Oxidative transformation of artificial sweetener acesulfame by permanganate: Reaction kinetics, transformation products and pathways, and ecotoxicity

Acesulfame has attracted much attention due to its wide application, environmental persistence and potential safety risk of transformation products (TPs). Little information is known on acesulfame transformation in the presence of oxidants/disinfectants. The acesulfame oxidation by permanganate (Mn(VII)) in water under environmentally relevant conditions was systematically evaluated. The pH of water showed negligible influence in acesulfame oxidation. Inorganic ligand (pyrophosphate) exhibited insignificant effect whereas organic ligands (oxalate, ethylene diamine tetraacetic acid, and humic acid) exerted obvious suppression on acesulfame oxidation. Natural organic matter in real water had important influence in acesulfame oxidation by Mn(VII). Acesulfame transformation pathways were initiated by the attack of Mn(VII) on double bond of ring via [3+2] addition electrocyclic reaction and rich electron of N moiety through electrophilic reaction, followed by oxidation and hydrolysis reactions to produce TPs. Among them, five TPs were for the first time identified. The ecotoxicity tests uncover higher toxicity of the TPs than acesulfame itself. The study on oxidative transformation of acesulfame by Mn(VII) would illumine comprehensive evaluation of this emerging contaminant. Water treatment plants need to consider cautiously to protect the safety of downstream system when using Mn(VII) to dispose the water resource containing acesulfame or other artificial sweeteners.