title: Aquatic photochemistry of fluoroquinolone antibiotics: kinetics, pathways, and multivariate effects of main water constituents.
abstract: The ubiquity of fluoroquinolone antibiotics (FQs) in surface waters urges insights into their fate in the aqueous euphotic zone. In this study, eight FQs (ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin, enrofloxacin, gatifloxacin, and balofloxacin) were exposed to simulated sunlight, and their photodegradation was observed to follow apparent first-order kinetics. Based on the determined photolytic quantum yields, solar photodegradation half-lives for the FQs in pure water and at 45 degrees N latitude were calculated to range from 1.25 min for enrofloxacin to 58.0 min for balofloxacin, suggesting that FQs would intrinsically photodegrade fast in sunlit surface waters. However, we found freshwater and seawater constituents inhibited their photodegradation. The inhibition was further explored by a central composite design using sarafloxacin and gatifloxacin as representatives. Humic acids (HA), Fe(III), NO(3)(-), and HA-Cl(-) interaction inhibited the photodegradation, as they mainly acted as radiation filters and/or scavengers for reactive oxygen species. The photodegradation product identification and ROS scavenging experiments indicated that the FQs underwent both direct photolysis and self-sensitized photo-oxidation via *OH and (1)O(2). Piperazinyl N(4)-dealkylation was primary for N(4)-alkylated FQs, whereas decarboxylation and defluorination were comparatively important for the other FQs. These results are of importance toward the goal of assessing the persistence of FQs in surface waters.
authors.affiliation: Key Laboratory of Industrial Ecology and Environmental Engineering (MOE), Department of Environmental Science and Technology, Dalian University of Technology, Dalian, P. R. China.
authors.forename: Linke
authors.initials: L
authors.lastname: Ge
authors.forename: Jingwen
authors.initials: J
authors.lastname: Chen
authors.forename: Xiaoxuan
authors.initials: X
authors.lastname: Wei
authors.forename: Siyu
authors.initials: S
authors.lastname: Zhang
authors.forename: Xianliang
authors.initials: X
authors.lastname: Qiao
authors.forename: Xiyun
authors.initials: X
authors.lastname: Cai
authors.forename: Qing
authors.initials: Q
authors.lastname: Xie
mesh_terms: D048908:Aliivibrio fischeri / Q000187:drug effects; D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000633:toxicity; D004777:Environment; D024841:Fluoroquinolones / Q000737:chemistry* / Q000633:toxicity; D006812:Humic Substances; D006863:Hydrogen-Ion Concentration / Q000187:drug effects; D007501:Iron / Q000494:pharmacology; D007700:Kinetics; D008956:Models, Chemical; D015999:Multivariate Analysis; D009566:Nitrates / Q000494:pharmacology; D055668:Photochemical Processes / Q000187:drug effects; D010782:Photolysis / Q000187:drug effects; D013056:Spectrophotometry, Ultraviolet; D018675:Toxicity Tests; D014867:Water / Q000737:chemistry*
chemical_list: D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D006812:Humic Substances; D009566:Nitrates; D014867:Water; D007501:Iron