## 4 Discussion  
### The Waste Tops Soils  
The concentrations of As, Hg and Sb from Le Lame topsoils, developed on the tailings mainly derived by the former Hg-mining area of Abbadia San Salvatore, showed relatively \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Sample** & **Al** & **Mn** & **Fe** & **SiO\({}_{2}\)** & **As** & **Sb** & **Hg** \\ \hline  
& 106 & 0.1 \\
**LM26** & 69 & 158 & 29 & 8.3 & 1.1 & 2.7 & \textless{}0.1 \\
**LM27** & 191 & 11 & 47 & 4.8 & 7.9 & 1.7 & \textless{}0.1 \\
**LM28** & 102 & 34 & 109 & 5.9 & 25 & 0.6 & \textless{}0.1 \\
**LM29** & 109 & 130 & 34 & 8.5 & 26 & 1.5 & \textless{}0.1 \\
**LM30** & 178 & 57 & 98 & 5.0 & 29 & 60.7 & \textless{}0.1 \\
**LM31** & 57 & 3.1 & 560 & 4.5 & 0.5 & \textless{}0.1 & \textless{}0.1 \\
**LM32** & 17 & 23 & 5 & 3.7 & 26 & 662 & 0.6 \\
**LM33** & 17 & 9.7 & 11 & 5.0 & 35 & 116 & 0.2 \\
**LM34** & 225 & 47 & 181 & 6.2 & 50 & 23.8 & \textless{}0.1 \\
**LM35** & 133 & 101 & 55 & 9.8 & 14 & 10.5 & \textless{}0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Concentrations of metals and metalloids (\(\text{ug}\cdot\text{L}^{-1}\)) and SiO\({}_{2}\) (\(\text{mg}\cdot\text{L}^{-1}\)) in the CO\({}_{2}\)-saturated MilliQ leachates. high values. By comparing the results of the three elements (Table 3) with those imposed by the Italian Law (Legislative Decree 152/06), 12 and 10 soil samples out of 35 showed that As and Sb had concentrations higher than those for areas intended for industrial use (50 and 30 mg kg\({}^{-1}\), respectively). Additionally, all samples except LM 8 exceeded the Hg legal limit for areas intended for residential (1 mg kg\({}^{-1}\)) and industrial (5 mg kg\({}^{-1}\)) use. According to the data in Table 4, the considered variables do not show good symmetry with respect to the arithmetic mean as barycenter, since they are affected by strong positive skewness due to a certain prevalence of low values with a few isolated high values. These observations were confirmed by applying the Anderson Darling normality test where, in each case, a \(p\)-value \(<<\) 0.05 was found. According to [47; 48; 49], the frequency distribution of elements is rarely showing a normal (Gaussian type) behavior, as they generally have positive skewness approaching a log-normal distribution, i.e., logarithms of concentrations are approximately normally distributed. However, for the sake of a better visualization, the following diagrams are reported in mg kg\({}^{-1}\). As shown by the violin plots [50] (Figure 4). As and Sb are characterized by two populations, highlighted by the kernel density, as follows: (1) low-to-medium concentrations (10-33.8 and 0.18-62.50 mg kg\({}^{-1}\), respectively) located in the southern part of the dumping area; and (2) high values (33.8-616, and 63-1610 mg kg\({}^{-1}\), respectively) in the northern portion. These two populations also show a different origin of the materials deposited in the La Lame landfill. According to [27], ore and waste materials from other Hg exploitations areas (e.g., Morone, Bagnore and Siele) were different from that of the ASS mine, being generally more enriched in Sb [13; 16] and stored adjacent to the building hosting the old Spirek and Cermak-Spirek furnaces. Therefore, it can be assumed that materials from the above-mentioned mines were preferentially accumulated in the northern portion of the Le Lame dumping area. Conversely, a single population characterizes the Hg concentrations, which is mainly related to medium-high values. Additionally, Hg is not correlated with neither As nor Sb (correlation coefficient 0.23) and, consequently, its spatial distribution differs from those of the others' metals, whereas As and Sb have a similar behavior, as also suggested by a significant positive correlation coefficient (0.86). In order to better represent the distribution of these three elements, the dots maps of As, Hg and Sb (in mg kg\({}^{-1}\)) are reported in Figure 5.  
Figure 4: As, Hg and Sb violin plots.