An Overlooked Source of Nitrosamines from Tire-Derived Amine Additives: The Contribution and Transformation Mechanism of N -Isopropyl- N ′-phenyl- p -phenylenediamine (IPPD) during Chlorination

Identification of disinfection byproducts (DBPs) precursors remains a longstanding challenge due to the complexity of contaminated source water. Tire wear particles (TWPs) can be an overlooked source of DBPs precursors. To figure out the specific amine additives in tire rubber serving as potential nitrosamine precursors during chlorination, six frequently measured tire-derived amine additives, including N-(1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), N-isopropyl-N′-phenyl-p-phenylenediamine (IPPD), N-cyclohexyl-N′-phenyl-p-phenylenediamine (CPPD), N,N′-dicyclohexylurea (DCU), diphenylamine (DPhA), and N,N′-dicyclohexylamine (DCHA), were selected to simulate their degradation processes, and their DBPs formation potentials were evaluated under various water matrices. IPPD was found to have a high molar yield of N-nitrosodimethylamine (NDMA, up to 8%), while 6PPD exhibited a lower molar yield (∼0.1%) with the molar ratio of chlorine-to-ammonium nitrogen (Cl2:N = 2) and disinfectant-to-precursor (D/P = 10). Suspect and target screening approaches were further applied to identify the transformation products of IPPD, and the formation pathway of NDMA via IPPD was proposed. Furthermore, we assessed NDMA formation from IPPD in simulated TWP leachates through chlorination experiments in the presence of ammonia, which revealed that IPPD contributed up to 24% of the total NDMA formed. This study offers new insights into the previously overlooked source of nitrosamines from tire-derived amine additives.