Structure-dependent degradation kinetics of sulfonamide antibiotics in gamma irradiation/periodate treatment: Reactive species and molecular descriptors

Abstract

Gamma irradiation with periodate (PI) has been shown to enhance the oxidation of organic contaminants, but the molecular factors governing the reactivity of structurally related antibiotics in this system remain unclear. Herein, nine commonly detected sulfonamide antibiotics (SAs) were selected as model compounds to investigate their structure-dependent degradation kinetics by gamma irradiation/periodate (gamma/PI) treatment. Reactive intermediates, molecular descriptors, transformation pathways, iodine species evolution, and water matrix effects were systematically investigated. The addition of PI markedly accelerated SAs degradation compared with gamma irradiation alone (gamma) and gamma irradiation combined with H2O2 (gamma/H2O2) or persulfate (gamma/PS). For sulfadiazine (SDZ), one representative SA, the observed rate constant in the gamma/PI system was 3.47, 2.09, and 2.01 times higher than those in the gamma alone, gamma/H2O2, and gamma/persulfate (PS) systems, respectively. Reactive species analysis suggested the involvement of multiple intermediates, including •OH, O2•–, O(3P), and 1O2, and 1O2 was the predominant species. The degradation rates varied substantially among the nine SAs, indicating structure-dependent reactivity. Among the examined molecular descriptors, log Kow showed the strongest correlation with log kobs (R2=0.87), suggesting that molecular hydrophobicity contributed to the kinetic differences among SAs in gamma/PI system, more hydrophobic SAs were degraded faster within this structurally related compound group. Degradation pathways of pollutants and transformed iodine species were elucidated. IO3- was the sole iodine species formed during reaction. Furthermore, the gamma/periodate system also maintained SDZ degradation capacity in representative water matrices and showed reactivity toward several structurally different micropollutants. These findings demonstrate that gamma/PI treatment can efficiently degrade SAs and that molecular hydrophobicity is useful for comparing their relative degradation rates in antibiotic-contaminated water treatment.