Photochemical transformation of terbutaline (pharmaceutical) in simulated natural waters: Degradation kinetics and mechanisms Wenli Yang a , Sihem Ben Abdelmelek b , Zheng Zheng a, *, Taicheng An c , Danny Zhang a , Weihua Song a, ** a Shanghai Key Laboratory of Atmospheric Particle Pollution and Prevention, Department of Environmental Science & Engineering, Fudan University, Shanghai 200433, PR China b Department of Chemistry, Faculte ´ des Sciences de Bizerte, University of Carthage, Tunisia c State Key Laboratory of Organic Geochemistry and Guangdong Key Laboratory of Environmental Resources Utilization and Protection, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, PR China article info Article history: Received 7 May 2013 Received in revised form 26 July 2013 Accepted 23 August 2013 Available online 3 September 2013 Keywords: Terbutaline Photodegradation DOM Singlet oxygen Hydroxyl radical abstract In this study, varied nature organic matter isolates were employed to investigate the in- direct photo transformation of terbutaline, which is a major feed additive medicine to increase the proportion of lean meat in the livestock. In the indirect photolysis of terbu- taline under solar simulated irradiation, 1 O 2 plays an important role among the OH and 3 DOM*. The reaction rate constant of 1 O 2 was determined as (7.1  0.3)  10 6 M 1 s 1 at pH 7.0, while the reaction rate constant of OH was (6.87  0.43)  10 9 M 1 s 1 . The contri- bution of singlet oxygen to the indirect photolysis of terbutaline (19e44%) was higher than that of the hydroxyl radical (1e7%). The pseudo first order rate constants for the photo- degradation of terbutaline increase with increasing pH, which indicates that pH mainly affects the reaction rate of the singlet oxygen with the phenolic part of the terbutaline. The Quinone was identified as the main photosensitized product through LCeMS/MS analysis. It is also proposed that the degradation pathway of terbutaline involves reaction between the phenolic part of terbutaline and singlet oxygen. This finding strongly suggests that singlet oxygen was important factor for the photodegradation of terbutaline in natural waters. ª 2013 Elsevier Ltd. All rights reserved. 1. Introduction Pharmaceuticals and personal care products (PPCPs) are emerging contaminates that have received extensive consid- eration due to their possible human health effects and ecological impacts, even at trace concentrations (Schwarzenbach et al., 2006). The widespread therapeutic and preventative use of pharmaceuticals in both human and vet- erinary provides a continuous release of these substances or their metabolites to the aqueous environment (Fatta-Kassinos et al., 2011). In general, human used medicine can enter wastewater treatment plants via excretion, manufacturing * Corresponding author. Tel.: þ86 21 6564 3342. ** Corresponding author. Tel.: þ86 21 6564 2040. E-mail addresses: zzhenghj@fudan.edu.cn (Z. Zheng), wsong@fudan.edu.cn, wsong@uci.edu (W. Song). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/watres water research 47 (2013) 6558 e6565 0043-1354/$ e see front matter ª 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.watres.2013.08.029