Sequential extraction as a tool for mobility studies of radionuclides and metals in soils and sediments

To assess the long term environmental impact of radioactive contamination of ecosystems, information on source terms including radionuclide speciation, mobility and biological uptake is of high importance. The speciation of radionuclides deposited or occurring naturally depends on source term and release scenario characteristics, transport and dispersion mechanisms and ecosystem properties. If mobile species are present, ecosystem transfer is relatively fast, whereas the ecosystem transfer is delayed if radionuclides are present as particles or incorporated in mineral lattices. This paper discusses cases showing important factors influencing the mobility of different radionuclides and metals. As examples can be given: - the difference between Cs-137 and Sr-90 from Chernobyl fallout and stable Cs and Sr in the soil showing that the fallout has not reached a steady state and therefore shows different mobility properties, thus the time since contamination is important. - the presence of organic matter affect the mobility of plutonium in soils and sediments even though the source term is the same. -physical properties(i.e. pH, OM, clay content, grain sice etc.) is important to interpret mobility data between similar sites. - the influence of industrial activity on radionuclides and metals shows that any man-made activity might change the mobility.