Evaluation of trace metal fluxes to soils in hinterland of Porto Marghera, industrial zone: comparisons with direct measurements in the Lagoon of Venice

Trace metal (As, Cd, Cr, Ni, Hg, Pb) concentrations in soil samples collected around the Porto Marghera (Italy) industrial zone (2–40 km) near the city of Venice were compared with direct measurements of atmospheric deposition measured at comparable distances from the same source. Concentrations of Cd and Pb in soils decreased exponentially with increasing distance from the source; less clear signals were detected for As, Cr and Ni. Significant differences were found among the soils, which were partially resolved when their clay contents were normalised. Preliminary comparisons of fluxes of Cd and Pb derived from soil with direct deposition measurements showed increasing values with longer integration times. Annual Cd and Pb flux values of one year of direct deposition were 5 to 10 times lower than mean annual fluxes derived from soils,integrating 50 to 100 years. Values range from 0.1–0.4 to 1–2 mg m-2 yr-1 for Cd, and from 3–18 to 50–100 mg m-2 yr-1 for Pb. These results fit information on `historical' emission trends as recorded in sediments of the lagoon.