Intermediate Fe(III) of goethite oxidized As(III) to As(V): Roles of oxytetracycline and oxygen vacancies

Goethite is widely present in soils or sediments, which exhibit great influence on the environmental fates of pollutants. Concomitant pollution of antibiotics and arsenic has attracted increasing attention recently. The effects of goethite on antibiotics and arsenic transformation under combined pollution condition has not been reported. This study firstly reported that Fe(II) produced from the interaction between oxytetracycline (OTC) and structural Fe(III) of goethite could be re-oxidized by structural Fe(III), generating reactive intermediate Fe(III), which was capable of oxidizing As(III) to As(V). Based on DFT calculation, the electron transfer process between Fe(II) and structural Fe(III) was significantly promoted by oxygen vacancies of goethite and this process could be occurred both under oxic and anoxic conditions. Furthermore, oxygen vacancies could also accelerate the electron transfer between adsorbed O₂ and As(III) under oxic condition, promoting the direct oxidation of As(III) by O₂. This study highlighted the reductive effect of residual tetracycline antibiotics on iron oxides for the transformation of coexisting As, providing novel insights into the environmental fates of the combined contaminants in soils, and enriching the current understanding of the environmental behavior of arsenic.