Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: Implications for the photochemical modeling of sulfadiazine

WATER RESEARCH

卷:128

Article

Vione, Davide^1,2  Fabbri, Debora¹  Minella, Marco¹  Canonica, Silvio³ 

[1] Univ Torino, Dipartimento Chim, Via P Giuria 5, I-10125 Turin, Italy

[2] Univ Torino, Ctr Interdipartimentale NatRisk, Largo Paolo Braccini 2, I-10095 Grugliasco, TO, Italy

[3] Eawag, Swiss Fed Inst Aquat Sci & Technol, Ueberlandstr 133, CH-8600 Dubendorf, Switzerland

关键词: Antioxidants;    Sulfadiazine;    Electron donating capacity;    Dissolved organic matter;    Environmental photochemistry;   

DOI  :  10.1016/j.watres.2017.10.020

来源: Elsevier

【 摘 要 】

Previous studies have shown that the photodegradation of some pollutants, induced by the excited triplet states of chromophoric dissolved organic matter ((CDOM)-C-3*), can be inhibited by back-reduction processes carried out by phenolic antioxidants occurring in dissolved organic matter (DOM). Here, for the first time to our knowledge, we included such an inhibition effect into a photochemical model and applied the model predictions to sulfadiazine (SDZ), a sulfonamide antibiotic that occurs in surface waters in two forms, neutral HSDZ and anionic SDZ(-) (pK(a) = 6.5). The input parameters of the photochemical model were obtained by means of dedicated experiments, which showed that the inhibition effect was more marked for SDZ(-) than for HSDZ. Compared to the behavior of 2,4,6-trimethylphenol, which does not undergo antioxidant inhibition when irradiated in natural water samples, the back reduction effect on the degradation of SDZ was proportional to the electron-donating capacity of the DOM. According to the model results, direct photolysis and center dot OH reaction would account for the majority of both HSDZ and SDZ- photodegradation in waters having low dissolved organic carbon (DOC < 1 mgC L-1). With higher DOC values (>3-4 mgC L-1) and despite the back-reduction processes, the (CDOM)-C-3* reactions are expected to account for the majority of HSDZ phototransformation. In the case of SDZ- at high DOC, most of the photodegradation would be accounted for by direct photolysis. The relative importance of the triplet-sensitized phototransformation of both SDZ(-) and (most importantly) HSDZ is expected to increase with increasing DOC, even in the presence of back reduction. An increase in water pH, favoring the occurrence of SDZ-with respect to HSDZ, would enhance direct photolysis at the expense of triplet sensitization. SDZ should be fairly photolabile under summertime sunlight, with predicted half-lives ranging from a few days to a couple of months depending on water conditions. (C) 2017 Elsevier Ltd. All rights reserved.

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