Spatial Distribution, Sources And Exposure Risks Of Heavy Metals In Typical River Valley Cities In Northwest China

Cities are the places where human beings live.With the rapid development of modern industrialization and urbanization,urban environmental pollution,especially potentially toxic metal/metalloid pollution,has become a prominent problem that can not be ignored and has attracted great attention worldwide.Potentially toxic metals/metalloids are persistent pollutants,which are difficult to be degraded in organisms and accumulate easily through the food chain.They have a certain impact on the ecosystem and human health.Therefore,systematically exploring the content distribution,source,pollution and human exposure risk of heavy metals in urban multi-media is a key scientific problem to be solved in comprehensive regulation and control of urban environmental pollution and urban risk management.In this study,Lanzhou,Urumqi and Yan'an Lanzhou,which are typical Valley cities in Northwest China(due to their topographic characteristics,which make it difficult to dilute and diffuse pollutants),were taken as research areas.To assess the health risk of heavy metal population in the study area,spatial distribution,pollution characteristics and sources of 8 metal elements in plants and 25 heavy metals in urban soils and dust were systematically studied,and the migration and accumulation of heavy metals in various environmental media were explored.In order to provide important scientific theory and technical support for the establishment of characteristic pollutant account,comprehensive regulation and risk management of urban environmental pollution in Western Valley cities,IEUBK model was used to predict the blood lead and its spatial distribution characteristics of children aged 0-6 years in the study area.The main conclusions are as follows:(1)The distribution of potentially toxic metals/metalloids in soil and dust in typical Western Valley Cities is similar to each other.The average contents of Ba,Ce,Co,Cr,Cu,La,Pb,Sr,U,Zn and Zr in soil and dust of Lanzhou City exceed the local background values.The average contents of Ba,Cos Cr,Cu,Mn,Pb,U,V,Y and Zn in soil and dust of Urumqi City exceed the local background values.The content and distribution of potentially toxic metals in soil and dust are much higher than that of plants,and the content and distribution of potentially toxic metals in plants are strongly influenced by human activities.Generally speaking,Urumqi has the highest content of potentially toxic metals in the three environmental media,followed by Lanzhou and Yan'an.Source analysis using positive definite matrix factor(PMF)method shows that the main sources of potentially toxic metals/metalloids in soil and dust in three cities are coal combustion.petroleum and alloy manufacturing industries,transportation and nature.(2)The evaluation results of pollution load index show that the pollution levels of heavy metals in soil and dust in typical Valley cities are all mild pollution.The results of single factor evaluation showed that the elements of Pb and Zn in soil and dust in Lanzhou were slightly polluted,while the other elements were in a slightly polluted and non-polluted level.In the soil of Urumqi,except for the slight pollution of Zn element,the pollution degree of other elements is low,while in the dust of Urumqi,the pollution degree of Zn is moderate,and that of Cu and Pb is slight.In Urumqi dust,zinc is moderately polluted,while copper and lead are slightly polluted.In Yan,an,only Co element in dust is moderately polluted,while the other elements are less polluted in soil and dust.From the point of view of regional environmental element pollution,Cu,Pb and Zn are the main characteristic pollutants in three cities,and their pollution level is related to human activities such as urban industry and traffic emissions.(3)EPA population health risk assessment model was used to assess the human health risk of harmful elements in soil and dust in typical Valley cities.The results showed that the non-carcinogenic risk index of harmful elements(As,Cr,Pb,V,Co,Mn,Ni,Cu,Sr,Zn)in soil of Lanzhou,Urumqi and Yan'an was greater than 1 through digestive tract,respiratory and skin exposure.The risk is higher than 10-4.Except for Yan'an,the non-carcinogenic and carcinogenic risks of harmful elements in urban dust of Lanzhou and Urumqi exceed the human body's tolerance.However,the risks of heavy metals to adults in soils and dust of three cities are all within the scope of safety,and all heavy metals have the highest risks to human body through hand-to-mouth pathway,which should be paid great attention to.(4)The results of IEUBK model predicting children's blood lead showed that children's blood lead values were basically below 100 ug/L,which did not exceed the acceptable level of children's blood lead in China,but the predicted value of children's blood lead in some age groups had exceeded 50 ug/L(acceptable level of children's blood lead in the United States).It was suggested that infants and young children should reduce their exposure to lead-contaminated soil and dust,and reduce the intake of lead-contaminated food.From different regions,except for children aged 0-1 in Lanzhou,the predicted value of blood lead in other age groups is higher than 50 ug/L;the predicted values of blood lead of children aged 1-2 and 2-3 in Urumqi and children aged 1-2,2-3 and 3-4 in Yanlan were all higher than 50 ug/L.The results showed that children aged l-3 years were the main target of environmental lead pollution in Western Valley cities.Great attention should be paid to the protection and protection of lead exposure of children aged 1-3 years.