Adsorption and Desorption Behaviors of Four Endocrine Disrupting Chemicals in Soils from the Water-Level Fluctuation Zone of the Three Gorges Reservoir, China

As a special zone of periodic impoundment and flooding in the Three Gorges Reservoir (TGR), the water-level fluctuation zone (WLFZ) of TGR acts as a short-term ‘sink’ for hydrophobic endocrine disrupting compounds (EDCs). This study was conducted on the adsorption/desorption kinetics and equilibriums of four target EDCs (i.e., estrone (E1), 17β-estradiol (E2), 17α-ethynylestradiol (EE2), and bisphenol A (BPA)) in soil samples (i.e., S1, S2, S3, and S4), which were collected from different elevation gradients of the WLFZ at Qingxi Town of Fulin in TGR. Under the influence of the water-level fluctuation, S1 and S2 from the frequent inundation area had smaller particle sizes with more organic matter (OM) and total nitrogen (TN) content, whereas soils S3 and S4 from the long-term exposed area had a higher fraction of sand with lower OM and TN. All four target EDCs could achieve an adsorption equilibrium within 24 h, and the kinetics of the adsorption/desorption fitted the pseudo-second-order model excellently. The adsorption/desorption isotherms of the EDCs were better described by the Freundlich equation. The adsorption capacity decreased, as 17α-ethynylestradiol (EE2) > 17β-estradiol (E2) > estrone (E1) > bisphenol A (BPA), in each tested soil. S1 and S2 exhibited a greater capacity but a lower degree of nonlinearity to adsorb the target EDCs than S3 and S4. The values of the Gibbs free energy suggested that the EDCs adsorption in the tested soils was dominated by unstable physical adsorption. The desorption hysteresis of E1, E2, and EE2 were stronger in S1 and S2, whereas the BPA exhibited weak or almost no hysteresis in all of the tested soils. The substantial water-level fluctuation imposed on the TGR would have a continuous influence on the EDCs adsorption/desorption by altering the soil properties. Thus, long-term monitoring and further research of EDCs in this region are urgent