Effects of microplastic aging on the adsorption and desorption of trihalophenolic disinfection by-products in drinking water distribution systems.

Microplastics (MPs) and disinfection by-products (DBPs) commonly coexist in drinking water distribution systems (DWDSs), raising concerns regarding MP-mediated DBP migration. This study investigated the adsorption and desorption of typical halogenated phenolic DBPs, namely 2,4,6-trichlorophenol (TCP) and 2,4,6-tribromophenol (TBP), on pristine and aged polyamide microplastics (PAMPs), with aging induced by UV irradiation and ClO2 oxidation. Molecular dynamics simulations were employed to elucidate the adsorption mechanisms. Additionally, TCP adsorption on colloidal polystyrene microplastics (CPMPs) in the presence of pipe scales was examined to assess the role of pipe scales in regulating TCP migration in DWDSs. Findings demonstrated that the adsorption of TCP and TBP on PAMPs was primarily driven by van der Waals interactions, with contributions from hydrophobic, electrostatic, and hydrogen bonding interactions. UV aging at 254 nm significantly increased the O/C ratio, elevated carbonyl indices, and reduced the hydrophobicity of PAMPs compared with UV aging at 340 nm, resulting in decreased adsorption. ClO2 oxidation enhanced the adsorption by increasing electrostatic interactions between PAMPs and TCP/TBP. Aging elevated DBP desorption by 5.10%-29.43% (TCP) and 2.47%-10.10% (TBP), and TCP exhibited weaker desorption hysteresis than TBP. CPMPs acted as important carriers of TCP in DWDSs, while pipe scales functioned as effective sinks by adsorbing TCP-loaded CPMPs, thereby reducing TCP migration. Overall, this study elucidates how the aging of MPs alters the fate of DBPs and highlights the role of pipe scales in regulating the fate of DBPs in DWDSs, providing important insights for the risk assessment and control of MPs and DBPs.