## 3 Results and Discussion
### Geochemical Baseline  
Table 2 shows the threshold values obtained in calculating each method analyzed. The threshold values differ between the three methods; the distributions are altered and skewed towards higher values in the upper whisker method and the percentiles. The MAD method gives intermediate values about the other methods. This is why it was decided to opt for the MAD method to generate the geochemical background value, as this method tends to show intermediate values that are more representative of the various populations observed and will allow us not to overestimate or underestimate the posterior section. The geochemical baseline concentrations of the elements As, Cu, Pb, and Zn were approximately twice as high in the Aconcagua River basin as in the Casablanca River basin. This difference in soil element concentrations can be explained by the difference in rock types in these two river basins. Specifically, the Casablanca River basin comprises predominantly plutonic (intrusive) and sedimentary rocks, while the Aconcagua River flows through terrain covered mainly by volcanic (effusive) and sedimentary rocks [13]. It is important to note that volcanic rocks (basalts, andesites, and dacites) tend to be enriched in Cu and Zn compared to plutonic rocks (gabbro, diorites, and granodiorites). Thus, the difference in the predominant rock types (volcanic and plutonic) defines the Cu and Zn contents in the soils of the Aconcagua River basin (volcanic rocks) and the Casablanca River basin (plutonic rocks) [13]. Spearman correlations were analyzed to process the data and identify possible trace metal contamination sources (Table 3). The element pairs As/Pb and Cu/Zn in the Aconcagua River basin without mining activity indicated that these elements have a common source. One level for the element pairs Cu/Zn and Pb/Zn was detected in the Aconcagua River basin in random sectors, including mining activity; in addition, a level of significance was observed for the elements As/Cu and Cu/Pb, indicating that their levels were from the same source. Finally, a significant level for Cu/Zn and Pb/Zn was observed in the Casablanca River basin. Moreover, a significant level was observed for the Cu/Pb elements, indicating that their levels were similar or came from the same source. Principal component analysis (PCA) in the Aconcagua River basin reveals two components. Principal component 2 may be associated with the mining activities (Table 4a and Figure 3a), while PC1 appears to be influenced by both activities: mining and agriculture activities. Table 4b and Figure 3b present PCA results for the Casablanca River basin. Principal component 1 is likely related to agricultural activity, and PC2 is attributed to a geogenic origin. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Geochemical Baseline**} & \multicolumn{4}{c}{**Aconcagua River Basin**} & \multicolumn{4}{c}{**Aconcagua River Basin**} & \multicolumn{4}{c}{**Casablanca River Basin**} \\  & \multicolumn{4}{c}{**(Including Mining Activity)**} & \multicolumn{4}{c}{**(Without Mining Activity)**} & \multicolumn{4}{c}{**(Only Agricultural Activities)**} \\ \cline{2-13}  & **As** & **Cu** & **Pb** & **Zn** & **As** & **Cu** & **Pb** & **Zn** & **As** & **Cu** & **Pb** & **Zn** \\ \hline
90 & 26.2 & 545 & 55 & 253.2 & 18.4 & 133.5 & 33 & 230.6 & 10 & 51.8 & 28 & 84.4 \\
95 & 29.6 & 1610.6 & 69.6 & 290 & 23.8 & 158.7 & 35.9 & 386.9 & 12.4 & 61.2 & 33.8 & 105.4 \\ MAD c & 6.29 & 271.1 & 6.81 & 48.7 & 14.5 & 94 & 37. & 194 & 1 & 31 & 17 & 69 \\ Upper Whisker a & 40.5 & 655 & 59.5 & 360 & 21.4 & 204.5 & 47.5 & 255.6 & 4.4 & 69 & 27.5 & 116 \\ \hline \hline \end{tabular}  
* Upper whisker or upper limit, c Median absolute deviation  
\end{table} 
Table 2: Comparison of statistical methods for the geochemical threshold value for soil samples from the Aconcagua River basin with and without mining activities and the Casablanca River basin.