0.1 g of iron nanoparticle powder was mixed manually with 1000 g of dry soil. To have a moisture equivalent of about 20%, 200 mL. of deionised water was added drop- wise to this soil. Then it was homogenized with a Teflon rod attached to a mechanical stirrer for 30 minutes and kept for equilibration for 12 h. A control soil sample, without adding iron nanoparticles, was prepared in a similar manner.