Environmental exposure enhances the internalisation of microplastic particles into cells

, Ramsperger Anja Frm, Bangaloore Narayana Vinay K, Gross Wolfgang, Mohanraj John, Thelakkat Mukundan, Greiner Andreas, Schmalz Holger, Kress Holger, Laforsch Christian.

Research efforts and public attention on microplastic pollution was exponentially increasing during the last years due to the observed variety of effects on an organismal and environmental level. Plastic introduced to the environment undergoes processes of degradation and fragmentises down to microplastic. Furthermore, the colonisation by microbes, together with biomolecules, forms an ecocorona on microplastic particle surfaces that enhances the ingestion of microplastic by organisms. Once ingested there is evidence that microplastics harm organisms and translocate in tissues causing histological changes and inflammatory responses. The reason for cellular internalisation is unknown, since this has only been shown for specifically surface-functionalised particles. The translocation of environmentally relevant microplastics into tissues may occur via the paracellular or transcellular pathway. Paracellular transport occurs in between cells by gap junctions for instance, whereas the transcellular transport occurs via the internalisation into cells directly. Due to the size of microplastics the transcellular pathway into tissues seems more realistic. Therefore, we investigated the cellular internalisation of environmentally relevant microplastic particles. We show for the first time, that the exposure of microplastic particles in the aquatic environment significantly enhances the internalisation into macrophages compared to pristine microplastic particles. We identified biomolecules forming an ecocorona on the surface of microplastic particles from both, fresh- and saltwater by using scanning electron microscopy, µ-Raman spectroscopy, and X-ray photoelectron spectroscopy. Our findings suggest that the environmental exposure of microplastic particles promotes their cellular internalisation. Our results provide new insights that the transcellular pathway via cellular internalisation is a key route by which microplastic particles can translocate into tissues. These findings will help to better understand the risks deriving from plastic pollution.

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