Abstract
Recently, plastic food contact materials such as tea bags can release large amounts of nanoplastics when exposed to hot water. These particles may enter the human body through ingestion and have the potential for absorption and bioaccumulation. The size of nanoplastics is one of the crucial factors affecting the efficiency of absorption. Therefore, it is important to understand how size of nanoplastics change during digestion. In the study, we selected the commercial fluorescent polystyrene (PS) with two diameters (200 nm and 750 nm) and the fluorescent 366 nm melamine-formaldehyde resin (MF) as models. Nanoparticle Tracking Analysis (NTA) operated in the fluorescence model was used to measure the three types of nanoplastics in artificial digestive fluids with and without food matrix. All nanoplastics formed larger agglomerates in gastric juice, but the agglomeration was reduced after intestinal digestion. In gastric juice with pH adjusted while no enzyme added, 200 nm nano-PS agglomeration did not decrease after intestinal digestion. On the other hand, 750 nm PS and 366 nm MF showed similar size of agglomerates throughout the digestion process. The size changes were all associated with zeta potential of the nanoplastics. However, when pH was not adjusted, all particles retained their original secondary size as observed in saliva. Hence, we suggested that in the absence of food matrix, the pH affects differently between various nanoplastics in determining the agglomeration states. Considering the presence of food matrix, all nanoplastics have a larger size in saliva and intestinal fluids, but in gastric juice we observed a lower degree of agglomeration. We thus believed that the formation of protein or lipid corona on the surface of the nanoplastics contributed the size of nanoplastics (e.g. thicker shell or stereo barrier) in the presence of food matrix.
