Sorption mechanism of enrofloxacin on humic acids extracted from Brazilian soils
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Veterinary antimicrobials are emerging environmental contaminants of concern. In this study, the sorption of enrofloxacin (ENR) onto humic acids (HAs) extracted from three Brazilian soils was evaluated. HAs were characterized by elemental analysis and solid 13C nuclear magnetic resonance spectroscopy. The sorption of ENR onto HAs was at least 20-fold higher than onto the soils from which they were separated. Ionic and cation bridging are the primary interactions involved. The interactions driven by cation exchange are predominant on HAs, which appear to have abundant carboxylic groups and a relatively high proportion of H-bond donor moieties with carbohydrate-like structures. Interactions explained by cation bridging and/or surface complexation on HAs are facilitated by moieties containing conjugated ligands, significant content of oxygen-containing functional groups, such as phenolic-OH or lignin-like structures. HAs containing electron-donating phenolic moieties and carboxylic acid ligand groups exhibit a sorption mechanism that is primarily driven by strong metal binding, favoring the formation of ternary complexes between functional groups of the organic matter and drugs.
KeywordsHumic acids from Brazilian soils Fluoroquinolone sorption on humic acids Veterinary drugs Sorption mechanism Ionic and cation bridging
The authors gratefully acknowledge financial support from FAPESP (Proc. 2012/01767-0, 2013/09543-7). The authors thank CNPq for the research grants awarded to Mónica J. Martínez-Mejía (CNPq 159676/2013-9).
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Conflict of interest
The authors declare that they have no conflict of interest.
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