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 12 sorbents studied were found to exhibit statistically significant sorption-desorption hysteresis, with those containing diagenetically-altered soil organic matter (kerogens) doing so to greater extents than those containing geologically- younger humic soil organic matter. Correlations between the extent of hysteresis and the characteristics of ¹³C-NMR spectra indicate that particle-scale soil organic matter heterogeneity significantly affects this phenomenon. The experimental observations are mechanistically consistent with a conceptual model based on polymer sorption theory, the Dual Reactive Domain Model (DRDM). The work reinforces the general suitability of the DRDM for characterizing sorption-desorption interactions between hydrophobic organic contaminants and soils and sediments.