The Adsorption And Transport Of Tetracycline By Roots Of Macrophyte Under The Influence Of Copper Complexation

There has been an increase concentration of emerging contaminants involving heavy metals and antibiotics detected in livestock and poultry wasterwater which posing more and more environmental risk due to the rapid development of intensive livestock and poultry farming.In this study,Eichhornia crassipes was chosen as a phytoremediation plant for the removal of combined pollution of heavy metals-copper(Cu)and widely-used veterinary antibiotic-tetracycline(TC).The interaction of TC and Cu on removal efficiency of pollutants by Eichhornia crassipes and their fate in water and Eichhornia crassipes were investigated.In this study,both absorbance enhancement and red shifts of TC’s UV-Vis absorption spectra were observed when TC cooperated with Cu2+.The results obtained by the continuous variation and mole ratio method were employed to clarify the complexation between Cu and TC,and the results showed that Cu2+ could chelate with TCs on the ratio of 1:1 and 1:2 to form the stable complexes,depending on Cu level.TC was founded to bind with Cu via the oxygen atom of hydroxyl group at site 3 and the nitrogen atom of dimethylamino group though FTIR spectrum analysis.Batch experiments were conducted to investigate the sorption characteristics of TC,and the interactive effects of Cu on the sorption of TC onto Eichhornia crassipes’s roots.In addition,Fourier transform infrared spectroscopy(FTIR),X-ray photoelectron spectroscopy(XPS)and blocking of functional groups method were employed to clarify the sorption mechanisms.The results were shown as following:the pseudo-second-order kinetic model and the Freundlich isotherm model fitted the sorption data well.There were both physical and chemical forces during the sorption process.The additions of Cu2+ significantly increased TC sorption onto Eichhornia crassipes roots.When the amino and carboxyl groups on the surface of Eichhornia crassipes roots were blocking,the sorption of TC by roots was reduced by 20%to 30%.In addition,the results of FTIR and XPS analysis also comform that carboxyl and amino groups on the surface of Eichhornia crassipes roots might be the chief functional groups combined with Cu2+ which plays as a strong metal bridge between root surface and TC molecule,facilitating the sorption of TC by roots.Eichhornia crassipes could effectively remove TC from water,with dissipation percentage reached up to 94.9%after 10 d of cultivation.TC was mainly taken up by Eichhornia crassipes’ roots and rarely transported to the aerial part.The co-existence of Cu influenced the amount of TC in fresh/dead Eichhornia crassipes’ roots.That is,an increase of Cu2+ concentration associated with the higher TC amount accumulated in plant roots.The removal mechanisms of TC by the dead roots and fresh plants might be quite different.The removing efficiency of TC by the roots was significantly lower compared with the fresh Eichhornia crassipes’ roots.And the amount of TC accumulated by fresh Eichhornia crassipes’ roots were gradually decreased with duaration,while the opposite trend was observed for the dead roots.