Studies On The Sorption Behavior Of Ofloxacin On Marine Sediments

Fluoroquinolone antibiotics (FQS) is the third-generation synthetic quinoloneefficient antibacterial drugs, with a broad spectrum antibiotic, good oral absorption,antibacterial activity, and no cross-resistance characteristics, clinical medicine athome and abroad, livestock and aquaculture and others widely used, and even abused.In many countries, shares and use of the FQSin the drugs market showed a trend ofincreasing year by year. A large numbers of FQSin the original drug or metaboliteforms into the environment through various means, occurred a series of environmentalbehavior (sorption, degradation, migration and transformation etc), and ultimatelythrough the delivery role of food chain threat to human health. In recent years, in viewof the potential risks to human and ecological environment, more and more scholarsto carry out exploration about FQSenvironmental behaviors, relatively, few relevantreports about the FQSpollutants sorption behaviors in the marine/freshwater riversediments. From the long-term development perspective, it is very necessary to carryout the study on the sorption behaviors of the FQSthoroughly and systematically inthe natural sediments.Ofloxacin (OFL) is a typical representative product of FQS, an efficientbroad-spectrum antimicrobial drug, widely used. Through simulation experiments, thesorption behaviors of OFL in the Yellow Sea and the East China Sea nearshoremarine sediments were systematically investigated in this paper. Firstly, theequilibrium time of ofloxacin was determined through kinetic experiments curve andmodel analysis, as a preliminary understanding of the sorption rate on sediments.Then,in single system, the effect of properties and composition of the sediments (such asparticle size, different station, different treatment), environmental factors (such assalinity, pH, temperature) on the OFL sorption behaviors were explored. At last, inthe combined system, with four surfactants (SDBS, CTAB, Tween80, Tween20,) asthe coexisting pollutants, explored the sorption behaviors of ofloxacin, discussion and analysis the sorption mechanism initially. The main conclusions were as follows:(1) Under the conditions of different initial concentrations, different pH values, anddifferent kinds of surfactants, Lagergren pseudo-first-order kinetic model could welldescribed the OFL sorption kinetics behaviors on marine sediment, which was dividedinto two stages of rapid sorption and slow adsorption. Under different conditions,there was a significant change in the equilibrium sorption amount (Qe), but thesorption equilibrium time little change were all about4hours.(2) Freundlich nonlinear sorption model can better fit the thermodynamic sorptionbehaviors of OFL on sediments. The order of the sorption capacity of OFL on threekinds of sediments treated by different ways was: HCl treatment> H2O treatment>H2O2treatment; the order of the sorption capacity of OFL on three kinds of differentsize sediments was:40-80mesh>80-150mesh>150-250mesh; the order of thesorption capacity of OFL on five stations was: S4> S3> S5> S1> S2. Those resultsindicated that the sorption capacity of OFL on sediments was positively correlatedwith the sediment organic matter content and cation exchange capacity (CEC).(3) With the decreasing of medium salinity, the equilibrium sorption amount of OFLon sediment increased, mainly because of the competitive sorption of metal cations.(Ca2+, Mg2+, etc).(4) The equilibrium sorption amount of OFL increased with the decreasing pH valuesat the studied range, because the sorption mechanism changed due to change in thedifferent existence forms of OFL at different pH values.(5) With the decreasing of the experimental temperature, the sorption capacity of OFLon sediments increased slightly, by calculating the thermodynamic functions andparameters, ΔGθ<0indicating that the sorption was a spontaneous process, and ΔHθ<0indicating that the sorption was a exothermic process.(6) In the combined system, the addition of different surfactants had a differentsignificant influence on the sorption capacity of OFL on sediments. The resultsindicated that, ionic surfactants could promote the OFL sorption on marine sediment,and the effect of anionic surfactants was stronger than that of cationic ones. Nonionicsurfactants inhibited the adsorption, Tween80had stronger inhibited effect than Tween20.