Dipartimento di Chimica, Università degli Studi di Torino, Via P. Giuria 5, I-10125, Turin, Italy; Università di Torino, Centro Interdipartimentale NatRisk, Largo Paolo Braccini 2, I-10095, Grugliasco (TO), Italy.
Dipartimento di Chimica, Università degli Studi di Torino, Via P. Giuria 5, I-10125, Turin, Italy.
Water Res. 2018 Jan 1;128:38-48. doi: 10.1016/j.watres.2017.10.020. Epub 2017 Oct 9.
Previous studies have shown that the photodegradation of some pollutants, induced by the excited triplet states of chromophoric dissolved organic matter (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 (pK = 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). With higher DOC values (>3-4 mgC L) and despite the back-reduction processes, the 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.
先前的研究表明，某些污染物的光降解过程可被激发态生色溶解有机质（CDOM*）的三重态敏化作用所诱导，而溶解有机质（DOM）中存在的酚类抗氧化剂的还原逆反应过程可以抑制光降解的发生。在此，我们首次将这种抑制效应纳入光化学模型，并将模型预测应用于磺胺嘧啶（SDZ）。磺胺嘧啶是一种在地表水中以两种形式存在的磺胺类抗生素，分别为中性磺胺嘧啶（HSDZ）和阴离子磺胺嘧啶（SDZ，pK=6.5）。光化学模型的输入参数是通过专门的实验获得的，实验表明，SDZ 的抑制效应比 HSDZ 更为显著。与在天然水样中辐照时不发生抗氧化抑制的 2,4,6-三甲基苯酚相比，SDZ 的还原逆反应对其降解的影响与 DOM 的供电子能力成正比。根据模型结果，在低溶解有机碳（DOC<1mgC L）的水中，直接光解和 OH 反应将主导 HSDZ 和 SDZ 的大部分光降解过程。而在较高的 DOC 值（>3-4mgC L）下，尽管存在还原逆反应过程，CDOM*反应预计仍将主导 HSDZ 的光转化。对于高 DOC 下的 SDZ，大部分光降解将归因于直接光解。SDZ 和（最重要的是）HSDZ 的三重态敏化光转化的相对重要性预计会随着 DOC 的增加而增加，即使存在还原逆反应也是如此。水 pH 值的增加有利于 SDZ 的生成而不利于 HSDZ 的生成，这将有利于直接光解而不利于三重态敏化。在夏季阳光的照射下，SDZ 应该具有相当的光不稳定性，其预测半衰期范围从几天到几个月不等，具体取决于水质条件。
