Chelate-assisted phytoaccumulation: growth of Helianthus annuus L., Vigna radiata (L.) R. Wilczek and Pennisetum glaucum (L.) R. Br. in soil spiked with varied concentrations of copper

Phytoextraction is an economic, environment-friendly and growing technology for clean-up of metal-contaminated soil. Several factors play pivotal role in making phytoextraction a successful technique. Soil fraction is an important parameter that may affect phytoextraction potential. There has been an increased realization on the role of chelates in accelerating metal uptake by plants. Thus, the present study examined the influence of different soil fractions, spiked metal concentrations and chelate dosages on Cu accumulation by Helianthus annuus L. (common sunflower), Vigna radiata (L.) R. Wilczek (mung bean) and Pennisetum glaucum (L.) R. Br. (pearl millet). To mimic the mill tailings of various mined-out sites in India, five soil fractions containing different proportions of garden soil and silica were prepared (S1: 100% soil; S2: 75% soil + 25% silica; S3: 50% soil + 50% silica; S4: 25% soil + 75% silica; and S5: 100% silica) and each fraction was spiked with known Cu (100, 250, 500 and 1000 mg kg⁻¹) concentration. Upon maturity of the plant, EDTA and NTA in different dosages (0.25, 0.5, 1.0 and 2.0 g kg⁻¹) were applied to each pot. Bioconcentration factor (BCF), bioaccumulation coefficient (BAC) and translocation factor (TF) were estimated for each set. The accumulation of Cu by H. annuus, V. radiata and P. glaucum indicated direct relation between soil fractions and harvesting periods. Better plant growth and Cu uptake were observed in pots with silica < 50% of fraction, whereas growth was arrested in pots with silica > 75%. The Cu accumulation varied significantly (p < 0.05) among the species, spiked metal concentration, chelate dosages and plant parts. Best accumulation was reported in pots with 50% soil and 50% silica either under 1.0 g kg⁻¹ EDTA or 2.0 g kg⁻¹ NTA. Irrespective of the combinations of various variables, the harvesting time affected Cu accumulation considerably. Among the species, H. annuus emerged out to be the most efficient for Cu translocation. Apparently, soil amendments facilitated enhanced uptake thereby playing an active role in improving the BAC and TF. Assisted phytoextraction is still a need until full-fledged alternatives are established in the market. The future of chelate-assisted phytoextraction seems to be limited to ex situ condition.