Simultaneous adsorption and desorption of cadmium and tetracycline on cinnamon soil

Heavy metals and antibiotics often coexist in agricultural soils and their concentrations are increasing with land application of wastes from concentrated animal feeding operations. This study aims at evaluating interaction of cadmium (Cd) and a widely-used veterinary antibiotic tetracycline (TC) on the basis of their adsorption and desorption on cinnamon soil using the batch experiments. The results indicated that adsorption and desorption of Cd and TC were strongly dependent on soil characteristics, and adsorption and desorption isotherms of Cd and TC on the soils were well fitted with the Freundlich equation. In particular, there was an apparent sorption-desorption hysteresis of Cd and TC in soil, which will probably pose a threat to soil-environmental quality and human health. Moreover, the presence of TC increased Cd adsorption on the tested soil (K(f)=602.2-737.6), which can be attributed to increasing Cd adsorption via the bridge of TC, or stronger affinity of the TC-Cd complex to soil minerals than Cd ion itself. The presence of TC also enhanced the hysteresis effect of Cd sorption-desorption (H=0.86-0.96). Similarly, the sorption K(f) values of TC increased from 1095 in absence of Cd to 1305 in presence of Cd, respectively. In the meantime, the presence of Cd enhanced adsorption of TC by the bridge of Cd, which is similar to that of Ca(2+) and Mg(2+). However, the presence of Cd decreased the hysteresis effect of TC sorption-desorption (H=0.99-0.84). It is thus important to consider the interaction between Cd and TC when studying on the fate of Cd and TC in soil environment.