6 



AGRICULTURAL HANDBOOK 395, U.S. DEPT. OF AGRICULTURE 



complexing agents, such as ethylenediaminetetra- 

 acetic acid, has also shown little advantage for 

 removing radioactive strontium (27). 



Acids and salts also have been applied to con- 

 taminated soil surfaces in order to increase the 

 movement of strontiimi-00 during leaching (33). 

 Hydrochloric acid and ferric chloride, at rates 

 of 15 and 22 tons per acre, respectively, were 

 most effective. When these treatments were fol- 

 lowed by leaching with 5 feet of irrigation water, 

 about 20 percent of the stroiitium-90 remained in 

 the top foot of a fine sandy loam, and about 60 

 percent in the top foot of a loam. In addition 

 to being expensive and rather ineffective, the 

 latter two treatments would leave an infertile 

 soil. 



A series of field experiments have been re- 

 ported (8) in which irrigation was used in an 

 attempt to modify the uptake of strontium-90 

 from deep or shallow placement in the soil. No 

 modifying effect of irrigation could be detected. 



Applications of Lime, Fertilizers, 

 and Other Soil Amendments 



Soil amendments have been used to reduce 

 the uptake of radionuclides in difl'erent ways. 

 Calcium- and potassium-bearing materials pro- 

 vide cations that compete, respectively, with 

 strontium and cesium and thus reduce their en- 

 try into plants. Soluble phosphates added in 

 large amounts precipitate strontium so that less 

 of it may enter plants. Additions of materials 

 with a high cation exchange capacity, such as 

 peat, compost, or clay minerals, may also reduce 

 the amounts of radionuclides taken up by plants. 



Many experiments have shown that applica- 

 tions of lime or gypsum to acid soils reduce 

 the uptake of radioactive strontium by plants 

 grown on these soils {J, 4, 10, U, 17, 24). The 

 reduction depends upon increasing the available 

 calcium supply of the soil, so that little effect 



is seen on soils already well supjilied witli cal- 

 cium. Even on very acid soils, application of 

 lime or gypsum does not usually reduce uptake 

 of radiostrontium to less than one-third of the 

 uptake from the untreated soil. 



Potassium fertilizers reduce the uptake of ra- 

 dioactive cesiiuii from soils (/, J7). Tliis is simi- 

 lar to the effect of lime on uptake of radioactive 

 strontium. Potassium also reduces the uptake 

 of radioactive strontium, but to a much smaller 

 degree than applications of lime or gypsum {1. 

 6, 8). 



Nitrogen fertilizers tend slightly to increase 

 the uptake of radioactive strontium and cesium 

 from soils (1). 



Phosphate fertilizers added to soils at the 

 usual agronomic rates have shown little effect 

 on uptake of radionuclides {10. pp. 197-200). 

 However, large additions of soluble phosphates 

 have resulted in very striking reduction in the 

 uptake of radioactive strontium [10). Wlien di- 

 ammonium or tripotassium phosphates were 

 added in amounts equivalent to the cation ex- 

 change capacity of the soil (4 to 12 metric tons 

 per hectare, or 2.2 to 6.5 avdp. tons per acre), 

 the uptake of radioactive strontium was reduced 

 to one-tenth of that without these materials. 

 Tlie treatment was more effective in soils with a 

 higher pH value. At the higher rates of appli- 

 cation, some difficulty with plant growth was 

 noted. 



Materials with a high cation exchange capac- 

 ity have reduced uptake of radioactive stron- 

 tium when they were added to soils. Decom- 

 posing organic materials or compost liave re- 

 duced uptake as much as a factor of five when 

 mixed with mineral soils in amounts greater than 

 2 parts per 100 of soil {10. pp. 170-180; 17). 

 Clay minerals such as kaolinite and montmorillo- 

 nite have also reduced uptake of radioactive 

 strontium when added to a sand culture {11) or 

 soils {28). 



FEASIBILITY OF TREATMENTS FOR CONTAMINATED AREAS 



Treatments for land areas that are contami- 

 nated with radioactive materials will not be fea- 

 sible unless the following i-equirements are met. 

 First, the treatment must make a significant re- 

 duction in the radiation hazard, either by remov- 



ing the radioactive material or by reducing its 

 uptake into crops. Second, it must leave the land 

 in a productive state for agricultural use. Third, 

 equipment and materials for the treatment must 

 be available. Finally, the treatment should meet 



