| Heavy metal pollution of soil is a serious and pressing increasingly important environmental issue which need to be solved urgently now. The invention and application of phytoremediation technology provide the new way for the soil restoration, especially, the phytoextraction has become the most promising method of phytoremediation for its characteristic of permanence and wide area.The chelate-induced phytoremediation technology is a method that activates the heavy metal in the soil using chelating agent, promotes the heavy metal transportation to the upper parts of plant, achieves the goal of raising metal extraction efficiency of the plant. Heavy metal which is activated often exist by water-soluble metal chelate complex, that is advantageous to plant for their absorption and accumulation of heavy metal, but simultaneously also increased the latent risk of heavy metal pollution to ground water. In this experiment the blackland was taken as the object of study, the influence of three kind of chelating agents EDTA, oxalic acid and EDDS on sprouting and the growth of the maize seed, the influence on soil and their potential impact to the ground water were studied. The main results are as follows:(1)In water culture experiment of the maize, three kinds of chelating agents had certain influence on germination percentage, seedling height and germination index of maize seeds, which decided by the type, concentration and action time of chelating agents.As a whole, the influence of three kinds of chelating agents on germination and growth of maize seed was most intensively when they were at high concentration, showed that EDTA, oxalic acid and EDDS had obvious toxic effect on maize seed germination and growth.(2) The influence of three kinds of chelating agents on soil microbial quantity was fluctuant with treatment time and had increasing trend. Overall, the inhibition of EDTA and oxalic acid on the soil microorganism enhanced with the chelating agents concentration, but inhibition of the EDDS on soil microorganism was basically in inverse proportion to the concentration.(3)The soil added EDTA and oxalic acid gradually changed from neutra (pH=7.2) to weak acid (pH=6.2～6.4) with increase of concentration, while pH value of soil added EDDS increased slightly.(4) Soil catalase activity basically showed declining trend along with the increase of concentration of oxalic acid and EDTA, but the catalase activity of soil added EDDS showed the rising trend along with the increase of EDDS concentration. The peroxide enzyme activity of soil can be promoted by three kinds of chelating agents. The stimulative action of oxalic acid and the EDTA assumed declining trend along with the increase of their concentration, on contrary, the stimulative action of EDDS assumed increased trend along with the increase of the concentration.(5)The TOC content of soil treated by chelating agents were higher than the control, showed that the chelating agents can increase the total organic carbon (TOC) of soil.TOC content of soil treated by EDTA and EDDS basically assumed the increasing trend along with the increase of concentration, but the change of TOC content of soil treated by oxalic acid with concentration was not very remarkable.(6) Copper concent of leachate in soil colum treated by chelating agents increased significantly compared with control. From the view of copper concentration, the leaching risk to ground water is in the order of:EDDS>EDTA>Oxalic acid. TOC content of colum soil treated by EDTA and EDDS increased significantly, while TOC content of the soil treated by the oxalic acid was similar to the control.As a whole, degradation difficulty of three chelating agents in soil is in the order of:EDTA, EDDS,Oxalic acid. |
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