HYSTERESIS IN THE SORPTION AND DESORPTION OF HYDROPHOBIC ORGANIC CONTAMINANTS BY SOILS AND SEDIMENTS - 2 - EFFECTS OF SOIL ORGANIC-MATTER HETEROGENEITY

Sorption and desorption equilibria were measured for phenanthrene and 12 different soil and sediment samples using an experimental protocol described in the companion paper of this two-part series. Ten of the 1 2 sorbents studied were found to exhibit statistically significant sor ption-desorption hysteresis, with those containing diagenetically-alte red soil organic matter (kerogens) doing so to greater extents than th ose containing geologically-younger humic soil organic matter. Correla tions between the extent of hysteresis and the characteristics of C-13 -NMR spectra indicate that particle-scale soil organic matter heteroge neity significantly affects this phenomenon. The experimental observat ions are mechanistically consistent with a conceptual model based on p olymer sorption theory, the Dual Reactive Domain Model (DRDM). The wor k reinforces the general suitability of the DRDM for characterizing so rption-desorption interactions between hydrophobic organic contaminant s and soils and sediments. (C) 1998 Elsevier Science B.V.