Effects of the antioxidant moieties of dissolved organic matter on triplet-sensitized phototransformation processes: Implications for the photochemical modeling of sulfadiazine. (1st January 2018)

• Record Type: Journal Article
• Authors: Vione, Davide; Fabbri, Debora; Minella, Marco; Canonica, Silvio
• Is Part Of: Water research. Volume 128(2018)
• Page Start: 38
• Page End: 48
• Publication Date: 2018-01-01
• Subjects: Antioxidants -- Sulfadiazine -- Electron donating capacity -- Dissolved organic matter -- Environmental photochemistry; Water -- Pollution -- Research -- Periodicals; 363.7394
• DOI: 10.1016/j.watres.2017.10.020
• Languages: English
• ISSNs: 0043-1354

Abstract

Abstract: Previous studies have shown that the photodegradation of some pollutants, induced by the excited triplet states of chromophoric dissolved organic matter ( 3 CDOM*), 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 − (pKa = 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 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 3 CDOM* 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. Graphical abstract: Image 1 Highlights: Phenol inhibits the triplet-sensitized degradation of SDZ. The acidic form of SDZ (HSDZ) undergoes lesser inhibition than basic SDZ (SDZ − ). The inhibition effect of organic matter was included into a photochemical model. Triplet sensitization is more important for HSDZ, and direct photolysis for SDZ − . SDZ is predicted to be quite photolabile in the natural environment.