Oseltamivir phosphate (OP; Tamiflu) has been used to treat and prevent H1N1 influenza. OP is primarily excreted in urine as oseltamivir carboxylate (OC), the active form of the drug, and OC may be subsequently released into the environment via sewage treatment plant (STP) wastewater. Ghosh et al. used solid-phase extraction followed by liquid chromatography