SELECTED ELEMENT CONCENTRATIONS IN ALLUVIAL SEDIMENTS UNDER GARBAGE DISPOSAL SITE (ZAGREB, CROATIA)

Ag, Ba, Cd, Ce, Cs, Co, Cr, Cu, Eu, Fe, Ga, Mn, Ni, Pb, Rb, Sb, Sc, Sr , Th, Ti, V, Zn and Zr concentrations in alluvial sediments were deter mined by INAA and OES in the area used as a garbage disposal site in t he vicinity of a water-well field. Results show that total concentrati ons of analysed elements depend on sediment characteristics: mineral c omposition, specific surface area, cation exchange capacity, organic m atter and clay-grain size fraction content. On the other hand, concent rations in sediment depend on physico-chemical forms and geochemical c haracteristics of the elements in question. Most of the elements revea l excellent/very good correlations with iron, while strontium shows ne gative correlation with iron. Strontium has a very good, positive corr elation with carbonate content, while all other analysed elements, exc ept silver, have excellent negative correlations with carbonates. Corr elations with clay-grain size fraction are good or very good for all e lements, except strontium and silver. The only element which is not co rrelated, either with iron, carbonate, or with clay-grain size fractio n is silver. One can conclude, therefore, that silver is introduced as discrete particles. Extremely high silver concentration was found 6.5 -6.8 m below the garbage in the aerated layer, occasionally under the water table. The enrichment factor for silver is found to be 127, whic h is a clear indication of sediment pollution with silver. Long-lastin g clandestine deposition of industrial wastes on a disposal site meant for domestic wastes might be the reason. The elevated concentrations found on the 11.2-11.4 m depth are concordant with mineralogical compo sition (MnO-hydroxides, iron minerals, illite, chlorite) and enrichmen t factors for the majority of analysed elements are below 2. For the t ime being, this sediment layer acts as a chemical filter preventing in filtration in the vertical direction. Concentrations and enrichment fa ctors of all determined elements from the uppermost and deeper water b earing layers are of natural values. Taking into account these, and ad ditional, piezometer results, it can be concluded that the quality of water taken from the water-well field downstream of the garbage dispos al site is not endangered so far. (C) 1997 Elsevier Science Ltd.