Plutonium is known to bind to soil particles very strongly; see above for an X-ray spectroscopic study of plutonium in soil and concrete. While caesium has very different chemistry from the actinides, it is well known that both caesium and many actinides bind strongly to the minerals in soil. It has been possible to use Cs -labeled soil to study the migration of Pu and Cs is soils. It has been shown that colloidal transport processes control the migration of Cs (and will control the migration of Pu) in the soil at the Waste Isolation Pilot Plant.