Soil Colloids as a Factor in the Uptake of Cobalt, Cesium, and Strontium by Plants

A study of the uptake of Co, Cs, and Sr by rye, garden peas, and soybeans showed that the amount of these elements harvested, as well as the concentration in the plants, varied with the nature of the soil colloid on which they were grown. Illite, kaolinite, montmorillonite, peat (fibrous), peat (sedimentary), and Putnam clay were Ca-saturated, mixed with nutrients and sand; and treated with known amounts of radioactive Co⁶⁰, Cs¹³⁷, and Sr⁸⁵. Cultures of rye, peas, and soybeans were started in sand-nutrient solution mixtures, then transferred to the radioactive colloid-sand-nutrient mixture. After a period of growth, the plants were harvested, weighed and assayed for their content of radioactivity. A study of the adsorption of the nuclides by the colloids was made by the determination of the distribution coefficient of each radioactive nuclide as a trace amount in Ca-saturated exchange systems in 0.01M CaCl₂ solution. The order of uptake of Co by the rye plants was highest on illite followed in order by kaolinite, Putnam clay, peat (sedimentary), montmorillonite, and peat (fibrous). The uptake of Cs by the rye plants was highest in the plants grown on (fibrous) peat (10.59% harvested), and lowest for the plants grown on Putnam clay (0.36% harvested). The uptake of Sr by the rye plants was highest for the plants grown on montmorillonite (2.08% harvested). The uptake of the nuclides by peas and soybeans followed closely that of rye. Data obtained from the distribution coefficient studies of the elements for the exchangers after equilibration in 0.01M CaCl₂ solution reveals more Co adsorbed by the peats than by the clays; a high adsorption of Cs by illite and Putnam clays; and small differences with Sr with exchangers other than kaolin. The adsorption of the three elements was lower for kaolin than for the other cation-exchangers. The percentage of Co and Cs harvested by the plants was correlated with the reciprocal of the distribution coefficient.