EVALUATION OF HEAVY METALS LABILE-POOL IN POLLUTED SOIL: USE OF DIFFUSIVE GRADIENT IN THIN FILMS

The objective of this study was to give an insight to the techniques for measuring the lability of the heavy metals in the solid pool of soils within the frame of the environmental pollution risk assessment. Diffusive gradient in thin films (DGT) technique was used to quantify the solid-liquid interfacial concentrations of Cu and Ni either directly in the field condition or in a laboratory constructed microcosm. The ratio of DGT-apparent soil solution concentration to that directly-analysed was conclusive to delineate the actual limit of DGT technique. High soil solution metal concentration with a lower fraction observed by DGT was attributed to the presence of colloidal speciation. The use of this technique allowed to calculate leaching parameters of the free metal cations labile pool. In all the cases the Cu labile pool resulted basically unchanged even when the soil was altered by external addition of growing amounts of metal. On the contrary the behaviour of Ni resulted different since it increased its labile pool along with the metal additions. The DGT technique to be helpful as characterization procedure for contaminated sites needs a preliminary investigation on the extent of the free cation form to delineate its limit of applicability.