The Role of Condensed Organic Matter in the Nonlinear Sorption of Hydrophobic Organic Contaminants by a Peat and Sediments

ABSTRACT This study examines the effect of soil organic matter heterogeneity on equilibrium sorption and desorption of phenanthrene, naphthalene, 1,3,5‐trichlorobenzene (1,3,5‐TCB), and 1,2‐dichlorobenzene (1,2‐DCB) by soils and sediments. Two estuary sediments, a Pahokee peat (PP; Euic, hyperthermic Lithic Haplosaprist), and two subsamples (base‐ and acid‐treated peat [TP] and acid‐treated peat [FP]) of the peat were used as the sorbents. The contents of black carbon particles were quantified with a chemical extraction method. Petrographical examinations revealed the presence of the condensed soil and sediment organic matter (SOM) in Pahokee peat. The Freundlich isotherm model in two different forms was used to fit both sorption and desorption data. The results show that the sorption and desorption isotherms are generally nonlinear and that the apparent sorption–desorption hysteresis is present for phenanthrene and TCB. Detailed analysis of sorption data for the tested sorbent–sorbate systems indicates that black carbon is probably responsible for sorption isotherm nonlinearity for the two sediments, whereas the humic substances and kerogen may play the dominant role in nonlinear sorption by the peat. This investigation suggests that the microporosity of SOM is important for the hydrophobic organic contaminant (HOC) sorption capacity on the peat.