Effect of nitrilotriacetic acid (NTA) and ethylenediaminetetraacetic acid (EDTA) on arsenic uptake from contaminated soil by Mmimosa pudica Ll.

Abstract

This study investigated the arsenic (As) accumulation in the underground part (root) and aboveground parts (stem and leaves) of Mimosa pudica L. and the effects of chelating agents, NTA and EDTA for enhancing As uptake by the plant. Uncontaminated soil and plants were used in this experiment. A preliminary study was also conducted to determine the phytotoxicity using added disodium hydrogen arsenate (Na2HAsO4.7H2O) at different concentrations of As (5, 10, 20, 40, 80, 120, 160, 200, 300 and 400 mg/kg soil) and three doses of NTA and EDTA (50, 100 and 200 mg/kg soil). Then plants were grown on prepared soil and monitored for a month. The preliminary results showed that plants could grow healthy in As contaminated soil up to 10 mg/kg soil while higher concentrations showed phytotoxicity in the plant. The symptoms varied including dry and curly in plant leaves and stems. NTA and EDTA did not produce phytotoxicity during plant growth. For the main experimental procedure, 5 mg As/kg soil was added into uncontaminated soil pots and left for three months. Then one seedling of Mimosa pudica L. per pot was grown in As contaminated soil and followed by adding three doses of NTA or EDTA (50, 100 and 200 mg/kg soil) separately. Soil and plant samples were collected every 30 days for a 120 day period and analyzed for As concentration. The results showed that As accumulation in the underground part of the plant (root) was significantly higher than in the aboveground parts (stem and leaves) (P0.05). The maximum As accumulation in the root after 120 days was at 29.71 mg As/kg plant while the combined concentration in the stem and leaves was only 6.32 mg As/kg plant. The average As accumulations in all parts of the plant during four months were in the range of 2.71 - 36.03 mg As/kg plant and set EDTA 100 mg/kg soil showed the highest As accumulation in Mimosa pudica L. Overall, at the same harvesting times and application doses of chelating agents, EDTA has more efficiency for enhancing As uptake by this plant than NTA. Moreover, the synchrotron µ-X-ray fluorescence spectroscopy (Beamline 6b) analysis provided an unexpected result on the distribution of As in the plant caused by the limitation of radiation beam line. However, this research did not study the chemical reactions between As and chelating agents. Therefore, for future studies it is recommended to investigate the detail in molecular level and study more on the difference between the application of fertilizers and without fertilizers.