The use of Phytoremediation as a non-destructive and cost-effective in-situ technology for the clean-up of spent oil contaminated soils was investigated using two common plants, Chromolaena odorata (siam weed) and Helianthus annuus (sunflower).The experimental set-up was established in three locations and consisted of a system of treatment of polluted sites with Chromolaena odorata,Helianthus annuuswith a separate control. The experimental design was Randomized Complete Block Design (RCBD) with three replications per treatment. Plants and soil samples were collected and analyzed before and after the experiment to determine the presence and concentration of heavy metals such as Cu, Mn, Zn, Pb, Cd, and Fe. Data obtained were subjected to Analysis of Variance (ANOVA) and Duncan's multiple range test used for mean separation. The two plants grew successfully in all the experimental plots. However, there was a significant reduction of Zn, Cu, Cd, Mn, Pb and Fe in the soil and a significant absorption of Pb, Cd, Cu, and Zn by Chromolaena odorata. A significant absorption of Fe and Mn by Helianthus annuus without a corresponding level of absorption of Pb, Cd, Cu and Zn was also evident. Chromolaena odorata absorbed more of the heavy metal contaminants than Helianthus annuus which was significant at P = 0.05. This study has established the capacity of the two plants to absorb heavy metal contaminants in the soil. They can, therefore, be recommended for use in the remediation of spent oil- polluted soils.
Keywords: phytoremediation, contamination, Chromolaena odorata, Helianthus annuus and spent oil.