Contrast Effect of Citric Acid and Ethylenediaminetetraacetic Acid on Cadmium Extractability in Arable Soil

Abstract

Chelating agents have been proposed to improve the efficiency of phytoextraction of heavy metal hyperaccumulator. However, little studies to elucidate mechanism of chelating agents to increase cadmium (Cd) extractability have been conducted. The objectives of this study were to evaluate effect of different chelating agents on Cd extractability and to determine mechanism of Cd mobilization affected by these agents. An arable soil was spiked with inorganic Cd (CdCl 2 ) to give a total Cd concentration of 20 mg Cd kg -1 . Ethylenediaminetetraacetic acid (EDTA) and citric acid (CA) were selected and mixed with the arable soil at the rates of 0 and 5 mmol kg . The mixture soils were incubated at 25°C for 4 weeks in dark condition. Concentration of F1 Cd fractions (water soluble) significantly increased with addition of EDTA but did not changed with addition of CA. Especially; concentration of F5 Cd fractions (residual) significantly increased with addition of CA. Increase in water soluble with EDTA might be attributed to complexation of Cd and EDTA. Dissolved organic carbon concentration significantly increased with EDTA addition, but did not with CA implying that considerable amount of CA was decomposed to inorganic carbon by microorganism. Log activity of carbonate (CO 3 2-) which might be generated from CA increased with addition of CA. Increase in residual Cd fraction might be due to precipitation of Cd as CdCO 3 . As a result, EDTA was effective in increasing Cd extractability, by contrast CA had significant effect in reducing Cd extractability.

Evaluation of the effects of mandarin (Citrus reticulate) by-products containing citric acid on immobilization of cadmium in arable soils

“…Therefore, the application of chelating agents to conventional phytoremediation techniques in Cd contaminated soil has received keen interest. Although these techniques are highly effective, we observed Cd immobilization with CA in our recent pilot study [20]. We reported that concentrations of non-bioavailable Cd fractions increased following addition of CA, but we did not precisely demonstrate the related mechanism of Cd immobilization with CA.…”

“…To identify the availability of heavy metals in contaminated soils, we performed a sequential extraction method for heavy metals as described in previous studies [20,29,32,33]. Among the present fractions, F1 contained the most bioavailable Cd.…”