Studies On The Stabilization Of Lead And Cadmium Contaminated Soils By The Combination Of Biological Humus Fertilizer,Sepiolite And Kaoline

The combined pollution of lead and cadmium in agricultural soil could threaten the humans being's health through the biological accumulation directly,and the lead-cadmium contaminated soil is widely distributed in our country,which has seriously affected the quality of the agricultural production.Meanwhile,unreasonable use of pesticides and fertilizers would exacerbate soil lead and cadmium pollution.Many literatures have shown that although clay minerals can reduce the bioavailable state of lead and cadmium in soil,they might cause a series of environmental problems such as reducing soil fertility,poor soil structure,and soil compaction,and so on.Therefore,in the field soil restoration,clay minerals and organic materials are often used to prevent the vegetation adsorption of lead and cadmium from soil,which could help to guarantee the safety of agricultural production.In this study,medium and light soils containing lead and cadmium in Shaoguan were used as model soils.The extractable lead and cadmium were leached by diethylenetriamine pentaacetic acid(DTPA)and Tessier morphology analysis of lead and cadmium in soil.To set up single,composite and pot experiments of biological humic fertilizer,sepiolite and kaolin.The dosages of biological humic fertilizers in single experiments were 0.0%,0.4%,0.8%,1.2%,1.6%,and 2.0% of soil mass respectively.The dosages of sepiolite and kaolin in single experiments were 0.0%,1.0%,2.0%,3.0%,4.0% and 5.0% of soil mass respectively.Orthogonal experiments were three factors and three levels,among which biological humic fertilizers were 0.3%,0.6% and 0.9% while sepiolite and kaolin were 1.0%,3.0% and 5.0%,respectively.Pot experiments were set as 0.9% biological humic fertilizer +3.0% sepiolite +3.0% kaolin(T1);0.9% biological humic fertilizer +3.0% sepiolite +5.0% kaolin(T2);0.9% biological humic fertilizer +5.0% sepiolite +3.0% kaolin(T3);0.9% biological humic fertilizer +5.0% sepiolite +5.0% kaolin(T4)and blank control group(CK).Under comprehensively consideration,the selection of the optimal compounding ratio to provide technical support.The results were as followings:(1)When different amounts of biological humus fertilizer,sepiolite and kaolin were used separately,the soil available lead and cadmium were decreased,and the remediation effect of sepiolite and kaoline was better than that of biological humus fertilizer.When the dosage was 5.0% of the soil quality,the content of extractable lead in soil decreased by kaoline was only 30.51% and by sepiolite was only 26.74% on 30 d;the soil extractable cadmium content decreased when kaoline was only 30.73% and sepiolite 41.00%;(2)After application of biological humus fertilizer-kaoline-sepiolite,concentrations of soil extractable lead and cadmium in were significantly reduced that the soil extractable lead decreased 66.46% after 35 days,when 0.9% biological humus fertilizer + 1.0% sepiolite + 3.0% kaoline were utilized to the model soil,and the soil extractable cadmium decreased 65.42% when 0.9% biological humus fertilizer + 3.0% sepiolite + 1.0% kaoline were used.(3)Pot experiments were conducted using four optimum doses of the above-mentioned materials.During the first 56 days,the soil pH values in different treatments increased 5.65% to 11.62%;and the soil extractable lead and cadmium reduced.The Tessier morphological analysis showed that the content of soil exchangeable lead and cadmium and the content of soil residual lead and cadmium increased obviously.After 56 days' treatment,the soil exchangeable Pb content decreased 67.02%,while the residual Pb content increased significantly for T2 and T4 treatment,6.64% and 5.44%,respectively.And the soil exchangeable Cd decreased in a range from 55.59% to 15.81%.Soil residual Cd content of T3 and T4 treatments increased significantly after 56 days,48.68% and 53.35%,respectively.(4)After application of the compound materials,the above-ground biomass of lettuce increased a lot,while the lead and cadmium concentration of the above-ground decreased,among which the T3 treatment was especially obvious.The aboveground Pb content of lettuce was relatively low for T2 treatment but decreased rapidly for T4 treatment.In our experiment,the T3 treatment was the optimum method for the restoration of Pb-Cd polluted agricultural soil when the soil and vegetation factors were taken into account.