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<p>This study clarifies the key environmental mechanisms controlling the occurrence forms and transformation of typical antibiotics, namely norfloxacin (NOR), oxytetracycline (OTC) and sulfamethoxazole (SMX), in the Zaohe-Weihe River estuary. Sequential flocculation method was employed to separate the freely dissolved and DOM-associated forms. The results indicate that antibiotics mainly exist in freely dissolved form in the aquatic environment. Groundwater conditions characterized by higher DOC and anoxia significantly enhanced the complexation of antibiotics with dissolved organic matter (DOM). Variations in DOM content, pH, and ionic composition collectively regulate the speciation of antibiotics. Organic matter content is the primary factor governing DOM-associated antibiotic, showing a significant positive correlation (<i>p</i> &lt; 0.05). Furthermore, hydrogen bonding, surface complexation, and hydrophobic interactions were identified as the drivers of the association processes. Near-neutral conditions enhanced DOM binding of NOR and OTC, whereas SMX showed greater association under alkaline conditions. Coexisting ions further modulated partitioning through ionic strength effects and competitive binding. These findings advance the mechanistic understanding of antibiotic environmental behavior in estuarine systems, providing a scientific basis for more accurate contamination assessment.</p>

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Occurrence forms and transformation mechanisms of typical antibiotics in the aquatic environment of the Zaohe-Weihe River estuary

  • 期刊论文

  • 发表日期：

    2025年10月16日

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  • Wenqing Wang,
  • Lei Duan,
  • Yaqiao Sun,
  • Siyue Yang,
  • Fei Ye,
  • Houtao Xiong,
  • Fei Shi,
  • Chen Yang

摘要

This study clarifies the key environmental mechanisms controlling the occurrence forms and transformation of typical antibiotics, namely norfloxacin (NOR), oxytetracycline (OTC) and sulfamethoxazole (SMX), in the Zaohe-Weihe River estuary. Sequential flocculation method was employed to separate the freely dissolved and DOM-associated forms. The results indicate that antibiotics mainly exist in freely dissolved form in the aquatic environment. Groundwater conditions characterized by higher DOC and anoxia significantly enhanced the complexation of antibiotics with dissolved organic matter (DOM). Variations in DOM content, pH, and ionic composition collectively regulate the speciation of antibiotics. Organic matter content is the primary factor governing DOM-associated antibiotic, showing a significant positive correlation (p < 0.05). Furthermore, hydrogen bonding, surface complexation, and hydrophobic interactions were identified as the drivers of the association processes. Near-neutral conditions enhanced DOM binding of NOR and OTC, whereas SMX showed greater association under alkaline conditions. Coexisting ions further modulated partitioning through ionic strength effects and competitive binding. These findings advance the mechanistic understanding of antibiotic environmental behavior in estuarine systems, providing a scientific basis for more accurate contamination assessment.