Driving iodine speciation toward iodate limits iodinated disinfection byproducts

Disinfection byproducts (DBPs) remain a persistent concern for long-term public health. Among them, iodinated disinfection byproducts (I-DBPs) are especially problematic owing to their higher toxicity. In drinking water treatment, iodide is oxidized to hypoiodous acid (HOI), a highly reactive intermediate that rapidly iodinates NOM and promotes I-DBP formation. This issue is particularly acute during chloramination. Herein, we propose a synergistic disinfection strategy by introducing low-dose peroxymonosulfate (PMS) to the chloramine (NH₂Cl) system, aiming to promote the selective transformation of HOI to iodate (IO₃^-) with negligible toxicity and thereby mitigate the formation of I-DBP precursors. Kinetic analyses revealed that PMS significantly accelerates HOI oxidation with second-order rate constants increasing to 10²-10⁴ M^-1 s^-1 contrasting with NH₂Cl's lack of oxidant capacity to oxidize HOI. Further investigation using representative phenolic compounds (bisphenol A and 4-methylphenol) demonstrated that PMS effectively scavenges HOI and inhibits iodinated byproduct formation, particularly under neutral to alkaline conditions. Across simulated and real waters, PMS-NH₂Cl converts 77-98% of aqueous iodine to IO₃^-, reduces target I-DBP formation by 83-90% and substantially decreases total organic iodine (TOI) at just 20 µM PMS, alongside a 60% decrease in cytotoxicity risk. Notably, this PMS-NH₂Cl approach requires only minimal PMS addition and may be readily integrated into existing NH₂Cl-based disinfection processes, offering a potentially practical and cost-effective strategy to mitigate organic iodine formation and associated toxicity risks in iodine-rich source water.