Responses of five local plant species to metal exposure under controlled conditions

This work focused on the determination of the accumulator potential of five local plant species for use in phytoremediation. In plants, trace elements such as Zn, Fe, Cu, Co, Mn, Mo and Ni are necessary for biological processes, but their excessive accumulation can be toxic. Other non-essential elements, such as Cd and Pb, can also be absorbed by plants, thus constituting a potential hazard since they enter the food chain. Phytoremediation is the use of plants and their associated microbes to clean up the environment. A controlled trial was conducted with five species (Vetiveria nigritana (Benth.), Oxytenanthera abyssinica (A. Rich), Barleria repens (Ness), Cymbopogon citratus (DC.) Stapf and Lantana camara (Linn.) on soils contaminated by municipal solid waste at a rate of 15 t/ ha or 5.1 kg of waste. Bioaccumulation of heavy metals, bioconcentration factors, tolerance, and correlations between accumulated metal element content were determined. In this study, it was demonstrated that Vetiveria nigritana and Oxytenanthera abyssinica could accumulate relatively high concentrations of metals (Cd, Cu, Pb and Zn) compared to the other three species, eg 15-20 mg/ kg of Foliar dry matter Cd, 15 times more than other species. The plant species studied have high bioconcentration factor values, for example 24.7 with Cd in lixisols. All species exhibited high tolerance for metals in terms of Vetiveria nigritana and Oxytenanthera abyssinica 359.63% and 382.75% respectively at leaf level. Positive and strong correlations are noted between Cd-Zn, Cu-Zn, Cu-Cd, Pb-Cd and Pb-Cu.