Abstract
Plants accumulate minerals essential for their growth from the environment alongside with heavy metals from contaminated areas.This study investigated bioaccumulation of heavy metals by Moringa oleifera in automobile workshops in three selected local government areas in Ibadan. This was done with a view to determining the concentration and type of heavy metals accumulated in the tissues of Moringa oleifera grown around automobile workshops. Barks, leaves and seeds of M. oleifera were collected from three automobile workshops in each of the local government area and from a control site. The samples were dried, ground and analyzed for heavy metals content (Cu, As, Pb, Cd, Cr, Mn and Zn) using ICP-MS. The mean level of heavy metals obtained ranged from 0.018 ± 0.001 to 0.356 ± 0.021 in the leaves, 0.012 ± 0.001 to 0.255 ± 0.016 in the seed and 0.048 ± 0.003 to 0.989 ± 0.003 in the bark. The concentration of heavy metals recorded followed the trend of Cu > Zn > Mn > Pb > Cr > As > in the leaves; Zn > Cu > Pb > Cr = Mn > As in the seeds and Zn > Cu > Mn > Pb > Cr > As> in the barks. The overall concentration of heavy metals bioaccumulated by this plant follows the trend; bark > leaves > seeds. The increase in the concentrations of heavy metals observed in the barks, leaves and seeds of M. oleifera collected from automobile workshops to that of control site indicated the impact of mechanical activities in introducing trace metals to the environment.The study further suggested that Moringa olifera in polluted sites may accumulate trace metals in any of its parts; hence care should be taken when harvesting the plant for medicinal purpose.