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 (NH 2 Cl) system, aiming to promote the selective transformation of HOI to iodate (IO 3 − ) 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 10 2 –10 4 M −1 s −1 contrasting with NH 2 Cl’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–NH 2 Cl converts 77–98% of aqueous iodine to IO 3 − , reduces target I-DBP formation by 83–90% and substantially decreased total organic iodine (TOI) at just 20 µM PMS, alongside a 60% decrease in cytotoxicity risk. Notably, this PMS–NH 2 Cl approach requires only minimal PMS addition and may be readily integrated into existing NH 2 Cl-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.