Colloidal stability of UV-aged and protein-coated nanoplastics in natural waters under warming

Nanoplastics, particles smaller than 1000 nm that are produced by degradation of plastic debris, pose an environmental threat and may endanger natural ecosystems and human health. In aquatic environments, the large surface area and high surface energy of NPs facilitate their interactions with the surroundings; thus, understanding their behavior, transport, and fate is essential. In this study, we investigated the individual and combined effects of UV aging and protein coating on the stability of NPs in aquatic environments under elevated temperatures. UV-aged NPs were created via indoor UV lamp exposure, and protein coating was achieved by introducing bovine serum albumin (BSA). Sequential processes produced UV + BSA and BSA + UV-coated NPs for comprehensive analysis. Aggregation kinetics and stability were examined in electrolyte solutions (NaCl and CaCl₂) and natural waters. Results indicated that BSA coating improved the colloidal stability of NPs in electrolyte solutions by promoting steric repulsion, a trend observed in rivers, lakes, and seawater but not in groundwater. Sequential UV aging after BSA coating caused protein denaturation, reducing the stability of NPs. Additionally, increased temperatures led to a greater level of NP aggregation due to lower energy barriers. These findings highlight UV aging, protein coating, and temperature as critical factors influencing the behavior and fate of NPs in natural environments.