Adsorption of Levofloxacin to Goethite: Batch and Column Studies

Batch experiments were conducted to investigate the adsorption of a widely used fluoroquinolone antibiotic levofloxacin (LEV) to goethite and effects of nitrate, sulfate, small organic acids, and humic acid (HA). The concentrations of LEV and small organic acids in single systems or mixtures were determined by a high-performance liquid chromatography. Presence of nitrate or sulfate almost had no influence on the adsorption of LEV to goethite. HA promoted the adsorption significantly, and similar results were also observed in column experiments. LEV adsorption to goethite increased slightly in the presence of small organic acids. The pi-pi interactions between LEV molecules and the aromatic ring of organic acids (or HA) might be the main mechanism. In column experiments, LEV adsorption to the goethite-coated sand was well fitted with the two-site nonequilibrium model using the CXTFIT 2.1 program within the software STANMOD. The desorption process was well predicted with the model using the same parameters. In the presence of HA, more LEV was adsorbed to goethite-coated sand, and the desorption process showed some delay. Some LEV adsorbed to goethite-coated sand could not be desorbed with NaCl but was desorbed with phosphate. Presence of HA (or natural organic matters, phosphate) had a great influence on the mobility and distribution of LEV in soils and waters, which might also affect its degradability and antibacterial activity. Results obtained in this study were seldom reported in previous studies, which help us to better understand the behavior of antibiotics in the natural environment.