Transport of Fullerene Nanoparticles (<i>n</i>C₆₀) in Saturated Sand and Sandy Soil: Controlling Factors and Modeling

Understanding subsurface transport of fullerene nanoparticles (<i>n</i>C₆₀) is of critical importance for the benign use and risk management of C₆₀. We examined the effects of several important environmental factors on <i>n</i>C₆₀ transport in saturated porous media. Decreasing flow velocity from approximately 10 to 1 m/d had little effect on <i>n</i>C₆₀ transport in Ottawa sand (mainly pure quartz), but significantly inhibited the transport in Lula soil (a sandy, low-organic-matter soil). The difference was attributable to the smaller grain size, more irregular and rougher shape, and greater heterogeneity of Lula soil. Increasing ionic strength and switching background solution from NaCl to CaCl₂ enhanced the deposition of <i>n</i>C₆₀ in both sand and soil columns, but the effects were more significant for soil. This was likely because the clay minerals (and possibly soil organic matter) in soil responded to changes of ionic strength and species differently than quartz. Anions in the mobile phase had little effect on <i>n</i>C₆₀ transport, and fulvic acid in the mobile phase (5.0 mg/L) had a small effect in the presence of 0.5 mM Ca²⁺. A two-site transport model that takes into account both the blocking-affected attachment process and straining effects can effectively model the breakthrough of <i>n</i>C<sub>60