Desorption, Persistence, and Leaching of Dibenzofuran in European Soils

Polycyclic aromatic hydrocarbons (PAHs) and their heterocyclic analogs (hetero-PAHs) represent the predominant chemical classes in many contaminated soils. Despite the fact that hetero-PAHs are more soluble and hence potentially more mobile and bioavailable than similar nonsubstituted compounds, the existing information about the fate of these compounds in the soil environment is limited. In this article, laboratory experiments were designed to assess the desorption, persistence, and leaching behavior of the hetero-PAH dibenzofuran in four European soils with different physicochemical characteristics. Previous research has shown that organic matter was important in the extent of sorption of dibenzofuran by the soils studied, although sorption was not predictable exclusively from the organic carbon content. Dibenzofuran desorption isotherms showed little hysteresis, in particular from higher equilibrium points of the sorption isotherms, indicating weak interaction mechanisms between dibenzofuran and the soils. The half-life of dibenzofuran in the soils during incubation experiments ranged between 5 and 55 d, depending on soil type and experimental conditions. In general, the persistence of dibenzofuran decreased with the organic carbon content of the soils (0.56–2.09%) and with temperature (4°C/20°C) and increased with the initial concentration of the chemical in soil (10 mg kg⁻¹/100 mg kg⁻¹). Leaching tests, performed in hand-packed and undisturbed soil columns, indicated that dibenzofuran is likely to move slowly through the soil profile, although dissolved organic matter and soil structure can influence the amount of dibenzofuran leached. The effect of dissolved organic matter on leaching of dibenzofuran was found to be soil dependent and less important than the effect of soil structure.