Quaternary ammonium compounds (QACs) are not completely removed during wastewater treatment and are frequently detected in surface waters and sediments. The photochemical transformation of QACs has not been thoroughly investigated as a potential degradation pathway affecting their fate in the environment. Kinetic studies of common QACs with and without aromatic groups under simulated and natural sunlight conditions were performed with model sensitizers and dissolved organic matter to estimate photochemical half-lives in the aquatic environment. All QACs investigated react with hydroxyl radicals at diffusion-controlled rates (∼2.9 × 10⁹ to 1.2 × 10¹⁰ M⁻¹ s⁻¹). Benzethonium reacted via direct photolysis (Φ_BZT,outdoor = 1.7 × 10⁻² (mol Ei⁻¹)). Benzethonium also reacted with the triplet excited state model sensitizer 2-acetylnaphthalene, but evidence suggests this reaction pathway is unimportant in natural waters due to faster quenching of the triplet 2-acetylnapthalene by oxygen. Reactivity with singlet oxygen for the QACs was minimal. Overall, reactions with hydroxyl radicals will dominate over direct photolysis due to limited spectral overlap of sunlight emission and QAC absorbance. Photolysis half-lives are predicted to be 12 to 94 days, indicating slow abiotic degradation in surface water.

中文翻译：

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河流水中季铵化合物的光化学命运。

季铵化合物（QAC）在废水处理过程中并未完全去除，并且经常在地表水和沉积物中检测到。QACs的光化学转化尚未作为影响环境命运的潜在降解途径进行彻底研究。使用模型敏化剂和溶解的有机物，在模拟和自然阳光条件下，对带有或不带有芳族基团的常见QAC进行了动力学研究，以估计其在水生环境中的光化学半衰期。所有研究的QAC都以扩散控制的速率（约2.9×10 ⁹至1.2×10 ¹⁰ M ^-1 s ^-1）与羟基自由基反应。苯并鎓通过直接光解反应（Φ _BZT，室外= 1.7×10 ^-2（摩尔荣^-1 ））。苯并tho也与三重态激发态模型敏化剂2-乙酰基萘发生反应，但证据表明该反应途径在天然水中并不重要，因为三重态2-乙酰基萘被氧更快地猝灭。QAC与单线态氧的反应性极低。总体而言，由于太阳光发射和QAC吸收的光谱重叠有限，因此与羟基自由基的反应将比直接光解更为重要。预计光解半衰期为12至94天，表明地表水中非生物降解缓慢。