Influence of Groundnut and Rice Activated Charcoals Addition on Oil Polluted Soil and Mobility of Heavy Metals in the Root and Shoot of Vigna unguiculata L. Walp in the Tropical Rainforest

In Nigeria, spent oil destroys crops, contaminate farmland, aquaculture and drinking water. It also alters the soil properties, leads to deficit of water and oxygen, shortages of soil nutrients like N and P, adsorbs to soil particles and reduces porosity and aeration of soil. The study aims to determine the potential of groundnut hull (GAC) and rice husk (RAC) activated charcoal in biodegradation of spent lubrication oil in soil with reduction in mobility and bioaccumulation of heavy metals in the tissues of the cultivated cowpea (Vigna unguiculata L. Walp) plants. Experimental units were set up in a screen house containing cowpea seedlings planted in different soil treatments: polluted, unpolluted as well as RAC and GAC remediated polluted soil, each in 5 replicates. Mobility and bioaccumulation of the heavy metals in the root, shoot and seeds of the cowpea were analyzed. Cd, Cr and Pb were below detectable limit (BDL), Cu was 0.21 and Zn was 0.26 mg/kg in unpolluted soil while the levels of heavy metals were elevated in spent oil polluted soil: Cd 0.1, Cr 0.25, Pb 0.12, Cu 0.7 and Zn 0.63 mg/kg. RAC treatments significantly decreased the mobility and bioaccumulation of the heavy metals in the root (F3, 14 = 19.338, Sig = 0.00 (p < 0.05) so also, GAC significantly decreased the heavy metals mobilization and bioaccumulated in the cowpea roots (F3, 14 = 91.224, Sig = 0.000 (p < 0.05). RAC and GAC are potential effective and low cost phytoremediation materials.