Impact of manganese sulfide (MnS) oxygenation-induced oxidization on aqueous organic contaminants: Insight into the role of the hydroxyl radical (HO·)

Abstract

Manganese sulfide (MnS) has unique reactive abilities and can affect the fate and toxicity of contaminants in the natural environment, specifically sulfidic sediments that undergo biogeochemical changes due to natural and artificial processes. However, the effect of oxidization induced by the oxygenation of MnS on organic contaminants remains poorly understood. Herein, we revealed that the hydroxyl radical (HO·) was the dominant reactive oxidant for the rapid degradation of the assessed hydrophobic organic contaminants (including azo dye, nitroaromatic compounds, pesticide, and an endocrine disrupt chemical) during the oxygenation of MnS based on the competitive dynamic experiments, quenching experiments and electron spin resonance (ESR) methods. The removal rates of the assessed organic contaminants were significantly dependent on MnS dosage and co-solutes, including sediment humic acid, metal ions (Mn2+and Fe3+), and inorganic anions (PO43−and Cl−). HO· scavenging by sulfide and its oxidation products (e.g., elemental sulfur), rather than dissolved Mn2+, was responsible for the low utilization efficiency of HO· for the assessed contaminants. The contribution of the manganese oxide (MnO2) generated by the oxygenation of MnS to the examined degradation of contaminants could be neglected. Considered collectively, the reaction between H2O2 and MnO2 generated superoxide radicals (O2−·) which dominated the generation of HO· in an oxic MnS suspension. The results suggest that the impact of oxidization induced by the oxygenation of MnS on environmental contaminants should be of concern in both natural and engineered systems.