Heavy Metal Fractionation in Soil Obtained from Selected Mechanic Shops and Dump Sites in Obio Akpor Local Government Area, Rivers State Nigeria

Abstract

The improper dumping, management and siting of refuse and mechanic sites have largely contributed to the contamination of soil by heavy metals. This study evaluates heavy metal fractionation in soil obtained from some mechanic shops and dump sites in Obio Akpor Local Government Area, Rivers State Nigeria. Two mechanical shops and two dumpsites in Obio/Akpor local government area in Rivers State were selected for metal speciation analysis. The total heavy metal contents of Cu, Pb, Zn and Cd were determined; thereafter, the sequential extraction of these heavy metals were carried out using the BCR scheme to determine the bioavailability of these heavy metals in the selected sites. The four metal fractions obtained were fraction 1 (exchangeable + acid soluble, fraction), fraction 2 (reducible fraction), fraction 3 (oxidizable fraction) and fraction 4 (residual fraction). The metal concentration of in the soil samples were as follows: Copper: 72.3 mg/kg (Site B)  – 78.5 mg/kg (Site D), Lead: 3.0 mg/kg (Site A) – 19.4 mg/kg (Site D), Cadmium: 4.50 mg/kg (Site D) – 6.56 mg/kg (Site B), Zinc: 7.2 mg/kg (Site D) – 63.0 mg/kg (Site D). In the dumpsites Cd, Cu, and Zn were not available for uptake by plants and animals, while Pb was bioavailable; in the mechanic shops Cu, Pb, and Zn were not bioavailable, while Cd showed bioavailability. The Contamination Factor (CF) of the heavy metals in this study revealed gave the trend: Cd > Cu > Pb > Zn, whereas the Geoaccumulation index (Igeo) showed that all samples’ sites were minimally contaminated with copper, lead and zinc (Igeo ˂ 0), except cadmium which showed high contamination in all sites. In conclusion, the pollution load index (PLI) assessment of the study sites showed that the sites are undergoing a progressive deterioration of their soil quality.