Research On Prediction And Pollution Risk Assessment Of Heavy Metal Content In Site Soil

Along with our country to promote the pace of urbanization,urban ecological civilization construction as the key indicators of evaluation of China’s urbanization progress,the city of large industrial enterprises were shut down or moved by environmental pollution,to produce more pollution sites,these contaminated sites at the same time there are many heavy metal elements in soil,cause there are a range of soil heavy metal pollution.Soil is the carrier of all life activities.Once soil is polluted,it will bring great harm to human beings and the ecological environment.Therefore,it is urgent to analyze and evaluate the pollution situation of the remaining site and carry out restoration and treatment on the basis of this.This paper takes a rubber factory in South China as the research object.Secondly,GRNN-OK,a prediction model for heavy metal content considering spatial correlation,was used to predict the heavy metal content in the site and analyze the spatial distribution characteristics of pollutants.At the same time,in order to avoid the one-sidedness of single evaluation method,four different evaluation models were used to evaluate and analyze the risk of contaminated site.Finally,the visualization system of site pollution risk assessment based on B/S architecture is designed and developed,which provides information support and reference for environmental protection departments or relevant repair units to treat and repair the site.The main research contents of this paper are as follows:(1)To analyze the characteristics of heavy metal content in the site.According to the descriptive statistics of the four heavy metals in the site,the contents of the four heavy metals in the soil have exceeded the local regional soil background value,and the severely polluted points are mainly distributed near several production workshops in the site.The pollutant concentration decreases layer by layer with the increase of sampling depth,and the surface pollution is the most serious.According to the coefficient of variation of the four heavy metals,the four heavy metals are in a highly variable state with uneven spatial distribution,indicating that human activities have a great impact on site pollution.Through the analysis of the correlations among the four heavy metals,it can be seen that the heavy metals copper,nickel,lead and zinc in the soil of the site have extremely significant correlations,indicating that heavy metal pollution has homology and is closely related to human production activities.(2)A GRNN-OK prediction model of heavy metal content considering spatial correlation is established.In order to more accurately analyze the spatial distribution of heavy metals in the site,based on the preprocessed experimental data,this paper constructs a GRNN-OK model considering spatial correlation.Through the comparative analysis with Kriging interpolation method and GRNN neural network,the results show that the prediction accuracy of GRNN-OK model is the highest and the error is small.On this basis,the spatial distribution map of four kinds of heavy metals in the site is drawn.Through the analysis of the spatial distribution characteristics of pollution,it can be seen that lead,zinc and copper have similar spatial distribution patterns,the concentration decreases from southwest to northeast,and the heavy metal nickel is seriously polluted in the rubber mixing workshop,machine repair workshop area in Northwest and southwest of the site.To sum up,the pollution of heavy metals is distributed in varying degrees in the whole plant,but the extremely high value is mainly distributed near several production workshops.Therefore,relevant departments need to carry out targeted repair and adjust measures to local conditions.(3)The risk assessment of contaminated sites was carried out based on four different risk assessment methods.The risk of contaminated site was evaluated by single factor index method,Nemerow comprehensive pollution index method,potential ecological risk index method and ground accumulation index method.The results showed that copper,nickel,lead and zinc all reached the level of severe pollution from single factor index analysis.From the comprehensive pollution index of Nemero,except the fourth layer is in the moderate pollution level,the other three layers have reached the severe pollution level,and the pollution level decreases gradually,and the surface layer is the most serious pollution.From the perspective of potential ecological risk index,the first layer is at extremely strong risk level,the second layer is at relatively strong risk level,and the third and fourth layers are at moderate risk level.From the analysis of ground accumulation index,the risk of surface heavy metal pollution is the highest,among which zinc belongs to moderate to severe risk,copper belongs to moderate risk,nickel and lead belong to mild to moderate pollution,and the pollution grade decreases with the sampling soil layer.On this basis,the site risk grade map is drawn.According to the four evaluation results,the results of the four different evaluation models are basically the same,and the site has a high risk of pollution,which requires the relevant departments to focus on restoration.(4)Design and develop the visualization system of site pollution risk assessment.The system mainly includes four functional modules: home page,feature analysis,risk evaluation and data management.The system can assist relevant departments to manage complex site pollution related data,and can provide information support and reference for site treatment and restoration.