Assessment Of Contamination And Its Potential Risk Of Trace Elements In Street Dust In Urumqi City

As the main carrier of"source"and"sink"of urban environmental pollutants,urban street dust plays an important role in the migration,transformation and diffusion of urban environmental pollutants.The trace elements with physiological toxicity in urban street dust are easy to rise under the external power because of the characteristics of slow migration rate,strong latency,serious pollution consequences and complex ecological environment effects.Trace elements not only affect the safety of urban ecological environment through the circulation transformation between urban soil atmosphere water environments,but also via three main routes:ingestion,inhalation,and dermal contact pose serious health risks,which has become one of the most important urban ecological environmental problems in the scientific community.In this study,Urumqi,a typical oasis city with the highest degree of urbanization and industrialization in Xinjiang,is taken as the research target.A total of 83 dust samples were collected from four different functional areas（traffic area,park area,culture and education area,residential area）in Urumqi city and determined for the concentrations of As,Cd,Cr,Cu,Hg,Mn,Ni,Pb,and Zn elements.The concentration characteristics,spatial distribution,contamination levels,main sources,potential ecological risks and potential health risks of these trace elements were determined based on geostatistical analysis,geo-accumulation index,multivariate analysis,potential ecological risk index and the health risk assessment model introduced by the US EPA（United States Environmental Protection Agency）,respectively.The main conclusions of this study are as follows:1)The average concentrations of As,Cd,Cr,Cu,Mn,Ni,Pb,Zn,and Hg in street dust from Urumqi were 9.49,0.24,66.80,36.79,435.48,34.08,40.51,224.48,and 0.14 mg·kg^-1,respectively.Among which the average concentrations of Hg,Zn,Pb,Cd,Cu,Cr,and Ni exceed the corresponding background values determined in Xinjiang soils by factors of 8.24,3.26,2.09,2.0,1.38,1.35,and 1.28 times,respectively.The accumulation of trace elements in street dust is apparently.The concentration of trace elements in the street dust from different functional areas and different administrative areas in Urumqi city is different.2)The spatial distribution patterns of the nine trace elements in street dust were found to be substantially heterogeneous,and there are high value areas or high value points.The concentration high value area of As in the dust is distributed in the northwest and east of the study area;there are two high value points of Mn element concentration in the dust of the study area;the spatial distribution pattern of Cd element concentration in the dust is gradually increasing from west to east,and the high value area is found near the industrial area in the northwest of the study area;the concentration spatial distribution pattern of Cr and Ni in the dust is similar,the high concentration areas are mainly distributed around the coal mines in the northeast of the study area;the spatial distribution pattern of Cu,Pb and Zn in the dust is similar,and the high value areas of these three elements are distributed in the northwest and southeast of the study area;the high value areas of Hg in the dust are mainly distributed in the traffic intensive areas in the middle of the study area.The correlation analysis and cluster analysis indicated that As,Cd,Cr,Cu,Hg,Ni,Pb,Zn and in street dust from study area are mainly produced by anthropogenic sources,while Mn originate from soil geochemical characteristics.3)The geo-accumulation index showed that,the contamination level decreased in the following order:Hg>Zn>Pb>Cd>Cr>Cu>As>Ni>Mn.Among them the investigated street dust is moderately polluted by Hg,and non-pollution to moderate pollution by Cd,Pb,and Zn.The remaining elements unpolluted by As,Cr,Cu,Mn,and Ni.The load pollution index indicated that,the average contamination level about single pollution index of trace elements in street dust decreased in the following order:Hg>Zn>Pb>Cd>Cr>Cu>As>Ni>Mn.Hg and Zn showed the heavy pollution level,whereas Pb showed the moderate pollution level,Cd,Cr,Cu,and Ni showed the slight pollution level,and Mn showed the non-polluted level.In general,there are little differences about the contamination level of trace elements in street dust from each functional area in the study area;the average value of comprehensive pollution index decreased in following order:culture and education area>traffic area>Park>residential area,showed a light pollution level.4)The potential ecological risk index indicated that,the single ecological risk index of trace element in street dust decreased in following order:Hg,Cd,Pb,As,Cu,Ni,Zn,Cr,Mn,among which extremely strong ecological risk for Hg,medium ecological risk for Cd,and the remaining seven elements showed slight ecological risk level.The average comprehensive ecological risk index value of trace element in street dust for each functional area showed the relatively strong ecological risk level.Cd and Hg were the main ecological risk factors of street dust in the study area.5)The results of potential health risk assessment showed that,the non-carcinogenic and the total carcinogenic health risk index calculated by three exposure pathways of nine trace elements were lower than their threshold values,which within the limits of the acceptable risk level introduced by the US EPA,and no health risks for public.In terms of exposure routes,the exposure of trace elements in dust is the largest via the ingestion route,followed by the dermal route and through the inhalation route is the smallest.The potential health risk of trace elements in street dust for children is slightly higher than adults.As and Cr are the main non-carcinogenic risk factors and Cr is the main carcinogenic risk factor in street dust from the study area.