Transfer of U-238, Ra-226 and Pb-210 from slag-contaminated soils to vegetables under field conditions

The uptake of U-238, Ra-226 and Pb-210 by beans (dwarf bean Modus), kohlrab i (brassica oleracea var. gongylodes), mangold (beta vulgaris var macrorhiz a), lettuce (American gathering brown), carrots (Rotin, Sperlings's), celer y, and radish from a control soil and from soil/slag mixtures was investiga ted in field experiments. The observed concentration ratios (CR) suggest th at Ra-226 in the slag/soil mixtures is less available for root uptake than Ra-226 in the control soil. This is especially evident for beans, mangold a nd carrots, and less conspicuous for lettuce. A similar behaviour was obser ved for the uptake of U-238 by celery and radish, but not in the case of le ttuce. In this latter case, the CR was even higher when this vegetable was grown on a coal slag contaminated soil when compared to the pure control so il. It is shown that the root uptake of a natural radionuclide from a slag contaminated soil in excess to that from an uncontaminated soil can be char acterized best by defining a fractional concentration ratio (CRfr). In this way, all above results are quantified with respect to the root uptake of t he radionuclides from the slag fraction in the soils. Because CRfr is not a ffected by atmospheric contributions to the plant activity, this quantity c an be also used to obtain the root uptake of Pb-210 by vegetation which res ults only from the slag fraction in the soil. By comparing the CRfr-values observed for different radionuclides, it is shown that e.g. the amount of P b-210 root-uptake by lettuce from the slags is similar to that of U-238 and Ra-226. (C) 1999 Elsevier Science B.V. All rights reserved.