Following the fate of polystyrene micro and nanobeads during in vitro digestion

The objective of this project was to follow the fate of nano and microplastic particles during gastrointestinal transfer. Polystyrene latex nano (60 nm) and micro (1 μm) beads were employed as model system for microplastic particles and mixed (68 mg/mL) with 5 % (w/v) whey protein solution to study the food effect. The digestion of this mixture was then subjected to the INFOGEST <i>in vitro</i> digestion protocol. Residual particles in the digesta were then loaded on 21 days differentiated co-cultures of Caco-2/HT29-MTX, to further determine their potential transfer through intestinal monolayers. Digested samples diluted 1:16, showed no cytotoxic effect on Caco-2 cells, possibly due to the presence of a protective mucus layer. Digestion and permeability experiments were further analysed using gas chromatography with mass spectrometry (GC-MS), and different monomers (styrene), styrene oligomers (1-phenyl-1,2-ethanediol; 1,4-diphenyl-1,3-butadiene; 1,2-diphenylcyclopropane; α-methyl benzenemethanol), other intentionally added substances (caprolactam, benzaldehyde, di(2-ethyl hexyl) phthalate) and non-intentionally added substances (e.g. 2,4-di-tert butylphenol, isophthalaldehyde) were identified. Analysis of the basolateral fraction indicated a notable transfer of these compounds through cell membranes. This holistic approach using a food matrix to follow the fate of microplastic during digestion leads to a better understanding of the risks of microplastics and nanoplastics through food.