西安城市路边土壤重金属污染与天然放射性水平研究

【作者】 陈景辉；

【导师】 卢新卫；

【作者基本信息】 陕西师范大学 ， 环境科学， 2011， 硕士

【摘要】 本研究以西安城市路边土壤重金属地球化学特征与天然放射性水平为内容,详细分析了西安城市路边表层土壤样品的理化特征和常量元素组分；利用X-Ray荧光光谱仪测定了土壤中主要重金属元素的含量水平；采用欧共体修正的BCR四步连续提取法分析了土壤中主要重金属的赋存形态：通过机械筛分实验探讨了土壤粒径组成以及重金属元素在不同粒径土壤中的分布情况；并运用多道低本底γ能谱仪测定了路边土壤的天然放射性核素水平。本研究的主要结论如下：(1)西安城市路边土壤的各项理化指标分别为：pH值为8.61,电导率值为482.5μs/cm,低频磁化率、高频磁化率和频率磁化率分别为181.37x10-8m3/kg、171.55×10-8m3/kg和5.93%,烧失量为2.53%,粒度分析结果显示土壤主要以砂粒和粉粒为主。土壤常量元素组成与地壳丰度基本一致。(2)西安城市路边土壤重金属As、Co、Cr、Cu、Mn、Ni、Pb和Zn的平均含量分别为10.9、17.7、106.1、43.1、641.0、33.7、52.8和131.9 mg/kg。整体来看,Co、Cr、Cu、Mn、Ni、Pb和Zn7种重金属元素的平均含量均高于陕西土壤元素背景值和中国土壤元素背景值,其中Cu、Pb和Zn的富集程度高,累积量大, Co和Cr含量较高,As、Mn和Ni含量与背景值相近或稍高于背景值。(3)西安城市路边土壤重金属以残渣态为主要存在方式,重金属的直接危害性(主要指弱酸提取态)大小为：Cr>Mn>Zn>Pb>Ni>Cu>Co。重金属的“非稳态”环境生态风险大小为：Pb>Mn>Cr>Zn>Ni>Co>Cu。(4)西安城市路边土壤中重金属元素主要集中在较小粒径范围内,即0.063～0.050 mm和<0.050 mm土壤颗粒中。(5)多元统计分析结果显示西安城市路边土壤中As、Mn和Ni之间表现出显著的正相关性,Cu、Pb和Zn之间的正相关性极为显著,Co与Cr的相关性较好。分析得出As、Mn和Ni主要来自于自然源和交通源,Cu、Pb和Zn主要来自于交通源,Co和Cr主要来自于工业源。(6)西安城市路边土壤中天然放射性核素40K、226Ra和232Th的平均比活度分别为：707.67、39.05和48.75 Bq/kg；高于陕西土壤中天然放射性核素的比活度。通过计算得知路边土壤外照射指数处于安全范围之内,可作为建筑材料使用,对居民不会构成任何重大的放射性威胁。更多还原

【Abstract】 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.更多还原