Heavy metals in sediments and halophytes of saltmarshes in the Marano and Grado Lagoon (Northern Adriatic Sea)

Abstract

The content of several heavy metals (As, Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn) was determined in sediments and in plants (the halophytes Sarcocornia fruticosa and Limonium vulgare) from two selected saltmarshes located in the Marano and Grado Lagoon (Northern Adriatic Sea). This environment has been affected by severe Hg contamination from both industrial and long-term mining activities. In both saltmarshes, Hg content in sediments exceeded the estimated background value (0.13 µg g -1 ), showing the highest concentrations (13.7 µg g -1 ) in the eastern sector (Grado Lagoon), the most affected by cinnabar ore extraction. On the other hand, the saltmarsh, located in the Marano Lagoon, showed a higher degree of contamination for As, Cd and Pb, which can be related to industrial sources. The rhizo-sediments of both halophytes reflected the characteristics of the non-vegetated sediment, with higher organic carbon content and similar metal concentrations. Enrichment Factors (EF=(metal)root/(metal)rhizo-sediment) for each sediment layer were calculated for both halophytes, showing metal enrichments in the roots and the presence of preferential layers of metal accumulation. Hg showed accumulation (EF>1) in the roots below the 20 cm depth, with higher contents in S. Fruticosa. As and Cd were accumulated by both halophytes, more efficiently by S. Fruticosa, and the same species showed also accumulation of Pb and Zn. Translocation of metals from the roots to the aboveground biomass was investigated by measuring metal contents in shoots and leaves of the two species. With the exception of Cd and Hg, all metals were present in the aboveground biomass, most evidently for Cr in S. Fruticosa and Zn in L. Vulgare, although the presence of the latter in leaves could be due to plant physiology rather than translocation of the contaminant.