FACTORS AFFECTING THE SORPTION AND FIXATION OF CESIUM IN ACID ORGANICSOIL

Radioactive caesium deposited on upland Britain following the Chernoby l accident in 1986 remains available for uptake by plants, despite the potential of the contaminated soils to fix Cs. The minimum concentrat ion of Cs+ required to cause Cs+ fixation is 0.60 to 0.75 mM, and this is unlikely to be reached in any contaminated upland soil, It is sugg ested that the fixation is caused by interlayer collapse of the illiti c clay. The observed Cs+ fixation in lowland mineral soils and its abs ence from acidic upland soils is explained by the action of K+ ions, w hich can also induce interlayer collapse. Although Cs+ ions are unlike ly to be fixed in acid organic soils, they can be strongly sorbed on a ny unoccupied Cs-specific sorption sites in the narrow parts of illiti c wedge zones. A method for determining the number of such sites is de scribed. For two of the soils studied the number of sites ranged betwe en 8x10(-8) and 1x10(-5) mmol kg(-1); for two others there appeared to be no unoccupied Cs-specific sites, Although Cs+ ions sorbed on such sites do not exchange with other ions, they can be desorbed if the con centration of Cs+ in solution is decreased, Thus, radioactive Cs in su ch soils will remain available for plant uptake, unless interlayer col lapse can be induced.