# Seasonal Pollution Levels and Heavy Metal Contamination in the Jukskei River, South Africa
## 2 Methodology
### Sediment Quality Assessment  
The amounts of heavy metals were used to assess pollution levels, source identification, and ecological risk in the river system. Pollution indicators, including enrichment factor (EF), contamination factor (CF), and geo-accumulation index (Igeo), have been employed to evaluate the level of contamination, with Fe serving as the reference element [21, 31]. The reference values used for calculation of selected pollution indices were as described by several researchers as As (12.7 mg/kg), Cd (mg/kg), Hg (0.02 mg/kg), Pb (10 mg/kg), Th (10 mg/kg), U (10 mg/kg), and Fe (10,000 mg/kg) [4, 31, 32]. The contamination level to assess severity of water pollution followed similar pollution indices as sediment quality, however, differing by reference values for each parameter as described by [PERSON] et al. [21]. The range of contamination levels were evaluated for the effect of human activities on accumulation of hazardous components. The EF value determined from Equation (1) in the range of 10 to 50 indicates severe to extremely high enrichment for both water and sediments quality assessment. Equation (2) was used to determine the values that determined the CF, where a CF > 6.0 indicated extreme contamination. The Igeo was calculated using Equation (3) and was used to quantify the accumulation of heavy metals only in sediments to explain the variations brought on by the lithogenic factors taken into consideration by using a background matrix factor of 1.5.  
\[\text{Enrichment factor }(\text{EF})=\frac{\frac{\text{Cr}}{\text{C}\text{F} \text{F}}\text{sediment}}{\frac{\text{C}\text{C}\text{F}}{\text{D}\text{F}} \text{background}} \tag{1}\]  
\[\text{Contamination factor }(\text{CF})=\frac{\text{C}\text{x}\text{ sediment}}{ \text{C}\text{x}\text{ reference}} \tag{2}\]  
\[\text{Geo-accumulation index }(\text{Igeo})=log\frac{\text{C}n}{1.5 Bn} \tag{3}\]  
The relationship between the concentration of element \(x\) and that of the sediment's reference element is represented by the (C\(x\)/C\(ref\)) sample while the background value denotes the ratio of element x's concentration to that of the reference element for Equation (1). The CF values were determined using Equation (2), where (C\(x\))reference represents the amount of the reference element and (C\(x\))sediment indicates the concentration of element x in the sample. In Equation (4), Cn represents the concentration of the sediment element x, whereas Bn denotes the background value of the reference [26].  
Potential ecological risk index is a calculated statistic that indicates the possible ecological risk of heavy metals and metalloids in sediments in a certain aquatic system (ERI) [33]. The RI was calculated using Equation (4). The potential ecological risk of sediments is be divided into five grades shown in Table 1.  
\[\text{RI}=\sum\text{E}_{\text{i}}=\sum\text{T}_{\text{i}}(\text{C}^{\text{i} }_{\text{s}}/\text{C}^{\text{i}}_{\text{n}}) \tag{4}\]  
where RI represents the potential ecological risk index, C\({}^{\text{i}}_{\text{s}}\) represents the heavy metal \(i\) level in the sediment, C\({}^{\text{i}}_{\text{n}}\) represents the background value of heavy metal \(l\), and T\({}_{\text{i}}\) represents the toxicity coefficient of the \(i\)th heavy metal that reflects the toxicity level of the heavy metal.