| In recent years,with the rapid development of industry and mining,the problem of soil heavy metal pollution has increasingly become a global concern.Soil heavy metal pollution has the characteristics of long-term,concealment and accumulation,which is easy to accumulate in organisms through the food chain and threaten human health.Traditional methods of soil heavy metal remediation,such as physical filling and chemical passivation,cannot fundamentally solve the problem.In this study,chelating agent induced soil leaching and plant extraction were used to achieve better remediation effect.In two typical agricultural heavy metal polluted soil,soil leaching was carried out under indoor condition to screen out the best chelator,and then a series of conditional optimization experiments were conducted,the feasibility of this method was evaluated by analyzing the morphological distribution and enzyme activity of heavy metals in soil.Traditional chelating agents,such as EDTA,will exist in the soil for a long time,easy to cause secondary pollution,and a single leaching agent in certain conditions due to the limitations of its own structure and properties,the leaching effect is often limited.Therefore,four biodegradable chelating agents were used in this study: chelating agents [N,N]-trisodium glutamate diacetate(GLDA),[S,S]-ethylenediamine disuccinate tetrasodium(EDDS),nitrotriacetic acid(NTA)and citric acid(CA).The results showed that the mobilization effect of single chelating agent on soil heavy metals was significantly different.The removal efficiency of Cu,Zn,Cd and Pb reached 38.2,9.8,71.4 and 19.5%(low contaminated soil)and 25.0%,5.2%,59.7% and 18.5%(high contaminated soil),respectively.Optimization of leaching conditions tests showed that the GN chelating agent group had a wider application range of pH than the single chelating agent,and the adsorption process of the GN combinations on heavy metal ions was mainly chemical adsorption.In order to evaluate the feasibility of the leaching method,the effects of chelating agents on the distribution of heavy metals and soil enzyme activities were studied,and the results showed that GN combined leaching could effectively reduce the effectiveness of heavy metals in soil,and had no significant inhibitory effect on some enzymes in soil.All in all,chelating agent combination leaching is a potential leaching method for soil.On the basis of soil leaching experiment,it is feasible to enhance the accumulation of soil Cd by using chelating agent or chelating agent combination.Phytoremediation of heavy metals has some technical defects.Firstly,the accumulation of heavy metals by plants is a relatively time-consuming process.Secondly,the mobilization effect of plants on heavy metals in soil is limited.In this experiment,GLDA,NTA,CA,EDDS and their combinations were used to enhance the accumulation process of Cd by amaranthus hypochondriacus L,and the feasibility was evaluated by analyzing the Cd morphological changes of rhizosphere soil and soil enzyme activities before and after plant extraction.The results showed that the total amount of Cd extracted by single chelating agents GLDA and NTA at the concentration of 5mM increased significantly,reaching 3.87,2.81(low contaminated soil)and 3.28,2.50(high contaminated soil)times of that in the control group,respectively.Compared with other treatments,GN(GLDA = 3 mM,NTA = 2 mM)had the highest removal amount of Cd,which reached 0.36 mg/pot(low contaminated soil)and 0.52 mg/pot(high contaminated soil),respectively.Moreover,GN combinations had significant promoting effect on some enzymes in the soil,such as catalase,indicating that the combined chelating agent had great application potential in plant extraction.In conclusion,biodegradable chelating agent enhanced plant extraction can effectively improve the total amount of soil Cd extracted from amaranthus hypochondriacus L,which is a promising green cadmium pollution remediation method. |
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