Capability of Vetiver (Vetiveria Zizanioides), Guinea Grass (Panicum Maximum) and Organic Manures to Remove Total Hydrocarbon and Heavy Metals from Crude Oil Contaminated Soil in Port Harcourt
In a field study conducted at the Teaching and Research Farm of Rivers State University PortHarcourt, Nigeria, to examine the ability of vetiver and guinea grasses amended with organic manures in remediation of crude oil polluted soil; soil polluted with Bonny light crude oil at 0 and 2% v/w was subjected to a remediation processes using vetiver (Vetiveria zizanioides) and Guinea grass (Panicum maximum) amended with organic manures for a period of twelve months. Two weeks after pollution, poultry and rabbit manures were applied at 0, 10, 20 and 30 tons per hectare respectively. Vetiver and guinea grasses were planted two weeks later. It was fitted in factorial split plots randomized block design. Results of the study revealed that remediation of the soil with grasses degraded the Total hydrocarbon content (THC) to 23 and 21.2% for vetiver and guinea grass respectively, while the quantity of heavy metals removed from the soil were 28.4% and 25.9% for iron, 37.3 and 32.8% for zinc, 35.8 and 30.8% for lead (Pb) and 23.1 and 38.5% cadmium for vetiver and guinea grass respectively. Amendment of the soil with 30 tons’ /ha organic manures increased the quantity of THC degraded to 70.6% and 67.9% for vetiver and guinea grass respectively while the concentration/quantity of heavy metals removed from the soil increased to 58.4 and 54.7% for Fe, 66.9 and 65.1% for Zn, 69.4 and 66.6% for Pb and 80.8 and 71.2%, in Cd for vetiver and guinea grass respectively. The quantity and concentration of THC and heavy metals degraded in the soil was higher in vetiver than guinea grass plots and in vetiver amended with poultry manure than in guinea grass amended with rabbit manure. There was a significant (P<0.05) difference in uptake of THC and heavy metals in plant tissues between vetiver and guinea grass. Vetiver accumulated more of the contaminants in their tissues than guinea grass. Amendment of the soil with organic manures reduced the uptake of the contaminants (THC and heavy metals) from the plant tissues. Generally, both grasses have the capability to remediate crude oil contaminated soil. Augmentation of the two grasses with organic manures enhanced their capability.