Effect of PM2.5 on the growth of human SMMC-7721 cells (A) SMMC-7721 cells were cultured in the presence of various concentrations (5, 25, 50μg/ml) of PM2.5 for 24 h. Cell proliferation was measured by CCK8 assay. The optical density was then measured at 450 nm and the results were presented as percentage of control (arbitrarily set at 100%). All data shown are the of three separate experiments. (B) SMMC-7721 cells were cultured in the presence of 25 μg/ml PM2.5 for different time (12, 24, 48h). Cell proliferation was measured by CCK8 assay. The data were shown as the optical density measured at 450 nm. All data shown are the of three separate experiments. *, p < 0.05, **, p < 0.01.