Iron plaque formation on wetland-plant roots accelerates removal of water-borne antibiotics

Abstract

The effects of iron plaque on the removal of antibiotic or antifungal drugs, such as macrolides (MLs) and sorption mechanism are important for the selection of plants in constructed wetlands. We aim to evaluate the sorption of water-borne MLs by iron plaque on root surfaces of plants with different rates of radial oxygen loss (ROL). Aquatic sorption activity was determined in three wetland plant species, Canna indica, Juncus effusus and Iris pseudacorus) and four MLs, anhydroerythromycin A (ETM-H2O), roxithromycin (ROX), clarithromycin (CLA) and tilmicosin (TIL). The adsorption mechanism and iron plaque characteristics before/after adsorption were investigated. Roots of Juncus effusus removed more MLs than the other two plant species. This species with higher ROL also formed more iron plaques, which consequently adsorbed more MLs. MLs were largely immobilized by sorption onto the Fe (hydr)oxides formed. Multiple mechanisms included hydrophobic interaction, surface ionic exchange and surface complexation between the carbonyl group on the lactone ring of the ML and the ferric ions. Iron plaque enhances MLs removal by wetland plants. Selecting the dominant plant with high ROL can improve the formation of iron plaque on root surfaces and promote the removal of antibiotics in constructed wetlands.