title: Photodegradation of veterinary ionophore antibiotics under UV and solar irradiation.
abstract: The veterinary ionophore antibiotics (IPAs) are extensively used as coccidiostats and growth promoters and are released to the environment via land application of animal waste. Due to their propensity to be transported with runoff, IPAs likely end up in surface waters where they are subject to photodegradation. This study is among the first to investigate the photodegradation of three commonly used IPAs, monensin (MON), salinomycin (SAL) and narasin (NAR), under UV and solar irradiation. Results showed that MON was persistent in a deionized (DI) water matrix when exposed to UV and sunlight, whereas SAL and NAR could undergo direct photolysis with a high quantum yield. Water components including nitrate and dissolved organic matter had a great impact on the photodegradation of IPAs. A pseudosteady state kinetic model was successfully applied to predict IPAs' photodegradation rates in real water matrices. Applying LC/MS/MS, multiple photolytic transformation products of IPAs were observed and their structures were proposed. The direct photolysis of SAL and NAR occurred via cleavage on the ketone moiety and self-sensitized photolysis. With the presence of nitrate, MON was primarily degraded by hydroxyl radicals, whereas SAL showed reactivity toward both hydroxyl and nitrogen-dioxide radicals. Additionally, toxicity tests showed that photodegradation of SAL eliminated its antibiotic properties against Bacillus subtilis.
authors.affiliation: School of Civil and Environmental Engineering, Georgia Institute of Technology , Atlanta, Georgia 30332, United States.
authors.forename: Peizhe
authors.initials: P
authors.lastname: Sun
authors.forename: Spyros G
authors.initials: SG
authors.lastname: Pavlostathis
authors.forename: Ching-Hua
authors.initials: CH
authors.lastname: Huang
mesh_terms: D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000528:radiation effects*; D007476:Ionophores / Q000737:chemistry / Q000528:radiation effects*; D007700:Kinetics; D008985:Monensin / Q000737:chemistry / Q000528:radiation effects; D009566:Nitrates / Q000032:analysis; D010782:Photolysis / Q000528:radiation effects*; D011714:Pyrans / Q000737:chemistry / Q000528:radiation effects; D011789:Quantum Theory; D013057:Spectrum Analysis; D053719:Tandem Mass Spectrometry; D018675:Toxicity Tests; D014466:Ultraviolet Rays; D019155:Veterinary Drugs / Q000737:chemistry / Q000528:radiation effects*; D014867:Water / Q000737:chemistry; D014874:Water Pollutants, Chemical / Q000032:analysis; D000095662:Polyether Polyketides
chemical_list: D000900:Anti-Bacterial Agents; D007476:Ionophores; D008985:Monensin; D009566:Nitrates; D011714:Pyrans; D019155:Veterinary Drugs; D014867:Water; D014874:Water Pollutants, Chemical; C010327:salinomycin; D000095662:Polyether Polyketides; C013612:narasin