Source Analysis Method And Empirical Study Of Heavy Metals In Soils Of Typical Urbanized Areas

Soil is the most important component of the environment,and it is also an important resource for human to carry out agricultural production and life.In the past decades of rough development,due to blind pursuit of rapid economic development,neglect of environmental pollution,resulting in a large number of heavy metals into the soil system.These heavy metals accumulate and accumulate in the soil,which ultimately has a significant impact on crop growth and safety,and then poses a serious threat to human health and safety through the transmission of food chain.In recent years,the pollution of heavy metals in soils has gradually come into the public's view.Clear control of pollution sources is the premise of effective control of heavy metal pollution in soils.Therefore,it is of great significance to identify the sources of heavy metal pollution in soil for the prevention,control and protection of heavy metal pollution in soil and the safety of agricultural production.Source analysis technology has been widely used in the practice of source analysis of heavy metals in environmental receptors.This paper summarizes the common methods and principles for the analysis of heavy metals in soil in recent years,compares the advantages and disadvantages of each method,and proposes a method of Positive Matrix Factorization(PMF),Isotope Ratio Analysis(IRA)and substances.Material Flow Analysis(MFA)is a method system that combines three methods.Based on the project of soil environmental investigation and pollution source analysis in typical areas of Zhongshan City,the practice of soil heavy metal source analysis was carried out.105 soil samples were collected during the study period.The results showed that the contents of Cr,Ni,Cu,Zn,As,Cd,Pb and Hg ranged from 2.87 to 84.64,1.40 to 56.00,2.75 to 125.05,15.05 to 201.39,1.46 to 89.92,0.001 to 0.92,15.29 to 160.07,0.006 to 0.52 mg/kg,with an average of 37.22,30.07,41.98,110.59,18.43,0.39,43.81 and 0.13 mg/kg,respectively.The content of Cd,Cu,As and Pb in local soil exceeded the national screening value of agricultural land.Compared with the screening value of agricultural land pollution risk,the exceeding rate of Cd was 60.1%,19.0%,8.5% and 4.76%,respectively.Overall,compared with the screening value of agricultural land pollution risk control standard,the situation of heavy metal Cd exceeding the national screening value in surface soil of Zhongshan City was more common,but most of them exceeded the national screening value.Although there is a phenomenon of exceeding the risk screening value,the content of all samples is generally lower than the risk management control.From the frequency distribution,the variation coefficients of Cr,Ni,Cu,Zn,As,Cd,Pb and Hg are higher,indicating that heavy metals in surface soil may be affected by some exogenous inputs.The average concentration of soil Cd in the study area was 0.39 mg/kg,the maximum was 0.92 mg/kg,while the background value of soil Cd in the study area was only 0.034 mg/kg.Cd is the main pollutant in the soil of this region.Human activities play an important role in the accumulation of Cd.There are problems of the input of existing agricultural sources.According to the survey,the amount of chemical fertilizer applied in Zhongshan City reached 31018 tons in 2015,and the average cadmium content is 12 mg/kg.At the same time,the region is also facing the problem of heavy metal import from emerging industries to soil,which is the location of the top electroplating industrial park in the country.Therefore,it is necessary to use a variety of methods to study the sources of Cd and clarify the sources of local heavy metal Cd.Based on previous studies on source analysis,the advantages and disadvantages of various methods were compared,and the method system of combining positive definite matrix factor method,isotope ratio method and material flow analysis method was used to explore the source of heavy metals in Zhongshan soil.The results show that the predicted values of Cd,Ni,Zn and Hg simulated by the positive definite matrix factor analysis method are more than 90% linearly fitted with the measured values,and the other elements are more than 60%,showing a good correlation to meet the research needs.The contribution rates of transportation and agriculture to soil lead accumulation calculated by positive definite matrix factor model and lead isotope ratio method were 86.0% and 84.8%,respectively.The contribution rates of agriculture to soil Cd calculated by positive definite matrix factor model and material flow analysis method were 86.7% and 79.7%,respectively.The results were close.Similar results also show that positive definite matrix factor method,isotope ratio analysis method and material flow analysis method can be well combined for the analysis of heavy metal sources in soil.This paper enriches the theoretical and practical research on the source analysis of heavy metals in soil,and provides scientific decision-making and management basis for the managers to control and prevent the pollution of heavy metals.