4-chloro-3,5-dimethylphenol (PCMX), as a typical antimicrobial compound, has been widely used in medical products and cosmetics and has been detected in municipal wastewater. Significant concerns about its persistence and potential toxicity has been paid to in the aquatic environment. In this study, we explored UV and UV/persulfate (UV/PS) advanced oxidation process as potential options to remove PCMX for the first time. A steady-state kinetic model was established to simulate the experimental results and to predict the concentration of reactive oxidant species (ROS) under different reaction conditions. The second-order rate constants for PCMX reacting with SO₄^-• and HO• were determined to be (1.75 ± 0.04) ×10⁹ M^-1 s^-1 and (2.74 ± 0.14) ×10⁹ M^-1 s^-1, respectively, with SO₄^-• as the dominant species in PCMX decay by UV/PS. Interestingly, the pseudo-first-order rate constant of PCMX changed slightly in a broad pH range of 3.0 – 11.0, but was significantly increased when pH > 14.0. Natural organic matter (up to 5 mg/L as C) hindered the degradation rate of PCMX from 3.85 × 10^-4 s^-1 to 1.43 × 10^-4 s^-1 due to the effects of radical scavenging and the “inner filter” effect. Furthermore, the potential reactive sites (i.e., certain carbons in the benzene ring and phenolic hydroxyl group), in PCMX were identified based on the electronic structure of the molecule, using frontier molecular orbital theory, natural population analysis (NPA), and density functional theory (DFT) calculation. A variety of byproducts were identified using HPLC/MS/MS, which, in combination with the reactive site analysis, led to six main degradation pathways. Quantitative Structure Activity Relationship (QSAR) method of Toxicity Estimation Software Tool was applied to estimate the developmental toxicity of the byproducts.

4-氯-3,5-二甲基苯酚（PCMX）是一种典型的抗菌化合物，已广泛用于医疗产品和化妆品中，并已在城市废水中检测到。在水生环境中已经对其持久性和潜在毒性引起了极大的关注。在这项研究中，我们探索了UV和UV /过硫酸盐（UV / PS）先进的氧化工艺，这是首次去除PCMX的潜在选择。建立了稳态动力学模型，以模拟实验结果并预测不同反应条件下反应性氧化剂（ROS）的浓度。确定PCMX与SO _4- ^•和HO•反应的二阶速率常数为（1.75±0.04）×10 ⁹ M ^-1 s ^-1和（2.74±0.14）×10 ⁹ M ^-1 s ^-1，其中SO _4- ^•是UV / PS引起PCMX衰变的主要物质。有趣的是，PCMX的拟一级反应速率常数在3.0 – 11.0的宽pH范围内略有变化，但在pH> 14.0时显着增加。天然有机物（以C计高达5 mg / L）阻碍了PCMX的降解速率，从3.85×10 ^-4 s ^-1降至1.43×10 ^-4 s ^-1由于自由基清除作用和“内部过滤器”作用。此外，使用前沿分子轨道理论，自然种群分析（NPA）和密度泛函，基于分子的电子结构，鉴定了PCMX中潜在的反应位点（即苯环和酚羟基中的某些碳）。理论（DFT）计算。使用HPLC / MS / MS鉴定了多种副产物，与副反应位点分析相结合，导致了六种主要降解途径。使用毒性估计软件工具的定量结构活性关系（QSAR）方法来估计副产物的发育毒性。