How Bioavailable Are Polypropylene Microplastics? In Vitro Evidence and Potential Health Relevance

Introduction: Microplastics (MPs) are solid polymer particles of various shapes and sizes, typically ranging from 0.1 to 5,000 µm. Their presence has been widely documented in both the environment and food products. Their occurrence in food suggests that the gastrointestinal tract is one of the primary routes of human exposure to these contaminants. However, their fate within the gastrointestinal tract remains poorly understood. The aim of this study was to develop and evaluate an in vitro methodology for assessing the bioavailability of MPs in the human digestive system.

Methods: The bioavailability of polypropylene microparticles was assessed using a three-stage in vitro digestion model that simulates the functioning of the human gastrointestinal tract. The particles were subjected to simulated digestion under conditions corresponding to the oral, gastric and intestinal phases, at a temperature of 37°C. Dialysis membranes were used in the model to assess the extent to which the MPs passed into the intestinal lumen. After digestion, the particles were separated by filtration and analyzed using optical microscopy and μ-FTIR spectroscopy.

Results: The results showed that, independent of the type of matrix used, the MPs pass through the dialysis membrane. However, the presence of digestive processes leads to physicochemical changes of the polymer. Surface oxidation and morphological changes were identified using FTIR microspectroscopy (μ-FTIR) and optical microscopy.

Conclusions: The study suggests that polypropylene MPs undergo physicochemical changes in the gastrointestinal tract and may become bioavailable. In vitro models are useful tools for preliminary exposure risk assessment; however, they do not fully reflect the complexity of the human body These findings highlight the need for further research using more advanced biological models and in vivo studies to better determine the health relevance of exposure to MPs.

The research was funded by the National Science Centre in Poland (OPUS 25, grant number NR2023/49/B/N29/0061).