Thermo-activated persulfate oxidation system for tetracycline antibiotics degradation in aqueous solution

• Increasing pH facilitated the degradation of TTC.
• Seven intermediates of TTC were identified by SPE–LC–MS/MS.
• TTC was transferred via N-demethylation, hydroxylation–oxidation and dehydration.
• Degradation of TCs followed the order of OTC > CTC > TTC.
• TTC was degraded much faster in artificial surface water.

Tetracyclines (TCs), including tetracycline (TTC), oxytetracycline (OTC), and chlorotetracycline (CTC), are frequently detected in natural waters, soils, and sediments, which raised great concerns about the proliferation of antibiotic resistant genes. This study investigated the degradation of TCs by sulfate radical produced by thermo-activated persulfate in aqueous solution. Increasing the temperature significantly enhanced the degradation of TTC, and the relationship between pseudo-first-order rate constant (kobs) and temperature obeyed Arrhenius equation. The degradation of TTC showed pH dependence, and kobs increased markedly with increasing pH. Seven intermediate products of TTC were temporarily identified by solid phase extraction and liquid chromatography–tandem mass spectrometry (SPE–LC–MS/MS). The transformation pathways of TTC included N-demethylation, hydroxylation–oxidation and dehydration. Detailed mechanisms for sulfate radical-induced N-demethylation and hydroxylation–oxidation were proposed. The degradation of the three TCs followed the order of OTC > CTC > TTC, highlighting the structure-specific reactivity. Interestingly, TTC was degraded extremely fast in artificial surface water (ASW), implying sulfate radical-based oxidation of TCs may be efficient in environmentally relevant conditions. The antimicrobial potency and ecotoxicological effects of the degradation products warrant further studies.

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