Evaluation Of Pollution Levels And Potential Risks Of Heavy Metals In Surface Dust In Changji City,Xinjiang,China

As the receptor of various pollutants in urban ecosystem,urban surface dust is enriched with various inorganic and organic pollutants including heavy metals,which are constantly transformed in urban soil-atmosphere-water environment under the external disturbance due to its fine particles,loose structure and the specificity of the interface where it is located.Due to their material properties and toxicological characteristics,the long-term exposure to a highly toxic and concentrated environment can lead to cellular damage and even induce the death of plant and animal organisms,thus becoming one of the hot issues of concern for urban ecology.In order to investigate the pollution status of heavy metals in the typical oasis cities in the northwest arid zone of China under the background of rapid urbanization and industrialization,52 representative surface dust samples were collected in the main urban area of Changji City,Xinjiang,and the contents of six heavy metals,including lead（Pb）,nickel（Ni）,Arsinic（As）,cadmium（Cd）,mercury（Hg）and copper（Cu）,were determined.The contents,pollution levels,ecological risks,spatial distribution,and potential health risks of the six heavy metals in surface dust in the study area were evaluated using mathematical statistical analysis,pollution index method,ecological risk method,geostatistical method with GIS technique and US EPA health risk model,respectively;the pollution sources of dust heavy metals were traced by combining correlation analysis,cluster analysis and PMF receptor model.The main conclusions of this study are as follows:1)The mean values of Pb,Ni,As,Cd,Hg,and Cu in surface dust of Changji City were46.83,26.35,9.92,0.21,0.047,and 59.33 mg/kg,respectively,and the median values were 39.50,24.00,9.72,0.20,0.0421,and 54.50 mg/kg,respectively.The mean values of their contents were2.41,0.99,0.89,1.71,2.76,and 2.22 times of the corresponding elements of soil background value in Xinjiang.In terms of the coefficient of variation,Pb and Hg were highly variable,while Ni and Cu were moderately variable,indicating that the heavy metals in surface dust in Changji were significantly influenced by human activities.2)The spatial distribution pattern of each heavy metal in the surface dust of Changji City varies greatly,and overall,the high values of Pb,Hg and Cu are mainly distributed in the central and northeastern coal-fired industrial areas where transportation and commercial activities are frequent;Ni and Cd are mainly distributed in the electrical and mechanical industrial parks in the southern part of the study area;the trend of As content is a"basin"-shaped distribution pattern of low in the central part of the study area and high in the surrounding area.The trend of As content in the study area is a"basin"-shaped distribution pattern of low in the central part of the study area and high in the surrounding area.The high values of non-carcinogenic risk for children and adults in the study area were mainly in the central and northeastern parts of the study area,and the spatial distribution pattern of carcinogenic risk was basically consistent with that of As content.3)The results of PMF analysis showed that the contribution of traffic emissions to Pb and Cu was 47.2%and 47.4%,respectively;the contribution of industrial emissions to Ni and Cd was 64.1%and 37.2%,respectively;the contribution of natural sources to As was 41.8%;the contribution of coal-fired sources to Hg was 54.8%.The contribution rates of industrial emissions to Ni and Cd were 64.1%and 37.2%,respectively;the contribution rate of natural sources to As was 41.8%;and the contribution rate of coal-fired sources to Hg was 54.8%.Overall,the total contributions of industrial,traffic,coal combustion and natural sources to the six heavy metals were 31.08%,26.80%,23.31%,and 18.81%.This indicates that human activities are the main cause of heavy metal enrichment in surface dust in the study area.4)The results of the geo-accumulation index(I_geo)evaluation show that the decreasing order of the mean I_geo values of the six heavy metals in the dust of the study area were:Hg>Pb>Cu>Cd>Ni>As,in which Hg,Pb,Cu and Cd show slight pollution,and Ni and As show no pollution;the results of the single pollution index（P_i）evaluation show that Hg,Pb and Cu are moderately polluted,Cd is lightly polluted,and Ni and As are no pollution.Cd is lightly polluted,Ni and As are no pollution,and the NPI of six elements is between 1.36～7.17,with an average value of 2.57,which is a moderate pollution situation;the pollution load index shows that the pollution load index of six elements is between 0.98～3.34,with an average value of 1.68,which is a light pollution situation.That is,Hg and Pb are the most dominant pollution factors in the study area.5)The results of the ecological risk evaluation showed that the average size of the single ecological risk index（Er）of heavy metals in dust on the surface of the study area were:Hg（110.52）>Cd（51.29）>Pb（12.07）>Cu（11.11）>As（8.56）>Ni（4.95）,in which the average single ecological risk of Hg and Cd showed strong and medium risks.The mean value of the combined potential ecological risk index（PLI）of the six elements was 198.1,which showed moderate ecological risk;the mean value of the dust heavy metal environmental risk warning index（IER）was 4.98,which was a moderate warning situation,with Hg,Pb and Cu as light warning,Cd as warning,and Ni and As as no warning.Hg is the largest ecological risk element in the study area.6)The non-carcinogenic risk index of heavy metals from surface dust in Changji City was0.492,which was 6.15 times higher than that of adults,and its carcinogenic risk(1.25×10^-5)was11.79 times higher than that of adults(1.06×10^-6),but its carcinogenic and non-carcinogenic risks to humans were within the safety threshold,As and Pb were the major non-carcinogenic elements in the study area,and As was the largest carcinogenic As and Pb are the major non-carcinogenic elements in the study area,and As is the largest carcinogenic element,and the risk relationship among the three exposure routes was:hand-oral intake>skin contact>respiratory inhalation.Overall,heavy metals in surface dust in Changji City did not pose any health risk to humans.