## 4 Results and Discussion  
### Assessment of Hg Delivery to the Augusta Harbor: Direct Inputs or Resuspension? The chlor-alkali plants discharged without treatments in the harbor until the 1970s, when a demercurization plant and the consordial biological depturator for waste treatments became operative, in response to national laws. In spite of that, high Hg levels are still measured in surficial sediments [30; 34; 35; 36] implying the possibility of a recent contribution. As written in Section 2.1, this possibility was the focal point to be verified by the historical and scientific reconstruction here summarized. Sediment chronologies defined for the cores collected in 2003 in the Augusta Bay and Harbor were of great interest for the purpose of this scientific investigation. For most sites, they covered time intervals sufficiently extended to include the industrial setting, its development, and decline (i.e., early 1960s-late 1980s) up to 2003 (Figure 3a). \({}^{210}\)Pb\({}_{\text{ex}}\) derived accumulation rates (S, cm y\({}^{-1}\)) were calculated with the assumption of constant flux of the radiotracer and constant sedimentation (CF-CS), thus providing an average S useful for a first approximation dating, but probably overestimated. Associated errors for S ranged from 0.01 cm\(\cdot\)year\({}^{-1}\) at the core top to 0.05 cm\(\cdot\)year\({}^{-1}\) at the core bottom [27]. Since no evaluation of the effect of bioturbation could be achieved, surficial levels were excluded from its calculation. Despite these difficulties, in most cases \({}^{210}\)Pb derived chronologies were confirmed at deeper layers by \({}^{137}\)Cs results (see Figure 2b) and other parameters (e.g., magnetic susceptibility peaks, HCB production history) [27]. S values in the Augusta Bay ranged from 0.21 cm year\({}^{-1}\) (site F) to 0.42 cm year\({}^{-1}\) (site H), in agreement with box core data from the same area [50] and determined that 50 years of industrial history of the area were represented by 11-21 cm thick sediment layers. S values in the Augusta Harbor were higher (from 0.43 cm year\({}^{-1}\) at site A to 1.12 cm year\({}^{-1}\) in the sub-surficial sediment of site L) therefore the time intervals represented by these cores are shorter, starting from the mid-1940s or early 1950s. As expected, site G proved to be very peculiar, with an unrealistic high rate of 1.08 cm\(\cdot\)year\({}^{-1}\), most likely influenced by the massive sediment input generated by the undocumented illegal dumping of dredged material on the way to the disposal areas. Further investigation through core sampling at different locations throughout the Augusta Bay were necessary to verify the extent and pathways of this illegal habit (Figure 1a) but it was beyond the scope of the presented research. Chronologies were also confirmed by magnetic susceptibility measurements related to documented Etna eruptions in 1892 [51]. Great variability was observed for Hg concentrations in sediments: values ranged from a minimum of 0.07 mg kg\({}^{-1}\) to a maximum of 575 mg kg\({}^{-1}\); [27], due to the presence of point sources that strongly influenced nearby locations. Chronologies were reliable enough to allow the reconstruction of Hg historical trends in sediments of the Augusta Harbor. As an example, Figure 3a shows Hg temporal profiles in cores A, L, and D (Figure 1a). The sedimentary record of core A covered the entire 20 th century and evidenced significant variations of Hg concentrations, passing from near background values in the pre-industrial period to ca. 6-8 mg kg\({}^{-1}\) in the 1950s, at the peak of the industrial development of the area. Then, concentrations gradually and constantly decreased from the early 1970s, as the result of both technological improvements and remediation measures that came into use in that period [30; 31; 32; 34; 35; 36]. However, the value measured at the sediment surface was still well above the natural background determined at the core bottom, as observed also in the box core sediments of the Augusta Bay [50].