BIOACCUMULATION OF TRACE METALS IN PLANTS GROWING NEARBY A DECOMMISIONED Zn-Pb MINE (SALAFOSSA, NORTHEASTERN ITALIAN ALPS)

The Salafossa mineral body (Eastern Dolomites) was one of the largest lead/zinc containing mineral deposits in Europe. Both metals were mainly present as sulphides (sphalerite, ZnS and galena, PbS). Mining activity started around 1550 and definitively closed in 1985. The concentration of several heavy metals (Tl, Fe, Mn, Pb, Zn) was determined in soils and plants (Biscutella laevigata) from twelve sites elected outside the mine. B. laevigata is a "metal tolerant" species, and it often grows near mining areas, where soil metal contents are significantly higher than natural geochemical background levels. Heavy metal total concentration in inorganic and organic (roots and leaves of B. laevigata) samples were determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectroscopy) and by GFAAS (Graphite Funace Atomic Absorption Spectroscopy) after total mineralization. In addition, metal bioavailability in the soil - including the B. laevigata root system (rhizo-soil) was estimated by using a DTPA (Diethylene Triamine Penta-acetic Acid) extracting solution. Then, to assess absorption and translocation processes of heavy metals, resulting in their bioaccumulation, two indices were calculated: the Enrichment Factor in roots (EFr) and the Translocation Factor (TF). For both indices, a >1 value denotes an enrichment of the metal in the roots or its translocation to the upper tissues. Results showed that metals were present in a chemical form available for absorption by the plants roots. High concentrations of the metals were found in the roots and leaves of B. laevigata, and these concentrations were higher than those in the corresponding rhizo-soil. The calculated indices showed that EFr and TF were >1 only for Tl, reaching a maximum value of 60 for EFr and 11.6 for TF. Conversely, the other metals did not show significant bioaccumulation (EFr<1) and they showed TF>1 only at a few sites. This study showed the ability of B. laevigata to absorb metals from the soil and to accumulate them in the roots and/or translocate them to the aboveground biomass, especially Tl, thus representing a good indicator of Tl bioavailability in the rhizosoil of the study area.