Uptake by plants and migration of uranium and chromium in field lysimeters

Plant growth, plant uptake, and the redistribution in soil of U and Cr were studied in field lysimeters. The objective of the experiment was to characterize the plant uptake and migration in the soil of U and Cr when placed at different depths in the unsaturated soil zone within the influence of a water table. Lysimeters with and without vegetation were studied and two soils, and two plant species were investigated. Total uptake of Cr by the plants was directly proportional to Cr concentration in the soil, over eight orders of magnitude. Thus, independent of the amount of Cr applied, the plant took up a similar fraction, about 0.007. Chromium placement depth in the soil did not influence Cr uptake by the plants although the Cr was relatively immobile in both soils. Plant uptake of U was independent of plant species and U placement depth for loam soil, but highly dependent on placement depth in sandy soil. In the latter, much more U was taken up by the plants when it was placed near the soil surface, implying that uptake was dependent upon root activity. Migration of U from the contaminant band was substantial only in the sandy soil