Phytoremediation of heavy metal contaminated soil using Chromolaena odorata and Lantana camara

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Phytoremediation, the use of plants specifically chosen for the rehabilitation of polluted lands, is an emerging biotechnology for the removal of heavy metals from contaminated sites. Though the technology is now established in temperate regions and industrialized countries, its use in the tropics and developing countries is very limited. The phytoremediation potential of two commonly found high biomass weed species, Chromolaena odorata and Lantana camara was evaluated in a pot experiment using heavy metal contaminated soil from the Sansu tailings dam of AngloGold Ashanti Ghana Limited in Obuasi, Ghana. Soil treatments included tailings soil and tailings soil amended with NPK fertilizer. The concentrations of six heavy metals (As, Fe, Cu, Pb, Zn and Cd) were analyzed in soil and plant tissues at two harvest times using the Atomic Absorption Spectrophotometer. At the end of the first harvest there was a general reduction in all metal concentrations in all soil samples. Tailings soil planted with L. camara (TLc) recorded the highest percentage metal reduction by Pb with 81.9%. Percentage reduction in metal concentrations was greater in tailing soil and in tailing amended with fertilizer planted with L. camara than those planted with C. odorata. Chromolaena odorata in tailing soil (TCo) recorded the highest metal accumulation for As with a ratio of 63.2. Results of the second harvest showed a maximum metal accumulation ratio of 49.0 for As in C. odorata growing in tailing soil amended with fertilizer (FTCo). In general accumulation of all metals by the two plants was found to be higher at the first harvest (one and half months) than at the second harvest (three months). The level of fertilizer application was not effective in enhancing metal uptake by both plant species. The species accumulation factors and bioaccumulation factors showed their specific metal affinity and time limitations for their application as phytoremediants. Both Chromolaena odorata and Lantana camara showed significant accumulation for Arsenic (As) and Iron (Fe). Lantana camara was a good candidate for hyperaccumulation of Copper (Cu) and Lead (Pb) whilst Chromolaena odorata was a good candidate for hyperaccumulation of Zinc (Zn) and Cadmium (Cd). In general accumulation in Latana camara was more effective and at optimum on short term cultivation whilst Chromolaena odorata was found to be a more effective phytoremediator on long term cultivation. The adaptability of these two indigenous plants species to heavy metal stress thus provides useful information for their selective exploitation in phytoremediation of contaminated mine sites.
A Thesis submitted to the School of Graduate Studies, Kwame Nkrumah University of Science and Technology, Kumasi, in partial fulfilment of the requirements for the Degree of Master of Science in Environmental Science,
Heavy metals, Phytoremediation, Accumulation ratio, Bioaccumulation ratio, Tailings dam