Adsorption–Desorption Interaction Characteristics of Ammonium Nitrogen and Typical Antibiotics in Soil

Conventional pollutants like nitrogen and emerging contaminants such as antibiotics are widely detected in soil and water, and exhibit combined pollution characteristics. Meanwhile, nitrogen and antibiotics migrate together during infiltration and are influenced by adsorption–desorption behaviors in soil. However, existing studies have mainly focused on the adsorption–desorption behaviors of single nitrogen or antibiotics, with fewer studies focused on the adsorption–desorption interactions between nitrogen and antibiotics. To address this gap, the adsorption–desorption dynamics of NH₄⁺-N coexisting with two antibiotics—ciprofloxacin (CIP) and tylosin (TYL)—were investigated by batch equilibrium experiments in this study. The isothermal adsorption data were simulated by Langmuir, Freundlich, and linear models, with the Langmuir model (R²>0.99) being more suitable than the Freundlich and linear models to describe the adsorption of NH₄⁺-N. The increase of CIP concentration inhibited the adsorption of NH₄⁺-N, but no significant influence was observed on the adsorption of NH₄⁺-N with the increasing of TYL concentration. The isothermal adsorption characteristics of CIP and TYL were a better fit for the Freundlich model (R²>0.99). The increase of NH₄⁺-N concentration inhibited the adsorption of CIP, whereas adsorption of TYL was promoted by lower NH₄⁺-N concentration but inhibited at higher concentration. The hysteresis index (HI) reflects the irreversibility of adsorbate retention on adsorbents during desorption. After calculating the HI of NH₄⁺-N, CIP and TYL, it was found that NH₄⁺-N exhibited an HI range of 0.370–2.306, whereas the HI values of both CIP and TYL were below 0.7, indicating significant desorption hysteresis. This suggests that CIP and TYL are prone to remain in soil and form persistent residues. The results of this study revealed the adsorption–desorption interaction characteristics between NH₄⁺-N, CIP, and TYL, providing fundamental data to further understanding the environmental behaviors of nitrogen and antibiotics in soil. The BRIEF REPORT is available for this paper at http://www.ykcs.ac.cn/en/article/doi/10.15898/j.ykcs.202503290065.