The transformations of water-stable C-60 clusters (nC(60)) to oxidized C-60 derivatives via photoreactions and ground-state reactions have been described as critical processes in understanding the ultimate environmental fate of fullerene-based materials. However, (photo) oxidation of aqueous-based C-60 (as water stable, nanoscale aggregates termed nC(60)) with hydrogen peroxide (H2O2) and/or hydroxyl radical (center dot OH), common environmental oxidants, has not been fully explored. To address this, the aqueous physicochemical transformations of C-60 (as nC(60) aggregates) in the presence of H2O2 and/or center dot OH in both photoexcited-state and ground-state under environmentally relevant conditions are quantitatively described. Results show that nC(60) undergoes facile oxidation in the presence of H2O2 under UVA irradiation but not under dark conditions, and the oxidation reaction rates increase with effective center dot OH concentration (via photodecomposition of H2O2), while being inversely related to solution pH. Product characterization via dynamic light scattering, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, total organic carbon, high-performance liquid chromatography, and octanol-water partition experiments collectively describe resulting C-60 derivatives with new covalent oxygen functionality which are also relatively more hydrophilic. For all cases, photoirradiation was observed to significantly enhanced the rates and extent of C-60 oxidation.