Adsorption and desorption of steroid hormones on saline soil

Soil organic matter content was the main driving factor affecting adsorption and desorption process of 17β-estradiol (E2) and 17α-ethynylestradiol (EE2) on saline soil. The adsorption and desorption of E2 and EE2 on three saline soils showed the similar behavior that soil with the highest organic content possessed the highest adsorption capacity and the lowest desorption capacity for E2 and EE2. The adsorption capacity of untreated soil samples (with organic matter) was larger than that of soil samples without organic matter. For soil with the largest adsorption capacity, adsorption capacity of E2/EE2 on the untreated soil and soil colloid (with organic matter) respectively reached 0.15/0.30 µg/g and 0.16/0.33 µg/g while the soil and soil colloid without organic matter hardly adsorbed pollutants. The adsorption capacity of E2/EE2 at the initial concentration of 100 µg/L was 25/15 times higher than that at the initial concentration of 5 µg/L. E2 and EE2 had the same adsorption sites on saline soil while EE2 possessed higher competition intensity for adsorption sites than E2. Pseudo-first-order model (R² = 0.995−0.986) and Langmuir model (R² = 0.989–0.999) could better fit the adsorption process of E2 or EE2. The thermodynamic study further showed that the adsorption of E2/EE2 on saline soil was a spontaneous exothermic process. The desorption capacity of EE2/E2 accounted for 40%/78% of the total adsorption capacity to possibly exert potential risk to the groundwater. The variation of the salinity led to the variation of soil organic carbon which subsequently changed the adsorption and desorption behaviors of endocrine disrupting chemicals in coastal saline soil. This study provides a new insight on the interfacial behavior of endocrine disrupting chemicals on saline soil.