Use of organic ligands in lead Phytoextraction by Castor bean (Ricinus communis L.)

Plant species with high biomass production can be used to remove metals through the harvest of aboveground biomass. However, low availability of metals in soil often limits their absorption and translocation, which reduces efficiency in phytoextraction process. The addition of organic ligands to soil is a potential strategy for increasing metal availability. A pot experiment was conducted to evaluate the phytoextraction potential of Castor bean (Ricinus communis L.) through the application of EDTA (5.1 mmol. kg(-1) of soil), EDDS (5.1 mmol. kg(-1)), citric acid (5.1 mmol. kg(-1)) and compost extract (66 mg C. kg(-1)) to soil contaminated with 600 mg. kg(-1) of Pb. The amendments were added 12 months after sowing. Two application forms were tested: a) a single application of the dose 7 days before the harvest and b) three separate applications with 1/3 of the doses on the 21st, 14th and 7th day before harvest. None of the treatments decreased plant biomass. EDDS and EDTA application significantly increased Pb concentration in plant shoot and roots in both application forms compared with control pots whereas citric acid and compost extract had no effects on Pb concentration in plants. EDTA applied 7 days before plant harvest was the most effective treatment in solubilization of Pb associated to oxides of Fe and Mn, carbonates and organic matter, which favored the uptake of Pb from soil by the roots and its translocation to shoot. The value of bioconcentration factor (1.03) and translocation factor (1.73) of Castor bean by adding EDTA in an application showed the potential suitability of Castor bean in soil remediation contaminated with Pb. Furthermore, the time required for phytoextraction process was acceptable.