Heavy metal concentrations in plants growing in crude oil contaminated soil in Akwa Ibom State, South-Eastern Nigeria

A field study was conducted to assess heavy metal concentrations in plants grown on crude oil contaminated soil in Akwa Ibom State. Plant samples obtained from polluted and unpolluted (control) sites were digested and analysed for manganese (Mn), iron (Fe), lithium (Li), zinc (Zn), copper (Cu), cadmium (Cd), chromium (Cr), lead (Pb), cobalt (Co), vanadium (V), molybdenum (Mo), mercury (Hg) and selenium (Se). The selected plants were Dissotis erecta (DE), Urena lobata (UL), Selaginella myosurus (SM), Diodia scandens (DS) and Pityrogramma calomelanos (PC). Considerable amount of Mn and Fe were found to accumulate in all the plants grown on contaminated soil, while other elements assessed were obtained in trace amount. The order of bioacculation of trace metals were Mn > Fe > Zn > Li > Co > Pb > Mo > Cd > V = Hg > Cu = Se > Cr, while the plants accumulated the highest amount of trace metals were found to be in the order of: Dissotis erecta (DE) > U. lobata (UL) > S. myosurus (SM) > D. scandens (DS) > P. calomelanos (PC) indicating that DE and UL plants can be used for remediation of contaminated soils. The result of the correlation analysis showed positive relationships among the trace metals in both contaminated and uncontaminated soils. Results also imply that consuming plants growing in the vicinity of oil spills may pose a health risk to humans and animals.