Application Of Zinc Loaded Biochar In Cadmium Polluted Farmland

The 2021 China Ecological Environment Status Bulletin shows that the overall quality of agricultural land soil environment in China is stable,and the main pollutant affecting the quality of agricultural land soil environment is heavy metal,with cadmium being the primary pollutant.The situation of cadmium pollution in agricultural soil and even vegetable food safety remains severe.At present,chemical passivation is the main method for controlling soil cadmium pollution,which converts available cadmium in the soil into residual cadmium through passivation to reduce the bioavailability of cadmium.However,due to immature technology,limited costs,increasingly strict food safety standards,and high cadmium enrichment coefficients in leafy vegetables,some passivation treatments can only reduce the available cadmium content in the soil,failing to achieve a lower cadmium accumulation in leafy vegetables than food safety standards.Therefore,it is necessary to use biochemical actions to inhibit plant uptake of cadmium on the basis of passivation,in order to reduce the accumulation of cadmium in plants below food safety standards.Zinc and cadmium are the same main group elements with similar chemical properties.They often show interaction in plants,competitive antagonism effect in some plants,and synergistic effect in some plants.The purpose of this thesis is to add zinc loaded biochar to cadmium contaminated soil on the basis of passivation,and use the antagonism of zinc and cadmium absorption by plants and the passivation effect of biochar to inhibit the enrichment of cadmium,so that plants can meet the food safety standards.This article is divided into two parts: a hydroponic experiment and a potted simulation experiment.Using Chinese cabbage,which is widely used in leafy vegetables,as the test material,the absorption mode of zinc and cadmium by Chinese cabbage was studied through hydroponic experiments,and the specific interaction and mechanism of its main absorption and transportation of heavy metals were clarified.Through pot experiments,the total zinc content of cadmium contaminated pot experiments was determined in the study of ordinary soil planting.In the cadmium pollution experiment,zinc loaded biochar(BAC-Zn)and biochar(BAC)were added to soil contaminated with cadmium at concentrations of 0.1 mg/kg,0.3 mg/kg,0.5mg/kg,and 1 mg/kg.The cadmium and zinc content in the edible parts of Chinese cabbage,plant transport coefficient,quality and enzyme activity of Chinese cabbage,p H of Chinese cabbage root soil,zinc and cadmium forms in soil,available nutrients in soil,and zinc desorption from zinc loaded biochar were studied,Objectively evaluated the practical application feasibility of BAC-Zn.The main conclusions are as follows:(1)Plants absorb zinc and cadmium ions in the same way.They are all enriched at the cell wall-transported to the cell through transmembrane transport-transported to the ground through the xylem.Due to the point competition at the cell wall and the sharing of transport proteins during transmembrane transport,the interaction between zinc and cadmium in plant roots presents a antagonism effect,while in the xylem it presents a synergistic effect.However,the transport capacity of the aboveground part is affected by the absorption capacity of the underground part,which generally presents a antagonism effect.(2)In the pot experiment,when BAC was used to treat 0.1mg/kg cadmium contaminated soil,the cadmium content in the edible part of Chinese cabbage was0.189mg/kg,slightly lower than the food safety standard of 0.2mg/kg.However,when BAC-Zn was used to treat 0.5 mg/kg cadmium contaminated soil,the cadmium content in the edible part of Chinese cabbage was 0.198mg/kg,which was close to the food safety standard.BAC-Zn treatment increased the threshold of cadmium contaminated soil concentration by five times,Its treatment cost is much lower than reducing cadmium pollution in soil from 0.5 mg/kg to 0.1 mg/kg.It has practical application significance.(3)In the BAC-Zn treatment,the total zinc concentration in the soil reached 150mg/kg,which is lower than the threshold of agricultural land(170 mg/kg),and the zinc accumulation in plants is lower than the food safety standard(20mg/kg).The research on plant biomass,soluble sugar content,vitamin C content,protein content and enzyme activity found that the high concentration of zinc in BAC Zn treatment did not stress plants,but significantly increased the biomass and protein content of Chinese cabbage through the synthesis of auxin and RNA polymerase,and did not find the result of alleviating cadmium toxicity by improving enzyme activity.(4)Studying the changes of soil p H and heavy metal forms,it was found that the soil p H did not show an upward trend in BAC Zn treatment,and the bioavailable content of cadmium in soil was higher than that in BAC treatment,indicating that in BAC Zn system,the accumulation of cadmium in plants should be reduced through the antagonism of zinc and cadmium,rather than by increasing p H to precipitate cadmium and reducing the bioavailability of cadmium through biochar passivation,Biochar is used to improve soil fertility and load zinc.Compared with direct spraying,although there is some waste,the mixing effect is better.(5)Studying the changes in soil available fertility,it was found that the addition of biochar increased the content of alkali hydrolyzed nitrogen and available potassium in the soil.The content of available phosphorus in the BAC-Zn treatment was lower than that in the BAC treatment and control group.Due to the complex formation of precipitation between zinc and inorganic phosphorus in biochar,the combination of BAC-Zn and phosphate fertilizer can achieve the best ideal effect in practical application.In general,the interaction of plants in the absorption of zinc and cadmium is generally antagonism,so it is theoretically feasible to use high zinc cadmium ratio to produce antagonism to inhibit the absorption of cadmium.In the actual pot experiment,it was found that the use of biochar loaded with zinc did not cause zinc stress due to high concentration of zinc,while inhibiting the absorption of cadmium by plants.It also improved plant growth and soil fertility to a certain extent.Compared with the single passivation treatment,it has technical and cost advantages and has good practical application feasibility.