Leaching of Co-60, Cs-137 and Ra-226 in lysimeter experiments

The present report describes the first results obtained from lysimeter experiments started in 1990. The lysimeter plant consists of twelf soil monoliths from four different sites (three replicates each). Since 1990 the following agricultural crops were grown: endive, corn, winterwheat, mustard, sugar beet and potato. Gravitational water ranged from 3.9% to 18.3% of precipitation plus irrigation water, calculated as half years average values excluding the first six month of operation. The two Cambisols on sediments exhibited a mean percentage of app. 10%. The Dystric Cambisol on silicate rock and the Gleysol showed average values of 20%. In 1990 the top layers (20 cm) were contaminated with three radionuclides. The leaching of the contaminants Co-60, Cs-137 and Ra-226 differed distinctly between the elements. The lowest leaching rates were observed for Cs-137, followed by Co-60. The Ra-226-concentrations in the gravitational water were clearly highest of all. However, the comparison of the Ra-226/Ra-228 ratios in deep soil layers and in gravitational water showed that the Ra-226 measured in the leachate originates from the natural contents in the subsoil and not from the artificial Ra-226 contamination of the topsoil. The mobility of the artificial radionuclides decreased therefore in the following order: Co-60 > (Ra-226) > Cs-137.