Comparison of lincomycin reaction with manganese oxide under oxic and anoxic environments: Reactivity, Mn speciation and toxicity assessment

Manganese oxides have strong reactivity to decompose many emerging organic contaminants. However, how redox conditions govern the reactivity of manganese oxides, the associated surface/bulk Mn speciation, and the toxicity of degradation products are still unclear. In this study, lincomycin (LIN) reaction with manganese oxide under oxic and anoxic conditions and the associated mechanism were investigated, and redox condition was regulated by the amount of dissolved oxygen in solution. An enhancement of the reaction by dissolved oxygen in the solution was confirmed in both batch and column experiments. The results revealed that the reduction of Mn(IV) and Mn(III) in birnessite play the major role in LIN decomposition, the reoxidation of Mn(II)→Mn(III) and Mn(III)→Mn(IV) in birnessite facilitating the formation of more reactive sites on birnessite for LIN degradation. Specifically, LIN is decomposed through transformation of pyrrolidine ring, dehydrogenation, hydroxylation, and detachment or cleavage of pyranose ring. The presence of dissolved oxygen did not cause additional reaction pathways for LIN, but promote its transformation towards lower toxicity. The insights into the role of dissolved oxygen in pollutant degradation mediated by manganese oxides offer new perspectives on Mn geochemical cycling dynamics and the environmental regulation of manganese oxides' redox reactivity by dissolved oxygen.