| Under the background of the increasingly serious problems of soil environmental pollution,studying the spatial distribution of heavy metals in the soil of industrial land,analyzing the degree of pollution,and then taking targeted risk control and treatment measures have an important and positive impact on the sustainable utilization of soil resources and the sustainable development of regional economy.This study takes the typical smelting area of Hunan Province as the research object.The content of seven heavy metals such as Cadmium(Cd),Lead(Pb),Arsenic(As),Zinc(Zn),Mercury(Hg),Copper(Cu)and Nickel(Ni)were determined.Arc GIS and inverse distanceweighted(IDW)were used to analyze the spatial distribution trend and characteristics of heavy metals.Using the single pollution index,the Nemero pollution index and the geological accumulation index method to study the soil heavy metals in the study area.The pollution status were discussed.The potential ecological risks of heavy metals in soils were evaluated using improved potential ecological assessment methods.The heavy metal elements of the soil with a heavily polluted degree are mainly analyzed and evaluated by vertical profile analysis and pollution evaluation.The main conclusions are as follows:(1)The seven elements in the study area belong to strong mutation,indicating that they are greatly affected by human beings.None of the point about Ni exceed the standard.The over screening value rate is in order:As(63.03 %)>Pb(42.99 %)>Cd(41.04 %)>Zn(22.05 %)>Hg(7.69 %)>Cu(0.97%).The highest rate of As is 63.03 %,and Cd,As and Pb elements have a large number of over screening values and intervention values.(2)Seven heavy metal elements in the study area showed different degrees of pollution.The evaluation results of the single index showed that As,Pb and Cd were heavily polluted,while Zn,Hg,Cu and Ni were at safe levels.The Nemerow synthesis pollution index showed that the overall pollution of the study area is in a state of pollution,only 14 points are in a safe state,and the overall point pollution level is mainly heavily polluted.The evaluation of the geological accumulation index showed that the cumulative pollution of Cd,Pb,As,Zn,Hg,Cu and Ni was serious,the pollution ratio was above 85 %.The concentration of Ni elements was relatively light.The results of the potential ecological risk assessment showed that the overall points are still dominated by slight risk,and Cd and As are the main sources of risk.(3)The spatial characteristics of heavy metals in the surface soil of the study area showed that the spatial distribution pattern of Pb,Cu,Zn and Hg is basically the same,which is higher in the northeast and southwest and lower in the southeast and northwest.The content of Cd element is higher in the West than in the East.The high value areas of as content are mainly concentrated in the northeast and southwest,and the content in the southeast and northwest is relatively low.The overall content of Ni is low,which is lower than the screening value,and some areas are higher than the background value of Hunan Province.There are regional differences in enterprise pollution in the study area.Enterprises A,B and F are mainly polluted by Cd,Pb and As;C enterprise has four kinds of element pollution: Cd,Pb,As and Hg;Enterprise D is polluted by Pb,As and Cu,while enterprise E is polluted by Pb and As;G enterprise has As pollution.Areas with high content of heavy metals are mainly production workshops,solid waste storage or disposal areas and wastewater treatment areas.The high content of heavy metals in soil may be caused by the improper disposal of solid waste,dust settlement,rainwater scouring,inadequate anti-seepage work of waste water tank and other comprehensive factors in the long-term production process.(4)The profile distribution law of soil heavy metal elements in the study area showed that the content of Cd decreases with the increase of depth.The area with high value in the first layer decreases in the second layer,the range of high value area gradually shrinks,and the overall content of soil in the third layer is low.Pb element is mainly enriched in the second layer,which is located near enterprise B and F.As element is mainly concentrated in the third layer,which is located near G enterprise.Risk control measures should be strengthened in this area to prevent further downward diffusion of pollution and pollution of groundwater.(5)The evaluation results of heavy metal pollution on the profile showed that the number of pollution points decreased with the increase of the depth of the three elements,Cd,Pb and As.As the two elements of Cd and Pb increase in depth,the pollution point is also reduced,and the third layer is basically pollution-free.As element pollution is more serious,the proportion of pollution points in the first layer accounted for 58.24 % of the total sample,59.26 % in the second layer,and 41.33 % in the third layer,showing a downward migration trend of pollution. |
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