Migration Of Tetracycline And Heavy Metals On Goethite-coated Sands And Their Interaction

Tetracycline(TC),extensively used in livestock and poultry breeding and clinical treatment,is one of the most widely detected antibiotics in the environment.Complexes of TC and metal ions can be formed due to its electron-donating groups,further affecting their environmental behavior.Goethite is abundant in soils and sediments and usually coats soil particles with low activity in the natural environment,such as silica sand.The static/dynamic adsorption and desorption behavior of TC and metal(Cu and Cd)on goethite coated sand(GCS)was studied by batch and column experiments,and the interaction between the two pollutants was analyzed.The study found that:(1)GCS has certain adsorption on TC and heavy metals.The adsorption of GCS on TC is strongest at pH 3.0,which may be due to the complexation between TC and GCS.With the increase of pH,the adsorption of heavy metals on GCS is stronger.The main reason is that the hydrolysis of heavy metals occurs when the pH increases,resulting in more easily adsorbed substances.(2)Heavy metals and TC can inhibit each other desorption from GCS surface,,and the reasons are similar.Heavy metals inhibit TC mainly because: heavy metals can change the charged condition of GCS surface;and the complexes of TC with heavy metals are more easily adsorbed by GCS,or heavy metals act as bridging to form GCS-heavy metals-TC ternary complexes.(3)The results of column experiments show that heavy metals can inhibit the migration of TC in the GCS column.and the inhibition of Cu is stronger than that of Cd,which is related to the stronger complexation of Cu.Similarly,TC can also inhibit the migration of copper in GCS column.However,TC has little effect on the migration of cadmium under low pH conditions and promote the migration of cadmium under high pH conditions,which were caused by the complexation ability of heavy metals and TC and the migration characteristics of the two in GCS column.This study shows that the complexation between antibiotics and heavy metals has a great impact on their migration in solid media.Therefore,the role of coexisting contaminants should be fully considered,when assessing their environmental risks.