Relationship of Morpho-Sedimentological Variations to the Fate of Hg- and Zn-Polluted Sediments in the Contaminated Site of Porto Marghera, Lagoon of Venice, Italy

Abstract

<p align="justify"> <span style="font-family:verdana;">New data collected from twenty-six sites during 2008 inthe contaminated Site of National Interest (SIN) of Porto Mar</span><span style="font-family:verdana;">ghera within the Lagoon of Venice (Italy), which has been affected by the presence of an industrial zone for the last 80 years, were compared with data from a campaign performed in the same site 30 years before (1976-1978). The SIN was found to be heavily polluted in the earlier study, and several tons of Hg and Zn are still stored in soils and industrial channel sediments, potentially affecting the lagoon part of the SIN. Bathymetric variations, grain-size, Hg and Zn con</span><span style="font-family:verdana;">tent in sediments were analysed. The severe contamination of the late 1970s (Hg 1.7 μg/g; Zn 754 μg/g) had fallen by the late 2000s (Hg 0.9 μg/g; Zn 225 μg/g). The fall in Hg and Zn contamination over the 30-year period was mainly linked to the patterns of geomorphological change inside the SIN that affected two distinct sub-areas: </span><span style="font-family:verdana;">1</span><span style="font-family:verdana;">) a stable-depo</span><span style="font-family:verdana;">sitional (SD) area in the Northern part, which exerted a “dilution” effect on contaminants, with significant deposition (~11%) of coarse-grained sediments (63</span><span> </span><span style="font-family:verdana;">-</span><span> </span><span style="font-family:verdana;">8 μm), and </span><span style="font-family:verdana;">2</span><span style="font-family:verdana;">) an area characterised by moderate-to-severe-erosion (MSE) to the South, which saw the loss (~13%) of pollutant-bearing fine-grained sediments (<8 μm). A budget calculation in the MSE sub-area showed a loss of ~2.5 tons for Hg and ~700 tons for Zn over three decades, most of which was exported to other parts of the LV or at the open sea. A similar amount is still stored in the SD area, which will be subject to ero</span><span style="font-family:verdana;">sion if hydrodynamic conditions change in the future. This study provides useful support to decision-making systems by helping to select hot-spots for remediation measures.</span> </p

Anthropogenic contaminants in Venice Lagoon sediments and their pore fluids: Results from the SIOSED Project

“…Increases in Zn and Cu concentrations with sediment depth observed in cores C, SO, and drill hole SM3 reflect sediment re-deposition, and also can, in part, be ascribed to lower pollution levels since the mid 1970-ies. This agrees with the proposal of Molinaroli et al (2013) that gradual changes in the trace metal contents are caused by diminished inputs and exchange with the Adriatic Sea (see also Bernardelo et al, 2006). Dredging and redeposition of the dredged sediments leads to much greater depths of the excessive Cu and Zn contents, shown clearly in SM3 sediment profiles.…”

“…In SM3 the Zn and Cu concentrations reach maxima at~3 m into the hole, below which these sediments become Class A. Most of Core C sediments were classified as Class C sediments for Zinc, which is typical for sediments in the Porto Marghera region of Venice Lagoon (Molinaroli et al, 2013). Copper concentrations in Core C were also in the Class C sediment range.…”

“…Special attention has also been given to the distribution of mercury in its various forms, both in the waters and the sediments of the Lagoon (Bloom et al, 2004a(Bloom et al, , 2004bHan et al, 2007Han et al, , 2010. For mercury there also are higher concentrations in the vicinity of Porto Marghera and around the southern end of the city of Venice (Magistrato alle acque di Venezia, 2005;Han et al, 2010;Molinaroli et al, 2013).…”

“…Molinaroli et al (2013) present comparisons of mercury and zinc contents in these sediments between the years 1970 and 2008 in the vicinity of Porto Marghera. These authors showed by means of mass balance calculations, that as a result of reduced contamination as well as redistribution and exportation of the sediments into other areas of the lagoon and into the Adriatic Sea, surface sediments in the Porto Marghera area indicate diminished contamination.…”

Mercury in the food chain of the Lagoon of Venice, Italy

“…The most contaminated sediments are located close to the Marghera site (Zonta et al, 2007). These have been partially eroded and dispersed to other parts of the Lagoon (Molinaroli et al, 2013). In other coastal sites, it has been observed that after the reduction of Hg load from point sources, the contamination in benthic organisms and fish decreases.…”