Eeffect Of Heavy Metals On Soil-water Interfacial Behavior And Bioavailability Of PAHs In Soils

Combined pollution by organic pollutants and heavy metals in soil is found in several areas of China. The interaction between organic pollutants and heavy metals plays an important role in their interfacial behavior and bioavailability. In this thesis, polycyclic aromatic hydrocarbons (PAHs) were chosen as the representative organic pollutants, while Cu(Ⅱ), Pb(Ⅱ) and Cr(Ⅲ) were selected as the representative heavy metals. The effect of heavy metals on the adsorption/desorption behavior of PAHs to soils was quantified with the quantum chemical calculation. The effect of heavy metals on the speciation of PAHs in soils was studied. The effect of heavy metals on the bioavailability of PAHs in soils was evaluated using a semi-permeable membrane device and a potted-plant experiment. The main findings of this thesis are summarized below:(1) Sorption capacity and nonlinearity of PAHs to the soils were enhanced by the coexisting heavy metals. The enhancement showed the order of Cr(Ⅲ)>Pb(Ⅱ)>Cu(Ⅱ), which was positively correlated with the hydrophobicity of PAHs and negatively correlated with the content of soil organic carbon (SOC). The interactive force between PAHs and heavy metal cations exhibited a good linear relationship with the sorption increment (AKd) of PAHs. The desorption hysteresis of PAHs was reduced by the heavy metals cations, showing that the sorption nonlinearity of PAHs was enhanced.(2) Heavy metals affect the speciation of PAHs in soils and reduced their bioavailability. The water-soluble and acid-soluble fractions of PAHs in soils were reduced by the heavy metals, where the bound fractions increased while the bioavailable PAHs mainly consisted of the water-soluble and acid-soluble fractions. The amount extracted by the semi-permeable membrane and the ryegrass accumulation of PAHs in soils were significantly reduced by heavy metals, following the order of Cr(Ⅲ)>Pb(Ⅱ)>Cu(Ⅱ).