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

The uptake of U-238, Ra-226 and Pb-210 by beans (dwarf bean Modus), kohlrabi (brassica oleracea var. gongylodes), mangold (beta vulgaris var macrorhiza), lettuce (American gathering brown), carrots (Rotin, Sperlings's), celery, and radish from a control soil and from soil/slag mixtures was investigated in field experiments. The observed concentration ratios (CR) suggest that 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 and carrots, and less conspicuous for lettuce. A similar behaviour was observed for the uptake of U-238 by celery and radish, but not in the case of lettuce. 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 soil. 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 characterized best by defining a fractional concentration ratio (CRfr). In this way, all above results are quantified with respect to the root uptake of the radionuclides from the slag fraction in the soils. Because CRfr is not affected by atmospheric contributions to the plant activity, this quantity can be also used to obtain the root uptake of Pb-210 by vegetation which results 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 Pb-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.