Kinetics of C60 Fullerene Dispersion in Water Enhanced by Natural Organic Matter and Sunlight

The industrial-scale production of Buckminster fullerene C-60 elicits concerns over its impact on human health and ecosystems because of the reported, albeit debatable, toxicity. Assessment of the overall environment risk requires a good estimate of the level of exposure and careful characterization of the physicochemical properties of C-60 in natural aqueous environments. The reported study investigates the role of various environmental factors, i.e., ionic composition, natural organic matter (NOM), and light in dispersion of C-60 in the aqueous phase by simple mixing. The presence of NOM greatly enhances C-60 dispersion, and the dispersion process is further accelerated by sunlight. At typical NOM concentrations found in natural waters, C-60 concentrations of a few to tens of milligrams per liter can occur within 10 days of mixing, regardless of its extremely low water solubility. The rate of dispersing decreases with the increase of ionic strength. However, calcium ions significantly increase C-60 concentration in the aqueous phase. Results from UV/vis absorbance characterization strongly suggest that C-60 may have been chemically modified when dispersed in an NOM solution in the presence of sunlight. This reaction pathway has significant implication on the fate, transport, and environmental impact of C-60 fullerene.