TREATMEUSTTS FOR FARMLAND CONTAMINATED WITH RADIOACTIVE MATERIAL 



take from deep placement of strontium-9() varied 

 considerably with different crops and locations. 



In similar experiments carried out in Russia, 

 the uptake of mixed fission products was com- 

 pared from placements 30 and fiO or 7() cm. (12 

 and 24 or 28 in.) beneath the surface of a soddy 

 leached soil (10. pp. 20^-208). This type of soil 

 encourages shallow rooting of plants. Several 

 crops were grown in 3 or 4 successive years on 

 the same plots. The results with each crop varied 

 greatly fi-om year to year. In general, the up- 

 takes from the deeper placements were about 

 one-tenth of those from the shallow placement. 

 The reduction from deep placement was least 

 with oats and barley, intermediate with peas, and 

 greatest with vetch. 



Field tests with varying depths of plowing to 

 reduce radiostrontium uptake have been reported 

 from England (24) and Russia {13). Deep plow- 

 ing to 50 cm. (20 in.) on a leached chernozem 

 soil in Russia reduced average uptake of stron- 

 tinni-90 by oats to 60 percent of the U])take after 

 disking 10 cm. (3.9 in.) deep. The uptake by 

 individual plants was highly vai-iable, perhaps 

 because plowing tended to band the surface- 

 applied sti-ontium-90. In England, studies on 

 widely varying soil types showed that, in gen- 

 eral, the deepest plowing (12 inches) resulted 

 in least uptake for shallow-rooted crops such as 

 ryegrass and a grass-clover pasture. However, 

 plowing depths to 12 inches had little effect on 

 the strontium-89 uptake by deep-rooted crops. 



Various herbicides and inorganic chemicals 

 were used in greenhouse and field experiments 

 to limit uptake from a buried soil layer contain- 

 ing strontium-85 (19). Wlien sodium carbonate 

 was placed with the contaminated layer at the 

 rate of 10 tons per acre, the uptake of stron- 

 tium-85 was less than one-tenth of that without 

 sodium carbonate, but crop yields were only 

 slightly reduced. Seven other inorganic chemicals 

 and seven herbicides did not reduce strontium-85 

 uptake as effectively and tended to give greater 

 yield reductions. But this limited experience 

 does not establish that sodium carbonate is the 

 best material to use as a root inhibitor. A long- 

 lasting, immobile material that will stop root 

 growth into the contaminated soil volume with- 

 out reducing crop yields is needed. 



In a subsequent experiment on an irrigated 



silty clay loam in Texas, sodium carbonate at 

 the same rate of application was plowed to a 

 depth of 3 feet with contaminated surface soil 

 (20). A 36-inch moldboai'd plow with an at- 

 tached grader blade was used to push a 2-inch 

 layer of topsoil into the furrow behind the mold- 

 boai'd. Nearly all (95 percent) of the contami- 

 nated surface soil was placed deeper than 24 

 inches beneath the plowed surface. The uptake 

 of strontium-85 by Sudan grass, sugarbeets, soy- 

 beans, and cabbage was from one-fourth to one- 

 half as much as with rotary tillage to a 6-incli 

 depth. '\^nien sodium carbonate was applied with 

 deep plowing, the uptake of strontium-85 was 

 only one-fifth as much as without sodium car- 

 bonate. On this rather tight, deep, fertile soil, 

 crop yields were increased markedly by deep 

 plowing. They were not measurably affected by 

 the application of sodium carbonate. 



Heating contaminated soil to immobilize stron- 

 tium-90 has been tried in conjunction with deep 

 placement (2). Uptake of strontimn-90 with four 

 soil types that had been heated to 800° C. ranged 

 from one-eighth to one-half as much as with no 

 heating. In all cases, the contaminated soil was 

 placed 25 cm. (10 in.) deep for measuring plant 

 uptake. Extractability investigations suggested 

 that less uptake would be obtained if the soil 

 were heated to 1,000° C. or higher. 



Irrigation and Leaching 



Controlled applications of water to contami- 

 nated land might be used to leach radionuclides 

 out of the rooting zone of crops or to modify the 

 rooting depth of the crops. Until now, the re- 

 ported attempts to use irrigation have had little 

 success toward either objective. 



Leaching of radioactive strontium through soils 

 with water of dilute solutions is very slow. When 

 columns of various soils were leached with 30 

 inches of water, the maximum penetration of 

 strontium-89 was 4.3 inches (26) . In the same ex- 

 periment, leaching with 0.005 A^ CaCU increased 

 the penetration, but the average sti-ontium-89 

 movement in one soil was only 3 inches after 

 application of 16.4 inches of solution. With the 

 other soils, more solution (up to 250 inches) 

 was required to give the same average strontium- 

 89 movement. Leaching with dilute solutions of 



