[en] In order to explain changes in sorption of actinides by soils relative to the concentration of the actinide in the system, observations were made with respect to selected chemical and physical characteristics of the actinide in solution and the sorption of the actinide by soils. Sorption is discussed in relation to: the relative concentration of the various aqueous actinide specie; polymerization of aqueous actinides: and the formation of complexes with other ions. Most experimental work on aqueous actinides has been conducted under conditions unlike those in a soil/water environment, therefore, the evluation necessarily involves theoretical as well as experimental considerations