| Soil is the source of food and is closely related to human production and life.In recent years,with the influence of economic development and anthropogenic activities,heavy metal contamination of soil has occurred to varying degrees around the world and has become a hot spot of concern for all countries.The overall situation of China’s soil environment is also not optimistic,the 2014 “national soil pollution status survey bulletin” pointed out that the rate of soil pollution in China’s exceeds the standard by 16.1%,the quality of the soil environment in arable land is worrying.Heavy metals are the main pollutants affecting the environmental quality of agricultural soil due to their persistent,highly toxic,and cumulative nature,and have been listed as priority pollutants for control.Currently,due to environmental pollution and extreme climate,the soil-security relationship of farmland in the arid and semiarid regions of northwest China has become very fragile,especially in terms of heavy metal pollution in farmland.Therefore,there is an urgent need to carry out systematic research on the analysis of heavy metal sources and risk assessment of farmland soils in arid and semi-arid regions,which is of great significance to promote regional agricultural production and green development.In view of this,this study takes the oasis agricultural area of Suzhou District,Jiuquan city and the industrial agglomeration area of Jiayuguan City as the research objects and carries out a comprehensive study on the heavy metal pollution and ecological and health risk assessment of farmland soil in the key industrial and agricultural areas in the Hexi region by analyzing the current situation of heavy metal pollution and targeting different industrial clusters.By collecting farmland soil samples in the study area and using pollution index,soil environmental capacity,artificial neural network model,principal component analysis,correlation analysis,positive definite matrix factor model,risk assessment model,Monte Carlo simulation,and other methods,a soil heavy metal pollution assessment-source apportionment-risk assessment-pollution early warning system applicable to different industrial clusters is established;the pollution levels and spatial variability characteristics of heavy metals in agricultural soils in the study area are systematically evaluate;the sources and contribution of heavy metals to identified.The study also aims to systematically assess the ecological risk of heavy metals and the probabilistic health risk to adults and children;to measure the static and dynamic soil environmental capacity of farmland in the study area and to provide early warning of the soil heavy metal pollution status;to comparatively analyze the pollution status,sources,and risks of heavy metals in oasis agricultural areas and industrial agglomerations.The main results of this study are as follows:(1)The average concentrations of heavy metals in the agricultural soils of the study area all exceeded their background values,indicating that the agricultural fields in the study area were affected by anthropogenic activities.Among them,heavy metals in agricultural area farmland soils are at moderate pollution levels,with Cr,Ni,and Zn being particularly prominent;the contribution of Cr and Zn in the industrial zone to the heavy metal pollution in the surrounding farmland is high.In addition,the concentration of heavy metals in farmland in the two regions showed a large spatial heterogeneity,and the heavily polluted agricultural areas were mainly distributed in the southwest and central regions;the industrial areas accounted for 55% of the moderately heavy metal polluted soils,which were mainly distributed in the northwest and southeast regions.(2)Using a pollutant source apportionment model to apportion heavy metal pollution in the study area,the results showed that heavy metals in agricultural soils were divided into four sources,namely,fertilizer and pesticide sources dominated by As and Mn(27.8%);mixed sources of transportation and agricultural sources dominated by Cu,Zn,Cd,and Pb(26.9%).Cr and Ni dominate the sources of metal processing(22.6%);Ti,V,Cr,Mn,Fe,As,and Pb dominate the combined sources of atmospheric deposition and fuel combustion and other related activities(22.7%).The heavy metals in farmland soils around the industrial area come from a mixture of transportation and agricultural activities with Zn,Cd,and Pb as load elements(20.6%),Ti,Mn,Fe,Ni,Cu,and As as load natural sources and a mixture of integrated industrial activities(37.1%),V as load fuel and petrochemical activities(19.7%),and Cr(22.6%)for metallurgical activities.(3)Ecological risk indicated that Cd in the study area poses a moderate ecological risk to agricultural soils and should be given priority attention.The spatial distribution of high values of integrated ecological risk is basically consistent with the distribution of high values of heavy metal concentrations,which were mainly located in the central and western parts of the agricultural area and in the northwest and southeast of the industrial area.Based on the health risk assessment model,both noncarcinogenic and carcinogenic risks from the ingestion route were found to be higher in children than in adults in the study area.Among them,the total carcinogenic health risk in the agricultural area indicated that adults were already exposed to potential carcinogenic risk and was mainly distributed in the southwestern and central regions,with the highest in the central region in particular;the composite non-carcinogenic health risk index of adults in agricultural areas was greater than 1,and the composite non-carcinogenic health risk index of children in some areas(mainly in the central and southwestern parts)was higher than 1,and the spatial distribution pattern was basically the same as the carcinogenic risk,and these areas were the priority risk management areas in agricultural areas.Cr,Ni,Cu,Zn,and As in industrial areas all have carcinogenic effects on adults and children,but do not pose a non-carcinogenic risk to adults and children.The total non-carcinogenic risk index of As,Cr,and Cd for children is close to 1,more attention should be paid to pollution prevention management.(5)Monte Carlo simulation results showed that conventional deterministic risk assessment methods may overestimate the health risks caused by heavy metals in the study area.There was a very small probability of non-carcinogenic risk for children from As in industrial and agricultural areas.The probability of total non-carcinogenic risk for children from As in agricultural areas was 85.3%,while Ni had a probability of carcinogenic risk for children and adults of 69.5% and 11.4%,respectively,and the probability of total carcinogenic risk was 96.4% and 52.1%,respectively,indicating that elemental Ni is a priority control heavy metal in agricultural areas;the probability of carcinogenic risk of Ni in industrial areas for children and adults was 51.42% and0.23%,respectively,and its combined carcinogenic risk for children and adults was99.17% and 30.41%,respectively,which indicated that the carcinogenic risk of Ni in industrial agglomerations should be taken seriously.At the same time,the sensitivity analysis study showed that heavy metal concentration,intake rate,and body weight would have a large impact on the health risk evaluation results.Therefore,selecting representative exposure parameters to carry out health risk evaluation will reduce the uncertainty in the risk evaluation process.(6)Both the average environmental capacity index of soil and the overall environmental capacity index show that all heavy metals in the study area are in medium capacity,indicating that the overall condition of soil is good and there is a certain loading space of soil for heavy metal pollutants.Cr,Ni,and As elements in farmland soils in the agricultural area have been in low capacity at some sampling points.As,Cr,and Zn in agricultural soils in industrial areas were in low capacity at some sampling points,indicating that these heavy metals should be given priority attention.The study based on the soil dynamic capacity model shows that the dynamic capacity of heavy metal soil in the study area will show a decreasing trend with time change,and if no control measures are taken for the soil environment in the area,the soil capacity for heavy metal pollutants will be significantly reduced.This study can provide theoretical and practical references for the identification of heavy metal pollution sources,risk evaluation and environmental management measures in arid and semi-arid regions and similar areas,as well as for the sustainable development of agricultural soils. |
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