Research Group in Advanced Oxidation Processes (AdOx), Chemical Systems Engineering Center, Department of Chemical Engineering, University of São Paulo, Av. Prof. Luciano Gualberto, tr. 3, 380, São Paulo, SP, Brazil.
Dempster MS Lab, Chemical Systems Engineering Center, Department of Chemical Engineering, University of Sao Paulo, Av. Prof. Luciano Gualberto, tr. 3, 380, São Paulo, SP, Brazil.
Environ Sci Pollut Res Int. 2022 Jun;29(28):42231-42241. doi: 10.1007/s11356-021-17010-7. Epub 2021 Oct 22.
Polychlorinated biphenyls (PCBs) are a family of highly toxic, resistant, and persistent organic pollutants, among which 2-chlorobiphenyl (PCB-1) is one of the simplest. Most studies on PCBs' photochemistry are limited to their direct photolysis, while the important role of reactive photo-induced species (RPS) (hydroxyl radicals, HO; singlet oxygen, O; and triplet excited states of chromophoric dissolved organic matter, CDOM*) in removing PCBs in natural waters through indirect photolysis has not yet been evaluated. In this work, the rate constants of the reactions between aqueous PCB-1 and RPS were obtained under simulated solar radiation (450-W Xenon lamp and an AM 1.5 global filter) by competition kinetics, and the effects of the initial pollutant concentration and the physicochemical characteristics of the water were investigated. The direct photolysis quantum yield of PCB-1 in the range 290-800 nm was found as 1.60 × 10 mol Einstein. The value of k = (6.80 ± 0.09) × 10 L mol s is in good agreement with the literature. For O, k = (1.13 ± 0.20) × 10 L mol s, while for CDOM*, k = (2.44 ± 0.04) × 10 L mol s and k = (3.36 ± 0.04) × 10 L mol s were obtained using 4-benzoylbenzoic acid (CBBP) and anthraquinone-2-sulfonate (AQ2S) as CDOM proxies, respectively. These results show that the main pathways involved in PCB-1 photodegradation are the reactions with HO and CDOM* together with direct photolysis. In addition, the photodegradation of PCB-1 in sunlit waters was simulated using the kinetic model APEX (Aqueous Photochemistry of Environmentally Occurring Xenobiotics). According to simulations, a greater influence of the water depth and dissolved organic carbon concentration (DOC) on the persistence of PCB-1 is expected, being only slightly influenced by the concentrations of nitrite, nitrate, and bicarbonate. Finally, based on data reported for Brazilian surface waters, the average half-life (t) of PCB-1 is expected to vary from 2 to 14 days. In particular, the t in the Paranapanema River is estimated at 7 to 8 days.
多氯联苯 (PCBs) 是一组具有高度毒性、抗性和持久性的有机污染物，其中 2-氯联苯 (PCB-1) 是最简单的一种。大多数关于 PCBs 光化学的研究都局限于它们的直接光解，而活性光诱导物种 (RPS)（羟基自由基，HO；单线态氧，O；和发色溶解有机物的三重激发态，CDOM*）在通过间接光解去除天然水中的 PCBs 方面的重要作用尚未得到评估。在这项工作中，通过竞争动力学获得了在模拟太阳辐射（450-W 氙灯和 AM 1.5 全球过滤器）下，水相中 PCB-1 与 RPS 之间反应的速率常数，并研究了初始污染物浓度和水的物理化学特性的影响。在 290-800nm 范围内，PCB-1 的直接光解量子产率被发现为 1.60×10−4mol Einstein。值 k=(6.80±0.09)×10 L mol s与文献值一致。对于 O，k=(1.13±0.20)×10 L mol s，而对于 CDOM*，分别使用 4-苯甲酰苯甲酸 (CBBP) 和蒽醌-2-磺酸盐 (AQ2S) 作为 CDOM 探针时，k=(2.44±0.04)×10 L mol s 和 k=(3.36±0.04)×10 L mol s。这些结果表明，PCB-1 光降解的主要途径是与 HO 和 CDOM*的反应以及直接光解。此外，使用 APEX（环境 Xenobiotics 的水相光化学）动力学模型模拟了阳光下水体中 PCB-1 的光降解。根据模拟结果，水深和溶解有机碳浓度（DOC）对 PCB-1 的持久性的影响预计会更大，而亚硝酸盐、硝酸盐和碳酸氢盐的浓度对其影响则较小。最后，根据巴西地表水报告的数据，预计 PCB-1 的平均半衰期 (t) 将在 2 至 14 天之间变化。特别是在帕拉纳潘纳姆河，t 估计为 7 至 8 天。
