Effect of Biodegradable Chelates MGDA and EDDS on Phytoextraction of Chromium byVetiver Grass in Chromate Contaminated Soils

The combined use of chemical chelates along with the planting of hyperaccumulator plants has been suggested as an effective method to increasing the extraction efficiency of heavy metals and helping to improve contaminated soils. Vetiver is known as a resistant plant to salinity, drought and high concentrations of heavy metals. Recently, the use of biodegradable chelates in soil refining from heavy metals has been considered by researchers. This study was designed to investigate the effect of different levels of biodegradable chelates Ethylenediamine-N,N'-disuccinic acid (EDDS) and methylglycinediacetic acid (MGDA) on increasing the adsorption of Cr(IV) by Vetiver grass. Chelates concentration were defined at four levels (0, 1, 2, 4 mmol/Kg soil) and soil chromium contamination at four levels of potassium dichromate (0, 100, 200, 400 ppm). The results showed that the vegetative growth characteristic decreased with increasing soil chromium and chelates concentration. The use of 4 Mmol of MGDA on soil chromium concentrations (0, 100, 200 and 400 ppm) increased the chromium ratio in root by 1.26, 2.0, 1.48 and 2.5 times and this ratio in treatments of EDDS were 1.5, 2.7, 2.25 and 2.9 times more than the control treatment, respectively. Also, the use of 4 Mmol of MGDA in shoots increased the chromium ratio by 2.8, 3.7, 4.1 and 4.2 times and in EDDS were 1.5, 3.8, 4.1 and 6.7 times more than the control. Increasing chelates concentration from 1 to 4 Mmol in all soil chromium levels increased the ratio of shoo/root chromium and showed higher performance of EDDS than MGDA. The effect of soil chromium levels and chelate concentrations on biomass and vegetative characteristics of roots and shoots was decreasing, but EDDS increased plant diameter. The results of bioconcetration factor (BCF) and translocation factor (TF) showed that Vetiver have a special ability in phytoextraction of soils contaminated with hexavalent chromium. The treatment of EDDS at 4 Mmol intensifies the absorption of chromium, especially in the roots and to some extent increases its transfer to the shoot of vetiver grass. Therefore, this compound is introduced as a suitable biodegradable chelate to increase phytoremediation efficiency by vetiver in chromate-contaminated soils.