Destabilization of photochemical weathered nanoplastics by natural organic matter in monovalent electrolyte solutions

Photochemical weathering and eco-corona formation through natural organic matter (NOM) adsorption play vital roles in the aggregation tendencies and colloidal stability of nanoplastics (NPs) in aquatic environments. However, it remains unclear how photochemical weathering alters the adsorption patterns of NOM and the structure of the eco-corona, subsequently affecting the colloidal stability of NPs. The adsorption/interaction of Suwannee River NOM (2 mg C/L) on pristine and photoaged NPs (10 mg/L; exposed to mercury lamp irradiation for 0, 2, 4, and 8 days) was evaluated by determining the reduction of UV280 of NOM and changes in the hydrodynamic size and zeta potential of NPs in 10 mM and 100 mM NaCl. The effect of NOM (1-10 mg C/L) adsorption on the aggregation kinetics of pristine and photoaged polystyrene (PS) NPs was examined in monovalent electrolyte solutions (100-1000 mM NaCl). Monovalent salts commonly found in natural waters are suitable for determining the interaction between NPs and NOM without the interference of multivalent ions. The results elucidated that photochemical weathering might affect the structure of the eco-corona, which, in turn, determined NP stability in the presence of NOM. Hydrophobic components of NOM predominantly bound to pristine NPs through hydrophobic and π-π interactions, and extended hydrophilic segments of NOM in water hindered NP aggregation via steric repulsion. Conversely, hydrogen bonding facilitated the binding of these hydrophilic segments to more than one photoaged NP, thereby destabilizing them through polymer bridging. Additionally, the stabilization or destabilization capacity of NOM depended on its molecular weight, with higher molecular weight leading to stronger steric repulsion or polymer bridging. These findings have shed light on the destabilizing role of NOM in monovalent electrolyte solutions, offering new perspectives on environmental colloidal chemistry and the fate of NPs in complex aquatic environments. Also see: https://micro2024.sciencesconf.org/555697/document