Eco-Environmental Risk Assessment And Prediction Of Heavy Metal Contamination In Soil And Groundwater Mining Areas And Surrounding Area, Inner Mongolia

Heavy metals are highly toxic,easily enriched and difficult to degrade,posing a potential threat to the ecological environment.With the continuous exploitation of mineral resources and rapid social and economic development,heavy metal pollution problems are becoming more and more frequent.Due to the low recovery rate of heavy metals and other problems,which damage the ecological environment,an objective and reasonable assessment of the ecological and environmental risks of heavy metal pollution in soil and groundwater,and a more high-precision prediction and early warning are the main contents of the current urgent exploration and research.In the cold and arid region of Inner Mongolia,Linxi County Lituo Pb-Zn mine and its influence area and Ulath Houqi Xinxing copper mine and its influence area are typical representatives of heavy metal pollution,they were selected as the study area,and 507 and372 groups of soil and 57 and 98 groups of groundwater were collected in the two study areas during the abundant,flat,dry and transitional periods,respectively,to collect local hydro-meteorological and other information.We evaluated the environmental quality of heavy metal pollution,assessed the environmental quality of soil and groundwater pollution by using the potential hazard index,hierarchical analysis and PSO-BP（Particle Swarm Optimization-Back Propagation,PSO-BP）neural network nested coupling model.The ecological and environmental risks of heavy metal pollution in soil and groundwater were evaluated,and prediction and early warning studies were carried out.The main conclusions are as follows:1.The water chemistry type of Linxi County Lituo Pb-Zn mine and the influence area is mainly SO₄·Cl-Ca·Na·Mg,and the sparse dry water is SO₄·HCO₃-Ca·Na·Mg.groundwater and sparse dry water are mainly influenced by rock weathering,and the influence of atmospheric precipitation and evaporation concentration is very weak.The main type of water chemistry in Xinxing copper mine and influence area of Ulath Houqi is SO₄·HCO₃-Ca·Mg,SO₄·Cl-Ca·Na·Mg types,rock weathering and evaporation concentration are the main ionic components that determine surface water and groundwater,and the influence of atmospheric precipitation is weak.2.The potential hazard index of the soil in Linxi County Lituo Pb-Zn mine and its influence area is 8.17～6394.95,which is between slight and very strong pollution;the groundwater quality is from excellent to poor in the order of flat water period>dry water period>abundant water period,and the water quality is deteriorating from south to north;its heavy metal pollution is affected by both natural factors and low recovery rate of heavy metals as well as human activities,which makes the soil and groundwater heavy metals in this area appear High concentration or even pollution.The soil of the Xinxing copper mine and the affected area in Ulath Houqi is mainly slightly polluted,and the area near the tailings and outside is moderately and strongly polluted;the groundwater as a whole is Class III and above,and the water quality from excellent to poor is flat water period>dry water period>abundant water period;the surface water is mainly Class IV and V,and locally below Class III.The region’s soil,groundwater,and surface water heavy metal pollution is mainly the presence of foreign sources of pollution,as well as the local groundwater buried shallow,summer and winter temperature extremes,water evaporation concentration,ice enrichment effect is strong,so that heavy metal pollution exceeds the standard.3.The ecological and environmental risk assessment index system of heavy metal pollution in soil and groundwater includes 4 aspects and 19 influencing factors for soil and4 parts and 22 influencing factors for groundwater.The soil of Linxi County Lituo Lead-Zinc Mine and the impact area is 0.21～0.72,which is low to high risk,with low and medium risk dominating,and the risk level decreasing from northwest to southeast.The groundwater risk value is 0.16～0.67,which is low to high risk,with obvious differences in risk level in time and space,and a small range of high and low risk;the risk level is higher in space on the north side than on the south side,and the high risk is mainly in the tailings and near the outside.Xinxing copper mine in Ulath Houqi and the soil in the impact area is between low and high risk,with the tailings as the center,and the ecological environment around the risk decreases.Groundwater belongs to medium to high risk,with risk values of 0.49～0.61,and the high-risk local area is distributed inside and outside the tailings to the south.After comparison,the results are found to be more reasonable and can truly reflect the actual local ecological and environmental risk situation.4.Based on the tandem PSO-BP neural network nested coupled prediction and early warning model,when the soil surface layer concentration is reduced by 30%and 40%,the ecological and environmental risk range of the surface layer of Linxi County Lituo lead-zinc mine and the impact area changes significantly,the high and higher risk range and the heavy police level disappear or decrease,and the decrease is greater,and the other layers change less.The layers of soil in the Xinxing copper mine and the influence area of Ulath Houqi are0.25～0.53,which is low to medium risk,between no alarm and medium alarm,mainly low risk,medium risk is second to medium alarm;groundwater is medium risk and medium alarm,but when the concentration of surface layer is reduced by 40%,groundwater is low risk and the warning level is the light alarm.Due to the large burial depth of the groundwater in Linxi County Lituo Pb-Zn mine and the impact area,although the concentration of the soil surface layer is cut,the ecological and environmental risk and warning level are not significantly reduced due to the heavy metal legacy and lagging transfer.Under the scenario prediction,it is found that Linxi County Lituo lead-zinc mine and the impacted area and Ulat Houqi Xinxing copper mine and the impacted area need 37.61 years,18.31 years,or 45.22years,29.16 years respectively,and the reduction of surface soil maybe 30%or 40%.This thesis evaluates the spatial and temporal characteristics of heavy metal pollution,reveals the ecological and environmental risks of heavy metal pollution in soil and groundwater,and conducts a prediction and early warning study,which can provide a basis for local environmental pollution prevention and control,as well as a reference for ecological and environmental risk assessment and prediction and early warning studies in similar areas.