Assessment of selected heavy metal concentrations in soils from a mining area in Minna, Niger state

The study investigated the contents of selected heavy metals in top soils and sub-soils around the vicinity of artisanal gold mining site in Minna, Niger state, using standard procedures. Digestion was done using HNO₃-H₂O₂-HCl and heavy metal content using atomic absorption spectrometer. The results obtained showed some extent of contamination with mean values of 2.87 ± 0.17mg kg^-1, 286.21 ± 0.20mg kg^-1, 15,375.46 ± 0.52mg kg^-1, 2233.60 ± 0.46mg kg^-1, and 131.71 ± 0.15mg kg^-1 for Cd, Zn, Fe, Mn, and Pb, respectively. The surrounding environment (50 m away from the gold mining site) also showed significant contamination with mean values of 2.77 ± 0.17mg kg^-1, 295.27 ± 0.20mg kg^-1, 11,523.64 ± 0.25mg kg^-1, 1956.50 ± 0.54mg kg^-1, and 74.63 ± 0.15mg kg^-1 for Cd, Zn, Fe, Mn, and Pb, respectively. The values obtained were significantly higher when compared with those from the control soil samples. With the exception of Pb and Mn, the values of the other metals investigated were all below the WHO permissible limit. The trend of contamination with respect to contamination factor was in the order: Zn > Fe > Pb > Mn > Cd. The high contents of Pb and Mn in this area therefore show the need for more studies and immediate intervention measures.