The EDTA effect on phytoextraction of single and combined metals-contaminated soils using rainbow pink (Dianthus chinensis)

Rainbow pink (Dianthus chinensis), a potential phytoextraction plant, can accumulate high concentrations of Cd from metal-contaminated soils. The soils used in this study were artificially added with different metals including (1) CK: original soil, (2) Cd-treated soil: 10 mg Cd kg−1, (3) Zn-treated soil: 100 mg Zn kg−1, (4) Pb-treated soil: 1000 mg Pb kg−1, (5) Cd-Zn-treated soil: 10 mg Cd kg−1 and 100 mg Zn kg−1, (6) Cd-Pb-treated soil: 10 mg Cd kg−1 and 1000 mg Pb kg−1, (7) Zn-Pb-treated soil: 100 mg Zn kg−1 and 1000 mg Pb kg−1, and (8) Cd-Zn-Pb-treated soil: 10 mg Cd kg−1, 100 mg Zn kg−1, and 1000 mg Pb kg−1. Three concentrations of 2Na-EDTA solutions (0 (control), 2, and 5 mmol kg−1 soil) were added to the different metals-treated soils to study the influence of applied EDTA on single and combined metals-contaminated soils phytoextraction using rainbow pink. The results showed that the Cd, Zn, Pb, Fe, or Mn concentrations in different metals-treated soil solutions significantly increased after applying 5 mmol EDTA kg−1 (p < 0.05). The metal concentrations in different metals-treated soils extracted by deionized water also significantly increased after applying 5 mmol EDTA kg−1 (p < 0.05). Because of the high extraction capacity of both 0.005 M DTPA (pH 5.3) and 0.05 M EDTA (pH 7.0), applying EDTA did not significantly increase the Cd, Zn, or Pb concentration in both extracts for most of the treatments. Applying EDTA solutions can significantly increase the Cd and Pb concentrations in the shoots of rainbow pink (p < 0.05). However, this was not statistically significant for Zn because of the low Zn concentration added into the contaminated soils. The results from this study indicate that applying 5 mmol EDTA kg−1 can significantly increase the Cd, Zn, or Pb concentrations both in the soil solution or extracted using deionized water in single or combined metals-contaminated soils, thus increasing the accumulated metals concentrations in rainbow pink shoots. The proposed method worked especially well for Pb (p < 0.05). The application of 2 mmol EDTA kg−1 might too low to enhance the phytoextraction effect when used in silty clay soils.