Synergistic effects of indole-3-acetic acid and chelators on phytoextraction of heavy metals by Ricinus communis L. cultivated in a mine-contaminated site

Abstract Plant growth regulators (PGRs) and chelators can remediate heavy metals (HMs) in mine-contaminated sites; however, their combined use may be more effective. This work aimed to identify the optimal combination of diethylenetriamine pentaacetic acid (DTPA), ethylenediaminetetraacetic acid (EDTA), and citric acid (CA), as well as their combination with indole-3-acetic acid (IAA), to enhance and extract the tested heavy metals from the contaminated soil using Ricinus communis L. (castor oil). Furthermore, it assesses the potential impact of heavy metal uptake on morphological growth parameters of castor plants. In this investigation, a greenhouse experiment was conducted using an IAA solution (10 mL/pot), which was sprayed 35 days after sowing. At the same time,5 mmol kg⁻¹ DTPA, EDTA, and CA to R. communis seedlings 70 days after sowing. In contrast to IAA, applying 5 mmol/kg EDTA and DTPA drastically inhibited castor oil biomass and root and shoot lengths. Individual treatments with EDTA, DTPA, CA, and IAA significantly increased the bioconcentration factor (BCF) and translocation factor (TF) for Cd, Cu, Fe, Pb, and Zn compared with the control (CK). Moreover, the combination of treatments significantly enhanced the absorption and transfer of HMs from the soil substrate to the castor oil roots, demonstrating a synergistic effect. However, applying DTPA and EDTA increased HMs absorption but decreased biomass; therefore, total HMs uptake was reduced in the castor oil crop. Meanwhile, the maximum HMs uptake was observed in the CA + IAA treatment. The synergistic treatment of IAA and CA to enhance metal phytoextraction is a potential, environmentally sustainable method for the phytoremediation of mining soils, suitable for use with bioenergy crops.