Abstract

This study evaluates heavy metal contamination and ecological risk in surface soils across the three senatorial districts of Nasarawa State, Nigeria. A total of 45 surface soil samples (15 per district) were analyzed for Cd, Pb, Zn, Cu, Cr, Ni, and Fe concentrations. Contamination levels were assessed using contamination factor (CF), pollution load index (PLI), geoaccumulation index (Igeo), Nemerow pollution index (NPI), and potential ecological risk index (RI), while principal component analysis (PCA) was used to identify possible sources. Results showed a spatial trend of metal concentrations in the order Nasarawa North > Nasarawa West > Nasarawa South. Cadmium concentrations in Nasarawa North (0.82 ± 0.15 mg/kg) approached background levels, whereas Pb concentrations in Nasarawa West were significantly lower than background values. CF values were generally <1, indicating low contamination. PLI values (0.009–0.576) and Igeo values (−0.71 to −3.47) confirmed unpolluted soil conditions. Ecological risk indices were low (RI <150), although Cd contributed substantially to the total risk due to its high toxicity response factor. PCA extracted two principal components explaining 78.4% of the total variance, indicating predominantly lithogenic sources with minor anthropogenic contributions. Compared with heavily contaminated sites in Nigeria and other regions, metal concentrations in the study area were significantly lower. From all indication, the results indicate that surface soils in Nasarawa State are largely uncontaminated and pose low ecological risk. Although the soils are presently largely uncontaminated and pose low ecological risk, the proximity of the Nemerow pollution index to the warning threshold in Nasarawa North warrants sustained environmental monitoring and periodic reassessment to prevent future contamination.

Keywords

Heavy metals; soil contamination; pollution indices; ecological risk assessment; principal component analysis; Nasarawa State.