Transformation of tetracycline antibiotics with goethite: Mechanism, kinetic modeling and toxicity evaluation

Tetracycline antibiotics (TCs) are a group of the top selling and widely used antibiotics that have been frequently detected in various environments. The interaction between TCs and goethite (alpha-FeOOH), one of the most common crystalline oxide minerals in aqueous environment and soil, is unclear. Apart from adsorption, this study firstly demonstrated that transformation of tetracycline (TTC) occurred in the presence of goethite. The transformation kinetics and mechanism of TTC with goethite were investigated to gain a better understanding of the fate of TCs in the natural environment. The results showed that the transformation of TCs by goethite explicitly exhibited two-stage kinetics, wherein an initial period of fast transformation was followed by a continuous slow transformation. Hydroxyl groups on goethite were identified as major reactive sites, among which singly coordinated hydroxyls (equivalent to FeOH) were more reactive than doubly coordinated hydroxyls (equivalent to Fe-2 OH) towards the transformation of TTC. On the basis of transformation rates, speciation of TTC and functional groups on goethite surface, a kinetic model was established successfully describing the transformation of TTC by goethite under conditions of varying reactant concentration and pH. The transformation of TTC by goethite mainly resulted in a N,N-dedimethylation product that did not show antimicrobial properties towards Escherichia coli. This study indicates that Fe(III)(hydro)oxides in soils and sediments may play an important role in the natural attenuation of tetracycline antibiotics and their bioactivity. (C) 2021 Elsevier Ltd. All rights reserved.

Automated summary

This study demonstrated the transformation of tetracycline in the presence of goethite and investigated the kinetics and mechanism of this transformation. The results showed two-stage kinetics of tetracycline transformation by goethite, with a kinetic model successfully established under varying reactant concentrations and pH conditions. The study indicates that Fe(III)(hydro)oxides in soils and sediments may play a significant role in the natural attenuation of tetracycline antibiotics and their bioactivity.