Figure 6: Histograms show the number of colonies formed after 10 consecutive days exposure to increasing concentrations of Cd-SiO2NPs, CdCl2, SiO2NPs at the doses indicated in the figure. The formation of A549 colonies appeared to be serious compromised by both Cd-SiO2NP and CdCl2 treatments already at the lowest dose of 0.05 μg/mL, while SiO2NPs had no effects on their formation. Data are mean ± DS of two separate experiments each carried out in three replicates, expressed as percentage of control colonies. * significant difference from control. Error bars: ±SD.