Sunlight photodegradation of marbofloxacin and enrofloxacin adsorbed on clay minerals Michela Sturini a, *, Andrea Speltini a , Federica Maraschi a , Elisa Rivagli a , Luca Pretali b , Lorenzo Malavasi a , Antonella Profumo a , Elisa Fasani a , Angelo Albini a a Department of Chemistry, University of Pavia, via Taramelli 12, Pavia 27100, Italy b Parco Tecnologico Padano, via Albert Einstein, Lodi 26900, Italy A R T I C L E I N F O Article history: Received 24 September 2014 Received in revised form 14 November 2014 Accepted 15 November 2014 Available online 18 November 2014 Keywords: Fluoroquinolones Clays Photodegradation Photoproducts X-rays diffraction A B S T R A C T Fluoroquinolone antibiotics (FQs) are important “emerging” micropollutants, and their environmental diffusion is an issue of great concern. In this study, the photochemical degradation of marbofloxacin (MAR) and enrofloxacin (ENR) adsorbed on montmorillonite (MMT) and kaolinite (KAO) clays was investigated. Being FQs photosensitive molecules, the sunlight-induced degradation of clay-adsorbed FQs and of their photoproducts was monitored as function of irradiation time. The photoproducts were identified by high performance liquid chromatography electrospray tandem mass spectrometry (HPLC-ESI-MS/MS) and the photochemical pathways have been elucidated. X-ray diffraction (XRD) has been employed to deeply study the solid-state photodegradation process of MAR and ENR on MMT. Interestingly, the XRD results clearly evidenced a significative variation of the interlayer spacing of MMT not only as function of FQs adsorbed amounts, but also in relationship with their photodegradation, not investigated by means of XRD as yet. The results confirmed that FQs adsorption is a bulk phenomenon that occurs in the interlayer spacing of the MMT structure; moreover, it was proved that sunlight largely degraded the adsorbed FQs, both on the external surface and in the interlayer spacing. ã 2014 Elsevier B.V. All rights reserved. 1. Introduction The widespread of pharmaceuticals in the environment and their fate, effects and threats associated to their occurrence are matter of great concern. Among these drugs, fluoroquinolones (FQs) are an important class of “emerging” micropollutants [1–5]. In view of their broad activity spectrum against Gram bacteria and their good oral intake, FQs are the fourth largest class of human antibiotics and they are widely administrated also to animals for therapeutic purposes, and as feed additives to support growth in livestock [6]. Once administrated, FQs are metabolized to a minor extent and a large part of the unmodified initial dose reaches urban sewage treatment plants (STPs) that are not able to quantitatively remove such complex molecules [7,8]. This causes a continuous release of FQs in surface water overcoming their transformation and removal rates. These drugs rapidly move from water bodies to the soil compartment. Additionally, veterinary antibacterials can directly reach soil and groundwater through the common practice of recycling manure from animal husbandry and/or sewage sludge from STPs as fertilizers. Indeed FQs have been detected up to few micrograms per kilogram also in soil and sediment [9] due to their strong binding to natural organic matter and minerals, with the high distribution coefficients observed in loamy matrices [10]. Recent studies have attributed to FQs ecotoxicity and genotoxicity against Vibrio Fischeri,Daphnia Magna and Pseudomonas Putida [11–13]. Furthermore, FQ residuals are able to induce environ- mental bacterial resistance [14,15]. Although photochemistry represents a natural removal path- way for these antimicrobials from the environment [1–3,5], on the other hand the photochemical processes involve the release of significant amounts of photoproducts that contribute to the overall environmental impact of the parent compounds [16,17]. Indeed, it was proved that FQ photoproducts maintain significant antibiotic activity [4]. Montmorillonite (MMT) and kaolinite (KAO) clays are natural constituents of soils and, due to their high surface area, have been recently proposed for adsorption of 4-chlorophenol and 2,4,6-trichloroaniline [18], tetracycline antibiotics [19], diphenhy- dramine [20], polychlorinated biphenyl and other organic pollutants [21,22]. With regard to FQs, recent studies have investigated the mechanistic interactions of ciprofloxacin onto MMT [23] and KAO [24], and those of ENR on smectite clays [25]. * Corresponding author. Tel.: +39 0382 987347; fax: +39 0382 528544. E-mail address: michela.sturini@unipv.it (M. Sturini). http://dx.doi.org/10.1016/j.jphotochem.2014.11.015 1010-6030/ ã 2014 Elsevier B.V. All rights reserved. Journal of Photochemistry and Photobiology A: Chemistry 299 (2015) 103–109 Contents lists available at ScienceDirect Journal of Photochemistry and Photobiology A: Chemistry journal homepa ge: www.elsev ier.com/locate/jphotochem