Effect Of Passivation Treatments On Cd Contaminated Soil-rice System And Emergy Benefit Analysis

Soil is the foundation of human survival and social development and which is crucial in terms of sustainable development of ecological environment,agricultural production and even human.Under the background of increasingly serious heavy metal contamination,descent of soil quality,the great potential risk to human health,to carry out the research of restoration and treatment of heavy metal Cd contaminated soil is particularly important.In the Chengdu plain,In-situ passivation tests were conducted on paddy fields with light pollution of heavy metal Cd(0.76 mg/kg)setting conventional control(CK),lime(LI),sepiolite(SE),lime+sepiolite(LS),lime+sodium metasilicate+magnesium sulfate(LSM),lime+humic acid(LH),straw biochar(SB)and iron fertilizer(IF)treatment through two rice varieties to explore the effects of different passivation treatments on soil basic physical and chemical properties,soil Cd content,rice yield,biomass,Cd content in rice and Cd enrichment coefficient and transfer coefficient.In order to evaluate a superior passivation repair technique,broaden research idea of heavy metal contaminated soil remediation methods,and provide reference for system optimization through 6 traditional emergy value indicators and 3improved emergy value indicators,the disability adjustment life method was integrated by using the emergy theory and method.The main findings are as follows:(1)Compared with the conventional control(CK),other passivation treatments can increase the soil p H 0.02~0.41 except for iron fertilizer.Lime(LI),sepiolite(SE)and the compounding treatment can reduce soil alkaline nitrogen,available phosphorus,available potassium and organic matter content.The effect of different passivation treatment is not obvious in terms of soil CEC.(2)Compared with the conventional control(CK),the passivation treatment can increase the content of heavy metal Cd in the soil by 17.81%.The application of passivation material significantly reduced the exchangeable Cd content by4.21%~9.10% in the soil,increased the soil residual Cd content of 3.09%~23.12%,and is beneficial to the conversion of exchangeable Cd to reducible,oxidizable and residual state.(3)Compared with the conventional control(CK),although there were differences in the changes of effective plants,effective panicles,1000-grain weight and openness rate of rice under different passivation treatments,the number of grains per panicle,yield and biomass were effectively increasing.(4)Compared with the conventional control(CK),other passivation treatment can efficially decrease Cd content in root,stem,leaves,crust and borwn rice respectively by15.77%~42.70%?35.64%~37.70%?6.98%~29.30%?17.77%~56.47%?14.86%~53.16%,there by decreasing enrichment coefficient of various parts of panicles.The ability of Cd enrichment in various parts showed root>stem>brown rice>crust>leaf.The transfer coefficient of Cd in different parts of rice was leaf-brown rice>chaff-brown rice>root-stem>stem-brown rice>stem-leaf.(5)Compared with the conventional control(CK),based on the emergy value benchmark of 12.00E+24 sej/yr,the passivation treatment can increase the emergy input of the rice planting system,and the emergy value showed LS>SE>LSM>LI>LH>SB>IF>CK,and which can also increase the system emergy output to 1.0E+06~2.4E+07 sej.(6)Compared with the conventional control(CK),except for iron fertilizer(IF)other passivation treatment systems can reduce the emergy loss of human health caused by heavy metal Cd.Lime+sepiolite(LS),sea bubble stone(SE),lime+sodium magnesium metasilicate(LSM)passivation treatment have the characteristics of high emergy investment ratio,lime(LI),straw biochar(SB),chelated iron fertilizer(IF)passivation treatment have the characteristics of high emergy yield ratio and emergy self-sufficiency rate.Other passivation treatments except for iron fertilizer(IF)have the advantage of reducing the emergy loss proportion and environmental loading rate of rice planting systems,but which also reduce the ability to sustain development of systems,and increase the disadvantage of unit production emergy cost,net unit production cost and passivation unit heavy metal cost.Therefore,it is necessary to improve the level of mechanical modernization and application of the system,adhere to the production principle of “reduction,resource,and harmlessness”,continuously reduce emergy input,further increase the emergy investment ratio,decrease the system environmental loading rate,and enhance sustainable development capacity.(7)Lime + sepiolite treatment(LS)is an excellent passivation treatment technology from the perspective of the passivation treatment on the remediation effect of Cd contaminated soil,and the impact on soil basic physical and chemical properties,rice yield and biomass.On the view of emergy value theory method,straw biochar treatment(SB)is a passivation technology for the treatment of soil heavy metal Cd pollution with both economic and practical effects.