| Street dusts were collected in commercial area,traffic area,educational area,residential area and parks area of Chengdu,China,to investigate the concentrations of trace metals(Pb,Zn,Cu,Ni,Cd and Cr).The degree of pollution by trace metals were assessed with respect to the local soil background values by calculation and comparison of the Geo-accumulation Index and Potential Ecological Risk Index.The spatial distributions of trace metals in street dust of Chengdu were analyzed based on the metal concentrations in street dusts using the geostatistics method(Kriging).Correlation coefficient analysis,principal component analysis(PCA)and cluster analysis(CA)were used to analyze the data and to identify possible sources of these metals in the street dust.In vitro test was used to estimate the oral bioaccessibilities of trace metals in street dust.According to the Human Health Evaluation Manual(USEPA),human health risks were quantitatively assessed in terms of non-cancer and cancer risk.The main conclusions were as follows:(1)The average concentrations of Pb,Zn,Cu,Ni,Cd and Cr in the dust samples were 82.3,296,100,24.4.1.66,84.3 mg/kg,respectively.Especially for Pb,Zn,Cu,Cd and Cr,with the mean values of 3.04,3.98,4.34,17.1 and 7 times background values for Chengdu soil,respectively.(2)In comparison with other cities,the concentrations of Pb,Zn,Cu,Ni,Cd and Cr in the street dusts in Chengdu were in the medium level.There were some difference in total trace metal concentrations in street dust among five functional areas in Chengdu and could be classified as follows:commercial area>traffic area>residential area>educational area>parks area.The highest concentrations(mg/kg)of Zn(344),Cu(149),Ni(35.8),Cd(2.07)and Cr(153)in street dusts were found in commercial area.The highest Pb concentration in street dust was found in traffic area(98.5 mg/kg).(3)A pollution assessment by Geo-accumulation Index and Potential Ecological Risk Index showed that the pollution level for the trace metals was in the following order:Cd>Cu>Zn>Pb>Cr>Ni.The Cd levels can be considered "heavily contaminated" status.A certain level ecological risk were caused by the trace metals in street dust of Chengdu.Cadmium existed the highest ecological risk.In addition,there were more serious ecological risk in commercial area and traffic area than other functional areas.Therefore the monitoring the street dust is crucial.(4)The concentrations of Pb,Zn,Cu,Ni,Cd and Cr were interpolated using kriging.The higher concentrations of Pb and Zn were observed in the middle and north of Chengdu.Spatially,the middle-east parts of Chengdu were of higher Cu concentration.The concentrations of Ni and Cr decreased from the southwest corner and northeast parts of the city to outside.However,there was not obvious spatial distribution of Cd.(5)Three main sources were identified based on the results of correlation analysis,principal component analysis and cluster analysis.Pb and Zn mainly derived from traffic source.Cu,Ni,and Cr originated from nature(local soil)from nature(local soil),as well as corrosion of alloys used in vehicle components,vehicle covers or other metallic surfaces and weathering materials(paints and coatings).Cadmium was generally a unique-component factor and widely used to shelter the alloy surface and building materials and also used in galvanization,batteries,plastic,and fertilizer application.(6)The oral bioaccessibility of trace metals in the street dusts from five functional areas were ranked according:Zn>Cd>Pb>Cu>Ni>Cr,indicating that there were great differences in oral bioaccessibility of the trace metals.For non-carcinogenic effects,there were more health risks via street dusts for children than adults.The HQ values for the different exposure pathways of trace metals that were studied in inhabitants(children and adults)decreased in the following order:ingestion>dermal contact>inhalation.However,there were no non-carcinogenic and carcinogenic risks from trace metals for inhabitants. |
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