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Accumulation of multiple heavy metals in plants grown on soil treated with sewage sludge for more than 50 years presents health risks and an opportunity for phyto-remediation

Awonke Mbangi, Pardon Muchaonyerwa, Rebecca Zengeni

Abstract


Long-term application of sewage leads to heavy metal accumulation in soils, causing serious risks to plants, humans, animals and the environment, and phytoremediation could be essential. A study was conducted to determine the concentration of heavy metals in self-seeding vegetables, amaranthus (Amaranthus dubius), tomato (Solanum lycopersicum), black nightshade (Solanum nigrum), Rumex pulcher and turf grass, grown on land treated with sewage sludge for over 50 years. A pot experiment was conducted to determine phytoremediation potential of Indian mustard (Brassica juncea), lucern (Medicago sativa), vetch (Vicia sativa), rape (Brassica napus) and ryegrass (Lolium perenne), using the same soil. Another pot experiment was conducted to determine effects on tissue metal composition of Indian mustard of adding increasing concentrations of EDTA. All the self-seeding vegetables had tissue Zn, Cu, Cr, Ni, Cd and Pb concentrations higher than toxicity thresholds. Turf grass tissue had higher concentrations of all the metals than all the self-seeding vegetables growing on the soil. Indian mustard and rape had the highest biomass and tissue concentration of most of the metals studied. Addition of EDTA to the soil drastically increased uptake of Zn, Cu, Cd and Pb but not Cr and Ni. The findings of this study imply that self-seeding vegetables and turf grass growing on the polluted soils pose serious health risks and that Indian mustard, and to some extent rape, have potential for phytoremediation, especially if grown on the soil treated with EDTA.

Keywords: heavy metals, phytoremediation, risk, sewage sludge, turf grass, uptake




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