Comparing the Efficiency of Sunflower, Marigold and Spinach Plants for Their Phytoextraction Ability of Zinc and Copper in Contaminated Soil

Phytoextraction is a cost-effective technique to remediate contaminated soil. The efficiency of the phytoextraction process is limited by the slow growth, small biomass production of hyper-accumulator plants, and lower phytoavailability of contaminants in soil. The study is focused on comparing the efficiency of the three reported accumulator plants for phytoextraction of zinc (Zn) and copper (Cu) from contaminated soil and their effect on the bioavailability/toxicity of the elements after harvest. In a pot experiment, sunflower, marigold, and spinach were grown in Zn and Cu-contaminated soil. After harvest, the effect of phytoextraction on the distribution of Zn and Cu in various soil-solid phases was studied through a fractionation study as an indicator of bioavailability. The efficiency of phytoextraction was compared in terms of the metal uptake ability of the plants. The highest biomass yield of accumulator plants was obtained with marigold (30.1 g pot−1), followed by sunflower (16.3 g pot−1) and spinach (7.75 g pot−1). The concentrations of Zn and Cu in the three plants ranged from 58.0 to 222 mg kg−1 and 6.33 to 13.3 mg kg−1, respectively. In both the cases of Zn and Cu, sunflower was found superior to the other two plants in terms of phytoextraction of the metals from the contaminated soil. A fractionation study showed that in sunflower and marigold-grown soil, the carbonate bound fraction of Zn enriched water-soluble and exchangeable fraction of Zn, while in spinach-grown soil, the dissolved carbonate bound fraction of Zn enriched the organically bound fraction. Thus, it can be inferred that sunflowers and marigolds increased the bioavailability and toxicity of Zn and Cu more than that of spinach.