Uptake of ²⁴¹Am from major Indian soils and its distribution in plants

Abstract

Studies on the uptake of ²⁴¹Am from three major Indian soils indicated that higher amounts of ²⁴¹Am were absorbed by plants from the acidic laterite soil having low pH, predominantly kaolinite clay and low cation exchange capacity compared to those from an alkaline medium black soil containing predominantly montmorillonite clay and high cation exchange capacity, and a neutral alluvial soil. Americium concentration ratios (CRs) for beans (Phaseolus vulgaris L.) and maize (Zea mays L.) range from 1.0 × 10^-4 to 7.5 × 10^-4 for shoots and from 4.7 × 10^-4 to 12.5 × 10^-4 for roots in the case of plants grown using a split-root technique. For the plants grown under the Neubauer technique higher CR values, ranging from 0.2 × 10^-3 to 2.9 × 10^-3, were obtained for maize shoots. Split-root studies also indicated that ²⁴¹Am once absorbed by roots from soil was not subsequently released into the nutrient solution. The distribution pattern of ²⁴¹Am in aerial tissues of bean plants grown to maturity in a labelled nutrient solution showed the maximum concentration of the radionuclide in the oldest tissue (primary leaves) and a marked acropetal gradient. Chemical characterization of ²⁴¹Am in freshly harvested edible tissues (pods) of bean plants indicated a maximum amount of ²⁴¹Am (51.6%) associated with ionic forms, including salts of organic acids, phosphates and carbonates, extractable by 0.2 M HCl and 0.5 M HClO⁴; the levels of ²⁴¹Am next in significance were associated with the ethanol fraction (13.6%), the acetone insoluble fraction (10.8%), the soda fraction (8.1%) and the nucleic acid fraction (9.6%). The lignin and cellulose fraction was found to contain the lowest level (6.1%) of the radionuclide.