Stable colloidal dispersions of C60 fullerenes in water:: Evidence for genotoxicity

Stable aqueous suspensions of colloidal C-60 fullerenes free of toxic organic solvents were prepared by two methods: ethanol to water solvent exchange (EthOH/nC(60) suspensions) and extended mixing in water (aqu/nC(60) suspensions). The extended mixing method resulted in the formation of larger ((d) over bar (p) approximate to 178 nm) and less negatively charged ((xi) over bar approximate to -13.5 mV) nC(60) colloids than nC(60) prepared by ethanol to water solvent exchange ((d) over bar (p) approximate to 122 nm, (xi) over bar approximate to - 31.6 mV). Genotoxicity of these suspensions was evaluated with respect to human lymphocytes using single-cell gel electrophoresis assay (Comet assay). The assay demonstrated genotoxicity for both types of suspensions with a strong correlation between the genotoxic response and nC(60) concentration, and with genotoxicity observed at concentrations as low as 2.2 mu g/L for aqu/nC(60) and 4.2 mu g/L for EtOH/nC(60). The Olive tail moments (OTM) for these two concentrations were 1.54 +/- 0.24 and 1.34 +/- 0.07, respectively, which in comparison to the negative control OTM of 0.98 +/- 0.17 is statistically different with a p value of at least 0.05. Aqu/ nC(60) suspensions elicited higher genotoxic response than EthOH/nC(60) for the same nC(60) concentration. The results represent the first genotoxicity data for colloidal fullerenes produced by simple mixing in water.