EXCHANGEABLE FRACTION OF ELEMENTS IN ALLUVIAL SEDIMENTS UNDER WASTE-DISPOSAL SITE (ZAGREB, CROATIA)

Concentrations of Ag, Ba, Cd, Ce, Cs, Co, Cr, Eu, Fe, Rb, Sc, Sr, Th, and Zn exchangeable fractions were determined in alluvial sediments at waste disposal site area in the vicinity of water-well field. Samples have been leached with 0.5M NH4Cl at a sample/solution ratio of 1 : 2 0 during 24 hours without shaking. INAA of dry NH4Cl residues show tha t the concentrations of exchangeable elements determined in the most o f the sediments below the wastes have natural levels. Ag, Ba and Sr ar e readily exchangeable; Rb, Cs and Zn have lower exchangeability, whil e Cd, Ce, Th, Sc, Eu, Cr, Fe and Co are rather immobile. Extremely hig h total and exchangeable silver concentration was found at 6.5-6.8 met ers below waste in the aerated layer occasionally under the water tabl e. Exchangeable concentrations in deeper water-bearing sediment layers are not elevated. Due to this, one can presume that the upper sedimen t layers act as chemical filter generally preventing the infiltration from overlying wastes into water-bearing layers.