| dc.description.abstract |
An experiment was conducted in the greenhouse to compare the effect of a synthetic chelator, ethylenediaminetetraacetic acid (EDTA), with that of a natural low molecular weight organic acid i.e. citric acid (CA) in enhancing the heavy metal extraction potential of Andrographis paniculata (Burm.f.) Wall. ex Nees from iron ore tailings (IOT). The chelator treatments were applied at doses of 0.05, 0.10 and 1.5mmol kg(-1)dry tailings. IOT without any additives were used as control. The effect of IOT (both with and without additives) on growth, photosynthetic pigments (chlorophyll, pheophytins and carotenoids), antioxidant activity, as well as uptake and accumulation of various heavy metals (Fe, Cu, Zn, Ni, Cr, Cd and Pb) were analysed for four months. Results indicated that the total uptake (mass removal from tailings) of metals by A. paniculata was enhanced by the addition of chelators. The heavy metal concentrations in the parts of A. paniculata under all chelator treatments were significantly (p<0.05) higher than those for the control, as the total concentration of Fe, Cu, Zn, Ni, Cr, Cd and Pb increased from 175.34, 118.72, 110.51, 2.5, 21.9, 1.026 and 10.2 mu g g(-1), respectively, to 184.17, 161.94, 157.69, 4.41, 26.17, 1.79 and 20.79 mu g g(-1) in the presence of CA, and 187.04, 176.12, 172.85, 5.44, 28.46, 2.254 and 22.14 mu g g(-1) with EDTA application even at the lowest dose of 0.05mmol kg(-1). By increasing the doses of EDTA and CA that were applied, we achieved further increased mobilisation of the targeted heavy metals from tailings to the plant roots. Though EDTA was more efficient in mobilising metals from tailings to the plant parts than CA, yet the reduction of plant biomass caused by it (EDTA) also exceeds that caused by the CA. Therefore, (low molecular weight organic acid such as) CA should be preferred during assisted phytoextraction over the synthetic chelator like EDTA which has unacceptable percolation risks associated with it. |
|