Transport and Retention of Fullerene Nanoparticles in Natural Soils

Commercial production and use of fullerene (C-60) nanomaterials will inevitably lead to their release into the environment, where knowledge of C-60 fate and transport is limited. In this study, a series of one-dimensional column experiments was conducted to assess the transport and retention of nanoscale fullerene aggregates (nC(60)) in water-saturated soils. Under the experimental conditions, complete retention of nC(60) was observed in columns (2.5 cm inside diameter x 11 cm length) packed with Appling or Webster soil, which contain 0.75 and 3.33% organic carbon by weight, respectively. When the volume of aqueous nC(60) suspension (similar to 4.5 mg L-1) applied to Appling soil was increased from 5 to 65 pore volumes, the travel distance increased from 3 to 8 cm, and the retention capacity approached a limiting value of 130 mu g g(-1), although nC(60) was not detected in the column effluent The addition of 20 mg C L(-1)Suwannee River humic acid to the influent suspension increased the nC(60) transport in Appling soil but did not result in breakthrough. Attempts to simulate the experimental data using clean bed filtration theory were not satisfactory, yielding retention profiles that failed to match observed data. Subsequent incorporation of a limiting retention capacity expression into the mathematical model resulted in accurate predictions of the measured nC(60) retention profiles and transport behavior The sizable retention capacities observed in this study suggest that transport of nC(60) is limited in relatively fine textured soils containing appreciable amounts of clay minerals and organic matter with substantial accumulation of nC(60) aggregates near the point of release.