Natural background values for heavy metals in the sediments of a contaminated Northern Adriatic lagoon environment: a geochemical perspective

Abstract

Major and trace elements were determined in 14 sediment cores collected from the Marano and Grado Lagoon (northern Adriatic sea). The lagoon is contaminated by several harmful priority substances, heavy metals included, and it has also been declared a polluted site of national interest (SIN) mainly due to high Hg concentrations in sediments. Based on a normalization procedure involving predicted linear relationships for vs Al obtained from the core subsamples, background values for each metal were evaluated on a regional scale and according to the grain-size variability. Compared to Environmental Quality Standards reported in the Italian laws and regulations, the estimated background ranges show that bottom sediments are naturally enriched in some metals, such as Cr, Ni and Cd especially in sediments with a high percentage of the fine component. A correct evaluation on sediment quality status should be made on the basis of regional background values for each metal, taking into account local geochemical characteristics, i.e. mineralogical composition and grain-size variability of sediments.