Eco-Corona Formation on Photooxidized Plastics Exposed to Mixed Organic Matter

Current research regarding microplastic (MP) fate and effects has largely focused on pristine MPs in simplified aquatic solutions. Yet, MPs are readily transformed upon entering the environment through processes including photochemical weathering and the formation of eco-coronas by adsorption of natural organic matter. In this work, eco-corona formation on virgin and UV-aged polystyrene (PS) and polyvinyl chloride (PVC) was quantified using quartz crystal microbalance with dissipation and changes in the surface chemistry monitored using complementary techniques. The extent of adsorption of bovine serum albumin (BSA) and humic acid (HA) was measured separately and in mixtures representative of real water samples to elucidate important organic matter-MP interactions. UV aging was found to have a significant impact on the mass adsorbed of both organic compounds to polymer surfaces. BSA adsorption was consistent with electrostatic interactions where positively charged amide groups had higher affinity for UV-aged PS (more negatively charged) and lower affinity for UV-aged PVC (less negatively charged). HA adsorption decreased post-UV aging; this behavior was attributed to less favorable hydrophobic interactions and increased electrostatic repulsion relative to unaged polymers. In mixed organic matter solutions, the total mass adsorbed significantly decreased, indicating interactions between organic compounds that limit adsorption. Overall, this study demonstrates the importance of increasing the complexity of MP research where UV oxidation and the character of eco-coronas formed directly change the surface properties of PS and PVC surfaces.