Water soluble and insoluble components of urban PM_2.5 and their cytotoxic effects on epithelial cells (A549) in vitro

When PM_2.5 enters human bodies, the water soluble (WS-PM_2.5) and insoluble components (WIS-PM_2.5) of PM_2.5 would interact with cells and cause adverse effects. However, the knowledge about the individual toxicity contribution of these two components is limited. In this study, the physiochemical properties of PM_2.5 were well characterized. The toxic effects of WS-PM_2.5 and WIS-PM_2.5, which include the cell viability, cell membrane damage, reactive oxygen species (ROS) generation and morphological changes, were examined with human lung epithelial A549 cells in vitro. The results indicated that WS-PM_2.5 could induce the early response of ROS generation, multiplied mitochondria and multi-lamellar bodies in A549 cells, which might cause cell damage through oxidative stress. Meanwhile, WIS-PM_2.5 was predominantly associated with the cell membrane disruption, which might lead to the cell damage through cell-particle interactions. Moreover, the synergistic cytotoxic effects of WS-PM_2.5 and WIS-PM_2.5 were observed at longer exposure time. These findings demonstrate the different cytotoxicity mechanisms of WS-PM_2.5 and WIS-PM_2.5, which suggest that not only the size and dosage of PM_2.5 but also the solubility of PM_2.5 should be taken into consideration when evaluating the toxicity of PM_2.5.