Street Dusts, Soil And The Weihe River Sediment Heavy Metal Pollution Study

Urban dusts, urban soils, and river sediments are important parts of ecologically environmental system of city. Researches show that the heavy metal pollution of urban dusts, urban soils, urban water, and river sediments affected by industry, traffic, commerce, and construction of city is very heavy during the fast development of urbanization. However, the few researches related to Baiji in this field are reported.In order to clarify the environmental status of Baoji City, the paper chooses urban street dust and urban soil of Baoji City and river sediment of Baoji section in Weihe River as object researched, firstly researches the physical and chemical property and the content, distribution, origin, speciation, and mobility of heavy metal elements systematically, and attains the following results and cognitions:1. The physical-chemical property, including pH, Loss on Ignition (LOI), low frequency susceptibility (LF), high frequency susceptibility (HF), frequency-depended susceptibility (FD), physical formation, and the contents of constant elements, of urban street dust and urban soil of Baoji and river sediment of Baoji section in Weihe River is researched by means of pH-meter, Muffle, Susceptibility-meter, Laser Size Meter, and X-Ray Fluorescence Spectrometer (XRF). The analytical results show that the pH values of urban street dust, urban soil, and river sediment are respectively 8.983, 8.482, and 8.639 and are all alkaline; that the LOI are respectively 8.77%, 5.20%, and 2.47% and urban street dust has probably some organic pollution; that LF and HF in urban street dust are higher than urban soil and river sediment and the two later are basically same, while FD in urban soil is higher than urban street dust and river sediment and the two later are basically same; that urban street dust and urban soil of Baoji is dominated by silt (street dust: 71.300%, soil: 59.066%) and river sediment of Baoji section in Weihe River is dominated by silt and sand (silt: 45.610%, sand: 41.467%); that the diferences of constant elements in three environmental factors are not quite clear and their contents are basically same.2. The concentrations of heavy metal elements (Cu, Pb, Zn, Mn, Fe, Co, Ni, Cr, Cd, As, and Hg) of urban street dust and urban soil of Baoji and river sediment of Baoji section in Weihe River, are analyzed through XRF, Inductively Coupled Plasma Mass Spectrometer (ICP-MS), and Atomic Fluorescence Spectrometer (AFS). The analytical results show that in urban street dust, the mean contents of heavy metal elements (Cu, Pb, Zn, Mn, Fe-Fe₂O₃%, Co, Ni, Cr, Cd, As, and Hg) are respectively 123.2μg/g, 408.4μg/g, 715.1μg/g, 804.2μg/g, 7.22%, 15.9μg/g, 48.8μg/g, 126.7μg/g, 6.60μg/g, 28.3μg/g and 1.112μg/g; that in urban soil. the mean contents are respectively 35.4μg/g, 36.7μg/g, 102.4μg/g, 708.6μg/g, 4.90%, 19.0μg/g, 32.7μg/g, 89.3μg/g, 0.50μg/g, 13.4μg/g and 0.282μg/g; that in river sediment, the mean contents are respectively 24.2μg/g, 22.7μg/g, 68.3μg/g, 534.8μg/g, 3.85%, 15.1μg/g. 25.6μg/g, 90.9ng/g, 0.4μg/g, 9.7μg/g and 0.470μg/g. Compared with Chinese Soil Element Background Value (CSEBV), the pollution of heavy metal of urban street dust is very heavy, especially for Cd, Hg, Pb, Zn, and Cu, which are respectively 68.0, 17.1, 15.1, and 5.4 times than CSEBV, while the contents of urban soil and river sediment are basically same with CSEBV, except for Hg and Cd. Compared with other cities (street dust) and rivers (sediment), the contents of heavy metal elements of urban street dust are higher than other cities', and the contents in urban soil and river sediment are moderate. The analyses of Correlation and Cluster show that in urban street dust of Baoji, the heavy metal elements (Pb, Zn, and Mn) mainly originate from anthropogenic activities (modern industry, commerce, and traffic), and that the heavy metal elements (Cd, Hg, Fe, Co, Ni, As, Cu, and Cr) mainly come from natural sources.3. The relationships between heavy metal elements and physical-chemical items in urban street dust and urban soil of Baoji and river sediment of Baoji section in Weihe River are studied by means of Correlation Analysis. The analytical results show that in urban street dust of Baoji, there are significant correlation between LF, HF, FD and many heavy metal elements, but there is no correlation between clay, silt, sand and heavy metal elements, while in urban soil of Baoji and river sediment of Baoji section in Weihe River, the relationships are just adverse, and that there are significant correlation between constant elements and many heavy metal elements in urban soil and river sediment. The distribution of heavy metal elements in different grain size is researched using physical filtration, plus XRF. The results show that in urban soil of Baoji and river sediment of Baoji section in Weihe River, the difference of distribution of heavy metal elements in different grain size is not quite clear.4. The speciations of heavy metal elements (Cu,Pb,Zn,Mn,Fe,Co,Ni,Cr, and Cd) in urban street dust and urban soil of Baoji and river sediment of Baoji section in Weihe River are researched utilizing modified-BCR sequential extraction procedure, plus ICP-MS and Inductively Coupled Plasma Atomic Emission Spectrometer (ICP-AES). The results show that in urban street dust of Baoji, the order of mobility of heavy metal elements with environmental conditions is Cd (90.11%) > Pb (82.33%) > Zn (79.32%) > Cu (62.35%) > Mn (51.48%) > Co (29.02%) > Ni (23.62%) > Cr (18.68%) > Fe (10.21%); that in urban soil of Baoji, the order is Pb (68.75%) > Cd (63.93%) > Co (59.25%) > Mn (57.32%) > Zn (29.01%) > Cu (25.94%) > Ni (20.70%) > Cr (15.36%) > Fe (7.30%); that in river sediment of Baoji section in Weihe River, the order is Mn (56.70%)≈Pb (56.65%) > Cd (53.66%) > Co (48.82%) > Cu (43.99%) > Zn (21.93%) > Ni (15.49%) > Cr (11.43%) > Fe (9.62%); and that urban street dust has bigger potential risk than urban soil and river sediment.5. The level of heavy metal pollution in urban street dust and urban soil of Baoji and river sediment of Baoji section in Weihe River at present is assessed by means of Müller's Geo-accumulation Pollution Index and Lars Hakanson's Potencially Ecological Risk Index. The results show that urban street dust of Baoji is mainly polluted by the heavy metal elements of Cd, Hg, Pb, and Zn et al; that urban soil of Baoji and river sediment of Baoji section in Weihe River are contaminated by Hg and Cd; that the heavy metal pollution of urban street dust is heavier than urban soil and river sediment.