A mechanistic model for soil and sediment sorption-desorption hysteresis

Phenanthrene sorption and desorption equilibria were measured for twenty eight natural sorbents having different diagenetic profiles. The results of these measurements show that desorption hysteresis, as well as isotherm nonlinearity and the sorption affinity of these materials for phenanthrene, correlate inversely with the O/C atomic ratio of the associated SOM; that is, samples containing more physically condensed and chemically reduced SOM matrices appear to exhibit greater solute affinity, more nonlinear sorption equilibria, and greater desorption hysteresis. The observed relationships between diagenetic profiles and the sorption and desorption behaviors of SOMs are explained using a Distributed Reactivity Model (DRM) concept that appears to have more general applicability for characterization of the overall behavior of soils and sediments with respect to solute uptake and release than other models currently in use.