Prepared polypropylene microplastics: formation of eco-corona in aquatic systems and their combined toxicity with cadmium in <i>Artemia franciscana</i>

Our study investigated the interactions between colloids present in various aquatic environments and the surface of microplastics (MPs), with a specific focus on their behavior in tap water, lake water and marine water systems. This phenomenon is commonly referred to as "eco-corona". Polypropylene microplastics, although extensively utilized in various applications, have been less studied than polystyrene and polyethylene microplastics. The prepared polypropylene microplastics were characterized by ATR-FTIR and Raman spectroscopy, and the formation of eco-corona was monitored at specific time intervals (24, 48, 72, 96 and 120 h). Fluorescence spectroscopy was used to measure the corresponding fluorescence intensity. Further investigations through FTIR spectroscopy revealed a reduction or complete disappearance of the characteristic polymer peaks upon suspension in natural water systems. Eco-coronated MPs exhibit more cadmium adsorption than raw MPs. The combined exposure of eco-coronated MPs and cadmium to the brine shrimp <i>Artemia</i> leads to the bioaccumulation of microplastics. At its peak concentration (0.5 mg mL^-1), both weathered and true-to-life microplastics significantly increased reactive oxygen species production (<i>p</i> < 0.001) in a concentration-dependent manner. Similarly, superoxide dismutase activity increased in a dose-dependent manner, with weathered microplastics showing significant elevation (<i>p</i> < 0.001). Conversely, total protein content was reduced at higher concentrations of both weathered and true-to-life microplastics. The interaction between microplastics and biomolecules/colloids diminishes their presence in the environment, acts as a vector for pollutants, and mimics food for aquatic organisms. Additionally, it facilitates bioaccumulation in lower-to-higher aquatic organisms and contributes to the collapse of the food web.