Most of the immediate cell survival values, as determined by counting recovered cells after exposure to CSNPs, were above 70% at all times and concentrations tested with the exception of the 0.25-mg/mL concentration, which resulted in cell survival of 47% after 15 minutes of exposure
(Fig. 1A) . Cell survival immediately after CSNP exposure for 30 minutes was significantly higher (
P < 0.05) than after exposure for 15 or 60 minutes, as determined by the Scheffé post hoc test. Cell survival after 0.5- and 1 mg/mL CSNP exposure for 30 minutes was at its maximum (103% and 108%, respectively). These high cell survival rates were also observed when cells were maintained in culture medium for an additional 24-hour period after exposure to CSNPs
(Fig. 1B) . The only exception was for cells incubated in 1 mg/mL CSNP, where the 24-hour survival was of 45% for the 2-hour treatment. Cell survival rates after the 24-hour recovery period of PBS and CSNP-treated cells were significantly lower than those of the control culture medium–exposed cells (
P < 0.05). There were no significant differences in cell survival in the immediate or 24-hour recovery period among the different concentrations of CSNPs tested or the PBS-treated cells. The survival of BAC-exposed cells was significantly lower when determined immediately
(Fig. 1A)and after the 24-hour recovery period
(Fig. 1B) . The great majority of the recovered cells were living, as shown by exclusion of Trypan blue. The viability of recovered cells was always higher than 92% when measured immediately after CSNP exposure and higher than 86% in cells maintained for 24 hours in culture medium after CSNP exposure
(Figs. 1C 1D) . No significant differences in cell viability were observed among CSNP concentrations or incubation times, or when compared with culture medium controls. As expected, viability of BAC-treated cells was significantly lower of that of controls, both immediately after treatment and after the 24-hour recovery period.