Sorption of hydrophobic organic compounds (HOCs) in soils and geologic materials is of growing concern because of the strong affinity of these compounds for soil colloids and the potential risks associated with their long-term persistence in the environment. It is well accepted that soil organic matter (SOM) is the predominant sorbent of HOCs. The sorption of HOCs by humic substances has been extensively studied, and it is generally believed that partitioning and adsorption-like mechanisms are involved in the sorption process [1-5]. According to the dual-mode model [2,3], sorption in rubbery domains is anticipated to exhibit a linear (partitioning) isotherm contribution, while sorption in glassy domains is expected to represent the nonlinear (Langmuir) contribution.