Heavy metals distribution, risk assessment and water quality characterization by water quality index of the River Soan, Pakistan

• EF and Igeo were used to determine metals enrichment in sediment, River Soan.
• Cd, Zn and Pb enrichment were more in sediments.
• RI revealed moderate ecological risk in the suspended sediment samples.
• WQI suggests water quality was good during the pre-monsoon season.
• Cd, Zn and Pb threats to aquatic ecosystem should not be ignored.

Distribution of heavy metals, nutrients and some physico-chemical variables were studied in water, suspended and bed sediment samples along River Soan and its tributaries during pre- and post-monsoon seasons. Nutrient loading in water samples were relatively high during pre-monsoon season while metal concentrations were found to be high during post-monsoon season. Water quality as determined by water quality index (WQI) was found to be relatively better during the pre-monsoon season. Ni, Pb and Cd concentrations were found to be higher than recommended for water use for domestic or aquatic life. Metal concentrations were relatively high in the suspended sediment samples as compared to the bed sediment samples. Igeo results indicated that bed and suspended sediment samples were moderately contaminated with Cd while Ni, Cu and Cr showed moderate contamination in the suspended sediment samples. Further, results indicated that contamination sources in the bed (Cd, Zn and Pb) and suspended (Cd, Zn, Ni, Cu and Cr) sediment samples were from natural processes and anthropogenic activities. According to the classification carried out on the basis of EF, the bed sediment samples were significantly contaminated with Cd and moderately contaminated with Pb and Zn. While Cd, Pb, Ni, Cu and Cr showed significant contamination and Zn showed moderate contamination in the suspended sediment samples. Potential risk index revealed moderate ecological risk in the suspended sediment samples of urban areas. The results suggested that Cd, Zn and Pb threats to aquatic ecosystem should not be ignored.