Desorption of heavy metals and tetracycline from goethite-coated sands: The role of complexation

Tetracycline (TC) has been widely employed in livestock breeding and clinical treatment. The prolific use of TC has resulted in a high prevalence of the compound in the environment. The electron-donor groups of TC allow it to form complex compounds with heavy metals, resulting in changes to each molecule's environmental behavior. This study aims to evaluate the effects of the complexation of heavy metals and TC on their desorption from goethite-coated sands (GCS), using batch experiments and model calculations. Our results show that heavy metals can inhibit the desorption of TC from the GCS surface, and that TC exerts a similar influence on the desorption of heavy metals. The inhibition of copper (Cu) by TC was stronger than that of cadmium (Cd), possibly resulting from TC's stronger complexation with Cu. In addition, a correlation analysis between the complexation and amount of desorption showed that the inhibition of the desorption on GCS was significantly positively correlated with the complexation of heavy metals and TC. This indicated that the complex products of heavy metals and antibiotics have a stronger affinity with GCS than the individual components, or that the formation of ternary complex products promotes resorption of the remaining contaminants in the solution. This work revealed that the desorption inhibition resulting from complexation between antibiotics and heavy metals could improve contaminant retention, reducing contaminant transportation and minimizing the environmental risk.