Sorption mechanisms of coexisting PAHs on sediment organic fractions

Sorption of polycyclic aromatic hydrocarbons (PAHs) to natural sediment and isolated organic fractions, including demineralized organic matter (DM), condensed organic matter (COM), and black carbon (BC), was investigated to provide insight into sorption mechanisms. The organic carbon normalized distribution coefficient K(OC) measured for DM was 0.8 to 3.0 times higher than that of bulk sediment, indicating the physical protection of favorable PAH sorption domains by mineral conformation; that is, mineral enwrapping was supposed to prevent physically the accessing process of the sorbate molecules to the sorption domain. Surface area-normalized K(OC) values showed that the differences between COM and BC in the sorption capability were caused largely by their surface areas, additionally indicating the importance of solid physical structure. In considering specific interactions, mature organic fractions with polyaromatic sheets were implied to be affected by π-π interaction, whereas the DM sample that contained the electron-repulsive N-H group hardly sorbed PAHs via this interaction. Besides sorbent characteristics, PAH properties were also assumed to influence the sorption process. The hydrophobicity normalized sorption coefficient increased in the order of fluoranthene> phenanthrene> pyrene> fluorine> acenaphthene, with pyrene showing an exceptional order.