Colloidal stability and aggregation of polyethylene (PE) nanoplastics under UV weathering and PFOA contamination

Abstract

The colloidal stability of polyethylene nanoplastics (PE NPs) determines their environmental fate and transport in aquatic systems. This study investigates how surface modifications-specifically UV weathering and perfluorooctanoic acid (PFOA) adsorption-alter the aggregation behavior of 200 nm PE NPs in salt solutions using characterization techniques such as DLS, zeta potential, FT-IR, tensiometry and adhesion measurements. We found that pristine PE NPs remain stable below ~0.1 mol/L salt concentration due to heterogeneous surface charge from ion adsorption, even without stabilizing surfactants. Environmental modifications produce contrasting effects: PFOA adsorption maintains stability at higher salt concentrations by introducing an additional aggregation barrier, while UV weathering-whether in water or air-significantly promotes particle aggregation through free radical formation. These findings reveal that photochemical and chemical modifications can dramatically shift PE NP stability in opposite directions, with important implications for nanoplastic persistence, bioavailability, and toxicity in natural waters. Understanding these stability changes is critical for predicting nanoplastic behavior and risks in aquatic environments.