Heavy metal pollution and ecological risk assessment in the sediments of River Kaduna, Nigeria

This study evaluated the pollution level and ecological risk of Cd, Cu, Cr, Pb and, Zn in sediments of River Kaduna. The total metal concentrations were analyzed using Atomic Absorption Spectrophotometry (AAS), while the pollution level and ecological risk of the metals were evaluated using a combination of geo-accumulation index (Igeo), contamination factor (CF), pollution load index (PLI), Nemerow pollution index (NPI), and potential ecological risk index. While Cd was below detection limits, the level of other heavy metals in all the sites followed the order: Zn > Cr > Cu > Pb. Heavy metals in the sediment can be classified as unpolluted to moderately polluted (Igeo < 2), with the pollution level following the order of Cr > Cu > Pb > Zn. While PLI classified the sites as polluted, NPI further subdivided the pollution level of the sites as precaution domain, slightly polluted domain, and moderately polluted domain. Pollution of the sites decreased from March to September at sites MU and JI but increased at NK. The same pattern was also observed for the ecological risk of the sites. However, none of the metals posed an ecological risk in the area as the risk factors were all below the lower threshold (Er < 40), and there was also a low risk to the local ecosystem at all the sites from the studied metals (RI < 110). The metals showed seasonal and spatial variation with levels that did not pose a serious threat in the area