Chlorination of\nBiopterin in Water: Deciphering the\nKinetics, Disinfection Byproducts, and Toxicity

Pterins, including biopterin prevalent during cyanobacterial\nblooms,\nare nitrogen-containing heterocyclic compounds ubiquitous in both\nnatural and engineered environments. However, their roles and associated\nhuman risks in water treatment remain poorly understood. This study\nsystematically investigated the kinetics, disinfection byproducts\n(DBPs), and toxicity of biopterin in chlorination. For deciphering\nthe reaction kinetics, 1,3,5-trimethoxybenzene proved to be a more\neffective chlorine quencher than the commonly used reducing agents,\nas it preserved N-chlorinated intermediates without reversing them\nback to biopterin. The pH-dependent kinetics demonstrated that both\nchlorine and biopterin species had a significant influence on the\nreaction rates, with deprotonated biopterin exhibiting a markedly\nhigher reactivity toward HClO/ClO<sup>–</sup>. Based on time-of-flight\nmass spectrometry, ten transformation products (TPs) including seven\nhalogenated N–Cl ones, have been identified for the first time.\nThese cyclic TPs were transformed into various aliphatic carbonaceous\nand nitrogenous DBPs during the subsequent chlorination process. Notably,\ntheoretical predictions and the luminescent bacteria assay confirmed\npotential higher toxicities of these products than biopterin. These\nfindings highlight the potential risks of pterins during water disinfection\nand provide a reference framework for accurately revealing the chlorination\nbehavior of emerging nitrogenous chemicals.