Simultaneous Adsorption And Desorption Of Tetracyclines And Cadmium On Soils

Heavy metals and antibiotics often coexist in agricultural soils and their concentrations are increasing due to land application of wasters generated from concentrated animal feeding operations. This study aims at evaluating the interaction of widely-used veterinary antibiotic tetracyclines (TCs) and cadmium (Cd) regarding to their adsorption and desorption in two tested soils (cinnamon soil and red soil) using the batch experiments. The sorption mechanisms of TCs and Cd interaction in tested soils are proposed based on the results from Fourier transform-infrared (FT-IR) analyses. The results were abstracted as follows:Adsorption and desorption of antibiotic tetracyclines in two soils. TCs were strongly absorbed in two tested soils. In this study, more than 80.00% antibiotic TCs added in the solution were absorbed by soils under all condition. The adsorption and desorption isotherms of TCs on the two soils were well fitted with Freundlich equation. The presence of Cd increased TCs adsorption on tested soils in addition to oxytetracycline (OTC) adsorption on red soil. When using different loading methods, the sorption Kf values of TCs increased except for the sorption Kf values of chlortetracycline (CTC) and OTC on red soil.The impact of loading methods on oxytetracycline was weakest. As the removal of soil organic matter and soil oxide, the absorption capacity of soils on such antibiotics declined. There was unobvious effect of temperature on the absorption of TCs in two soils. The apparent sorption-desorption hysteresis of TCs was found in soil, which will probably pose a threat to soil-environmental quality and human health. Hysteresis index (HI) of desorption of TCs in cinnamon soil was higher than in red soil. The present of Cd enhanced the hysteresis effect. HI of desorption TCs were increased when TCs loaded before Cd and removal of red soil organic matter. On the contrary, HI of desorption TCs were decreased when Cd loaded before TCs and removal of cinnamon soil organic matter. Removal of soil organic matter is basically able to increase HI of desorption TCs in the soil. HI of tetratracycline (TC) in soils without soil organic matter and soil oxide were higher than other antibiotic TCs. The adsorption of TCs in the soils mainly was physical adsorption in addition to CTC adsorption on red soil.Sorption mechanisms of antibiotic tetracyclines in two soils. Base on the results from the spectra of TCs equilibrated with Cd in two soils, it can be found that hydroxyl groups, carbonyl groups in B and D rings, carbonyl and amino groups of the amide in ring D played a significant role in retaining TCs in soils. From the FTIR results, it indicated that TC complexation with Cd could be occurring at the 01-017, O13-O15 and N4-O3.