Study On The Effect And Mechanism Of Soil Passivation In Cadmium Contaminated Alkaline Wheat Field

The increase of human activities and the rapid development of industry have led to heavy metal pollution in farmland in some areas of China,which has brought harm and risks to human health and sustainable development of soil environment.As one of the heavy metal elements,cadmium has biological toxicity and non-biological necessity,and is easily enriched by food chain and enters the human body to cause various diseases.Wheat is the main food crop in the world,the soils in many wheat-growing areas were(have been)contaminated by heavy metal cadmium,so it is urgent to remediate.In-situ passivation remediation is one of the most effective remediation technologies for heavy metal contamination in soils.It can reduce the bioavailability and toxicity of heavy metals by adding passivators,and play a role in remediation of heavy metal contamination in soils..In this paper,the effects of sepiolite,mercaptopropyl modified palygorskite,sodium sulfide,sodium hydride,sodium silicate,trimethoxysilane(3-mercaptopropyl)and triethoxysilane(3-mercaptopropyl)on cadmium content in wheat plants were studied by pot experiments.Sulfhydryl modified palygorskite,a new high-efficient passivator for cadmium contamination in the alkaline wheat field soils,was screened out.The effects and mechanisms of sulfhydryl modified palygorskite on the soil physical and chemical properties,element availability,cadmium availability and cadmium speciation distribution in the alkaline wheat field soils were further explored.It will be significance for alleviating cadmium contamination in farmland,protecting the harmonious development of farmland ecological environment in China and ensuring food safety.Pot experiments results showed that compared with CK,adding different passivators had no adverse effect on wheat yield,but could reduce cadmium content in different parts of wheat plant.Adding sulfhydryl modified palygorskite could reduce Cd content in Zhoumai-27 and Dwarf-58 grains by 30.4%-67.0% and 31.0%-75.0% respectively,and could also significantly reduce Cd content in wheat hull,stem,leaf and root system of the two varieties.Thus,the sulfhydryl modified palygorskite had a significant passivation effect on soil cadmium in alkaline wheat fields,and can be used as a new efficient passivator for remediation of cadmium contaminated soil in alkaline wheat fields.By analyzing the bioavailability of cadmium in the soils and the physical and chemical properties of the soils,it was found that the application of sulfhydryl modified palygorskite did not cause significant changes in soil pH value and ECEC,but the zeta potential of soil colloids decreased,and with the increase of sulfhydryl modified palygorskite dosage,the trend of decreasing zeta potential was more significant.The sulfhydryl group of palygorskite modified by sulfhydryl group increased the concentration of available sulfur in the soil and provided sulfur nutrition for wheat growth.Adding sulfhydryl-modified palygorskite could also reduce the effective cadmium content extracted by DTPA,TCLP and DGT in wheat soils to varying degrees,and also reduced the exchangeable cadmium content,and thereby improved the stability of cadmium in wheat soils.The above results confirmed that sulfhydryl modified palygorskite could effectively control cadmium pollution in alkaline wheat field,and ensured the normal growth and development of wheat without destroying the soil environment.Therefore,sulfhydryl modified palygorskite could be used as a highly effective and harmless passivator for remediation of cadmium contamination in alkaline wheat field.This study provided a theoretical basis for alleviating cadmium contamination in the soils with high pH.