Non-steroidal anti-inflammatory drugs are recognized widely as emerging contaminants. Sulindac has received additional attention as a prodrug in cancer treatment and because of its detection in drinking water and wastewaters. Nevertheless, there is limited knowledge about its kinetic behaviour and fate in the aquatic environment. In this work, the direct photolysis of sulindac, in which photochemical reactions were monitored and phototransformation products identified, was investigated under prolonged periods using UV-A and UV-B radiation and pH conditions (2 and 7) to evaluate the effect of the protonation state and the efficiency of the photolytic process. A novel kinetic mechanism has been proposed in which sulindac exhibits a consecutive reaction pathway, with pseudo-first order kinetics for rapid and reversible Z to E isomerization. Once photoequilibrium was reached, second-order degradation of the isomers in the presence of the new photodegradation products was observed. Photochemical transformation was faster under UV-B irradiation and lower pH, which suggests greater persistence of sulindac at more relevant environmental conditions of UV-A and pH 7. Two novel and major byproducts were identified, corresponding to the oxidative cleavage of the alkene exo to the indene system. The degradation pathway is mainly photoinduced, enhanced by acidic conditions and presumes the double bond as the most reactive site for the parent compound. This research demonstrates an approach for determining kinetics of compounds under challenging conditions, including, absorption from multiple electronic transitions, photoinduced products with unknown extinction coefficients, concentration dependence, photoinduced sensitizing intermediates, and speciation effects. Our work greatly improves our understanding of the degradation process of sulindac and will contribute to exposure assessments and treatment methodologies for this compound in impacted waters.

中文翻译：

---

非甾体抗炎药舒林酸的光解：阐明水中的动力学行为和光降解途径

非甾体抗炎药被广泛认为是新出现的污染物。舒林酸作为癌症治疗的前药受到了额外的关注，因为它可以在饮用水和废水中检测到。然而，关于其在水生环境中的动力学行为和归宿的知识有限。在这项工作中，使用 UV-A 和 UV-B 辐射和 pH 条件（2 和 7）长时间研究了舒林酸的直接光解，其中监测了光化学反应并鉴定了光转化产物，以评估质子化的影响光解过程的状态和效率。已经提出了一种新的动力学机制，其中舒林酸表现出连续的反应途径，具有快速和可逆Z 的准一级动力学到É异构化。一旦达到光平衡，在新的光降解产物的存在下观察到异构体的二级降解。在 UV-B 照射和较低的 pH 值下，光化学转化更快，这表明在更相关的 UV-A 和 pH 值 7 环境条件下舒林酸的持久性更强。 鉴定了两种新的主要副产物，对应于烯烃外链的氧化裂解到茚系统。降解途径主要是光诱导的，通过酸性条件增强，并假定双键是母体化合物最具反应性的部位。这项研究展示了一种在具有挑战性的条件下确定化合物动力学的方法，包括来自多个电子跃迁的吸收、具有未知消光系数的光致产物、浓度依赖性、光致敏化中间体和物种形成效应。我们的工作极大地提高了我们对舒林酸降解过程的理解，并将有助于对该化合物在受影响水域中的暴露评估和处理方法。