Artificial digestion represents the worst-case scenario for studying nanoplastic fate in gastrointestinal tract

Humans may inevitably be exposed to nanoplastics (NPls) through ingestion. The size of NPls significantly influences their absorption efficiency, so understanding behaviors of NPls during digestion is vital for risk assessment. In this study, fluorescent polystyrene (PS) and melamine-formaldehyde resin (MF) NPls were characterized by different techniques after the in vitro digestion process both with and without a standard food model, or with and without pH adjustment in the absence of the proteins. Results derived from the in vitro method were compared to those using human and porcine digestive fluids. In summary, different types/charges of NPls caused distinct agglomeration states during the digestion procedure, and the pH and protein corona affected the agglomeration state of smaller PS particles more obviously than they did the other tested particles. The presence of a food matrix did not significantly change the particle size, while the protein corona composition was largely altered. Compared to real digestive fluids, size trends observed for NPls were consistent with those in artificial ones, while they were mostly underestimated, which for the first time, proves that the in vitro digestion can be regarded as a conservative model for predicting aggregation of NPls in gastrointestinal tract.