Heavy Metal Pollution Assessments Of Soil Around A Uranium Tailings Pond

Soil is the basic environmental element of human existence and development.With the development of industry,the problem of heavy metal pollution in soil has become more and more serious.A uranium tailings pond served more than 30 years,has accumulated a large number of uranium ore.It is the largest uranium mining and metallurgy system of radioactive pollution source.It not only pollutes the soil in the surrounding area,but also affects human health and safety through the food chain.Therefore,it is of great significance to study soil heavy metal pollution in this study area.Firstly,in this paper,descriptive statistical analysis,correlation analysis,single factor pollution index method,single index method of potential ecological harm,Nemerow multi-factor index method,and comprehensive potential ecological pollution index method pollution were used to evaluate the degree of soil heavy metals U,Mn,As,Pb and Cr pollution in the study area based on discrete sampling points.Secondly,combined with GIS and geostatistical methods,the spatial interpolation of discrete sampling points were carried out,and the spatial differentiation of heavy metals pollution in the study area was analyzed.In order to determine the extent of heavy metals pollution,the evaluation results of spatial interpolation and indicating kriging method are analyzed with uncertainty.Finally,scenario prediction model was used to predict scope of heavy metal pollution of U,combined with the current and future pollution range map to predict the spatial and temporal variation trend of the pollution range.The main contents and research results are as follows:(1)By using Descriptive statistical analysis,U,Mn,and As all belonged to strong variations.The coefficient of variation of them were 105.77%,67.94%,and 41.29%,respectively.The coefficient of variation of Pb was 30.36%,which belonged to medium variation.Cr belonged to weakly variation,with a coefficient of 12.43%,and the spatial differentiation was relatively insignificant.(2)Single factor pollution index method results show that the samples of heavy metal pollution of U accounted for 99.5%,heavy metal pollution of Mn accounted for 28.6%,As accounted for 71.4%,Pb accounted for 60.5% and Cr accounted for 66.2%.Single potential ecological harm index shows that 99.5% of the heavy metals U in the samples are in the medium and above rating of ecological hazard rating,100% samplings of Mn,Cr in mild ecological harm level,96.1% of As in mild ecological harm level,and 99.5% of Pb in mild too.According to the Nemerow comprehensive pollution index method,the proportion of moderate pollution was 45.8%,and that of severe pollution was 44.9%.The comprehensive ecological hazard index shows that the proportion of moderate pollution is 80.5%,and the overall performance is moderate ecological harm.(3)All 5 heavy metals conformed to normal distribution after normal transformation.The characteristics of five kinds of heavy metal semi-anova models were established.Because of pure nugget effect of Cr,the ordinary kriging method could not be used and the anti-distance weight method was used to make the spatial pollution distribution map of it.The ordinary kriging method was used for the other 4 kinds of heavy metals.Heavy metal U appeared to be heavily polluted around the tailings pond area,while others areas show light pollution or even more serious pollution.Heavy metal Mn shows a silight pollution condition in the west.Heavy metal As only appears clean in sporadic areas.Pb is clean in the north and east of the taillings pond,while the rest areas are slightly polluted.Heavy metal Cr appears in the north,west and south of the region,with half a circle of clean areas,and the rest areas were slightly polluted.(4)The spatial probability map of heavy metal pollution was obtained by using Indicator Kriging and combined with the spatial distribution map obtained by the above methods.The pollution range and uncertainty area of each heavy metal are analyzed and defined.The area of heavy metal U in moderate pollution and above pollution accounted for 8.5%.The area of uncertain area accounted for 10.6%,and the area under moderate pollution accounted for 80.9%.Mn,As,Pb,Cr pollution area accounted for 28.4%,91.5%,76.3%,45.3%.Areas that could not be determined accounted for 10.6%,15.3%,5.8%,16.9% and 31.3%,respectively.The proportion of unpolluted areas is 56.3%,2.7%,6.8% and 23.4%.(5)The pollution of heavy metal U in 2030 was studied by using the non-mutation model of scenario prediction method.Compared with 2016,pollution of U in research area will be more serious in 2030 if no governance.The polluted Area proportion more than moderate pollution of heavy metal U will reach 34.60%,increase by 26.15% in 2016 relatively.The area under the medium polluted level will be 54.12%,decrease by 26.82% relatively.The uncertainty area will be 11.28%,the result has not changed much since 2016.However,10.92% of the regions with uncertainty in 2030 were converted from areas with pollution below moderate level.Nearly all of the regions with original uncertainty were changed to areas with moderate or above pollution level.