## 2 Materials and Methods
### Pollution and Health Risk Assessment  
#### 2.4.1 Pollution Indices  
In recent decades, pollution indices have become increasingly valuable in evaluating the degree of soil and sediment contamination [31; 32; 33; 34; 35]. These indices provide crucial information about the origin of the contamination, whether it is natural, anthropogenic, or a combination of both. Additionally, they offer insights into the associated risks posed to the environment and human health. Different pollution indices have been used to evaluate the extent of soil contamination by toxic elements. These include the _Geoscumulation Index_ (Igeo), _Enrichment Factor_ (EF), _Single Pollution Index_ (PI), the _Potential Ecological Risk Index_ (PERI), the _Contamination Severity Index_ (CSI), and the _mean Effect Range Median quotient_ (mERM\({}_{\text{Q}}\)). These indices provide varying perspectives on the nature and degree of contamination, offering a comprehensive understanding of the contamination state of soil in the given area. The data generated can be useful in making decisions on land use and remediation efforts. The indices were calculated and evaluated according to [36; 37; 38; 39; 40]. _The Geoscumulation Index_ (Igeo), first introduced by [41], is the ratio of the concentration of HMs in soil to their natural geochemical background (Equation (1)). \[\text{Igeo}=\log_{2}\left[\frac{\text{C}_{i}}{1.5\cdot\text{Bi}}\right] \tag{1}\]  
where \(C_{i}\) refers to the concentration of a particular \(i\) metal in the soil (mg kg\({}^{-1}\)), and \(B_{i}\) refers to the concentration of that same metal in the natural background (mg kg\({}^{-1}\)). The constant 1.5 is used to facilitate accurate and consistent data analysis, while also minimizing the impact of lithological variations on the overall results. Soil contamination degree was classified according to the scale of interpretation developed by [PERSON] as follows: Igeo \(\leq\) 0--unpolluted (Class 0); 0 \(<\) Igeo \(\leq\) 1--unpolluted to moderate polluted (Class 1); 1 \(<\) Igeo \(\leq\) 2--moderate polluted (Class 2); 2 \(<\) Igeo \(\leq\) 3--moderate to high polluted (Class 3); 3 \(<\) Igeo \(\leq\) 4--high polluted (Class 4); 4 \(<\) Igeo \(\leq\) 5--high to very high polluted (Class 5); and \(>\) 5--excessively polluted (Class 6). The _Enrichment Factor_ (EF), first calculated by [42], is an index that helps to assess the impact of human activities on the concentration of metals in soil. It is calculated by dividing the concentration of a particular metal in the soil by the concentration of a naturally occurring element such as Fe, Al, Sc, Mn, or Zr, which remains constant over time. In this study, the element Al was used as a reference to normalize the metal enrichment (Equation (2)). \[\text{EF}_{i}=\left(\text{C}_{i}/\text{C}_{\text{Al}}\right)/\left(\text{B}_ {i}/\text{B}_{\text{Al}}\right) \tag{2}\]  
where C\({}_{i}\) refers to the concentration of the metal \(i\) in soil (mg kg\({}^{-1}\)), C\({}_{\text{Al}}\) is the concentration of aluminum in soil, \(B_{i}\) is the concentration of that same metal in the natural background (mg kg\({}^{-1}\)), and B\({}_{\text{Al}}\) is the concentration of Al in the natural background. The results were classified by [38] classes of interpretation: Class 1: \(<\)2--deficiency--minimal enrichment (unpolluted soil--low polluted soil); Class 2: 2-5--moderate enrichment (moderately polluted soil); Class 3: 5-20--significant enrichment (significant polluted soil); Class 4: 20-40--high enrichment (highly polluted soil); and Class 5: \(>\)40--extremely high enrichment (extremely polluted soil). The _Single Pollution Index_ (PI) is used to identify the metal with the highest impact on environment, and it was calculated according to Equation (3) [39]. \[\text{PI}_{i}=\frac{\text{C}_{i}}{\text{Bi}} \tag{3}\]  
where \(C_{i}\) refers to the concentration of the metal \(i\) in soil, and \(B_{i}\) is the concentration of that same metal in the natural background, both expressed in mg kg\({}^{-1}\).