Mobility of Natural Radionuclides and Selected Major and Trace Elements along a Soil Toposequence in the Central Spanish Pyrenees

Natural gamma-emitting radionuclides (U, Ra, Th, Pb) and selected major and trace elements (Ca, K, Mg, Na, Fe, Al, Mn, Pb, Ba, Zn, Sr, Li, Co, Ni, Cu, Cr, Cd) were determined in a soil toposequence along a mountain slope of the Tertiary Flysch landscapes in the Central Spanish Pyrenees. A variety of basic properties were also measured from the soil profiles. Mean radioisotope activities (Bq kg ) range from 22 to 33 for U; 25 to 32 for Ra; 23 to 33 for Pb and 37 to 46 for Th. The radionuclides showed different patterns in their depth distribution, thus U and Pb had largest differences in concentrations down the soil profiles whereas Ra and Th exhibited quite uniform depth distributions. U was depleted in all upper soil layers and enriched in deeper layers. Pb exhibits very different depth profiles along the soil toposequence and accumulated at upper layers in three sites. U/Ra activity ratios indicate disequilibrium in the U decay chain and reflect the leaching of U in