| This research is based on the heavy metal geo-chemistry characteristic and natural radioactivity level of roadside soil in Xi'an city, analyzed the physico-chemical characteristic and constant element composition of the surface soil sample. The main heavy metals concentration were determined by using the X-Ray fluorescence spectroscope and the main heavy metals speciation were analyzed through the BCR four-step sequential extraction method which was modified by the European Economic Community. At the same time, the soil particle size composition as well as the heavy metals distribution situation in different particle size soil was discussed through the screening experiment. At last, the natural radionuclide content level of roadside soil in Xi'an were determined by the multi-channel low background Gamma spectrum analyzer.The main conclusions of this study are as follows:(1) The physico-chemical paramrters of roadside soil in Xi'an are as follows respectively:the pH value is 8.61, the conductivity value is 482.5μs/cm, the low-frequency susceptibility, the high-frequency susceptibility and the frequency dependent susceptibility is 181.37×10"8m3/kg, 171.55×10-8 m3/kg and 5.93% respectively, the loss on ignition is 2.53%. The size testing results show that the soil mainly composized by sand and silt. The soil constant elemental composition is consistent with crustal abundance composition.(2) The average value of As, Co, Cr, Cu, Mn, Ni. Pb and the Zn of roadside soil in Xi'an is 10.9,17.7,106.1,43.1,641.0,33.7,52.8 and 131.9 mg/kg, respectively. Overall speaking, the mean concentrations of Co, Cr, Cu, Mn, Ni, Pb and the Zn of roadside soils in Xi'an are higher than the background values of Shaanxi soil and Chinese soil. These are especially true for Cu, Pb and Zn. Their enrichment levels in roadside soils are higher than As, Mn and Ni. Co and Cr content is high, As, Mn and Ni content are close or slightly higher than the soil background values.(3) The heavy metals speciation of roadside soil in Xi'an are maily exist by residual condition, the heavy metals direct hazardous level (mainly refers to weak acid extraction condition) is on the descending order:Cr>Mn>Zn>Pb>Ni>Cu>Co. The environmental ecology risk of heavy metals "unsteady state" is on the descending order:Pb>Mn>Cr>Zn>Ni>Co>Cu.(4) The heavy metals of roadside soil in Xi'an are mainly concentrated in the small particle size, namely 0.063-0.050 mm and 0.050 mm soil particle size.(5) Multi-statistical analysis results show that As, Mn and Ni are of significantly positive correlation relationship, Cu, Pb and Zn are also high corelated, Co are positive correlated with Cr. The analysis results show that As. Mn and Ni in roadside soil mainly come from natural source and transportation source. Cu. Pb and Zn mainly come from transportation source, and Co and Cr mainly come from industry source(6) The average specific activity of natural radionuclides 40K. 226Ra and 232Th of roadside soil in Xi'an are 707.67.39.05 and 48.75 Bq/kg, respectively, higher than the natural radionuclides specific activity of Shaanxi soil. The calculated results demonstrate that the external exposure index of roadside soil is in a safe range, can be used as a building material, will not pose any significant radioactive threat to the residents. |
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