Author Institution: Department of Agronomy, Ohio Agricultural Experiment Station, Wooster, Ohi

Haghiri, F.

Jones, J. Benton, Jr.

The Ohio Journal of Science

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REDUCING THE UPTAKE OF Sr90 BY PLANTS ONCONTAMINATED OHIO SOILS1J. BENTON JONES, JR. AND F. HAGHIRIDepartment of Agronomy, Ohio Agricultural Experiment Station, Wooster, OhioINTRODUCTIONRadioactive debris from atomic explosions deposited on vegetation and soilpresents a potential health hazard to man. The element of particular concernis the radioactive isotope of strontium, Sr90. Its long half life (28 years) andsimilar chemical reactivity to calcium makes Sr90 of biological significance.Strontium can be readily absorbed by plants either from the soil or directly throughthe foliage. Contamination in forage can be carried into the milk of dairy cowsand eventually into the calcified bone tissue of man (Comar et al., 1957; Russellet al., 1959). The increasing presence of Sr90 in bone tissue has been of concernto geneticists and other biologists.Methods for decontaminating soils or ways of reducing the uptake of Sr90from the soil by plants have been under study since the late 1940's (Shulz et al.,1959). Strontium is not very mobile in most soils and when deposited from theatmosphere onto the soil surface will not penetrate the surface to any great depth(Romney et al., 1959). The removal of the surface 2 in. of soil will remove mostof the Sr90. However, this method of decontamination may not be practicalwhen large acreages are needed for crop production.Calcium and strontium are similarly absorbed by plant roots. High concen-trations of calcium in the rooting media can restrict the absorption of strontium(Fowler et al., 1959). In acid soils the uptake of Sr90 can be significantly reducedby liming. Recent experiments conducted at The Ohio Agricultural ExperimentStation at Wooster have shown that the amount of Sr90 absorbed by plants canbe reduced by as much as 60 percent by liming the acid soils (Haghiri et al., 1961).Various crop species appear to differ markedly in their absorptive capacityof strontium (Haghiri et al., 1961; Vose et al., 1959). For example, sudangrassand corn have been found to be lower accumulators of strontium than buckwheat,soybeans, or alfalfa (Haghiri et al., 1961).Soil type also seems to be an important factor affecting the availability anduptake of Sr90 by plants (Fowler et al., 1959; Haghiri et al., 1961).The results published in this paper are an account of recent observations onthe effect of crop species, liming, and soil type on the uptake of Sr90 from Ohiosoils.MATERIALS AND METHODSThirteen soil samples representative of the Hoytville, Miami, Alexandria, andMuskingum soil series (Morse et al., 1958) in Ohio were included in this study.The samples were subdivided and limed at various rates to establish a pH rangeof approximately 5 to 7 for each soil type. Five of the soils had initial pH valuesof less than 5, while the remaining soils ranged from 6 to 7. Ten /xc of carrier-freeSr90 were thoroughly mixed into each soil sample, and the soils were cropped in thegreenhouse in sequence with corn, soybeans, wheat, and alfalfa. The aerialportions of the plant were harvested when 6 to 10 in. tall. The plant tops weredried at 70°C, weighed, and ground. A 200-mg sample was used for counting.The amount of Sr90 in the plant samples was determined using a Berkeley Decimalon work partially performed under contract number AT(11-1)-414, with the UnitedStates Atomic Energy Commission.THE OHIO JOURNAL OF SCIENCE 62(2): 97, March, 1962.98 J. BENTON JONES, JR. AND F. HAGHIRI Vol. 26Sealer, model 2000, with a 2.9 mg/cm2 thin mica window tube. All the plantsample counts were corrected for background.RESULTS AND DISCUSSIONThe amount of Sr90 found in the plant tissues varied considerably dependingupon the crop species, liming rate, and soil type. The Sr90 content of variousplant species was in the order: Soybean > corn ^  alfalfa > wheat (fig. 1).As the soil pH increased (as a result of liming), less Sr90 was accumulated inall crop species. An increase in soil pH from 5.0 to 7.0 reduced the Sr90 contentof all the plants approximately by one-half. These results are similar to thosereported by others (Haghiri et al., 1961; Romney et al., 1959).However, the Sr90 content of the plants was not similar in the case of all soilsused. A highly significant correlation was found between the percent clay contentof soil and the level of Sr90 in the plant. As the clay content increased, the Sr90content of the plant decreased (fig. 2). Therefore, it appears that soil textureand soil pH are equally important. Although liming may significantly reduce theuptake of Sr90 by plants on all soils irrespective of texture, the use of low claycontent soils may result in plants with a sufficiently high Sr90 level to make themundesirable for animal or human consumption.The colloidal clay fraction largely accounts for the cation