Research On Heavy Metal Pollution In Theof Street Dusts In Shijiazhuang City

Street dust in the urban area refers to a layer of incompact deposit on the surface of the urban streets.Under the external dynamics,the dust is easy to be kicked up and settled,and the repetition of kicking up and settling endangers the health of the pedestrians.Thus,it is very helpful to the research of the urban environment issues and the amelioration of the urban environment by researching on the characteristic of granularity distribution of Street dust as well as the feature of heavy metal element contents.This research sets the capital of Hebei Province—Shijiazhuang City as its region of study,which is the typical Northern city serious air pollution;to analyze the granularity characteristic of grains in the street,the content characteristic of heavy metal elements,and the spatial distributive characteristics of the contents of the nearing ground surface environment(take the leaves of Euonymus Japonicus as an example).This research gathers the 63 street dust and the resorted dust samples of several Euonymus Japonicus,and tests the heavy metal contents of the street dust samples by the Atomic Absorption Spectrometer(AA204Z and AA240FS,the U S A);Tests the granularity distribution of the samples by the Particle Size & Shape Analyzer(CIS-50,Netherland).And also analyzes the heavy metal elements of the street dust,the spatial distribution characteristics of the granularity parameter by applying ArcGIS9.0 and EXCEL2000.The result shows that particle size mean of the street dust of Shijiazhuang city is between 1.52～2.29μm,the proportion of PM₁₀ is more than 95%of the tiny grains number of the gathering dust in the streets.The mean content of the heavy metal elements as Pb,Zn,Cr, and As in the street dust is 2～3 times higher than the value of the earth background of Hebei Province,the value of Cd is 7.5 times higher.This shows that Cd enrichment occurred with the development of urbanization Shijiazhuang city.This research analyzed the ecological risk index and the health risk of the heavy metal elements in the street dust by applying Index of geoaccumulation.The evaluation result of the index of geoaccumulaiton shows that the index of geoaccumulaiton of Cd is the highest among all the elements,it is 4.14;the minimal value of Index of geoaccumulation of Pb is -5.39.There is extremely high pollution about Cd element because of the man-made pollution grade and the earth environment background value of heavy metal elements.The result of ecological risk index's evaluation shows that the ecological risk index of Cd is the highest,it is 225.17;index of Cd is the lowest,it is 3.10.Although there are some differences in result of the two methods,in general all the two method proves that the risk of Cd element is rather strong.In terms of spatial change,the spatial change of Pb element's pollution is bigger than other heavy metal elements.It is because of the multiple sources quality of Pb.The environmental influence index of heavy metal elements in the street dust in the urban district inside of the loop road of the city is evidently higher than the outside,except the northeast region.When the knowledge of suspended particle near ground level is not enough based on the limited routine air quality monitoring to understand the space distribution,relying on plants leaves would be an effective way.The analysis indicates that that the amount of the mean dust quantity of Euonymus Japonicus leaves is 0.3843g·m^-2·d^-1,and about 80%-90%is from the regional pollution of the near surface environment,and there are differences in space,it can reflect the spatial distribution situation of the street dust through the erosion process.At the same time the average mean size of the particle on the leaves surface is 1.9185μm,and 98.27 %of the grains are less than 10μm,that is to say there is separation quality in the scale of Euonymus Japonicus to the dust grains,and this separation quality becomes a good carrier of the eliminating and filtering of the urban inhalable particles.After comprehensive analysis of the spatial distribution,we can get three types of regions:the east second ying road and the region along the Beijing to Zhuhai highway,and the region around the Shijiazhuang railway stain,in these areas,the risk degree of dust pollution is high,and also the quantity of the restored dust in high,these areas are seriously polluted by restored dust.So we should pay the highest attention to these areas in the course of dust pollution treatment;the north of the east development area,the west of the urban area are two areas that are slightly polluted by restored dust,the values of the two are small;the region inside of the second ying road is the complicated area of comparison between the two, the comparison relationship between these areas is not certain,and need to be deeply analyzed.