The production of significant quantities of engineered nanomaterials will inevitably result in the introduction of these materials to the environment. Mobility in a well-defined porous medium was evaluated for eight particulate products of nanochemistry to assess their potential for migration in porous media such as groundwater aquifers and water treatment plant filters. Contrary to the assertion that nanomaterials present monolithic environmental risks, here we show that these nanomaterials exhibit widely differing transport behaviors. Fullerene-based nanomaterials that had been functionalized to facilitate dispersal in water displayed the highest mobilities, with a calculated potential to migrate approximately 10 m in unfractured sand aquifers. Colloidal aggregates of C60, which have been the focus of recent toxicity studies, were among the least mobile of the nanomaterials evaluated.