exchange capacityof mineral soils. As the clay content increases for a particular mineral soil, thecation exchange capacity usually increases. Although soil texture would beexpected to have an influence upon the uptake of Sr90, the extent of its influencewas unexpected. The colloidal organic matter in soils also exhibits a cationexchange capacity. The soils used in this study varied from 0.7 to 2.4 percentin organic matter content. Soils with similar textures but different percentagesof organic matter produced plants of different Sr90 contents. As the percentorganic matter increased the Sr90 content in the plant generally decreased. How-ever, there were exceptions and in some cases the decreases in Sr90 uptake werevery small compared to magnitude of the organic matter content differences.For example, three clay loam soils having organic matter contents of 0.6, 1.6 and2.4 percent produced plants with an average Sr90 activity of 2700, 2500 and 2110counts per min respectively. Two silt loam soils having organic matter contentsof 0.7 and 2.2 percent produced plants with an average Sr90 activity of 6790 and6860 counts per min respectively. Therefore, the effect of organic matter uponthe uptake of Sr90 for the soils used in this study is considered of slight significance.Ions held by the clay colloids are not available to plants until released into thesoil solution. Sr90 which has been absorbed on the clay colloids is not availableto plants. An equilibrium is established between the cations on the clay surfacesand those in the surrounding soil solution. The competitive effect of calcium onstrontium is exhibited within the soil solution. Calcium seems to have littleeffect upon the extent of absorption of strontium on the clay exchange surfacesin acid soils (McLean et al., 1960). However, as the soil pH reaches neutrality,the extent of absorption of strontium is influenced by clay type and calciumsaturation (McLean et al., 1960). Therefore, not all of the Sr90 added to the soilcan be prevented from entering the plant irrespective of clay type, amount ofclay or degree of calcium saturation. The asymptotic nature of the curves (withincreasing percent clay) in figure 2 tends to confirm McLean's et al. (1960)observations.The results obtained in this study indicate that the amount of Sr90 enteringthe plant from a contaminated acid soil can be significantly reduced by liming.In addition, texture strongly influences the amount of Sr90 absorbed by plants.As the clay content of the soil increases, the Sr90 uptake decreases. The uptakeof Sr90 from an acid soil appears to be equally influenced by soil texture and liming.The Sr90 content of plants can be effectively reduced by: (1) liming, (2) a selectionNo. 2 PLANT UPTAKE OF SR90 FROM SOIL 99FIGURE 1. Concentration of Sr90 (counts/minute/200 mg of dry matter) in wheat, alfalfa, cornand soybean tops grown in soils at the indicated pH levels.FIGURE 2. Average concentration of Sr90 (counts/minute/200 mg of dry matter) for all cropson soils with varying texture (percent clay) and soil pH levels.100 J. BENTON JONES, JR. AND F. HAGHIRI Vol. 62of a high clay content soil, and (3) selection of plant species which is a low accumu-lator of strontium.LITERATURE CITEDComar, C. L., R. S. Russell, and R. H. Wasserman. 1957. Strontium-calcium movement fromsoil to man. Science 126: 485-492.Fowler, E. B., and C. W. Christenson. 1959. Effect of soil nutrients on plant uptake of fallout.Soil calcium and potassium decrease strontium-90 /calcium and cesium-137/potassium ratiosin plants. Science 130: 1689-1693.Haghiri, F., and J. D. Sayre. 1961. Strontium-90 uptake by plants as influenced by soil typesand liming. Soil Sci. Soc. Amer. Proc. 25: 120-123.Libby, W. F. 1958. Beneficiation of soils contaminated with strontium-90: beneficial effectsof potassium. Science 128: 1134-1135.McLean, O. E., T. G. Arscott, and V. V. Volk. 1960. Absorption and release of strontium fromclays and soils with equilibration, isotopic tracer and plant uptake technique. Soil Sci.Soc. Amer. Proc. 24: 453-457.Morse, H. H., and Samuel Bone. 1958. Understanding Ohio soils. Ohio Agric. Ext. Serv.Bull. 368. 19 p.Romney, E. M., W. L. Ehler, and A. H. Lange. 1960. Some environmental factors influencingradio strontium uptake by plants. Plant and Soil. 12: 41-48.Russell, R. S., and F. B. Ellis. 1958. The movement of strontium-90 through food chains.Soils and Fert. 21: 269-273.Schulz, R. K., J. P. Mohery, and R. Overstreet. 1959. Some experiments on the decontamina-tion of soils containing strontium-90. Hilgardia 28: 457-475.Vose, P. B., and H. V. Koontz. 1959. Uptake of strontium by pasture plants and its possiblesignificance in relation to the fall-out of strontium-90. Nature Land 193: 1447-1448.

Reducing the Uptake of Sr90 by Plants on Contaminated Ohio Soils

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Reducing the Uptake of Sr90 by Plants on Contaminated Ohio Soils

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