[en] The potential radiological risk of contaminated areas by enhanced level of natural occurring radionuclides is depend on chemical and ecological behavior of these radionuclides. Fractionation is a proper method to determine the mobility of radionuclides which is assumed closely related to bioavailability and uptake by biota. In the present work four different areas were investigated. Sites which are located in Upper Silesia have been used for discharging of pit water. Sites in Hungary are used as a deposit of waste material from coal fired power plants. Because the ²²⁶Ra and ²²⁸Ra are the most prominent radionuclides among the potential contaminants around mining sites and waste deposit, our research was focused on investigation the behavior of Ra. The level of ²²⁶Ra activity-concentration in sediment samples from the regions of Upper Silesia is varied between 0.5-25 kBq/kg and the level in ash samples from Hungarian sites changes in a range of 0.20-3.30 kBq/kg. The paper summarized two studies. The first investigation has concerned to the determination of mobility of radionuclides in waste materials. The second study is dealing with plant uptake of ²²⁶Ra and ²²⁸Ra and the determination of site specific concentration factors on these areas. Different sequential extraction procedures were applied to investigate the speciation of radium. The ratio of radium was determined in 'water' fraction, 'readily exchangeable' fraction, in the 'bound to carbonate' fraction and in the 'bound to Fe and Mn oxide' fraction respectively. To calculate a realistic CR for ²²⁶Ra and ²²⁸Ra we take into account mobility of radionuclides. CR values were calculated on base of dry matters of sampled natural vegetation. The value of CR for the Ra on sites of depository in Hungary and on the settling ponds in Poland varied between (0.05-2.4), (0.06-51.0) respectively due to the mobile fraction. (author)