Uptake and effects of orally ingested polystyrene microplastic particles in vitro and in vivo

Evidence exists that humans are exposed to plastic microparticles via diet. Data on intestinal particle uptake and health-related effects resulting from microplastic exposure are scarce. Aim of the study was to analyze the uptake and effects of microplastic particles in human in vitro systems and in rodents in vivo. The gastrointestinal uptake of microplastics was studied in vitro using the human intestinal epithelial cell line Caco-2 and thereof-derived co-cultures mimicking intestinal M-cells and goblet cells. Different sizes of spherical fluorescent polystyrene (PS) particles (1, 4 and 10 µm) were used to study particle uptake and transport. A 28-days in vivo feeding study was conducted to analyze transport at the intestinal epithelium and oxidative stress response as a potential consequence of microplastic exposure. Male reporter gene mice were treated three times per week by oral gavage with a mixture of 1 µm (4.55 × 10⁷ particles), 4 µm (4.55 × 10⁷ particles) and 10 µm (1.49 × 10⁶ particles) microplastics at a volume of 10 mL/kg/bw. Effects of particles on macrophage polarization were investigated using the human cell line THP-1 to detect a possible impact on intestinal immune cells. Altogether, the results of the study demonstrate the cellular uptake of a minor fraction of particles. In vivo data show the absence of histologically detectable lesions and inflammatory responses. The particles did not interfere with the differentiation and activation of the human macrophage model. The present results suggest that oral exposure to PS microplastic particles under the chosen experimental conditions does not pose relevant acute health risks to mammals.