Sorption behaviour of norfloxacin on marine sediments

Pharmaceutical antibiotics are widely used, and their residues may represent potential hazards to organisms. Sorption of antibiotics to solid surfaces plays an important role in controlling their fate and effect on ecosystems in aquatic environments. As knowledge on the migration of norfloxacin (NOR) in the ocean environment is still limited, this study investigated the sorption behaviours of NOR on marine sediments, as well as the influence of the properties of the sediment and medium. Sediments were collected from the East China Sea and the Yellow Sea and were washed, air-dried and ground. Treatment by HCl and H2O2 was used to investigate the effect of sediment organic carbon on the sorption. Artificial seawater containing NaCl, MgCl2 and Na2SO4 with a salinity of 35 aEuro degrees was used as the medium. NOR was purchased from Shanghai Kaiyang Biological Technology Inc., China. Batch sorption experiments were performed to obtain the sorption kinetic curves and isotherms by mixing 500 mg of the sediments and 40 ml of NOR solution. The sorption quantity of NOR was determined by the difference of NOR concentrations before and after sorption, which was analyzed by UV spectrophotometry. The effects of salinity and temperature on the sorption were also investigated. The NOR sorption kinetics could be described by a pseudo-first-order equation, and the equilibration time was approximately 6 h at 298 K. The isotherms followed the Freundlich model. For the sediments treated in different ways, the K (F) values were in the order of K (F) (H2O2 treatment) < K (F) (H2O treatment) < K (F) (HCl treatment). For three H2O-treated sediments obtained from different sites, the K (F) values were in the same order as the sediment organic carbon contents. The sorption quantity of NOR in different media and at different temperatures showed that the sorption ability of NOR on marine sediments had a negative correlation with salinity and temperature. Estimation of thermodynamic parameters showed that the values of Delta G (theta) and Delta H (theta) were negative and the Delta S (theta) was positive. The kinetics of NOR sorption onto sediments followed the pseudo-first-order equation, and the isotherms agreed with the Freundlich model. A decrease of salinity and temperature and increase of sediment organic matter content were favourable for sorption. The process was spontaneous and exothermic, with an increased randomness at the solid-liquid interface during the sorption. Moreover, the values of Delta G(theta) and Delta H-theta indicated that the process could be considered as a physical sorption.