The role of dissolved organic matter in sorption process of polycyclic aromatic hydrocarbons on soils and sediments

The sorption behavior was determined for three model polycyclic aromatic hydrocarbons (PAHs), i.e., naphthalene (NAP), phenanthrene (PHN) and pyrene (PYR), from water to six soil and sediment samples. The humic substances dissociating from soils and sediments were characterized by liquid-state ¹H NMR. The experiments show that the sorption of PAHs on soils and sediments is bimodal. In initial stage, the properties of dissolved humics are more important for as compared with solid particles. The soils or sediments present larger DOC content produce the stronger sorption capacities for three PAH molecules except for sediment III. The relatively lower K_f´ values for sediment III possibly result from its less hydrophobic index of dissolved organic matter. With the increase of contacting time, the physicochemical properties of soils or sediment play more significent role. The larger SSA and smaller particle size produce stronger sorption capacities. These findings suggest that the dissolved organic matter is a nonnegligible consideration in studying PAH sorption process and only taking into account the solid humic characteristics cannot fully understand the whole sorption mechanism.