## 4 Results and Discussion
### Assessment of Hg Delivery to the Augusta Harbor: Direct Inputs or Resuspension?
Two main PCDD/F fingerprints were identified (Figure 4a): (1) one characterized exclusively the core collected in the Lusore-Brentelle canal in the 2 nd Industrial Area (core C9, Figure 1b), while (2) the other was found in the canals of the 1 st Industrial Area (core C12 in the Brentella Canal, Figure 1b) and at sub-surficial depths in cores collected all over the lagoon (cores E1 and M3, Figure 1b). The first pattern was composed almost exclusively of octachlorodibenzofuran (OCDF) with no significant contribution by other furrans and dioxins, while the second one was characterized by the presence also of other heavy furrans (Figure 4a). In addition, samples collected in the 1 st Industrial Area showed concentrations sensibly higher than those measured in the 2 nd Industrial Area (core C9, Figure 1b). This first evidence testified the presence of two different sources of PCDD/Fs in the industrial canals of Porto Marghera, one in the 1 st Industrial Area and another in the 2 nd Industrial Area. Different types of industries have settled in the two industrial areas: chemical and electro-metallurgical industries were located mostly along the Nord Industrial Canal in the 1 st Industrial Area, while the 2 nd Industrial Area hosted petrochemical plants [61]. It was therefore legitimate to hypothesize that the two observed PCDD/F signatures were linked to these different industrial clusters. The questions arising from this first evidence were then as follows: (1) Were there in the 1 st Industrial Area specific industrial metal processes that could have given levels of contamination and footprints of PCDD/Fs comparable to those measured in core C12 (Figure 4a)? and (2) Was it possible to recognize a similar link between industries located along the Lusore-Brentelle Canal (2 nd Industrial Area) and the congener composition of dioxins and furrans measured in its sediments (core C9; Figure 4a)? The results of the challenging literature search required to answer the first question are now summarized in the following part. Ref. [62] tried to correlate the contamination of the Venice lagoon sediments to potential sources, analyzing literature data (i.e., contaminated emissions and sediments) through a statistical approach (principal component analysis, PCA). Lagoon sediments presented in [62] for the Venice urban area and at the boundary with Porto Marghera fell into the same group with the sediment of the Norwegian Frijefjorden contaminated by a magnesium processing plant [63]. This industrial process involved the chlorination of Mg under carbon presence at high temperatures (800-900 \({}^{\circ}\)C) and plant discharges were found to be enriched in OCDF, with PCDD/F emissions in water amounting to about 500 g TEQs per year in 1989 [63]. Indeed, the congener composition (as chlorination classes, Figure 4b) of the Norwegian fjord sample was characterized by the presence of heavy furans with a small contribution of octachlorodibenzodioxin (OCDD), a pattern similar to that observed in sediments of the 1 st Industrial Area (C12, Figure 4a). In addition, total concentrations of PCDD/Fs measured in the fjord and in the more contaminated canals of the 1 st Industrial Area were of the same magnitude (hundreds of thousands of ng kg\({}^{-1}\), Figure 4a,b). A study conducted in 1997 [64] verified the level of sediment contamination about ten years after the emissions from the Mg production plant in the Frijefjord had been drastically reduced. The results showed that pollutant levels in surface sediments were reduced by about two orders of magnitude (in the most contaminated area, where Mg processing slags were located, concentrations passed from about 37,000 to 3800 ng kg\({}^{-1}\) TEQs), but the PCDD/F fingerprints were unchanged. This proved incontestably that the Mg industry was the major factor responsible for PCDD/F pollution at that site, with negligible contribution from other production processes.