21 



The average maximum uptake of cesium appears to be about one tenth of 

 one per cent of the applied dose. The cesium-to-potassium DF is small— about 0. 2 

 for uptake in nutrient solutions and 0. 02 for additions to the soil. 



In general, it appears that grasses accumulate less strontium than legumes. 

 The fruit and seeds contain less strontium than the leaves or stems because stron- 

 tium tends to accumulate in the vascular tissues of the plants. In contrast with 

 strontium, which only moves readily upward, cesium is easily translocated through- 

 out the plant, with perhaps slightly higher accumulation in young leaves and flowers. 



Strontium and cesium are retained in the soil partly by ion-exchange bonds on 

 clay minerals and organic colloids. A part of the strontium may be synthesized into 

 organic compounds by the microbial population. A third means of retention in the 

 soil can involve fixation processes. A large fraction of cesium- 137 appears to be 

 fixed irreversibly. Exchangeable strontium is leached through soils at the rate of 

 about one inch per 100 inches of leaching water. The downward movement of stron- 

 tium, and probably cesium, is essentially an exchange reaction and proceeds by 

 successive desorption-adsorption sequences. 



The soil that will provide minimum uptake of fission products usually appears 

 to be one considered ideal for maximum crop production. These requirements in- 

 clude high exchangeable calcium, high exchangeable potassium, high organic-matter 

 content, and a slightly alkaline reaction. 



