Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland; School of Architecture, Civil and Environmental Engineering (ENAC), Ecole Polytechnique Fédérale de Lausanne (EPFL), GC A2 454, Station 18, CH-1015 Lausanne, Switzerland.
Eawag, Swiss Federal Institute of Aquatic Science and Technology, Überlandstrasse 133, CH-8600 Dübendorf, Switzerland.
Water Res. 2021 Feb 15;190:116707. doi: 10.1016/j.watres.2020.116707. Epub 2020 Nov 30.
Dissolved organic matter (DOM) plays a crucial role in the photochemical transformation of organic contaminants in natural aquatic systems. The present study focuses on the characterization of a specific effect previously observed for electron-rich phenols, consisting in an acceleration of the DOM-photosensitized transformation of target compounds at low concentrations (< 1 µM). This effect was hypothesized to be caused by DOM-derived "long-lived" photooxidants (LLPO). Pseudo-first-order rate constants for the transformation of several phenols, anilines, sulfonamide antibiotics and phenylureas photosensitized by Suwannee River fulvic acid were determined under steady-state irradiation using the UVA and visible wavelengths from a medium-pressure mercury lamp. A significant enhancement (by a factor of 2.4 - 16) of the first-order transformation rate constant of various electron-rich target compounds was observed for an initial concentration of 0.1 μM compared to 5 μM . This effect points to a relevant reactivity of these compounds with LLPO. For phenols and anilines the enhancement effect occurred only above certain standard one-electron oxidation potentials. From these data series the standard one-electron reduction potential of LLPO was estimated to be in the range of 1.0 - 1.3 V versus the standard hydrogen electrode. LLPO are proposed to mainly consist of phenoxyl radicals formed by photooxidation of electron-poor phenolic moieties of the DOM. The plausibility of this hypothesis was successfully tested by studying the photosensitized transformation kinetics of 3,4-dimethoxyphenol in aqueous solutions containing a model photosensitizer (2-acetonaphthone) and a model electron-poor phenol (4-cyanophenol) as DOM surrogates.
溶解有机质 (DOM) 在自然水系统中有机污染物的光化学转化中起着至关重要的作用。本研究集中于对先前观察到的富电子酚类物质的一种特殊效应进行特征描述，该效应表现为在低浓度（<1µM）下加速 DOM-光增敏转化目标化合物。该效应被假设是由 DOM 衍生的“长寿命”光氧化剂 (LLPO) 引起的。使用中压汞灯的 UVA 和可见光波长在稳态辐照下，确定了几种酚类、苯胺、磺胺类抗生素和苯脲类物质在苏万尼河腐殖酸光增敏下的转化的伪一级速率常数。与 5µM 相比，在初始浓度为 0.1µM 时，观察到各种富电子目标化合物的一级转化速率常数显著提高（提高了 2.4-16 倍）。与 LLPO 发生反应的化合物的这种增强效应仅在某些标准单电子氧化电位之上发生。从这些数据系列中，估计 LLPO 的标准单电子还原电位在 1.0-1.3 V 与标准氢电极之间。LLPO 主要由 DOM 中电子贫乏的酚类部分光氧化形成的苯氧自由基组成。通过研究含有模型光敏剂（2-乙酰萘）和模型电子缺乏酚（4-氰基苯酚）作为 DOM 替代品的水溶液中 3,4-二甲氧基苯酚的光增敏转化动力学，成功地检验了这一假设的合理性。
