Chemical Characterization of Seasonal PM_2.5 Samples and Their Cytotoxicity in Human Lung Epithelial Cells (A549)

In order to study the toxicity of fine particulate matter (PM_2.5) sourced from different seasons on human health, we collected PM_2.5 samples quarterly from March 2016 to February 2017 in Nanjing, China. The component analysis results showed that high proportions of water-soluble organic carbon (WSOC), SO₄^2-, Ca²⁺ and Mg²⁺ were found in the summer samples, while high proportions of NO₃^-, NH₄⁺ and heavy metals were observed in the spring and winter samples. Then human lung epithelial cells (A549) were exposed to the PM_2.5 samples. The toxicological results indicated that reactive oxygen species (ROS) production in the spring and winter samples was higher than that in the summer and fall samples, which was related to the contribution of some heavy metals and inorganic ions (e.g., Pb and NO₃^-). However, the apoptosis rates of the cells showed the opposite seasonal changes as what the ROS did, which might be caused by the higher WSOC content in the summer. In addition, regression analysis also showed the importance of the PM_2.5 components in ROS production and apoptosis. Particularly, Zn had the strongest correlation with ROS production (R = 0.863) and cell apoptosis (R = 0.675); thus, the specific toxicity of Zn in PM_2.5 deserves further investigation. Our results could be beneficial for assessing the health risks and controlling the toxic components of PM_2.5 in Nanjing.