Improving Cobalt Phytoextraction by Astragalus Sinicus L. Grown in Co-Contaminated Soils Using Biodegradable Chelators

In this study, we investigated the effect of EDDS, NTA, CA, and OA on the phytoextraction of cobalt-contaminated soil by Astragalus sinicus L. The optimum concentrations of the chelators were determined for biomass, uptake, translocation, and accumulation. A low concentration (2.5 mmol/kg) of EDDS promoted growth, whereas a high concentration (7.5 mmol/kg) of EDDS produced maximum growth inhibition. All four chelators significantly increased the Co concentrations in the shoots and roots. The resultant order for Co uptake efficiency was as follows: EDDS > NTA > CA > OA. The maximum Co concentration in shoots (129.56 mg/kg in 2.5 mmol/kg EDDS) was 5.08-fold greater than that of the control groups. Translocation in the test plants was influenced by each chelator in the following order: EDDS > NTA > CA > OA. The translocation factor was greatest (1.76) following treatment with 2.5 mmol/kg EDDS. The maximum shoot Co accumulation achieved in 2.5 mmol/kg EDDS was 6.51-fold greater than that in the control groups. Activation efficiency of Co in the soil by the chelators occurred in the following order: EDDS > NTA > OA > CA. Therefore, the application of EDDS may be the most effective choice in chemical-enhanced phytoextraction of Co-contaminated soil.