Improvement of bromide ions on the degradation of sulfamerazine by horseradish peroxidase-H2O2 system and its interaction mechanisms

• Br − markedly enhances SMR degradation by HRP depending on Br − concentration. • Some SMR are first formed into Br substituted products and then are degraded rapidly. • H 2 O 2 , pH and HRP level can adjust the formation of Br substitutes and BrO 3 − . • Nether the degradation products nor bromate in the process inhibit bacteria growth. Degradation of sulfonamide antibiotics (SAs) by horseradish peroxidase (HRP) is an eco-friendly and sustainable approach but with relatively low efficiency. In this study, we present bromide (Br − ) enhances sulfamerazine (SMR) degradation in the process of HRP/H 2 O 2 . The removal rate of SMR is positively related to Br − concentration and increases over three times within 4 h as Br − concentration increases from 0 to 1 mM. The mechanism of promoting SMR degradation is mainly through oxidation and substitution by reactive bromine, which comes from the oxidation of bromide ions by HRP/H 2 O 2 . Moreover, structure and kinetics analysis of HRP confirm that Br − altered the hydrophobic structure of HRP and made it accessible to bind with SMR. Furthermore, eight degradation products are determined by ESI-Q-TOF-MS mass spectrometry. SMR transformation mainly involves two pathways: one way is hydrolysis and then breaking up of sulfonamide bond to generate small fragments, and another is demethylation and Smile rearrangement firstly, then through hydroxylation, SO 2 extrusion, and bromine substitution to form other products. Bacteria growth experiments present the fact that neither the degradation products nor bromate formed in the process inhibited bacteria growth, indicating they have no obvious environmental risk. This study first reports Br − could accelerate the degradation of SMR by HRP and proposes the scheme of bromine species changes and SMR transformation pathways. This study not only develops a novel method to enhance the degradation of sulfonamides, but also provides a reference for the environmental risk assessment of sulfonamides.