Safe Utilization Of Slightly-moderately Cadmium-polluted Farmland Soil

Soil is indispensable natural resource supporting the life of human beings.It is closely related to agricultural production,ecological environment and sustainable human development.However,along with the process of industrialization and urbanization,a lot of problems such as sewage irrigation,massive discharge of heavy metals and unreasonable use of fertilizers have led to increasingly severe cadmium pollution in farmland soils.Recently,China has focused on the prevention and control of soil heavy metal pollution and food safety production.How to control and remediate farmland soils with cadmium pollution and ensure food safety have been the hotspot of soil and environment research.In view of this,this dissertation investigated soil heavy metal pollution of a farmland which affected by e-waste dismantling in one village,Zhejiang Province,China.On the base of this work,a two-year in situ immobilization trial was conducted to study the effects of lime,biochar,soil conditioner and seaweed organic fertilizer on Cd bioavailability in soil and Cd accumulation and translocation characteristics in rice.Furthermore,field trial was conducted to verify the effect of best soil amendment.The main results are summarized as follows:(1)The soil was strongly acidic with a mean pH value of 5.66.The mean Cd concentration of soil was 0.83 mg kg-1 with a range from 0.53 to 1.66 mg kg-1,which was classified as slightly-moderately Cd polluted soil according to National Soil Pollution Assesment Technology Regulations.The mean CaCl2-extracted Cd was 0.44 mg kg-1.The mean concentrations of Cu,Pb,Zn,Cr and As of soil was 163.10 mg kg-1,58.51 mg kg-1,172.81 mg kg-1,25.19 mg kg-1 and 9.47 mg kg-1,respectively.(2)Lime,biochar,soil conditioner and seaweed organic fertilizer could increase soil pH and decrease Cd bioavailability.Among them,the soil conditioner showed the best immobilization performance,which increased soil pH by 1.33 units,and decreased bioavailable Cd by 46.13%.The first application of soil amendments could increase soil pH for 2 years,and the immobilization performance reduced in the second year.The Cd immobilization performance could last for one year at least.In the second year,the Cd immobilization efficiency of control treatment was 18.05%due to long-term flooding of paddy fields from late tillering to mature stage.And there was no significant difference between the other treatments and the control,so it could not be ascertained whether the amendments had a sustained performance.The regression analysis of soil pH and CaCl2-extracted Cd during the whole trial period showed that the change of soil pH significantly affected Cd bioavailability in acid Cd polluted soil.Therefore,increases in soil pH and decreases in Cd bioavailability could be achieved by applying alkaline soil amendments.(3)In slightly-moderately Cd-polluted soils,the Cd concentrations in brown rice of Yongyoul 7 and Xiushui09 were 0.34 mg kg-1 and 0.22 mg kg-1 for control treatments,respectively,while the Cd concentrations of brown rice using soil amendments were lower than the China Food Safety National Standard limit of Cd(0.2 mg kg-1).The soil conditioner showed the best performance with the decreased ratio of 88.23 and 44.49%for two cultivars,respectively.The accumulation of Cd in root of low Cd rice cultivar was higher than that of hybrid rice,but its translocaton capacity of Cd from root to shoot and brown rice was much lower than that of hydrid rice,and the Cd content in brown rice of low Cd rice was lower.Therefore,combined low Cd accumulation rice cultivar with in situ immobilization could achieve safe rice production.In the second year,Cd contents of all brown rice met the China Food Safety National Standard limit due to long-term flooding of paddy field.(4)The field trail results indicated that the the risk of excessice Cd contamination in conventionally planted rice is high,and the Cd accumulation ability of hybrid rice was significantly higher than that of conventional rice.The combination of application of soil conditioner and low Cd-accumulation rice could ensure safe rice production.In addition,the removal treatment of rice straw could reduce the total Cd content in soil,which was conductive to the safe utilization of cadmium-polluted farmland soil.