Sorption of phenanthrene, naphthalene and o-xylene by soil organic matter fractions

Sorption of hydrophobic organic compounds (HOCs) is an important process for determining their fate and transport in soils and sediments. Soil/Sediment organic matter (SOM) is believed to be the dominant sorbent but the mechanisms are not thoroughly understood. In this study, we examined the sorption of phenanthrene, naphthalene and o-xylene by a mineral soil, its base-extracted soil (BE), humic acid (HA), and deashed humin (DH) using a batch equilibration technique. All isotherms were nonlinear and nonlinearity increases in the order: soil HA < soil deashed humin < soil < BE. Aliphatic-rich deashed humin (DH) exhibited the highest sorption capacity for HOCs while mineral associated humin (BE) had the strongest nonlinearity. The results indicate that aliphatic components of SOM contribute greatly to sorption of HOCs in soils and sediments, which needs to be accounted for in determining the fate and availability of HOCs in the environment.