Assessment And Risk Early Warning Of Heavy Metal Pollution In Agricultural Soil Based On Environmental Capacity

The safety of agricultural land is related to the ecological environment and the welfare of the people.It is an important part of the sustainable development of agriculture and the construction of ecological civilization in China.However,according to the 2014 National Soil Pollution Status Survey Bulletin,the overall quality of the cultivated land soil environment in the country is not optimistic,and the over-standard rate of heavy metals is close to 20%.The problem of soil pollution needs to be solved urgently.To this end,the State has issued the "Soil Pollution and Prevention Action Plan"(Soil 10)and the "Soil Pollution Prevention and Control Act" in the past five years,with the intention of resolving ecological risks to the source of pollution through the Action Outline and the statutory provisions.It can be seen that the evaluation of heavy metal pollution,source analysis and risk early warning of cultivated soil can provide reference for cultivated land quality management and soil pollution prevention and control,and it is of great significance for sustainable use of agricultural land and quality control of agricultural products.To this end,a large number of scholars carry out regional soil heavy metal pollution and risk assessment based on sampling point data of small-scale areas such as counties and towns.However,considering the use of national standards for evaluation,the actual situation of the area cannot be well reflected,and the pollution and risk assessment are improved.The accuracy of this study is based on a grain-producing county in the north of Zhejiang Province in the Hangjiahu Plain.The soil sampling points are used to obtain the statistical characteristics of five heavy metals such as As,Hg,Cr,Cd and Pb in the local tillage soil.Based on the principle of clarifying the spatial distribution and heterogeneity of local soil heavy metal pollution,according to the national "Soil Environmental Quality/Agricultural Land Pollution Risk Control Standards(Trial)"(GB15618-2018)standard,regional soil background values and risk reference values The local soil heavy metal pollution was comprehensively evaluated,and based on the dynamic capacity of the soil,the heavy metal input-output flux model and the indicated Kriging interpolation were used to realize the visual early warning of the risk of soil heavy metal in the study area.The main conclusions of this study are as follows:(1)Spatial heterogeneity results show that the spatial correlation of five heavy metals in the cultivated soil in the study area is Hg>Pb>Cd>As>Cr,and Hg elements are spatially weakly correlated and are more susceptible to external pollution.The other four heavy metals are spatially moderately related,and their soil content is affected by the local soil parent material and human activities.(2)The average content of five heavy metals in the study area is in line with the national agricultural land pollution risk screening standard.Only a small amount of Cd elements exceed the standard(12.7%).The whole field of 69.49%of the cultivated land is clean and pollution-free,and 25.71%of the cultivated land is slightly polluted.In the state,only 4.74%and 0.06%of the cultivated land is in mild and moderate pollution.However,due to the low regional background values of local mercury(Hg)and cadmium(Cd)elements,the Hg and Cd content in the local soil did not exceed the national screening standards,but it has occupied the overall load capacity of the local soil to a large extent.It indicates that the pollution of exogenous Hg and Cd in the study area is serious,and it needs to be highly valued by relevant functional departments.(3)Finding the source of soil heavy metal pollution is the precondition for the prevention and control of soil environmental pollution.The correlation analysis of heavy metals shows that there is a complex nonlinear correlation between heavy metals As-Cr and Hg-Cd-Pb in soil,and the spatial accumulation may have certain homology.The overlapping analysis of ArcGIS software and remote sensing images can be used to qualitatively analyze the sources of heavy metal pollution.The qualitative source analysis results show that the soil high Cd area in the study area is highly correlated with the distribution of the main line of the traffic,and the soil Hg content exceeds the standard or is related to the local industrial enterprise emissions led by battery production.(4)The quantitative source analysis results calculated from the heavy metal input-output flux model show that atmospheric dry and wet deposition becomes the main source of heavy metal pollution in four soils except As,accounting for 45.84%-90.75%of the total input.The contribution rate of livestock manure to As is the highest,reaching 40.56%.In addition,fertilizer input and irrigation water will affect the heavy metal input of soil to some extent.(5)Risk probabilistic warning for the next 15 years(2030)and 35 years(2050).The results show that the three elements of As,Cr and Pb in the study area are generally good,and they will be in the study area in 2030 and 2050.The probability of risk exceeding the standard is<10%.The early warning result of Hg element shows that there are two small high-risk areas in the town of P in the research area in 2030.The early warning results of Cd elements show that some of the high-risk risks occur in the towns of O and P in the study area in 2030 and 2050.In the region,relevant departments of the study area should adopt certain control measures to reduce the threat of heavy metals in the soil to animals,plants and human health.The above research conclusions can guide the orderly development of the prevention and control of heavy metal pollution in the local cultivated land at the county level,and the towns under the jurisdiction can formulate corresponding control measures according to this.