Exposure of microplastics at levels relevant for human health : acute and long-term cytotoxicity and cellular localization of polystyrene microparticles in four human cell lines

The ubiquity of microplastics (MPs) in the environment raises concerns on human health through potential exposure via air pollution, the food chain and drinking water. However, little is known about the effects of MPs on human health at realistic exposure levels. Herein, the chronic and acute effects of MPs at human realistic exposure levels on four types of human cell lines derived from colon (Caco-2), liver (HepG2) and lung (A549 and BEAS-2B) were investigated. The undifferentiated and differentiated cells involved the most representative exposure routes (inhalation, ingestion, and physiological transport through the liver by the portal vein) were exposed to 2-µm fluorescent polystyrene (PS) microspheres (103-108 particles/L) for 48 h and 12 d. The measurements of flow cytometry and laser confocal microscopy showed that PS could be internalized in cell membrane and even in the nuclei. PS did not cause any significant toxic impacts on mitochondrial membrane potential and cell viability, but induced reactive oxygen species production in undifferentiated A549 and Caco-2 cells upon short exposure, and differentiated A549 cells upon short and chronic exposure. The adenocarcinoma A549 cells from the lung seems to be more sensitive to PS exposure than normal bronchial BEAS-2B cells. Differentiated cells show a higher tolerance to PS than undifferentiated cells under the same exposure conditions. This research is a first step towards more relevant exposure studies to assess risks associated with ingestion, inhalation and internal transport of MPs in the human body