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The desorption irreversibility of naphthalenes and tetrachlorobiphenyl have no significant effects on the solution phase concentration of the two compounds because the process is not facilitated through a diffusion-limited transport. The diffusion-limited process, a mechanism cited as the major cause of low-level residual desorption, is exhibited only by surrogate materials which manifest homogenous and nonporous characteristics during organic composition.

A surrogate sediment is developed and evaluated to study the mechanisms involved in adsorption/desorption of contaminants. Verification of the surrogate sediment revealed that both it and the natural sediment displayed similar desorption behavior. It was also observed that the surrogate exhibited adsorption of contaminants through a hydrophobic interaction in the same magnitude as a natural sediment for two different hydrophobic organic contaminants.

A method involving batched adsorption followed by successive desorption was used to identify the factors which influence the release of pollutants from sediments. The experiments used the organic pollutants naphthalene and phenanthrene as model compounds and were designed to eliminate experimental artifacts which may have caused apparent adsorption/desorption hysteresis in past studies. Results showed that only 30%-50% of adsorbed pollutant was desorbed. The results are discussed in terms of adsorption/desorption hysteresis and irreversible adsorption.

Stable colloidal suspensions of buckminsterfullerene (nC60) in aqueous environments can significantly affect the fate and transport of hydrophobic organic contaminants by serving as a contaminant carrier. In this study, we examined enhanced transport of 2,2',5,5'-polychlorinated biphenyl (PCB) in saturated sandy soil columns by a variety of nC60 samples, including an nC60 sample prepared by the typical solvent exchange method, as well as eight natural organic matter (NOM) or surfactant-modified nC60 samples, prepared by phase-transferring C60 from toluene to an NOM or a surfactant solution. Whereas the NOM- and surfactant-modified nC60 samples have mobility similar to the unmodified nC60, their contaminant-mobilizing capabilities are significantly greater: breakthrough of PCB increases by 47.2 to 227% with the surfactant-modified nC60 samples and by 233 to 370% with the NOM-modified nC60 samples. The significantly enhanced contaminant-mobilizing capability of the modified nC60 is likely due to a combined effect of increased adsorption affinities and increased tendency of desorption nonequilibrium, likely caused by the changes of nC60 aggregation properties induced by the presence of NOM or surfactant. Findings in this study indicate that nC60 formed in different processes might have vastly different effects on contaminant fate and transport. [ABSTRACT FROM AUTHOR]