Study On Remediation Of Pb And Cd Contaminated Soil By Chelating Agents And Organic Acids

The mining of a large number of metal minerals and the accumulation of tailings have caused the soil around the mining area to be polluted by heavy metals.As a herbaceous plant integrating ornamental and economic benefits,flowers have a wide range of sources,no food chain invasiveness,and can achieve both soil restoration and beautification of the environment.Based on this,this resear screened plants with strong tolerance and high enrichment to Pb and Cd heavy metals from the common 21 species of flower plants in 16 families on the market,and explored the stress conditions of single heavy metal and compound heavy metal and EDTA The effect of co-application with citric acid on plant physiology,biochemistry and heavy metal enrichment characteristics provides an important theoretical reference for the development and utilization of crops with enrichment,large biomass and economic benefits,and also for the recovery of heavy metal contaminated soil And technical support for environmental governance.The main findings are as follows:1.The heavy metal content of 21 common flower plants in the market and the heavy metal in the soil of concentrated planting areas were investigated.It was found that the content of Cd,Pb,Cr,Cu,Zn,As,and Hg in the soil of the flower planting base was higher than the background value of Yunnan soil.The average number of six heavy metals,and Hg is lower than the "Soil Environmental Quality Agricultural Land Soil Pollution Risk Control Standard,the average value of Cd is higher than the screening value and there is an over-standard phenomenon.The over-standard rate of Cd reaches70.4%,the over-standard rate of Pb is 54.3%,and the over-standard rate of As,Zn,Cu and They were 21%,16%,and 8.5% in order,while Hg and Cr did not exceed the standard.Among them,Cd is higher than the soil background value in the largest proportion,followed by Pb.At the same time,based on the characteristics of serious pollution of Pb and Cd in Yunnan,this research focuses on the study of flowers that are enriched in Cd and Pb.The total Cd content in 21 flower plants of 16 families from high to low,the top five in order are Consolida ajacis(L.)Schur > Snapdragon > Narcissus,the highest content of the above-ground part is still Consolida ajacis(L.)Schur,while the highest underground part Cockscomb;the order of total Pb content from high to low is Cockscomb > Narcissus> Consolida ajacis(L.)Schu,the highest content of the above-ground part is Cockscomb,and The highest underground part is Narcissus.The analysis of the transport coefficient and the enrichment coefficient found that Cockscomb was better than other 20 plants.The concentration and transfer coefficients of the above-ground and underground parts of Cockscomb were both greater than 1,which showed strong absorption from the soil.The capacity of the main heavy metal pollutants.The total amount of heavy metals absorbed is more than 50% distributed in the above-ground parts of the stems,leaves and flowers that are convenient for harvesting.The biomass of the Cockscomb is the largest.Therefore,the main flower species studied in this research was selected as the Cockscomb.2.The study on the enrichment of Cd and Pb by Celosia argentea var.plumosa shows that:(1)When the heavy metal Cd is increased from 0 to 25 mg.kg-1,it will have a greater impact on the above-ground part of Cockscomb,but less on the underground part,especially the flower position.During the process of increasing the heavy metal Pb from 0 to 2000 mg.kg-1,the roots,stems and leaves of Cockscomb of Pteris celosia were not changed significantly,showing good tolerance.In addition,the absorption of Cd and Pb by the flowers,leaves,stems and roots of Cockscomb was significantly positively correlated with the content of heavy metals in the soil.The accumulation of roots was the largest,followed by leaves.And under the compound treatment conditions,the accumulation of heavy metals in each part of the plant was increased.And when high concentrations of lead and cadmium are polluted by heavy metals(Cd:25mg/kg,Pb: 2000mg/kg),the root biomass decreased by 47.77%,and the stem,leaf,flower and plant height decreased by 49.56% and 35.79%,respectively.,44.95%,33.37%;(2)A single Cd has a greater impact on the SOD activity of Cockscombs,while a single Pb has a greater impact on the root vigor,chlorophyll a and carotenoids of Cockscombs.The effect of Cd and Pb compound pollution on the SOD activity of Cockscomb is greater than that of a single heavy metal,and the adverse effect on chlorophyll a,chlorophyll b and carotenoids is also greater than that of a single heavy metal.The mixture of Pb and Cd has an effect on root vitality.Among the adverse effects,the influence of Pb is greater than that of Cd.3.The intensive study on the enrichment of Cd and Pb in Cockscomb by the addition of single and compound EDTA and citric acid shows that:(1)The addition of single and compound EDTA and citric acid is beneficial to the growth of Cockscomb,and improves the enrichment of heavy metals in the aerial and underground parts of Cockscomb flower.When the amount of EDTA is 6.0mmol/kg,the above-ground and underground parts increased by 35.3% and 28.34% respectively.When the citric acid application amount was 10mmol/kg,the biomass of the above-ground and underground parts of Cockscomb was the largest.(2)In the heavy metal enrichment experiment,the addition of a single EDTA has a better effect on the enrichment amount than a single addition of citric acid.The mixed addition experiment shows that the mixed solution of high concentration of citric acid and medium concentration of EDTA is beneficial to the enrichment of heavy metals.The best addition group for Cd enrichment of Cockscomb was I3:E3,and the underground part was 10.57±0.83 mg.kg-1,and the Pb enrichment effect is also better at this concentration;the I3:E2 group has the best effect on promoting the enrichment of Pb,and it is effective at this concentration.The enrichment effect of Cd is also good,41.99±1.04 mg.kg-1.(3)Whether EDTA and citric acid are used alone or in combination,the enrichment coefficient and transport coefficient of Cd and Pb of Cockscombs are greater than 1,which indicates that under the application of EDTA and citric acid,Cockscomb has a better enrichment effect on Cd and Pb.;The addition of citric acid and EDTA or a mixed system of both have reduced the SOD activity of cockscomb,but the decline is not large,and citric acid has an effect on Cockscomb.The effect by citric acid of SOD activity in Cockscomb is greater than the addition of EDTA;For the effect of root vitality,the addition of citric acid and EDTA can increase the root vitality of Cockscomb to varying degrees,and as the concentration increases,the degree increase is greater.For chlorophyll and carotenoids,the addition of high concentration of EDTA and citric acid is conducive to the synthesis of plant chlorophyll,and the mixed component of low concentration of EDTA and citric acid is conducive to the improvement of carotenoids in tail cockcomb.