Chelator complexes enhanced Amaranthus hypochondriacus L. phytoremediation efficiency in Cd-contaminated soils

Abstract The use of degradable chelating agent to enhance phytoextraction is a promising and low-cost method for remediation of heavy metals-polluted soil. However, very limited information is available regarding the effect of chelating agent combinations on plant growth and its capacity to extract metals. In this study, a pot experiment was conducted to evaluate the applicability of [N, N]-bis glutamic acid (GLDA), nitrilotriacetic acid (NTA), [S, S]- ethylenediamine disuccinic acid (EDDS), and citric acid (CA) alone and in combination to enhance the phytoextraction efficiency of amaranth (Amaranthus hypochondriacus L.) in two Cd-contaminated agricultural soils (S1 soil 2.12 mg/kg and S2 soil 2.89 mg/kg; the environmental standard value of Cd in agricultural soils in China is lower than 0.8 mg/kg). The results showed that, except for EDDS, other treatments had no obvious effect on plant biomass, and even promoted biomass increase to reach 1.06 (S1), 2.07 (S2) g/pot. The increase in total Cd extraction amount by 5 mM of single chelators GLDA and NTA reached 3.87 and 2.81 (S1), and 3.28 and 2.50 (S2) times that of the control group, respectively. For complexed chelating agents, G-N (GLDA + NTA) combinations (GLDA = 3 mM, NTA = 2 mM) extracted the highest amount of Cd compared with other treatments, reaching 0.36 and 0.52 mg/pot (4.50 and 3.71 times that of the control group), respectively. The order of extraction amount was G-N > GLDA > NTA > G-E (GLDA + EDDS) > G-C (GLDA + CA) > CA (5 mM total Cd concentration). Moreover, soil enzyme activity of G-N treatment increased significantly compared to that of the control group, indicating the great application potential of a composite chelating agent relative to a single chelating agent. Therefore, degradable chelators, especially the G-N combination, can effectively increase the available Cd content and greatly enhance the ability of plants to absorb and transport Cd in soils.