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Photodegradation is a major elimination route of many pharmaceutically active compounds (PhACs) in natural surface waters, yet their photolytic behavior in estuarine waters with salinity gradient change is largely unknown. Herein, sulfamethazine and carbamazepine were taken as representative PhACs to explore the photolytic kinetic differences in Qinzhou Bay estuarine water samples collected from upper to lower reaches. Rapid photodegradation of sulfamethazine was found in lower estuarine water relative to upstream estuarine water; whereas for carbamazepine, photolytic rate was inversely proportional to the salinity of estuarine waters. Experiments with extracted estuarine dissolved organic matter (E-DOM) imply that the multivariate effects of triplet-excited E-DOM (3E-DOM∗) and halide ions are responsible for the enhancement photolysis of sulfamethazine. Radical scavenging experiments suggest that the photolysis enhancement can be ascribed to the contribution of reactive halogen species (RHS), while their contribution to carbamazepine is negligible and 3E-DOM∗ is the dominant reactive species for its photodegradation. This indicates that the reactivity differences with RHS and 3DOM∗ affect the photolytic kinetics of PhACs from upper estuarine waters to lower reaches, which is also supported by a good linear relationship between the ratios of photolytic rates for ten PhACs in E-DOM solution with/without halides and the ratios of the reactivity of these pollutants with RHS and 3DOM∗. These findings show that the different reactivity of PhACs with 3E-DOM∗ and RHS influences the photolytic kinetics in estuarine waters with different salinity, and highlights the photochemical behavior of organic micropollutants from upstream to downstream estuarine waters. Copyright © 2021 Elsevier Ltd. All rights reserved.


Zhichao Hou, Qi Fang, Huaying Liu, Yingjie Li, Qun Zhao, Zhiyu Zhang, Yajie Lei, Senlin Tian. Photolytic kinetics of pharmaceutically active compounds from upper to lower estuarine waters: Roles of triplet-excited dissolved organic matter and halogen radicals. Environmental pollution (Barking, Essex : 1987). 2021 May 01;276:116692

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PMID: 33592446

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