Source, Spatial Distribution And Ecological Risk Assessment Of Heavy Metals In Soil Of Longkou City

Heavy metal pollution,as a hot issue in soil pollution research,has an important impact on soil environment,ecosystem and human health.At present,researches on soil heavy metal pollution in China tend to focus on the current investigation of soil pollution,and the analysis of influencing factors of soil heavy metal pollution is not comprehensive enough,and the methods are not perfect enough,which may easily cause the phenomenon that the pollution assessment results are inconsistent with the actual situation.In this paper,heavy metals in the soil surface of longkou city,shandong province were taken As the research object and 80 sampling points were set up to measure the total amount of heavy metals Cr,Ni,As,Cd,Pb,Zn,Cu and Hg,As well As the main elements of soil parent material Fe₂O₃ and MgO in the topsoil.Descriptive statistics,correlation analysis,self-organizing mapping neural network（SOM）,principal component analysis and other multivariate statistical methods were used to reveal the characteristics,sources,influencing factors of heavy metal pollution in topsoil and its relationship with parent materials and land use.The pollution status of heavy metals in soil was studied by the methods of land accumulation index,Nemerow comprehensive index and potential ecological risk index.The spatial distribution characteristics of heavy metals were studied by geostatistical method,and the influencing factors were analyzed.The results are as follows:（1）Among the eight heavy metal elements in surface soil,the mean contents of Cu,Pb,Zn,Cd and Hg exceeded the background values of Shandong province,and Hg and Cd were 3.13 and 2.71 times of the background values,respectively.There was a high concentration in the soil.The mean contents of all heavy metals did not exceed the national secondary standard,but the maximum values of Hg and Cd exceeded the national secondary standard.According to the variation coefficient of heavy metals,Cd,Cu and Hg belong to high variation,which indicates that the variation degree of these three heavy metals is high and their distribution is not uniform,and they may be affected by human activities to produce characteristic values.The enrichment coefficients of Cd,Hg and Cu are all higher than 1,which may be influenced by human factors.The mean value of Hg’s ground accumulation index is the highest,which belongs to slight pollution grade.The other seven heavy metals’ground accumulation index are all pollution-free grade.（2）The correlation analysis shows that there is a significant correlation between Cr and Ni,and these two heavy metals have a high correlation with the main elements of parent material,and the correlation between Cr,Ni,Cd and As is also high,indicating that Cr,Ni,Cd and As may be natural sources;there is a high correlation between Cu,Pb and Zn,preliminarily judging that their sources are human activities;Hg and Cd have a similar source,preliminarily judging that Hg and As may be natural sources;The origin of Cd is human activities,while Cd is influenced by both natural and human activities.The study of soil heavy metals using self-organizing mapping neural network（SOM）found that Cr,Ni and As had very similar distribution patterns and were judged as natural sources;Cu,Zn,Pb and Hg may belong to anthropogenic sources,but affected by different human activities.The distribution pattern of Cd is complex and may be a mixed source.Three principal components were identified by principal component analysis.Cr,Ni,As and Cd occupy a higher load on PC1 and are considered as natural sources;Cu,Pb and Zn have a higher load on PC2 and are considered as"industrial and traffic factors";Cd and Hg occupy a higher load on PC3.It is inferred that PC3 represents artificial sources such as fertilizers,pesticides and sewage irrigation;Cd occupies a certain load on PC1 and PC3,which is a mixed source of natural factors and human activities.（3）The potential ecological risk values of Hg and Cd were the highest,reaching the level of moderate ecological risk,while the other six heavy metals were of low ecological risk.The average RI of potential total ecological risk of heavy metals in different sites in the study area is 158.95,which belongs to the middle ecological risk level.Among them,the RI value of 15 samples was low ecological risk,accounting for 18.75%of the total samples,the RI value of 55 samples was medium ecological risk,accounting for68.75%of the total samples,and the RI value of 10 samples was high ecological risk,accounting for12.50%.Generally speaking,the heavy metal pollution in Longkou City is not serious,but the accumulation of heavy metals in some areas is significant.Longkou municipality should strengthen legislation,supervision,strictly control pollutant discharge from industrial enterprises,rationally guide the application of chemical fertilizers and pesticides,strictly control the source of sewage irrigation,and more importantly,combine prevention and control,and use agricultural ecological engineering,biological and chemical measures to control heavy metal pollution in soil.