In this work nanorion (nanoscale zero-valent iron) was prepared by the borohydride reduction method. Nanoiron thus prepared was characterized to be an amorphous phase with a mesoporous structure and specific surface area of 66.34 m(2)/g. Various biodegradable dispersants were added in situ during nanoiron synthesis and tested to evaluate their effectiveness in enhancement of nanoiron stability. PAA (poly acrylic acid) was found to be the best among dispersants tested. One volume percentage of PAA-modified nanoiron slurry was further employed to study its transport behaviors in vertical silica sand/soil columns. It was found that PAA-modified nanoiron slurry could travel through the silica sand column easily, but not the loamy sand soil column. Characteristics of the soil matrix might have retarded the diffusion of nanoiron. Relevant sticking coefficients were determined under various conditions. Further, the transport distance of the PAA-modified nanoiron under typical groundwater conditions in the vertical soil column was estimated to be about 0.25 in. For the horizontal column packed with simulated groundwater-saturated loamy sand soil, the transport distance of the PAA-modified nanoiron under the influence of an external electric field was found to be 10 times greater regardless of potential adverse effects due to a high ionic strength of groundwater in the reaction system. (c) 2007 Elsevier B.V. All rights reserved.