This study provides further evidence for gastrointestinal uptake of submicro- and nanoplastics and points towards differences regarding bioavailability between microplastics and smaller plastic particles that may result following the ingestion of contaminated food and beverages. Toxic effects were detected after 24 h only in overload situations for the particles in the submicrometer range. Both types of particles resulted in observed differences of uptake behavior, most likely influenced by different lipophilicity, which varied between the polymeric test materials. The submicro- and nanoplastic test particles showed an increased uptake and transport quantity through intestinal cells. Polylactic acid (250 nm and 2 μm (polydisperse)), melamine formaldehyde (366 nm) and polymethylmethacrylate (25 nm) were thoroughly characterized. This work includes the development of cellular and subcellular detection methods for synthetic polymeric particles in the micro- and nanometer-range, using Scanning Electron Microscopy, Small-Angle X-ray and Dynamic Light Scattering methods, Asymmetric Flow Field Flow Fractionation, octanol-water fractionation, fluorescence microscopy and flow cytometry. This study aims to investigate differences between microplastic particles and particles in the submicron- and nanoscaled size derived from food-relevant polymers with a particle size range consistent with higher potential for cellular uptake, fate, and effects when applied to human intestinal and liver cells. Concerning nanoplastics, uptake, transport and potential adverse effects after oral uptake are less well understood. Available data on human health risks of microplastics after oral uptake increased immensely in the past years and indicates very likely only low risks after oral consumption. The continuously increasing use of plastics is supposed to result in a rising exposure of MNPs to humans. Surface modification and particle size show a clear influence on the uptake and cytotoxicity of nano- and microplastic particles. The results show that indeed some dispersants can cause a more pronounced cytotoxic effect than the particles themselves. Uptake and transport as well as biochemical endpoints were measured, complemented by particle characterization. A complex set of nine different polystyrene micro- and nanoparticles was used to elucidate the effect of particle size, surface modification and dispersant. Therefore, it is crucial to determine what causes the effect – size, surface or dispersant? In this study this question was investigated by applying established in vitro models for the intestinal barrier (differentiated Caco-2 monoculture and mucus- and M-cell co-culture) and hepatocytes (differentiated HepaRG cells), mimicking the oral route of particle uptake. This might be misinterpreted as particle effect. Moreover, nano- and microplastics as materials with probably a relatively low toxicity are often applied at high concentrations in in vitro tests, and therefore the solvating agent, namely the dispersant in which the particles are supplied may have a major impact on the outcome. Particles can also have different surface modalities and functionalizations. It is known from nanotoxicology that particles may acquire altered toxicological properties with decreasing particle sizes. Although suitable analytical methods are still lacking, it is likely that these contaminations also contain a nanoplastics fraction. There is increasing evidence that humans are exposed to microplastic particles through contaminated food.
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