| In recent years,agricultural soil pollution by heavy metal has become serious in China.In 2014,the Ministry of Environmental Protection published the investigation report of soil pollution,which showed the national soil pollution excessive rate reached 16.1%,with heavy metals(cadmium(Cd),chromium(Cr),mercury(Hg),lead(Pb),arsenic(As),copper(Cu)zinc(Zn)and nickel(Ni))accounted for 82.4%.Therefore,the control and remediation of heavy metal pollution in agricultural soils is extremely important,as it ensures the quality of soil environment and the safety of agricultural products.The prerequisite for effective prevention and control of heavy metal pollution is well understanding of current status and identification of emission sources.Although there were studies on heavy metal source apportionment,they all based on soil monitoring and analysis using geostatistical analysis,multivariate statistical analysis,receptor model.These methods are high cost,time consuming,and cannot provide specific and precise analysis for different scale of areas.Therefore,this study aims to establish a systematic method for heavy metal source apportionment in various scale of agricultural soils with well understanding of current status of heavy metal pollution in China.So that,it can provide efficient and accurate guidance for the prevention and control of heavy metal pollution in soil.The main innovative results obtained are as follows:1.In this study,meta-analysis was used to collect studied results on heavy metal pollution monitoring in agricultural soils published in 2005-2017,so that to explore the current status of pollution.The nationwide weighted average values of eight element was calculated based on standard deviation of heavy metals,number of sampling sites,and area of the study case.The results showed that the average content of Cd,Cr,Hg,As,Pb,Cu,Zn,Ni was 0.236 mg/kg,62.184 mg/kg,0.129 mg/kg,10.714 mg/kg,32.070 mg/kg,and 28.340 mg/kg,83.293 mg/kg,and 28.167 mg/kg,respectively,with higher contents in the east and lower in the west.The highest contents was highlighted in the more economically developed southeastern regions and southwestern areas with rich mineral resources.In addition,subgroup analysis indicated the accumulation of Cd,Hg,Pb,Cu,and Zn in vegetable fields and paddy land was significantly higher than other fields.This study provided a well understanding of current status of heavy metal pollution in agricultural soil in China,indicating the priority polluted elements,polluted areas,and cultivation types,and provides guidance for heavy metal pollution sources apportionment.2.In the first step of source apportionment,the study of national source apportionment was carried out with mercury pollution.Due to the high cost of nationwide soil monitoring,the analysis of sources apportionment in large scale can be achieved with quantification of emission amount using emission factors and socioeconomic data instead of field monitoring.In this study,the anthropogenic mercury emissions inventory in China was completed,the emission from agricultural activities was added,and the emission factors to three environmental medium(gas,water,and soil)were updated.The result showed that coal production and consumption,mercury mining,non-ferrous metal smelting,steel production,domestic wastes and cement production were the main emissions in China.Moreover,the emission amount in Beijing-Tianjin-Hebei region,Yangtze River Delta,Pearl River Delta,and Guizhou province are relatively high,while,low in the northwestern area.The source apportionment in large regions not only provided an overall state of pollution emissions in the country,but also supply a comprehensive inventory of anthropogenic emissions,showing guidance for source apportionment analysis in the following medium and small regions.3.Then,source apportionment analysis in medium region was conducted with a case study in a 120-square-kilometer region in the peri-urban area in southeast China.According to the characteristics of heavy metal migration in soil,a modified receptor model(Principal Component Analysis-Multiple Linear Regression with Distance Model,PCA-MLRD)was build.It used the fitting between location of potential emission and highpoints of component factor scores to identify the emission sources,and multiple linear regression between heavy metal contents and distance to emissions to quantify the influence extent.According to the results,the main anthropogenic sources of As,Cd,Hg,Pb in the area include,a lead-zinc mine,two dyeing plants,a fluorescent plant,a provincial road(S24),and an industrial hub.The Mine,industrial hub and dyeing plants have higher contributions,and their influence can spread to around 3 kilometers.The PCA-MLRD model established in the medium region can well identify specific anthropogenic emissions and quantify their influence,which is a great support to ensure the effective control of heavy metal pollution.In addition,compared with the conventional receptor model,this model can provide more stable and reliable results,but it cannot quantify the contributions from non-point emissions,like agricultural inputs.4.At last,the source apportionment analysis in small region was conducted with a 100-mu experimental base in Zhejiang province.At present,the majority of heavy metal remediation programs in China was conducted in experimental bases.In these area,heavy metal inputs from soil parent materials and agricultural emissions,like irrigation water and fertilizer,cannot be ignored.Therefore,a quantification model of parent materials and agricultural inputs based on soil profile analysis and long-term monitoring of agricultural emission was build.The results showed Cd and Pb pollution in the plough layer soil were derived both from soil parent material and anthropogenic emission.And the anthropogenic emission mainly came from atmospheric deposition,irrigation water,rice straw and fertilizers.Their annual contribution rates are 24.7%,34.1%,35.3%,5.9%(Cd),49.6%,45.9%,2.3%,2.2%(Pb),respectively.Therefore,in order to reduce heavy metal contents in soil,heavy metal inputs from irrigation water and rice straw should be control. |
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