Impact Of Mercapto Functionalized Palygorskite On Cadmium Immobilization And Microbial Dynamic In Cadmium Contaminated Soil

Cadmium,as one of the most active trace metals,enters the natural environment in various ways,and finally accumulates in the soil.Cd is transported to the edible part after root uptake and threatens human health through the food chain.Therefore,it is extremely urgent to remediate cadmium-contaminated agricultural soils,especially farmland soil to ensuring the safety of agricultural products.It is well known that the extraction and accumulation of heavy metals in plants are mainly controlled by factors such as the geochemical fractionations of trace metal,antagonistic ions,root uptake and transport in plants.Passivation remediation technology is widely used because of its low cost and quick effect,which does not interrupt the normal process of agricultural activities during the remediation period,and ensures the safety of production while ensuring the crop yield.In this paper,the migration and transformation of cadmium in soil aggregates under the influence of mineral passivation agents were investigated by the particle size separation experiment of cadmium-contaminated soil.A potted experiment was carried out to evaluate the effects of mercapto functionalized palygorskite on cadmium immobilization and Microbial dynamic in cadmium contaminated soil.The main results are as follows:(1)The cadmium content in aggregates initially decreased and then increased as the particle size decreased.The cadmium content was the lowest for the 75-45 ?m particle size fraction and the highest for the <15 ?m soil particles.Nano-montmorillonite(NMMT),nano-hydroxyapatite(NHAP)and mercapto functionalized palygorskite(PGS-SH)promoted the transfer of cadmium to the small aggregates,while palygorskite promoted the migration of cadmium to large soil particles.NHAP and PGS-SH significantly increased the residual cadmium content in each particle size of aggregate,others slightly influenced cadmium geochemical fractionations.(2)Mercapto functionalized palygorskite(PGS-SH)significantly decreased the available cadmium in the soils,thereby reduced its accumulation in plants and the toxicity on soil microorganisms.In addition the application of PGS-SH increased the soil respiration rate,dehydrogenase and catalase activities.The result showed that the Cd content of Brassica chinensis L treated with 0.3%PGS-SH was 59.14%lower than that of the control group(0%).(3)Soil pH decreased significantly with the increase of exogenous zinc content.(50 mg/kg exogenous zinc)significantly reduced the accumulation of cadmium in Brassica chinensis L and the soil microbial activity and enzyme activity.Combined application of exogenous zinc and PGS-SH reduced the accumulation of cadmium in Brassica chinensis L and the migration from root to overground.However excessive exogenous Zn inhibited the growth of Brassica chinensis L.(4)The fungi increased the cadmium activity in the soil,and the application of PGS-SH decreased the activation of the fungi to cadmium.The results showed that soil dehydrogenase activity was mainly affected by plants and soil bacteria,alkaline phosphatase,sucrase and urease activities were mainly affected by soil bacteria,and catalase activity was affected by soil bacteria and fungi.(5)Cadmium significantly reduced the Alpha diversity of soil bacteria and fungi,and decreased the abundance of soil microbial.The indexes of Chao1 and Observed species were significantly increased after the application of PGS-SH.The two passivations increased the abundance of bacteria in cadmium-contaminated soil,but had slightly effect on fungi.The results also showed that the soil fungi increased the activity of the root of Brassica chinensis Land the accumulation of cadmium in plants,and affected the degradation of organic matter in the soil.