Remediative potential of bambara nut on lead and zinc polluted soils

Abstract

The ability of Bambara nut (Vigna subterranea, Accession TVSU 102) in the phytoextraction and accumulation of lead and zinc, in polluted soils was investigated in a pot experiment. The soils were polluted with 100, 150 and 200  mgkg^-1 of lead and zinc nitrates respectively. Chelant Ethyldiaminetetraacetic acid (EDTA) and farmyard manure (cow dung) were added to increase the uptake of the metals to aerial biomass. Bambara nut extracted more Pb from the soil augmented with EDTA and manure. Plants sown in augmented soil had greater bioconcentration factor (1.25, 1.55, 1.62 and 1.65). Bambara nut was observed to accumulate more Zn within its tissues whether or not the soil was augmented or not, having bioconcentration and Plant soil co-efficient factor greater than one.  When the plant was treated with lead nitrate at a concentration of 150 mgkg^-1 , the amount of Pb removed and  accumulated within plant tissues was 25.84 mgkg^-1 . Farmyard manure enhanced metal uptake by bambara nut  significantly more than EDTA. When the soil was treated with 150 mgkg^-1 of Pb but assisted with EDTA, the  amount of Pb removed and accumulated within plant tissues was 84.20 mgkg^-1 . However, when plants from soils  treated with 150mgkg^-1 Pb was augmented with manure it accumulated 95.01 mgkg^-1. The same trend was observed for Zn bioaccumulation by the plants. Bambara nut (Accession TVSU 102) can stabilize Pb and Zn within its roots by immobilizing them. The treatment effects of the metal salt (Pb and Zn) were minimal on plant genomic DNA. Amendments (the use of farmyard manure and EDTA) generally improved Pb and Zn phytoextraction by the plant from the soils to a great extent. The results suggest that further Pb and Zn removal could be achieved by successive revegetation over a growing period.

 Key words: Phytoextraction, metal excluder, phytostabilization, amendment, bioconcentration factor, coefficient of similarity