Heat-activated peroxodisulfate oxidation of sulfapyridine: kinetics, transformation pathways, and nitrated byproducts

ABSTRACTThe widespread existence of sulfapyridine (SPD, a typical representative of sulfonamide) in natural environment has raised increasing interest because its potential to cause antibiotic-resistant genes. In this work, the degradation of SPD during heat-activated peroxodisulfate (heat/PDS) oxidation process was explored. The pseudo-first-order rate constant (k_obs) of SPD was 0.0149 min^-1 with 0.5 mM PDS at pH 7. The k_obs values were increased obviously with increasing PDS concentration. Such degradation was ascribed to the oxidation of sulfate radical (SO₄^•-) primarily according to radical quenching test. A total of 16 transformation products derived from hydroxylation, aniline moiety oxidation, and SO₂ extrusion & rearrangement pathways were identified by high-resolution mass spectrometry (HRMS) and theoretical calculations. Of which, the production of nitrated byproducts was attributed to the oxidation of aniline moiety in SPD molecule. The existence of natural organic matter (NOM) obviously reduced the degradation efficiency of SPD, while the effects of coexisting anions (i.e., NO₃^-, CO₃^2-, and Cl^-) were negligible. These findings illustrated that SPD can be effectively degraded but cause the nitrated byproducts generation during the heat/PDS oxidation process, which should be paid attention to when SR-AOPs is applied.