# Seasonal Pollution Levels and Heavy Metal Contamination in the Jukskei River, South Africa
## 3 Results and Discussion  
### Dry and Wet Season Concentrations of the Heavy Metals  
Quantitative determinations of As, Cd, Fe, Hg, Pb, Th, and U in sediment collected during the wet and dry seasons of the Juleskei River are presented in Table 2. The levels of heavy metals in sediments decreased in the following order: Fe \(>\) Pb \(>\) As \(>\) Th \(>\) U \(>\) Cd \(>\) Hg in the wet season and Fe \(>\) Pb \(>\) Hg \(>\) As \(>\) Th \(>\) U \(>\) Cd for the dry season. Compared to the wet season, the dry season has a greater concentration of Hg, attributed to sediment dilution because of the addition of run-off flooding during the rainy wet season [35]. The maximum concentration of Pb of 475 mg/kg was detected at sampling point Jules-P2 and the lowest concentration of 12.6 mg/kg at point Juk-P3. For the dry season, the maximum concentration for Pb was determined at the point Juk-P1 with a concentration of 267 mg/kg and the lowest 14.8 mg/kg concentration at Juk-DS-6. The concentration levels were high for both dry and wet seasons and they were higher than the 10 mg/kg Pb reference that was used for pollution indices determination in this study. The Pb pollution activities in sampling points Jules-P1 and Jules-P2 are indicative of concerning pollution and continual Pb input in the Juleskei River. Previous studies in the Juleskei River reported Pb concentration in the sediments ranging from 123 mg/kg to 1921 mg/kg [36]. The significance of measured Pb contamination was compared to the values obtained by other studies around the world. Pb concentration of an average of 14.2 mg/kg was detected at Afon Ystwyth River [37]; the study on the river sediments of Nakdong River, South Korea found a 78.5 \(\pm\) 25 mg/kg Pb concentration [38]; in the Pearl River Delta, China, the Pb concentration in the sediments was 73.0 mg/kg [39]. These Pb concentrations mentioned above recommended 5 mg/kg in the sediment by the Food and Agriculture Organization of the United Nations [40]. The highest concentration of 77.5 \(\upmu\)g/kg and lowest of 8.45 \(\upmu\)g/kg for Hg at respective Jules-P1 and Jules-DS-6 points during the wet season were at trace levels. The concentration for Hg in the dry season shows a considerable increase with the highest concentration of 12,100 \(\upmu\)g/kg at point Jules-DS-6 and lowest of 3650 \(\upmu\)g/kg at Jules-P1. The primary sources of Hg in river systems include industrial discharges, legacy contamination from historical gold and coal-fired power station activities, atmospheric deposition, and natural geological processes with each of these sources contributing differently to the Hg load in river systems. The considerable Hg contamination during the dry season in river systems could be attributed to a variety of sources that are mostly \begin{table}
\begin{tabular}{l c c c} \hline \hline
**Scope of Ecological Risk** & **Ecological Risk Level of** & **Scope of Toxicity Index (RI)** & **The Level of Potential** \\
**Index (E\({}^{\text{i}}_{\text{f}}\))** & **Single-Factor Pollution** & **Scope of Toxicity Index (RI)** & **Ecological Risk** \\ \hline E\({}^{\text{i}}_{\text{f}}\) \(<\) 40 & low & RI \(<\) 150 & low-grade \\ 40 \(\leq\) E\({}^{\text{i}}_{\text{f}}\) \(<\) 80 & moderate & 150 \(\leq\) RI \(<\) 300 & moderate \\ 80 \(\leq\) E\({}^{\text{i}}_{\text{f}}\) \(<\) 160 & higher & 300 \(\leq\) RI \(<\) 600 & severe \\ 160 \(\leq\) E\({}^{\text{i}}_{\text{f}}\) \(<\) 320 & high & 600 \(\leq\) RI & serious \\ E\({}^{\text{i}}_{\text{f}}\) \(\leq\) 320 & serious & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Relationship among RI, E\({}^{\text{i}}_{\text{f}}\), and pollution levels [33]. anthropogenic rather than natural inputs. These sources can instigate the complex cycling and distribution of Hg in aquatic environments, thus leading to detrimental impacts to the ecosystems and human health [21; 36; 41]. The dry-season Hg concentrations are higher than the background concentration, but they are lower than the sediment Hg concentration found in Kimbi River DRC [42; 43].