Unveiling the optical and molecular characteristics of aging microplastics derived dissolved organic matter transformed by UV/chlor(am)ine oxidation and its potential for disinfection byproducts formation

Abstract

The investigations into the existence and behavior of microplastics (MPs) in water environment were widely conducted, while the characteristics of dissolved organic matter derived from MPs (MPs-DOM) during advanced oxidation have garnered comparatively little attention. In this study, Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) was employed along with multiple statistical analyses to gain a deeper understanding of the conversion of MPs-DOM in UV/chlor(am)ine advanced oxidation processes (AOPs). The diverse treatments exhibited varying degrees of augmentation in both aging and fragmentation of MPs with the order of UV/Cl2 > UV > UV/NH2Cl. The fragmentation degree of MPs upon two UV-based AOPs (UV-AOPs) was dependent on their monomer chemical structure. The highest TOC values of three MPs-DOM were observed after UV/Cl2 AOP and the lowest after UV/NH2Cl AOP. Polyvinyl chloride (PVC) displayed a greater release of MPs-DOM under varying leaching conditions. UV/Cl₂ AOP favored the reaction with saturated MPs-DOM, while UV/NH₂Cl AOP reduced unsaturated MPs-DOM, alleviating disinfection byproducts (DBPs) formation after chlorination. The precursors generated by UV/Cl₂ AOP owned lower H/C, higher modified aromatic index (AImod), and lower molecular weight (MW) products after chlorination. PVC-DOM with fewer CH₂ groups was more reactive. -H₂O, +O and -CH₂ reactions dominated in PVC-DOM (CHO compounds), while -2H, +O, -CH₂ did in PVC-DOM (CHON compounds). The dominant chlorine addition/substitution reactions occurred in PVC-DOM treated by UV/Cl₂ AOP, identifying 195 Cl-DBPs with 220 precursor-product pairs. Mass difference analyses showed that +2H and +O reactions were the most frequent of the 24 reaction types. Environmental ImplicationMicroplastics derived dissolved organic matters (MPs-DOM) transformed into disinfection byproducts (DBPs) under advanced oxidation processes (AOPs), heightening environmental risks. In this study, Fourier transform ion cyclotron resonance mass spectrometry was employed to gain a deeper understanding of MPs-DOM conversion in UV/chlor(am)ine AOPs. MPs fragmentation and fluorescent components varied with monomer chemistry and polymers. UV/Cl₂ AOP reacted with saturated MPs-DOM. UV/NH₂Cl AOP reduced unsaturated MPs-DOM, alleviating DBPs formation. DBPs precursors generated by UV/Cl₂ AOP owned higher modified aromatic index, lower H/C and molecular weight. Unveiling the MPs-DOM transformation during AOPs can mitigate the negative environmental impacts of MPs and their derivatives.