strontium is leached slowly through the soil at a rate related inversely to the 

 CEC. Under cropping and fertilizer treatments in soil columns, calcium-45 moved 

 about four inches downward (11), but no detectable movement three inches laterally or 

 four inches downward was observed after 14. 5 inches of rain in 89 days of field ex- 

 periments (12). Strontium-90 from worldwide fallout was located primarily in the 

 upper two inches of uncultivated soil during 1954 and 1955. In 1957, as much as one 

 half of the strontium-90 was found in the two- to six-inch layer of some soils (1, 2). 



The desorption of cesium is less than that of strontium, possibly because of 

 fixation by micaceous minerals (113). The rate and depth of leaching increases with 

 increments in salt concentration, acidity, and complexing agents, and with a de- 

 crease in base saturation and buffer capacity of the soil. Lime and organic matter 

 also reduce the desorption of strontium and cesium (47). 



C. Effects of Other Ions 



The complementary ion exerts a strong effect on the adsorption of a cation. 

 All cations tend to reduce strontium and cesiunn adsorption if used in large amounts. 

 The order of replacement on soil materials is usually lithium< sodium<potassium 



< ammonium < rubidium < cesium < hydrogen < magnesium < calcium < strontium 



< barium < iron <aluminum< lanthanum (48; 60; 62; 124; 128, pp. 158-181; 134). Var- 

 ious exchange equations have been suggested, but none appears universally applicable. 

 The effect of anions cannot be neglected, for it was found that nitrate, chloride, and 

 sulfate reduce the sorption of strontium in that order, whereas oxalate and phosphate 

 tend to increase it (61, pp. 170-190). 



D. pH Effects 



In most studies of pH effects, the pH of the leaching solution has been varied. 

 In agriculture, the pH of the soil rather than the contaminating solution is variable. 

 The results of some studies (61, pp. 170-190; 91; 100; 101) indicate that the maximum 

 adsorption of strontium occurs between pH 7 and 9, cesium at 6 and higher, yttrium 

 and cerium above 6, and plutonium from 2. 5 to 9. 0. Since highly acid and alkaline 

 conditions result in the decomposition of the soil minerals, it is expected that under 

 such conditions there would be less fission-product adsorption as a result of com- 

 petition by the products of decomposition, particularly aluminum. 



E. Clays 



Clays differ in their exchange capacity per unit weight and in the energy with 

 which adsorbed ions are held. Exchange capacities in terms of milliequivalents of 

 strontium per g of some representative clays (38) are vermiculite, 1.36; Utah 

 bentonite, 1.28; illite, 0.23; and kaolinite, 0.05. The percentage of water-soluble 

 strontium in a bentonite suspension is 4 compared to 30 for kaolinite (82). Less 

 strontium is adsorbed on illite than on bentonite and a greater uptake of strontium 

 is observed in plants grown in illite (63). 



