ABSTRACT

The effect of crude oil polluted soil on the anatomy, heavy metal content and mineral composition of Centrosema pubescens and Pueraria phaseoloides was investigated the experiment was a factorial (2x4) arrangement in a completely randomized design (CRD). Factors and levels were the two legumes (C. pubescens, P. phaseoloides) and crude oil concentration (volume/weight) in the soil (0%, 1%, 3% and 4%). Anatomical changes in root, stem and leaves were observed in the treated samples (i.e. 1% - 4%V/W). Cortical parenchyma cells of stem and root had reduced intercellular air spaces in the treated/contaminated samples while those in non-treated (0%v/w) had large number of intercellular air spaces. Presence of oil droplets was observed in roots at 3% and 4% v/w with its accompanying tissue breakdown. Stomatai reduction and epidermal cell wall aberrations were observed in the leaves of the treated samples. Generally, heavy metal presence was significantly high (at P< 0.05) in the treated soil, roots and leaves ofthe studied plants parts as the level of pollution increased. Copper had the highest increase in concentration at the beginning ofthe experiment (from 0.13-0.98mg/g) while cadmium had the least (from 0.06- 0.41mg/g). Copper had about 59% reduction at 4%v/w level of pollution in P. phaseoloides grown soil 14 Weeks After Planting (WAP). Cadmium was the least reduced (20%) at 4% level of pollution in C. pubescens grown soil. The roots of the studied plants accumulated more heavy metals than the leaves. Lead concentration in P. phaseoloides and C. pubescens roots were 0.28mg/g and 0.31mg/g respectively and 0.20mg and 0.17mg/g in their respective leaves. The anatomical changes and observed heavy metal alterations in the plants and soil were discussed as possible tool in phytomonitoring and phytoremediation. The Ca, Mg and Na contents in the polluted soil at the beginning of the experiment increased, and reduced 14WAP with the studied plants while P, K and N reduced as the pollution increased at the beginning ofthe experiment but increased in soil content at the end ofthe experiment. Also, this study has demonstrated that crude oil contamination ofsoil had highly significant effect by altering the mineral component ofthe studied plants. The result was tabulated as possible information necessary in agricultural decisions. However, caution should be employed in the choice and disposal experimental soil and plant. The soil and plant used for experimental purposes should be properly buried beyond the uptake of the concentrated metal by plant roots. This prevent the reintroduction ofthe heavy metal laden parts ofplants and soil into the food chain, since not all accumulated heavy metal are phytoextracted or completely degraded by plants.