Potential concerns in fullerene application to water treatment related to transformation, cellular uptake and intracellular catalysis.

Fullerene (C) exhibits versatile properties that shows great potential for improving water treatment technologies. However, the probable transformation of C during water treatment, which consequently changes the physicochemical properties and toxicity of the parent compound, may introduce doubt concerning its application. Our results demonstrated that the C aggregate (nC) was transformed to a more oxidized form under common water disinfection processes (i.e., ultraviolet irradiation and photochlorination). The light-irradiated product (UV_nC) exhibited lower cytotoxicity toward macrophage J774A.1 cells relative to nC, whereas the photochlorinated product (UV/Cl_nC) increased the toxic effect. Particularly, the internalization of nanoparticles and the mimetic superoxide dismutase (SOD) activity resulted in the selective accumulation of intracellular hydrogen peroxide. Thus, sequential exposure to a nonlethal dose of nanoparticles followed by 5 μM copper ions (which is a much lower level than the EPA-regulated level of 20 μM in drinking water) led to the significant production of hydroxyl radicals inside cells. The uptake and SOD-like activity were highly structure-related, with the most noteworthy activity obtained for UV/Cl_nC. These results emphasize that environmental transformation-induced property changes should be given adequate consideration in the risk assessment of C.