西藏土壤汞的分布特征及污染评价

为了解西藏地区土壤汞的污染水平与现状,采集西藏四区-市（拉萨、林芝、那曲、阿里、日喀则）耕地、冲积土、草地、荒地4 种类型的土壤,其中表层土壤54 个,剖面样品18 个.利用直接加热-金管富集-原子吸收法对土壤中汞含量进行分析,结果表明,西藏地区土壤中汞含量平均含量为0.026 mg·kg^-1,低于我国土壤中汞的背景值,与先前西藏土壤中汞的含量相近.部分样品中汞的含量较高,其中最大值为0.563 mg·kg^-1,可能与人为源点状污染有关.西藏土壤汞的分布具有显著的地势分布特征,土壤中汞含量从东南到西北逐渐降低.这与西藏的地势条件和人为活动有关.由于土壤中有机质与人为影响的差异,不同类型土壤中耕地土壤汞含量最高（0.051 mg·kg^-1）,冲积土最低（0.015 mg·kg^-1）,偏远地区荒地汞含量最稳定.西藏东南和西北地区土壤汞的垂直分布特征有明显的差异,西北低汞含量地区垂直分布特征主要表现为表层〉中层〉底层,而东南地区分布规律并不明显,人为翻动频繁和较复杂汞来源与迁移是造成都东南部耕地土壤和河滩土汞含量垂直分布的主要原因.以西藏土壤背景含量水平为单因子污染评价标准,结果显示西藏27.4%的土壤处于中度或重度污染,31.5%处于无污染状态,人为活动对西藏地区土壤中汞含量的升高有较大的贡献.

Distribution and Pollution Assessment of the Mercury in Soils of Tibet

To investigate mercury pollution level in soils of Tibet, four types of soils （farmland, atteration, grassland and uncultivatedland）, including 54 surface and 18 profile soil samples, were taken from five different sites in Tibet （Lasa, Linzhi, Naqu, Ali andRikaze） during October, 2010. Mercury content in soils was analyzed using the Direct Heating-Gold CartridgePreconcentration-Atomic Adsorption Spectrometric Method. The results show that the geometric mean mercury level was 0.026mg·kg^-1, which was similar to former studies and lower than background mercury value of soils in China. Mercury in some sampleswas high, with the highest content of 0.563 mg·kg^-1, which may be related to anthropogenic point-source pollution. The distributionof the level of mercury showed a notable topography characteristic with a trend of descending from the Southeast to the Northwest,which was related to the topography and human activities of Tibet. Due to the differences of organic matter in soils and humaninfluence, the mercury concentration was the highest in farmland （0.051 mg·kg^-1） among all types of soils, the lowest in atteration（0.015 mg·kg^-1）, and the most stable in uncultivated land. The vertical distribution of mercury content in soils of Southeast Tibetdiffered obviously from that of Northwest Tibet. In Northwest Tibet, the mercury content was low and decreased from the surface tobottom layer soils. In Southeast Tibet, the vertical distribution didn’t show a distinctive feature, resulting from frequent digging byhuman and complex sources and transport of mercury. By the Single-factor Pollution Assessment Method, 27.4% of soils in Tibetwere moderately or severely polluted and 31.5% unpolluted. Human activities played an important role in increased mercury contentin soils of Tibet.