Heavy metal pollution in central Venice Lagoon bottom sediments: evaluation of the metal bioavailability by geochemical speciation procedure

Sediment samples from the central area of the Venice Lagoon in Italy and some lagoon canals, chosen as an anaerobic ref. environment, were analyzed for Cr, Cu, Ni, Pb, Zn, Mn, and Fe. Bio-available phases and non-bio-available phases were detd. in the Malamocco-Marghera Canal, to define the significant level of heavy metal contamination. Relations among metal distributions with Fe/Mn oxides/hydroxides and sulfides were detd. in both environments, using statistical methods. The central lagoon area shows low pollution and a balanced influence of all the sediment components in the metal complexing processes, mostly due to the Mn and Fe matrixes. The inner canals are very polluted with heavy metals strongly bonded to H2S that form highly insol. compds., as demonstrated through the correlation anal. The authors suggest different procedures for lagoon restoration due to the different sediment behaviors, i.e., to avoid sediment perturbation by dredging or by artificial bottom aeration which could result in an accelerated formation of more sol. oxygenated metal compds. making the toxic metals readily available to the aquatic environment. The sedimentol. study of the central lagoon given here evidenced the correlation between grain size and mineralogical compn. and heavy metal concns. in bottom sediments. While Fe, Mn, Zn and Cu show a good correlation with the percentages of mud (grain size