Enhanced transformation of sulfadiazine by horseradish peroxidase activated persulfate progress: Characteristics, pathways, mechanisms, and ecotoxicities

Abstract

The catalysis of horseradish peroxidase (HRP) and activated persulfate (PDS) are both feasible ways to remove heterologous contaminants. This work demonstrated that HRP/H₂O₂ can effectively activate PDS to degrade sulfadiazine (SDZ). Types of salt ions could suppress the efficiency of the system through free radical scavenging of anions and superposition effect of part cations, followed the series: FeCl₃ > CaCl₂> NaCl > NH₄Cl > NaHCO₃ > NaNO₃. 5 mg L⁻¹ humic acid (HA) could decrease 5.14 times transformation rate constants K. Interestingly, the addition of the above salt ion can slightly restore the level of inhibition by HA. Fourteen possible intermediates were identified, and potential pathways and mechanisms were proposed. There were three pathways to transform SDZ in systems. HRP directly acted on SDZ after being activated by H₂O₂, including δ/γ site-cleavage, hydroxylation, denitrification, carbonylation, and sulfur oxide (SO₂/SO₃) extrusion. In addition, both HRP activated PDS and thermal/H₂O₂, generating SO₄^-• and •OH for the oxidation of SDZ, including oxidation of the α-amine, hydroxylation of the benzene ring, ζ position cleavage on SDZ. The electron paramagnetic resonance (EPR) technique verified that specific free radicals had been generated and that HRP could activate the PDS process. The ECOSAR software predicted the biotoxicity of most transformation products was less toxic than the parent compound. The results of luminescence inhibition of Vibrio fischeri indicated the low toxicity of SDZ intermediates. These findings may help us expand our knowledge of PDS activation approaches and may also provide a potential method for antibiotic removal in environments.