Mechanism of ofloxacin fluorescence quenching and its interaction with sequentially extracted dissolved organic matter from lake sediment of Dianchi, China.

The wide use and occurrence of antibiotics in water environments have caused wide concerns. Ofloxacin (OFL) was selected as a target antibiotic, and the interaction between OFL and sequential extracted dissolved organic matter (DOM) from the sediment of Dianchi, a hypertrophic lake in Southwest China, was explored using fluorescence quenching technology. The method of fuorescence quenching was used to characterize the interaction between OFL and sequentially extracted DOM. The result indicated that static and dynamic quenching both existed in the interaction. The interaction in the background water (0.01 mol/L NaCl and 200 mg/L NaN3) became increasingly weak with the further extraction of DOM. A low non-linear factor N value (0.53∼0.63) of Freundlich model was observed, indicating a non-linear interaction between OFL and DOM. Elemental characterization and infrared spectrum analysis showed an enhanced OFL-DOM binding with the decrease in humic acid (HA) polarity. The effect of ion strength was tested in the OFL-DOM interaction to show the impact of usually existing metal ions in water environment on the OFL behavior. The result showed that K(+) had little influence, but Cu(2+) had a significant promotion (p < 0.05) in the OFL-DOM interaction in background water, indicating that divalent metal ions, which have the bridge bond or complexation capacity, are more active in the OFL-DOM interaction than monovalent ions, with no bridge bond or complexation capacity. This work would be useful in the fate and risk assessment of antibiotics in water environments.