From ingestion to transformation: in vitro evidence of nanoplastic alterations by biological fluids.

The presence of nanoplastics (NPs) in the environment raises concerns about human exposure, mainly through ingestion. However, little is known about their physicochemical transformations during digestion. This study investigated the behaviour of polystyrene (PS) NPs (350 nm, 500 nm, and a 1:1 mixture) during in vitro digestion. Dynamic light scattering (DLS), ζ-potential measurements, and single-particle extinction and scattering (SPES) were used to evaluate changes in particle size, surface charge, and number concentration. Protein corona formation was analysed by high-resolution automated electrophoresis. Digestive conditions significantly affected NPs colloidal stability, particularly during the gastric phase, promoting aggregation and changes in particle size distribution. NPs rapidly acquired a dynamic protein corona mainly composed of digestive enzymes, with composition varying across digestive compartments. These findings demonstrate that gastrointestinal digestion alters NP physicochemical properties. Further studies are needed to determine how these transformations influence intestinal uptake, barrier translocation, bioavailability, and ultimately their potential toxicological impact.