Effects Of Dissolved Organic Matter On Sorption And Desorption Behaviors Of Bisphenol A In Soils

Bisphenol A(BPA)is one of the common endocrine disrupting chemicals,which can seriously affect the human endocrine system,and its detection frequency is higher in groundwater and soil environment.Sorption is an important process affecting its migration in soil and groundwater.Dissolved organic matter(DOM)plays an important role in the sorption of pollutants.Two soils with different organic carbon(OC)contents were chosen as sorbents.Effects of endogenous and external DOM on BPA sorption/desorption behavior in soil were studied by microscopic characterization and batch experiments.The main conclusions are as follows:(1)The sorption of BPA in soil is mainly affected by OC content.Black soil has a higher capacity of BPA sorption than that of fluvo-aquic soil because of the high organic carbon content.At neutral solution pH,two soils have a similar normalized distribution coefficient(Koc),indicating that the sorption of BPA in soil was mainly affected by OC content.The results of the Freundlich model on the fitting of isothermal sorption data show that the sorption has a more obvious non-linearity,which indicates that the sorption mechanism includes both specific sorption and partition.BPA is more likely to be desorbed from the black soil.The pH of the solution has a weak effect on the sorption of BPA in two soils,indicating that the sorption of BPA on the soil at pH 7.0 was higher than that at pH 10.0.(2)The UV-visible spectrum and the three dimensional fluorescence spectra indicate that the endogenous DOM of fluvo-aquic soil has a higher aromaticity,higher molecular weight,more complex molecular structure and stronger hydrophobicity than that of black soil.Black soil DOM contains more humus-like substances,and its aromatic structural substituents are mainly carboxyl,hydroxyl,carbonyl and ester groups.The removal of endogenous DOM resulted in a slight decrease in OC content in two soils(2.62% ~ 3.23%)and an increase in the specific surface area.As a result,the removal of DOM caused a slight decrease in BPA sorption in soils.Desorption results showed that BPA desorption is more likely to occur in case that endogenous DOM was removed.(3)The Fourier infrared transform spectra show that there are more-COOH and-OH,carboxylic acids and phenols or alcohols in the external source DOM of natural humus.The effect of DOM on the sorption of BPA on fluvo-aquic soil was relatively small.For black soil,with increase of BPA concentration,the sorption of BPA was enhanced at the first stage and then inhibited at the second stage.Sorption enhancement might be due to the accumulation of sorption or co-sorption between BPA and DOM,and the decrease in sorption was caused by DOM covering on the soil surface,which prevented the sorption of BPA.There was no obvious effect on the desorption when the external DOM concentration was low.When the DOM concentration in solution is high,the desorption of BPA increases,and as the equilibrium concentration increases,the effect is more obvious.Both sorption and desorption indicate that DOM can interact with BPA through specific interaction.