MOBILITY AND BIOAVAILABILITY OF HEAVY METALS IN SOILS OBTAINED FROM OPEN-AIR AUTOMOBILE REPAIR SHOP IN JOS NORTH LGA, PLATEAU STATE, NIGERIA

Abstract

In this work, the forms of Cadmium (Cd), Lead (Pb), Zinc (Zn), Copper (Cu) and Nickel (Ni) were determined in soil samples from four automobile maintenance and repair shops (garages) within Jos North LGA of Plateau State. Samples were collected from four different garages namely; Army Engineer (site A), Angwan Rukuba (site B), Farin Gada (site C) and Tudun Wada (site D). The samples collected were prepared and analyzed for the various forms (exchangeable, reducible, oxidizable and residual) of the heavy metals using the Community Bureau of Reference (BCR) sequential extraction techniques and detected using an Atomic Absorption Spectrophotometer (AAS). The result showed Zn concentration as highest in all the sites with an average of 37.62±0.03 mg/kg, followed by Pb with average concentration of 3.38±0.01 mg/kg, CU and Ni with average values of 2.03±0.01 mg/kg and 0.18±0.00 mg/kg respectively. Cd was only found to be in the exchangeable form at site D and below the detectable limit in sites A, B, and C. However, Cu was more associated to the exchangeable forms in sites C and D while in sites A and B it was associated with the oxidizable and residual forms, respectively. The residual form of Ni was highest in all the sites while the reducible form showed highest for Pb. Zn was more associated with the exchangeable fraction in all the sites except site A which has more of the residual form. Zn and Cu were found to be mobile and bioavailable in all the sites while Ni was not. However, Pb was mobile and bioavailable in sites B and D, while Cd was only bioavailable in site D. The individual contamination factor (ICF) was highest for Cu, followed by Zn and Pb. This suggests higher risk of Zn, Cu and Pb pollution in garage soils. The work recommends in the immediate run that both in-situ and ex-situ remediation techniques be used to rectify the heavy metal contamination in this sites.