Dual roles of Atrazine as An Organic Contaminant and Indicator of Intermediate Oxidants during Sulfite Activation of Permanganate

The permanganate/sulfite (Mn(VII)/sulfite) process has shown promise for degrading recalcitrant organic micropollutants, yet current methods to differentiate the roles of intermediate manganese species (IMS) and sulfate radicals (SO₄ •- ) show limitations. In this study, atrazine (ATZ) - a widely detected and oxidation-resistant herbicide - was used as a probe compound to investigate the reactivity of IMS and SO₄ •- generated in the Mn(VII)/sulfite system. ATZ exhibited negligible degradation by Mn(VII) alone but underwent rapid transformation within seconds in the presence of sulfite, with degradation efficiency increasing at lower pH and optimal [Mn(VII)]/[sulfite] ratios. Using stopped-flow spectrophotometry, pseudo-first-order kinetics were confirmed. Six major transformation products were identified, among which atrazine amide (CDIT) and desethyl-atrazine (DEA) were predominant. The molar ratio of CDIT to DEA ([CDIT]/[DEA]) was evaluated as a mechanistic indicator. A consistent ratio of ~4.8 at low sulfite levels indicated Mn(V)-dominated oxidation, while lower ratios at higher sulfite concentrations reflected increasing contributions from Mn(III) and SO 4 •− . This trend was supported across pH 3, 5, and 7. Water matrix components such as natural organic matter and nitrite were found to inhibit ATZ degradation, likely due to their scavenging of reactive species. This study establishes the [CDIT]/[DEA] ratio as a novel mechanistic indicator in manganese-activated oxidation and highlights the Mn(VII)/sulfite process as an effective strategy for degrading recalcitrant micropollutants in water treatment.