Studies On The Sorption Behavior Of Two Fluoroquinolones On Marine Sediments

Fluoroquinolones (FQS) is artificially synthesized antibiotics with4-quinolones(pyridone carboxylic acids) as the basic structure, and has high antibacterial activity. Atpresent, FQS has been used widely in human clinical, animal husbandry and aquaculture inChina, and the phenomenon of FQS abuse appeared recently. The constant migration andtransformation of the residual FQS in the water environments may cause a potential risk tohuman health through the food chain ultimately. At present, the residual problem of FQS hasattracted wide attention. Domestic and foreign scholars have carried out some researches onthe environmental photochemical behavior, and its adsorption behavior at someenvironmental media has been also studied, but study on the adsorption behavior of FQS onthe ocean/river sediments was rare. In the long run, it is very necessary to carry out the studyon the adsorption behavior of the FQS drug thoroughly and systematically in the naturalsediment.Norfloxacin (NOR) and Ciprofloxacin (CIP) are two typical representative products ofthird-generation FQS. The adsorption behavior of NOR and CIP on marine sediments wereinvestigated systematically through simulation experiments in this paper. The influence of thecomposition of sediments and environmental factors of media, such as temperature, salinity,pH on the sorption behavior of NOR and CIP was discussed. Meanwhile the impacts of foursurfactants: tween20, tween80, SDBS, CTAB, on the adsorption behavior were alsoinvestigated. Additionally, the adsorption mechanism of NOR and CIP were analyzed anddiscussed. The main conclusions was showed as follows:A. The pseudo-first order adsorption rate equation and Freundlich adsorption fitted well withthe adsorption behavior of NOR and CIP on the sediment, which was divided into twostages of rapid adsorption and slow adsorption. Freundlich heterogeneous adsorptionshowed that the adsorption had a relation with the hard carbon.B. The order of the adsorption capacity of NOR and CIP on sediments treated by differentways was consistent, which was H2O2treatment<H2O treatment<HCl treatment. The sequence of the adsorption capacity on the sediments at different stations were exactly thesame, which was3#station<1#station<2#station. The results showed that the sorptioncapacity was positively correlated with the sediment organic matter content and cationexchange capacity (CEC).C. As the temperature changed, no obvious change was observed for the adsorptionequilibrium time of NOR and CIP, but the adsorption capacity reduced with theincreasing temperature. The thermodynamic parameter values of ΔHθand ΔGθwerenegative, which showed that the adsorption process of NOR and CIP was spontaneouswith exothermic, with physical adsorption as the major mechanism.D. The equilibrium adsorption amount of NOR and CIP decreased with the increasingsalinity, because of the competitive adsorption of metal cations.E. The equilibrium adsorption amount of NOR and CIP decreased with the increasing pHvalues at the studied range, because the adsorption mechanism changed due to change inthe different existence forms of NOR and CIP at different pH values.F. The addition of the surfactants hardly impacted the adsorption equilibrium time of NOR,but had a significant influence on the adsorption capacity, with different extents fordifferent surfactants. The results showed that the addtion of anionic surfactant SDBS orcationic surfactant CTAB could promote the adsorption of NOR, whereas the non-ionicsurfactant Tween20or Tween80inhibited adsorption of NOR.