Acacia nilotica L. Bark Removes Toxic Elements from Solution: Corroboration from Toxicity Bioassay Using Salix viminalis L. in Hydroponic System

The present investigation deals with the advantages and potential of the Acacia nilotica bark as an adsorbent of toxic metals. Bark (1 g) when added to 100 ml of aqueous solution containing 10 μg ml^-1 metal solution exhibited different metal adsorption values for different metals. The order of metal adsorption being Cr ≥ Ni > Cu > Cd > As > Pb. A similar trend of metal adsorption was observed when the bark is reused (1^st recycle) Cr> Ni > Cu > Cd > Pb and also in the column sorption. In order to verify the metal removal property of A. nilotica bark, toxicity bioassay with Salix viminalis stem cuttings in hydroponic system augmented with Cd, Cr, and Pb together with A. nilotica bark powder was carried out. The results of toxicity bioassay confirmed the metal adsorption property of the bark powder. The functions of toxicity studies include leaf area, root length and number of new root primordia produced per stump. The leaf area, root length, and the number of new root primordia increased considerably in the presence of A. nilotica bark. The order of metal toxicity for leaf area and new root primordial is Cd > Cr > Pb. However, for root length the order of metal toxicity is Cr > Cd > Pb. The metal budgets of the leaf and root confirmed that the bark powder had adsorbed substantial amount of toxic metals and thus alleviates the toxicity imposed by the various tested elements. Hence, the utility of A. nilotica bark in developing and designing innovative technology for the clean up of toxic elements in aqueous solutions and possible scope for its use in phytoremediation are discussed.