Sparfloxacin

Fluoroquinolones (FQs) are widely prescribed antibiotics that are commonly detected in aquatic environments, but the persistence, fates, and ecotoxicities of new generation FQs have yet to be fully investigated. We investigated the direct and indirect (hydroxyl radical (·OH), singlet oxygen (O21), and excited stated of organic matter (³CDOM^*)) photodegradation of three 3rd generation FQs, moxifloxacin (MOX), gatifloxacin (GAT), and sparfloxacin (SPAR). The photodegradation rates and photolytic quantum yields (Φ_FQ) of the FQs depended on their dissociation species at different pH in a range of 1×10^-4 to 1×10^-3 M mol-photon^-1. Unlike MOX and GAT whose zwitterions had the highest Φ_FQ, the anionic form of SPAR had the highest Φ_FQ. The k_·OH,FQ values were in the order of: k_·OH,SPAR > k_·OH,GAT ≈ k_·OH,MOX with the 10¹⁰M^-1s^-1 order of magnitude. The k_O21,FQ values were in the order of: k_O21,SPAR (∼10⁸M^-1s^-1) > k_O21,MOX (∼10⁷M^-1s^-1) > >> k_O21,GAT (insignificant). Higher k_LC*3,FQ values were observed for MOX (10⁹ to 10¹⁰M^-1s^-1) compared to GAT and SPAR (10⁸ to 10⁹M^-1s^-1). The zwitterions had the highest reactivities with ·OH and the lowest reactivities with O21 and ³CDOM^*. Reactions with ·OH enhanced the formation of transformation products (TPs) from decarboxylation and sidechain oxidation pathways, whereas reactions with O21 and ³CDOM^* enhanced the formation of TPs from sidechain oxidation pathways. Some of the TPs were predicted to exhibit aquatic ecotoxicity and environmental persistence. The half-lives of the FQs were estimated to be 0.42 to 0.67 h for MOX and SPAR, and 4.6 to 4.9 h for GAT. Their half-lives and main photochemical fates depended on the surface water pH and water column depth. These results highlight the key roles that photodegradation plays in removing new generation FQs from aquatic environments, though this might lead to the formation of TPs that are harmful to aquatic ecosystems.