Impacts of Eco-Corona on Surface Properties of Nanoplastics

Plastics exposed to environmental conditions can develop eco-coronas. Here, we investigated how the eco-corona impacts the surface properties and transport of nanoplastics in unsaturated sand. Four different plastics, polyethylene (PE), polypropylene (PP), polystyrene (PS), and poly(butylene adipate terephthalate)-based (PBAT) were used in pristine and UV-weathered forms. The nanoplastics were exposed to a water-extractable soil solution to form an eco-corona. Transport of nanoplastics was studied under unsaturated flow condition at 40\% water saturation. Weathering and eco-corona had no obvious effect on the transport of nanoplastics under low ionic strength conditions. For most UV-weathered nanoplastics the zeta potentials became less negative after UV-weathering, indicating decreased surface charge, except for PBAT, whose zeta potentials became considerably more negative after weathering. The eco-corona caused the zeta potentials of the different nanoplastics to become more similar, except for pristine PBAT, which had a considerably less negative zeta potential than the other plastics. The eco-corona decreased contact angles in some cases (PP and PS) but increased the contact angle in others (PE and PBAT). This study demonstrates that both UV-weathering and eco-corona formation modify the physicochemical properties of nanoplastics, such as surface charge and hydrophobicity, with a tendency to make different plastics more similar.