Photochemical transformation of terbutaline (pharmaceutical) in simulated natural waters: Degradation kinetics and mechanisms

In this study, varied nature organic matter isolates were employed to investigate the indirect 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 terbutaline under solar simulated irradiation, 1O2 plays an important role among the •OH and 3DOM∗. The reaction rate constant of 1O2 was determined as (7.1 ± 0.3) × 106 M−1 s−1 at pH 7.0, while the reaction rate constant of •OH was (6.87 ± 0.43) × 109 M−1 s−1. The contribution of singlet oxygen to the indirect photolysis of terbutaline (19–44%) was higher than that of the hydroxyl radical (1–7%). The pseudo first order rate constants for the photodegradation 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 LC–MS/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.