Enhancing the extraction of Zn from a polluted soil by radish using EDTA and H2SO4

Soil pollution by heavy metals is environmental problem which can affect human and animal health, environmental and agricultural productions. Phyto-extraction is the technology of using plants for cleaning polluted soils which is an effective, Cheap and environmental friendly method. Phytoremediation is a method in which clating agents and mineral acids are used to enhance uptake of heavy metal by plants. The aim of this study were: (a) to determine the potential of radish for extracting Zn from polluted soils and (b) to assess the effects of different additive (EDTA and H2SO4) in enhancing plant uptake of heavy metal and (c) to assess the effects of different levels of soil Zn on radish growth and Zn concentrations of above and below ground parts of this plant.
A Factorial experiment were conducted in Soil Science Department, using a completely randomized design and three replications. The experimental factors were type and rate of soil additive (10 and 20 mg/kg of EDTA and 0, 750 and 1500 mg/kg H2SO4) and Zn levels of polluted soils (0, 200, 400, 600, 800, 1000 and 1200 mg/kg).
The results showed that The Application of soil additives increasd the concentration and absoption of Zn in above and below ground part of radish and decreasd the dry weight of those. Application of 20 mg EDTA per kg of soil cause the highest concentration of Zn in the above and below ground part of radish, so that increased it respectively 304 and 182 mg.kg-1 compared to control. Rate of 20 mg EDTA/kg soil increasd absorption of Zn by plant 28.7 percent. After treatment with 20 mg EDTA /kg soil, treatment with 10 mg EDTA /kg soil, 1500 mg H2SO4 /kg soil and 750 mg H2SO4 /kg soil were better treatments respectively. Zinc concentrations of aerial parts were higher than those of below ground parts and the highest concentration of zinc in these parts were 810 and 425 mg/kg respectively. The dry weight of above and below ground part of radish decreasd but its concentration for Zn increasd as the Zn levels of polluted soils increasd. An antagonistic effect between p, K, Fe and Zn uptake was also observed.
In general the result showed that the radish plant was a Zn hyperaccumulator plant with translocation factor of greater than 1 and it can be used for phytoremediation of Zn polluted soil. The application rate of soil amendments had significant effects on their performance and unappropriate application rate of them had negative effects on phytoremediation. Based on the results obtained in this experiment application of 20 mg EDTA/kg soil is recommend for Zn phytoremediation.