Sorption behavior of 17α-Ethynylestradiol at the soil colloid/solution interface from different sources: Influence of organic/inorganic components and hydrochemical conditions.

The interfacial interaction between colloids and endocrine disrupting chemicals EDCs significantly regulates their environmental behavior. In particular, how properties of colloids from different sources affect these interaction mechanisms is a key focus in environmental research. This study systematically investigates the interfacial sorption of 17α-Ethinyl Estradiol (EE2) on soil colloids from three pedogenic environments: black soil (BS), cinnamon soil (CS), and loess soil (LS). The interfacial interaction mechanisms were examined with a multi-technique approach (SEM, XPS, XRD, FTIR, BET). Three types of soil colloids have organic and inorganic components. The content of organic colloids serves as the crucial determinant for their interfacial interactions with EE2. Significantly, the hydrophobic partitioning of EE2 into soft carbon fractions emerges as the predominant sorption mechanism. BS exhibits a stronger sorption capacity for EE2 than CS and LS, primarily due to its higher organic matter and soft carbon content. The contribution rate of slow sorption in BS is markedly higher than in LS and CS, due to the greater content of hard carbon in BS, which offers more non-specific sorption sites and a higher quantity of microporous structures, resulting in improved micropore filling. For inorganic colloid components, illite and kaolinite contents mainly affect EE2 interfacial sorption. The -OH group in EE2, along with carboxyl and quinone groups from -OH and acetylene group oxidation, can form complexes with Fe and Al in inorganic colloids by chemical sorption. These findings highlight the potential for EE2 to be transported over long distances in subsurface environments via association with mobile soil colloids, which raises concerns about its persistence and potential to contaminate groundwater resources.