The Pollution Status And Risk Assessment Of "Five Poisonous" Heavy Metal In The Surface Soil Of Cultivated Land,lanzhou City

Industrialization and urbanization are accelerating.The problem of heavy metal pollution in cultivated soil is becoming increasingly acute.Heavy metal pollution is not degradable,and regional heavy metals accumulate and damage the land ecosystem,resulting in a reduction in the area of arable land that can be safely used and declining arable land quality.The characteristics and risks of heavy metal pollution in arable land are of great significance to ensure food safety and environmental safe,and provide an important theoretical basis for the prevention and treatment of heavy metal pollution in soil.This article takes the cultivated land surface soil of Lanzhou City as the research object,analyzes and tests 5 heavy metal elements including As,Cd,Cr,Hg and Pb,and uses geostatistical methods and Arc GIS spatial analysis technology to combine the structure of the surface soil in the study area.Analysis and analysis of the distribution of heavy metal elements in cultivated soil,using correlation analysis and principal component analysis to explore the sources and influencing factors of heavy metals in cultivated soil,and using pollution index,land accumulation index,and potential ecological risk index evaluation methods on cultivated land The heavy metal pollution in the surface soil has been contaminated,accumulated,and evaluated for risks,with a view to providing a scientific basis for the prevention and control of soil heavy metal pollution in Lanzhou City.The main research results are as follows:(1)Compared with the screening value of GB15618-2018 in cultivated land surface soil,except Hg does not exceed the standard in all sample points,the remaining four metals exceed the standard rate by less than 0.75%.Compared with gansu soil background value,the mean value of heavy metal content except Cr did not exceed Gansu soil background value.As,Cd,Hg and Pb were 1.06,2.24,2.33 and 1.28 times of the background value respectively.Combined with the proportion of sample points exceeding the soil background value in Gansu province,it was found that heavy metals As,Cd,Hg and Pb had accumulated pollution trend to some extent.As,Cd,Pb and Cr all showed moderate variation.Hg is a strong variation,and the distribution is obviously discrete and strongly interfered by human activities.(2)The nugget effect of As,Cd,Cr,Hg,Pb heavy metal elements in the semivariogram is between 0.25-0.75,which is a medium spatial autocorrelation,affected by natural factors and human activities;As is affected by human activities Bigger.The spatial distribution characteristics of heavy metals As and Cr are similar,showing a trend of high in the west and southeast and low in the center;the spatial distribution characteristics of Cd and Pb are similar,showing a trend of high in the north and south sides,and low in the east and west;As and Cr,Cd and Pb have similar sources.The correlation between Cd,Pb,and Hg is strong,and the sources of these three elements are similar.The five heavy metals can be divided into 3 main components,with a cumulative variance contribution rate of 79.97%;the first main component is composed of Pb,Hg,and Cd,and is affected by industrial and agricultural factors;the second main component is composed of Cr,which is a natural component;The three principal components are composed of As,which are agricultural activity factors.(3)Evaluation of heavy metal index of "five poisons" in the surface soil of cultivated land in Lanzhou.Gb15618-2018 screening value is taken As the reference standard.The average value of single factor pollution index is As,Cd,Cr,Pb and Hg in descending order.As,Cd,Cr and Pb were slightly polluted,while Hg was not.The comprehensive pollution index of Nemerow indicates that the cultivated land in Lanzhou is in a safe state.The mean values of the local accumulation index are Cd,Hg,Pb,As and Cr in descending order.Cr is in the state of no accumulation;As and Pb were mainly non-accumulative,and very few of them were in non-accumulative to moderate accumulative degree.Cd is mainly non-accumulation-moderate accumulation,and the highest accumulation is moderate accumulation.Hg with no accumulation and no accumulation--moderate accumulation was high,and the highest accumulation was medium accumulation--strong accumulation.Cd and Hg accumulation were obvious in farmland soil in the study area.In the evaluation of the potential ecological risk index,As,Cr and Pb in the single pollution ecological risk index have no risk,but due to the risk of Elements Hg and Cd,the ecological risk level of cultivated land surface soil in Lanzhou is increased.In the prevention and control of soil pollution in Lanzhou,heavy metals Hg and Cd should be monitored.