ABSTRACT

Phytoremediation uses plants whose rhizospheres are able to accumulate heavy metals from the soil. The phytommediation and phytoindication potential of three Mucuna species in soils polluted with crude oil were assessed in a simulated field experiment. This experiment was a factorial (3 x 5) arrangement in a completely randomized design. Factors and levels were three species of Mucuna (M veracruz, M jaspodea and M ghana) and crude oil concentrations (volume/weight) in the soil (0 %, 1 %, 2 %, 3 %, and 4 %). From two weeks after planting (WAP), number of leaves, plant height, stem girth and leaf area were evaluated biweekly. Heavy metals (nickel, lead, copper and vanadium) concentrations of crude oil polluted soils were determined prior to planting and then at 12 WAP. Changes in anatomy in the vegetative parts of the three Mucuna species were examined. Plant height, number of leaves, stem girth and leaf area, the values obtained were higher for Mucuna plants growing in control soil (0%) and progressively decreased in Mucuna species grown on 1 —4 % crude oil polluted soils. The crude oil pollution only had a significant (P=0.05) effect on leaf area and number of leaves. The three Mucuna species accumulated heavy metals in their vegetative parts. Nickel accumulated more in the roots, than in the leaves, while copper and lead were more concentrated in leaves of the three Mucuna species, the concentration of copper was higher (highest value of 87 mg/g). However, the highest percentage of heavy metals reduction in the contaminated soils was that of lead with a percentage of 47.4 % reduction in the soil. The concentration of vanadium in soil and plant parts was less than 1 mg/g. The Mucuna species grown in higher concentrations of crude oil polluted soils (3 - 4 %) exhibited greater sinuosity in their epidermal cell walls than those grown in 0— 1% oil concentrated soils. The stomatal frequency progressively decreased as the oil concentration increased in soil. Cortical parenchyma cells of stems and roots of the three Mucuna species in higher oil polluted soils were flattened tangentially, smaller in size and had reduced intercellular air spaces. Those plants in control soils had large round polygonal cells. Presence of oil droplets on trichomes of leaves was noticed. Also dotted depositions of oil were noticed in the ground tissues, especially around the vascular bundles. The uptake of heavy metals by the vegetative parts of these Mucuna species and their changes in anatomy in response to oil pollution were discussed as a possible use in phytoremediation and phytoindication of oil polluted soils.