title: New insights into the aquatic photochemistry of fluoroquinolone antibiotics: Direct photodegradation, hydroxyl-radical oxidation, and antibacterial activity changes.
abstract: The ubiquity and photoreactivity of fluoroquinolone antibiotics (FQs) in surface waters urge new insights into their aqueous photochemical behavior. This study concerns the photochemistry of 6 FQs: ciprofloxacin, danofloxacin, levofloxacin, sarafloxacin, difloxacin and enrofloxacin. Methods were developed to calculate their solar direct photodegradation half-lives (td,E) and hydroxyl-radical oxidation half-lives (tOH,E) in sunlit surface waters. The td,E values range from 0.56 min to 28.8 min at 45° N latitude, whereas tOH,E ranges from 3.24h to 33.6h, suggesting that most FQs tend to undergo fast direct photolysis rather than hydroxyl-radical oxidation in surface waters. However, a case study for levofloxacin and sarafloxacin indicated that the hydroxyl-radical oxidation induced risky photochlorination and resulted in multi-degradation pathways, such as piperazinyl hydroxylation and clearage. Changes in the antibacterial activity of FQs caused by photodegradation in various waters were further examined using Escherichia coli, and it was found that the activity evolution depended on primary photodegradation pathways and products. Primary intermediates with intact FQ nuclei retained significant antibacterial activity. These results are important for assessing the fate and risk of FQs in surface waters.
authors.affiliation: Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China.
authors.forename: Linke
authors.initials: L
authors.lastname: Ge
authors.affiliation: Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China.
authors.forename: Guangshui
authors.initials: G
authors.lastname: Na
authors.affiliation: Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang 110016, PR China.
authors.forename: Siyu
authors.initials: S
authors.lastname: Zhang
authors.affiliation: Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China.
authors.forename: Kai
authors.initials: K
authors.lastname: Li
authors.affiliation: Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China. Electronic address: pzhang@nmemc.org.cn.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China.
authors.forename: Honglei
authors.initials: H
authors.lastname: Ren
authors.affiliation: Key Laboratory for Ecological Environment in Coastal Areas (SOA), National Marine Environmental Monitoring Center, Dalian 116023, PR China.
authors.forename: Ziwei
authors.initials: Z
authors.lastname: Yao
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry* / Q000633:toxicity; D024841:Fluoroquinolones / Q000737:chemistry* / Q000633:toxicity; D017665:Hydroxyl Radical / Q000737:chemistry; D007700:Kinetics; D008956:Models, Chemical; D010084:Oxidation-Reduction; D010782:Photolysis; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000737:chemistry* / Q000633:toxicity
chemical_list: D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D014874:Water Pollutants, Chemical; D014867:Water; D017665:Hydroxyl Radical
keywords: Antibacterial activity; Fluoroquinolones; Oxidation kinetics; Photolysis; Transformation products