Ecological risk assessment of heavy metal-contaminated soils of selected villages in Zamfara State, Nigeria

Abstract The incidence of heavy metal contamination in Zamfara State, northern Nigeria, due to artisanal mining in some villages has resulted in the pollution of a vast area of land and water. This study evaluated the extent of environmental risks caused by heavy metals. It involved five (5) villages (Bagega, Dareta, Sunke, Tunga, and Abare) where mining activities were taking place and Anka town with no record of mining activities served as control. In each of the five villages, three sites (3) were identified as a mining site, processing site, and village making a total of sixteen (16) sites. Bulked soil samples were collected in triplicate and analyzed for iron, lead, cadmium, chromium, zinc, and nickel using flame atomic absorption spectrophotometry. Measured concentrations of the heavy metals in soils were then used to calculate the pollution and ecological risk pose by heavy metals. Their concentrations were in the order Fe > Pb > Cr > Zn > Cd > Ni, with Pb and Cd having a concentration higher than permissible levels for soils and accounted for 98.64% of the total potential ecological risk. Also, all the different pollution indices examined showed that all the sites were polluted with Cd, and all the processing sites were polluted with Pb. This reveals that processing sites pose more risk to heavy metal contamination. Correlation analysis showed a highly significant (p < 0.001) positive correlation between Pb and Zn, Cr and Ni, and a significant (p < 0.01) positive correlation between Fe and Pb, Zn and Cr. The principal component analysis suggested that Pb, Zn, Cr, and Ni likely originated from the same source, i.e., mining activities, and Fe and Cd originated from the abundant parent material in the study area.