Eawag, Swiss Federal Institute of Aquatic Science and Technology, CH-8600 Dübendorf, Switzerland.
Institute of Biogeochemistry and Pollutant Dynamics, ETH Zürich, CH-8092 Zürich, Switzerland.
Environ Sci Technol. 2021 Nov 16;55(22):15110-15122. doi: 10.1021/acs.est.1c03301. Epub 2021 Oct 29.
Dissolved organic matter (DOM) has a dual role in indirect phototransformations of aquatic contaminants by acting both as a photosensitizer and an inhibitor. Herein, the pH dependence of the inhibitory effect of DOM and the underlying mechanisms were studied in more than 400 kinetic irradiation experiments over the pH range of 6-11. Experiments employed various combinations of one of three DOM isolates, one of two model photosensitizers, the model antioxidant phenol, and one of nine target compounds (TCs), comprising several aromatic amines, in particular anilines and sulfonamides, and 4-cyanophenol. Using model photosensitizers without antioxidants, the phototransformation of most TCs increased with increasing pH, even for TCs for which pH did not affect speciation. This trend was attributed to pH-dependent formation yields of TC-derived radicals and their re-formation to the parent TC. Analogous trends were observed with DOM as a photosensitizer. Comparison of model and DOM photosensitizer data sets showed increasing inhibitory effects of DOM on TC phototransformation kinetics with increasing pH. In systems with anilines as a TC and phenol as a model antioxidant, pH trends of the inhibitory effect could be rationalized based on the reduction potential difference (Δ) of phenoxyl/phenol and anilinyl/aniline couples. Our results indicate that the light-induced transformation of aromatic amines in the aquatic environment is governed by the pH-dependent inhibitory effects of antioxidant phenolic moieties of DOM and pH-dependent processes related to the formation of amine oxidation intermediates.
溶解有机物 (DOM) 在水生污染物的间接光转化中具有双重作用，既是光敏剂又是抑制剂。在此，通过超过 400 个动力学辐照实验，研究了 DOM 的抑制作用的 pH 依赖性及其潜在机制，pH 范围为 6-11。实验采用了三种 DOM 分离物中的一种、两种模型光敏剂中的一种、模型抗氧化剂苯酚和九种目标化合物 (TCs) 中的一种的各种组合，包括几种芳香胺，特别是苯胺和磺胺类化合物，以及 4-氰基苯酚。使用没有抗氧化剂的模型光敏剂，大多数 TCs 的光转化随着 pH 的增加而增加，即使对于 pH 不影响形态的 TCs 也是如此。这种趋势归因于 TC 衍生自由基的形成产率和它们重新形成母体 TC 的 pH 依赖性。使用 DOM 作为光敏剂也观察到类似的趋势。模型和 DOM 光敏剂数据集的比较表明，随着 pH 的增加，DOM 对 TC 光转化动力学的抑制作用越来越大。在以苯胺作为 TC 和苯酚作为模型抗氧化剂的体系中，基于酚氧自由基/苯酚和苯胺基/苯胺偶联物的还原电位差 (Δ)，可以合理地解释抑制效应的 pH 趋势。我们的结果表明，芳香胺在水环境中的光诱导转化受 DOM 中抗氧化酚基的 pH 依赖性抑制作用以及与胺氧化中间体形成相关的 pH 依赖性过程的控制。
