Transport and retention of colloidal aggregates of C60 in porous media: effects of organic macromolecules, ionic composition, and preparation method

The physical-chemical behavior of the fullerene C60 in environmental and physiological media is of interest for understanding the potential transport, exposure, and impacts of these materials on organisms and ecosystems. We considerthe role of electrolyte composition and concentration, the effect of organic macromolecules, and the mode of preparation of colloidal aggregates of C60 (nC60) on the deposition of these colloids in a porous medium such as a groundwater aquifer or a water treatment filter. Results for nC60 deposition are qualitatively consistent with trends anticipated by theory. Deposition was found to increase with increasing ionic strength, the presence of polysaccharide-type organic matter, and lower Darcy velocities. Factors that will tend to decrease the retention of these materials in porous media include a low ionic strength and the presence of humic-like substances, while the ionic strengths typical of many natural waters and the presence polysaccharide-based natural organic matter, as may be produced by algae or bacteria, will tend to favor deposition and reduced potential for exposure. Variability in the method of preparing colloidal aggregates of fullerenes was observed to yield significant differences in nC60 properties and transport behavior.