## 5 Discussion
### Evaluation of Sediment Metal Contamination Based on SQG (TEL-PEL) Criteria  
The results revealed that Cr concentrations in all sediment samples exceeded the TEL value (43.4 mg/kg), with many samples surpassing the PEL threshold (111 mg/kg), indicating a significant ecological risk. The results revealed that Cr concentrations in all sediment samples exceeded the TEL value (43.4 mg/kg), with many samples surpassing the PEL threshold (111 mg/kg), indicating a significant ecological risk. Sample K8 exhibited an exceptionally high Cr concentration (1153 mg/kg), suggesting intense anthropogenic input or localised contamination sources. Such elevated Cr levels may adversely affect benthic organisms and overall sediment quality. At such concentrations, Cr can inhibit key metabolic processes in sediment-dwelling invertebrates, leading to ecological imbalance.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Cr (mg/kg)** & **Ni (mg/kg)** & **Cu (mg/kg)** & **Zn (mg/kg)** & **Pb (mg/kg)** \\ \hline K1 & 113 & 39.9 & 52.7 & 48.3 & 2.90 \\ K2 & 114 & 37.5 & 39.0 & 42.8 & 4.01 \\ K3 & 120 & 40.9 & 55.6 & 57.1 & 4.28 \\ K4 & 171 & 61.5 & 216 & 439 & 7.59 \\ K5 & 152 & 42.2 & 145 & 329 & 5.82 \\ K6 & 112 & 42.8 & 158 & 363 & 5.31 \\ K7 & 114 & 45.4 & 158 & 307 & 4.98 \\ K8 & 1153 & 35.4 & 25.5 & 96.9 & 7.83 \\ K9 & 106 & 49.0 & 134 & **335** & 4.69 \\ K10 & 108 & 48.9 & 132 & **336** & 4.78 \\ K11 & 199 & 40.4 & 32.3 & 68.0 & 6.12 \\ K12 & 125 & 36.3 & 38.9 & 74.3 & 4.92 \\ K13 & 165 & 36.7 & 36.7 & 73.9 & 5.54 \\ K14 & 186 & 43.0 & 48.3 & 113 & 8.67 \\ K15 & 246 & 49.7 & 56.5 & **134** & 8.38 \\ \hline \hline \end{tabular}
\end{table}
Table 7: TEL and PEL values for metals in stream sediments [65] (values exceeding the Probable Effect Level (PEL) are highlighted in red, values between the Threshold Effect Level (TEL) and PEL are shown in black (regular font), and values below TEL are shown in blue).  
The spatial pattern indicates that contamination is not widespread, but highly concentrated, which may point to point-source pollution such as discharges from industrial facilities or urban runoff. This pattern points towards potential industrial or urban runoff impacts contributing to Ni enrichment in the sediments. The high Cu levels signify a probable adverse effect on aquatic biota and highlight the need for further monitoring and management. These findings suggest localised Zn pollution hotspots that may pose ecological risks. Such Zn hotspots may originate from vehicular emissions, galvanized materials, stormwater runoff, or sewage discharge--common sources of zinc in urban and semi-urban catchments. The low Pb concentrations indicate minimal Pb-related ecological concern in the studied sediments.  
The SQG evaluation demonstrates that sediments in the study area are contaminated primarily with Cr, Ni, Cu, and Zn at levels likely to exert adverse ecological effects. The results highlight the influence of anthropogenic activities, especially urban and industrial discharges, on metal enrichment. Lead contamination appears minimal in comparison. These findings emphasise the importance of continuous monitoring and implementation of pollution mitigation strategies to protect the region's sediment quality and aquatic ecosystems.