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<p>Antibiotic contamination in rivers threatens ecosystem integrity and promotes the dissemination of antimicrobial resistance. Dissolved organic matter (DOM) regulates antibiotic photodegradation via photosensitization, light screening, and complexation. This study examined the occurrence of representative antibiotics in the mainstream of the Xiaoqing River and evaluated the role of DOM composition in regulating their photodegradation under simulated sunlight conditions. Target compounds included macrolides (erythromycin [ETM], roxithromycin [RTM], and tilmicosin), fluoroquinolones (norfloxacin [NOR] and ofloxacin), and a sulfonamide (sulfamethoxazole [SMX]). Field monitoring combined with laboratory irradiation experiments was conducted to characterize DOM fluorescence components (C1–C3) and quantify their effects on antibiotic photodegradation. Most target antibiotics in the Xiaoqing River mainstream occurred at concentrations below global average levels reported for surface waters. However, SMX exhibited a high detection frequency, and RTM was detected in all samples with the highest mean concentration, longitudinal analysis showed that total antibiotic concentrations increased downstream into the urban center, indicating a substantial municipal wastewater influence. EEM–PARAFAC analysis identified three prevalent DOM components: C1 (visible-region fulvic-like), C2 (UV-region fulvic-like), and C3 (tyrosine-like protein-like), with C2 dominating the DOM pool. Photodegradation experiments revealed pronounced DOM-specific effects. Humic acid (HA) generally enhanced degradation (e.g., ETM, <i>k</i><sub><i>obs</i></sub> = 0.2628&#xa0;h<sup>−1</sup>, R<sup>2</sup> = 0.81), whereas fulvic acid (FA) strongly inhibited NOR photodegradation (<i>k</i><sub><i>obs</i></sub> = 0.0006&#xa0;h<sup>−1</sup>). Tryptone alone suppressed photodegradation but produced synergistic enhancement when combined with HA and FA (NOR, <i>k</i><sub><i>obs</i></sub> = 0.0671&#xa0;h<sup>−1</sup>). In contrast, SMX exhibited limited photoreactivity under simulated sunlight in all DOM treatments. Overall, these results demonstrate that DOM composition is a key regulator of antibiotic photochemical fate in anthropogenically impacted rivers, and that interactions among DOM components and antibiotic molecular structures govern photodegradation behavior.</p>

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Occurrence of Representative Antibiotics and their DOM-Influenced Photodegradation in a River System

  • 期刊论文

  • 发表日期：

    2026年7月10日

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  • Zhaoxin Su,
  • Yankai Xiong,
  • Zhijie Wang,
  • Xiufen Wang,
  • jiayi Li,
  • Mujie Wang

摘要

Antibiotic contamination in rivers threatens ecosystem integrity and promotes the dissemination of antimicrobial resistance. Dissolved organic matter (DOM) regulates antibiotic photodegradation via photosensitization, light screening, and complexation. This study examined the occurrence of representative antibiotics in the mainstream of the Xiaoqing River and evaluated the role of DOM composition in regulating their photodegradation under simulated sunlight conditions. Target compounds included macrolides (erythromycin [ETM], roxithromycin [RTM], and tilmicosin), fluoroquinolones (norfloxacin [NOR] and ofloxacin), and a sulfonamide (sulfamethoxazole [SMX]). Field monitoring combined with laboratory irradiation experiments was conducted to characterize DOM fluorescence components (C1–C3) and quantify their effects on antibiotic photodegradation. Most target antibiotics in the Xiaoqing River mainstream occurred at concentrations below global average levels reported for surface waters. However, SMX exhibited a high detection frequency, and RTM was detected in all samples with the highest mean concentration, longitudinal analysis showed that total antibiotic concentrations increased downstream into the urban center, indicating a substantial municipal wastewater influence. EEM–PARAFAC analysis identified three prevalent DOM components: C1 (visible-region fulvic-like), C2 (UV-region fulvic-like), and C3 (tyrosine-like protein-like), with C2 dominating the DOM pool. Photodegradation experiments revealed pronounced DOM-specific effects. Humic acid (HA) generally enhanced degradation (e.g., ETM, kobs = 0.2628 h−1, R2 = 0.81), whereas fulvic acid (FA) strongly inhibited NOR photodegradation (kobs = 0.0006 h−1). Tryptone alone suppressed photodegradation but produced synergistic enhancement when combined with HA and FA (NOR, kobs = 0.0671 h−1). In contrast, SMX exhibited limited photoreactivity under simulated sunlight in all DOM treatments. Overall, these results demonstrate that DOM composition is a key regulator of antibiotic photochemical fate in anthropogenically impacted rivers, and that interactions among DOM components and antibiotic molecular structures govern photodegradation behavior.