Ecological Risk Assessment Of Soil In Jiaozuo Farmland And Study On Passivation Of Heavy Metals In Soil By Different Materials

Soil passivation remediation is a technique for altering the morphology of heavy metals by adding a passivator,in order to reduce their toxicity and toxicity in organisms.After assessing the ecological risk of heavy metals in the soil and plants of a certain farmland in jiaozuo city,we used different passivating agents,such as humic acid,animal manure,zeolite,and mefan stone,to conduct in situ passivating repair test on the experimental field.The passivation effect of different passivation materials and the influence of passivation materials on the yield and quality of agricultural products were studied.In addition,health risks of food intake by local residents were evaluated based on dietary habits,so as to select passivation materials that could effectively reduce heavy metal content in crops and provide scientific basis for local agricultural production.The main findings are as follows:（1）The mean contents of heavy metals Cr,Cu,Zn,As,Cd and Pb in the soil before passivation were 65.74 mg/kg,111.15 mg/kg,77.05 mg/kg,33.95 mg/kg,1.47mg/kg and 88.29mg/kg,respectively,in which the content of Cu,As and Cd exceeded the limit value of soil risk screening value in agricultural land.According to the single pollution index,P（Cd）=2.45,the pollution level is light pollution.P（Cu）=1.11,P（As）=1.36,the pollution level is slight pollution.The nemero index of heavy metals is 1.87,which is classified as light pollution.The distribution of heavy metal Cr,Cu,As,Cd and Pb contents in different parts of plant was As follows:root>stem leaf>seed,and the distribution of Zn in different parts of the plant showed roots>stems and leaves>grains.The contents of As,Cd,and Pb in the grains were 0.60 mg/kg,0.11mg/kg,and 0.22 mg/kg,respectively.According to GB2762-2017,the P（As）in plant seeds=1.20,P（Cd）=1.13,and P（Pb）=1.11,all of which were of slight contamination.（2）After adding different passivation materials,the pH in the soil was not significantly affected,and the pH value of the soil in all treatment groups was basically stable at about 8.0,besides,the yield of wheat did not significantly change as well.Among humic acid,animal manure,zeolite and medical stone the four passivation materials,the passivation effect of humic acid on soil Cr was better,the effective content of soil Cr decreased by 28.29%after adding humic acid.Zeolite has a good passivation effect on Cu,Zn,As,Cd and Pb in soil.After zeolite addition,the effective state content of Cu in soil decreased by 33.74%,the effective state content of Zn decreased by 33.62%,the effective state content of As decreased by 34.75%,the effective state content of Cd decreased by 24.16%,and the effective state content of Pb decreased by 28.42%.The effective state of Pb in the soil decreased by 28.87%after the application of medical.stone.The passivation effect of animal manure on Cr was suited.The effective state content of soil As in the treatment group with the passivation of animal manure was 11.95 mg/kg,29.98%lower than that before the restoration,but the effective state content of soil Zn in the treatment group was51.88mg/kg,6.51%higher than that before the restoration.（3）The contents of Cr,Cu,As,Cd and Pb in different parts of wheat after treatment with humic acid and livestock manure were As follows:root>stem leaf>grain;the distribution of Zn content in wheat was as follows:root>grain>stem and leaf.The distribution of heavy metals Cr,Cu,Zn,As,Cd and Pb in wheat plants after the passivation treatment of zeolite and medical stone was As follows:root>stem and leaf>seeds.After the treatment of four passivation materials,the content of heavy metals in wheat seeds was reduced to the limit value of contaminants in food and below.The biological enrichment factor（BCF）and transfer coefficient（TF）of wheat indicated that humic acid reduced the transport capacity of Cu,Zn and Cd from wheat root to stem and leaf,and Cr,As and Pb from wheat stem and leaf to grain,which could significantly reduce the absorption of As by wheat root.The application of animal manure reduced the transport capacity of Cd from the wheat root to the stem and leaf,and reduced the transport capacity of Cr,Zn,Cd and Pb from the wheat stem and leaf to the grain,which significantly reduced the absorption of Cu and Zn in the wheat root.Zeolite can reduce the transport capacity of Cr,Zn,As and Cd from wheat stem and leaf to wheat grain,at the same time,it can reduce the absorption of Cr by wheat root to the greatest extent.The application of medical stone reduces the ability of Cr,Cu and Cd to be transported from the root to the stem and leaf.（4）Health risk assessment showed that the non-carcinogenic risk of children in the animal manure treatment group was the highest,while the non-carcinogenic risk of children in the humic acid treatment group was the lowest.However,the single non-carcinogenic risk index of children to As in all treatment groups was greater than1,which should be paid attention to.The non-carcinogenic risk of adults indicates that the heavy metals Cr,Cu,As and Cd are likely to have an impact on the physical health of adults.Among the passivation materials,the total non-carcinogenic risk of the heavy metals ingested by the animal manure treatment group is the highest,and the total non-carcinogenic risk of the adults is the lowest in the zeolite treatment group.Carcinogenic risk assessment showed that the carcinogenic risk index of heavy metals As and Cd in all groups was greater than 10^-4,which indicating significant risks.The four passivating materials all reduced the carcinogenic risk and the total carcinogenic risk of human consumption of wheat Cd,among which zeolite had the great effect on reducing the carcinogenic risk.