Exposure of microplastic at levels relevant for human health : cytotoxicity and cellular localization of polystyrene microparticles in four human cell lines

Microplastics (MPs), which are ubiquitous in our living environment, can enter into human body via diverse pathways such as food packaging, contaminated food and bottled mineral water. Therefore, it is essential to assess the risk of MPs daily human intake. Up to date, almost all of related publications used concentrations that are much higher than likely present in these sources. Thus, investigation at levels of MPs relevant for human health exposure can help us rationally understand the threats of MPs. This study is aimed to evaluate cytotoxicity and quantify the cellular uptake and localization of MPs within the concentration range reported in bottled mineral water in human cell lines. To this aim, four types of human cell lines derived from colon (Caco-2), liver (HepG2) and lung (A549 and BEAS-2B) were exposed to 2-µm fluorescent PS microspheres (1E+3-1E+7 particles/L). A series of cellular and biochemical assays (intracellular reactive oxygen species, mitochondrial membrane potential, sulforhodamine B and MTT assay) were conducted. To confirm the cellular uptake, the fluorescent cells containing PS were counted by flow cytometry to evaluate the probability of cells embedded PS under different concentrations. Furthermore, laser confocal scanning microscopy was used to observe the distribution and count the number of PS microspheres in four cell lines.