Phytoremediation Potentials of Common Nigerian Weeds for the Purpose of Cleaning up a Lead-Zinc Derelict Mine

Six common Nigerian weeds namely Helianthus annus, (Sunflower), Imperala cylindrical (Sword grass), Sida acuta burn (Broom weed), Gossypium spp (Cotton), Eleusine indica (Goose grass) and Chromoleaeceae Odarata (Siam weed) grown around Enyigba lead mines were investigated within a period of two years (2008-2010) for their abilities to remove heavy metals from the soils of the derelict mines. X-ray Fluorescence (XRF) spectrometric method was used to determine the concentrations of arsenic (As), cadmium (Cd), chromium (Cr), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb) and zinc (Zn) in the top and sub soils and also in the roots, stems and leaves of the studied plants. The Pollution Indices (PI) of the soil was evaluated as well as the Bioaccumulation Factors (BAF) and Translocation Factors (TF) of the weeds and they were used to determine the phytoremediation potentials of the weeds. The results obtained revealed the mean concentrations (mg/Kg) of metals in the studied plants were of the range: Pb (12.62 – 417.2); As (0.38 – 2.26); Cd (8.46 – 144.6); Cu (32.81 – 420.40); Cr (30.2 – 184.2); Zn (0.26 – 16.87); Mn (12.94 – 155.80) and Ni (3.86 – 47.42). Levels of heavy metals in Chromoleaeceae odorata and Imperata Cylindrical were significantly higher than in the other weeds. Higher accumulation of metals was observed in roots than in the stems and the leaves. High BAF and TF (<1) observed in some of the studied plants suggest that they could be employed as efficient phytoremediation agents in cleaning up polluted soil. Statistical analysis of variance (ANOVA) at P<0.05 showed variations in the heavy metal levels between and within groups while Fisher’s Least Significant Difference (LSD) Correlation analysis identified a strong relationship between the investigated plant and soil samples. Pollution Indices of metals in the studied soil sample in addition to the Bioaccumulation Factors and Translocation Factors of the studied weeds are important parameters to evaluate plants phytoremediation potentials.