Fractionation of Heavy Metals in Soil From Active Automobile Workshops in Benin City, Nigeria

Heavy metals are potentially toxic to human life and the environment. Therefore, determining the chemical forms of metals in soil is essential for evaluating their mobility and bioavailability. This study investigated the speciation of selected heavy metals (Cd, Cr, Pb, Ni, and V) in soils around automobile repair workshops in Benin City, South-South Nigeria. Soil samples were collected from a depth of 0–15 cm using a soil auger. Control samples were obtained from a farmland at the Faculty of Agriculture, University of Benin. The modified BCR sequential extraction procedure was used to fractionate the soil samples into four operational groups: exchangeable/carbonate (B1), Fe-Mn oxide-bound (B2), organic-bound (B3), and residual (R) fractions. Metal concentrations in the extracts were determined using atomic absorption spectrometry (AAS). Cadmium, Cr, Ni, and V were predominantly found in the exchangeable/carbonate fraction, while Pb was primarily associated with the residual fraction. The total bioavailable metal content across zones followed the order: SW > NE > SE > NW. The average mobility factors for Cd, Cr, Pb, Ni, and V across all zones were 22.08%, 30.75%, 24.47%, 32.63%, and 32.88%, respectively.