Particle-scale understanding sorption of phenanthrene on sediment fractions amended with black carbon and humic acid.

Black carbon (BC) and humic acid (HA) have been proposed to dominate the sorption behavior of phenanthrene in sediment. Nevertheless, little is known about the sorption mechanism that related to particle-scale by spiking of BC and HA in sediment particle size fractions. In this study, sorption isotherms for phenanthrene were determined in four particle-size sediment fractions (<2 μm, 2-31 μm, 31-63 μm and >63 μm) that amended with BC and HA, or not. The fitting results by Freundlich model indicated that the sediment particle size fractions amended with BC increased the sorption capacity and affinity for phenanthrene. Sediment coarser size fractions (31-63 μm and >63 μm) by spiking of BC contributed higher to sorption capacity factor (K) and nonlinearity factor (n) than the finer size fractions (2-31 μm and <2 μm). By contrast, the sediment particle size fractions amended with HA enhanced the sorption distribution coefficient (K), but reduced the sorption affinity for phenanthrene. All these phenomena are obviously affected by the distribution of heterogeneous organic matter that related to sediment particle-scale. Results of this work could help us better understand the impact of increased BC and HA content in sediments on the sorption of hydrophobic organic pollutants (HOCs) and predict the fate of HOCs in offshore sediments due to tidal action.