8. 



conditions the two sources of strontium-90 can be differentiated. We can deter- 

 mine the amount of strontiiiin-90 in the harvested crop and compare that with some 

 lower tissue that reflects only the specific amount absorbed from the soil. This 

 is possible since strontium-90 retained on leaves or grain is not transported 

 downward in the plant. The most useful tissues for determining the specific 

 activity absorbed from the soil will be small grain or hay stubble where the 

 leaves do not concentrate fallout near the stem base. The lower stalks of corn, 

 beans, tomatoes, and many other plants can also be used. 



Reaction of Strontium-90 with Soils 



Strontium-90 is leached slowly through soils. The movement in five widely 

 varying soil types averaged less than one inch per 100 inches of leaching water. 



About one per cent of the strontium falling on sloping land at Tifton, 

 Georgia and LaCrosse, Wisconsin was carried down the slope in runoff water. The 

 slopes were 3 per cent on sandy loam at Tifton and 16 per cent on silt loam at 

 Lacrosse. However, the concentration of strontium-90 in the eroded sediment was 

 10 times higher than that in the plow layer of soil left behind. Thus if a soil 

 were made up of such sediments, it could have 10 times the average strontium-90 

 concentrate for the area. 



Most of the strontium-90 in soils is exchangeable. This is the form of 

 cations in soils that is available to plants. Exchangeable strontium-90 and 

 calcium are taken up by plants in nearly the same ratio. The uptake of Sr-^ can 

 be affected by additions of lime, fertilizers, organic matter, and by placement 

 of these amendments and Sr'*^ in the soil. 



Factors Affecting Uptake of Strontium-90 by Plants 



Lime bearing amendments reduce the Sr^^/Ca ratio in the crop. The reduction 

 is about equal to the factor by which the available calcium content of the soil 

 can be raised. Even on the most acid soils, it is unlikely that available calcium 

 can be tripled, and therefore Sr^O/ca ratio will not be reduced by more than a 

 factor of three. If the amendment causes increased calcium uptake by the crop, 

 there miay be little or no reduction in Sr^O uptake* 



Fertilizers and organic matter change Sr^^ and Ca uptake proportionately if 

 account is taken of any available calcium added in these materials. Ammonium 

 nitrate (140 ppm N) almost doubled uptake of Sr^O, Potassium nitrate (270 ppra K) 

 decreased Sr"^ uptake by 40 per cent. 



Under field conditions, the uptake of strontium-90 may be greatly affected 

 by its placement and that of calcium relative to the plant root system. Experi- 

 ments are being initiated in which we plow the Sr"" as deeply as possible, and 

 keep the plant roots as shallow as possible by use of lime, fertilizer, and 

 irrigation. The immediate goal of these experiments is to reduce Sr-^ uptake by 

 a factor of 10. 



Land Utilization in Areas Seriously Contaminated with Strontium-90 



Land seriously contaminated with strontium-90 may be utilized by changing 

 production, removing contamination, fixing strontium-905 plowing deep, or 

 applying amendments. None of these measures have been adequately studied. Some 

 may be effective only in certain situations. 



