Sorption and remobilization behavior of 4-tert-octylphenol in aquatic systems.

The sorption and desorption of 4-tert-octylphenol in aquatic systems were studied to unravel the underlying controls. The sorption process was relatively slow, reaching a final sorption equilibrium in 10 d. The sorption process was interpreted as consisting of two stages: an initial rapid adsorption on particle surface followed by a slow intraparticle diffusion. The key parameter affecting the sorption of 4-tert-octylphenol by sediment is the occurrence of colloids, which in turn explains the so-called sediment concentration (SC) effect. This was confirmed by the increasing amount of colloids with increasing SC, and the relative constancy of intrinsic partition coefficient of 4-tert-octylphenol between sediment and water (K(p)) and between colloids and water (K(c)). Further evidence was from the nonoccurrence of SC effect from the addition of the same amount of colloids in different SC. The adsorption equilibrium is best described by the Freundlich model at low equilibrium concentrations. The adsorption of 4-tert-octylphenol was enhanced in the presence of salts, due to the salting out effect, and a salting constant of 1.3 L/mol was obtained. Desorption experiments showed that the release of 4-tert-octylphenol from contaminated sediments was highly dependent on the "age" of sediments, with kinetics of desorption being much faster in fresh sediments than in "aged" sediments.