Comparative Assessment of Heavy Metal Concentrations in Soils Across Four Local Government Areas of Southern Kebbi State, Nigeria: A Spatial Variability Study

Spatial variability of heavy metals in agricultural soils is a critical factor in determining the extent of contamination and formulating site-specific management strategies. This study compared the concentrations of heavy metals Cadmium (Cd), Copper (Cu), Iron (Fe), Manganese (Mn), Lead (Pb), and Zinc (Zn) in soils across four Local Government Areas (LGAs) of southern Kebbi State, Nigeria. A total of 48 composite soil samples were collected from Zuru, Danko Wasagu, Yauri, and Shanga LGAs. Heavy metal concentrations were determined using Atomic Absorption Spectrophotometry (AAS). Data were analyzed using Analysis of Variance (ANOVA), and means were separated using Duncan's New Multiple Range Test (DMRT) at a 5% probability level. The comparative analysis revealed no significant differences (p > 0.05) among the four LGAs for Cd, Cu, Mn, and Pb concentrations. However, significant differences (p < 0.05) were observed for Fe and Zn. Danko Wasagu recorded the highest mean Fe concentration (16.789 mg/kg), while Yauri had the lowest (13.990 mg/kg). For Zn, Shanga LGA recorded the highest mean concentration (0.7283 mg/kg), which was significantly higher than the other three LGAs, which were statistically similar. Cadmium concentrations exceeded the NESREA standard of 3.00 mg/kg in all LGAs, with Shanga recording the highest value (4.0350 mg/kg). The study reveals that while most heavy metals are uniformly distributed across the southern Kebbi State, Fe and Zn exhibit significant spatial variability. The widespread exceedance of Cd across all LGAs, particularly in Shanga, warrants immediate attention and site-specific remediation strategies