As disinfection by-products of parabens, halogenated parabens are frequently detected in aquatic environments and exhibit higher persistence and toxicity than parabens themselves. An interesting phenomenon was found that UV absorption redshift (∼45 nm) occurs after halogenation of parabens at circumneutral pH, leading to overlap with the spectrum of terrestrial sunlight. This work presents the first evidence on the direct photodegradation of seven chlorinated and brominated parabens under simulated sunlight. These halogenated parabens underwent rapid direct photodegradation, distinguished from the negligible degradation of the parent compounds. The photodegradation rate depended on their forms and substituents. The deprotonation of halogenated parabens facilitated the direct photodegradation. Brominated parabens exhibited higher degradation efficiency than chlorinated parabens, and mono-halogenated parabens had higher degradation than di-halogenated parabens. The pseudo-first-order rate constants (k_obs) for brominated parabens (0.075–0.120 min⁻¹) were approximately 7-fold higher than those of chlorinated parabens (0.011–0.017 min⁻¹). A quantitative structure-activity relationship (QSAR) model suggested that the photodegradation was linearly correlated with the C–X bond energies, electronic and steric effects of halogen substituents. The photodegradation products were identified using QTOF-MS analyses and a degradation pathway was proposed. The yeast two-hybrid estrogenicity assay revealed that the estrogenic activities of the photoproducts were negligible. These findings are important for the removal of halogenated parabens and predictions of their fate and potential impacts in surface waters.

作为对羟基苯甲酸酯的消毒副产品，卤代对羟基苯甲酸酯在水生环境中经常被检测到，并且比对羟基苯甲酸酯本身具有更高的持久性和毒性。发现了一个有趣的现象，在环境中性pH下对羟基苯甲酸酯卤化后，发生了紫外线吸收红移（〜45 nm），导致与地面太阳光光谱重叠。这项工作提供了在模拟阳光下直接光降解7种氯化和溴化对羟基苯甲酸酯的第一个证据。这些卤化的对羟基苯甲酸酯经历了直接的直接光降解，这与母体化合物的降解可忽略不计。光降解速率取决于它们的形式和取代基。卤代对羟基苯甲酸酯的去质子化促进了直接的光降解。溴化对羟基苯甲酸酯显示出比氯代对羟基苯甲酸酯更高的降解效率，单卤代对羟基苯甲酸酯比二卤代对羟基苯甲酸酯具有更高的降解率。伪一阶速率常数（ķ _OBS），用于溴化对羟基苯甲酸酯（0.075-0.120分钟^-1）的大约7倍的那些氯化对羟基苯甲酸酯的更高（0.011-0.017分钟^-1）。定量构效关系（QSAR）模型表明，光降解与卤素取代基的C–X键能，电子和空间效应线性相关。使用QTOF-MS分析鉴定了光降解产物，并提出了降解途径。酵母双杂交雌激素测定表明，光产物的雌激素活性可忽略不计。这些发现对于去除卤代对羟基苯甲酸酯以及预测其命运以及对地表水的潜在影响至关重要。