion accounts for solute-water interactions and applies the same inert reference medium for all compounds of interest, making it possible to classify sorbates according to the strength of sorbate-NOM interactions. Differences in strength of organic compound interactions in the sorbed phase as great as 4-5 orders of magnitude are demonstrated. The strongest interactions were observed for compounds with well-established H-bonding potentials. Considering hydrocarbons and Cl-substituted hydrocarbons, aliphatic compounds gain more upon distribution from the n-hexadecane medium to NOM than do aromatic compounds. Sorption nonlinearity was tested by comparing the change in n-hexadecane-hydrated NOM distribution coefficient (K d,i) versus sorbed concentration for the different compounds. Only those compounds that interact most strongly with NOM demonstrated significant sorption nonlinearity, expressed by a strong reduction in K d,i as a function of sorbed concentration. The relationship between compound ability to interact with NOM and reduction in K d,i as a function of sorbed concentration can be used to characterize compound distribution among different sorption domains.