Abstract
Phosphodiesterase-5 inhibitors (PDE-5i, such as Sildenafil, Tadalafil and Vardenafil, mainly prescribed to treat erectile dysfunction) and their generic drug equivalents have been widely marketed and consumed in Korea. From the concentrations detected in wastewater, we could deduce that relatively large amounts of PDE-5i were consumed without a legal prescription. Thus, PDE-5i’s presence in the environment via sewage is unavoidable, and their environmental fate within a sewage treatment plant (STP) should be evaluated. In this study, we investigated the occurrence of three PDE-5i analogs in the influent and effluent of two STPs and the receiving water bodies. The PDE-5i concentration in total reached 62 ± 12 (STP#1) and 88 ± 37 ng L−1 (STP#2) in the sewage influent; about 70% of it was Sildenafil in both STPs. However, they were hardly removed by the STPs as the removal efficiency of the STPs was less than 10% ± 5%. Therefore, the pharmaceuticals were detected in the receiving water (lower than 7 ng L−1as a total amount) and the concentration slightly increased downstream of the STPs. A simple mass balance model applied for the compounds in the STP effluent and receiving water bodies also confirmed that the discharged PDE-5i were quite persistent. Lastly, we identified temporal and regional patterns in the consumption of the drugs from daily variations of PDE-5i in the influent to these two STPs. For instance, the levels of PDE-5i in the sewage significantly increased on weekends (from Friday to Saturday), and especially in the area where adult-entertainment businesses are common. We estimated that the amount of PDE-5i consumption in this area was 31% higher than that in the area with fewer nightlife spots. Considering that they are pharmaceutically active and resistant to treatment processes within an STP, it is advised that a regular monitoring and management program for PDE-5i should be developed to prevent the discharge of the pharmaceuticals into the water environment.
Highlights
The statistical analysis and graphical presentation of the results in this study were made using Microsoft Office Excel 2016 (Microsoft Inc., Redmond, WA, USA) and Origin 2019 (OriginLab Corp., Northampton, MA, USA)
The result from our study demonstrated that PDE-5i, which continuously flows into the water environment, would not be removed by the STP and be persistently conserved in the receiving water
Sildenafil citrate (CAS No 171599-83-0), Tadalafil (CAS No 171596-29-5), and Vardenafil hydrochloride (CAS No 330808-88-3) standards were prepared with certified reference materials, which were purchased from the Sigma-Aldrich
Summary
The statistical analysis and graphical presentation of the results in this study were made using Microsoft Office Excel 2016 (Microsoft Inc., Redmond, WA, USA) and Origin 2019 (OriginLab Corp., Northampton, MA, USA).
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