北京市区表层土壤稀土元素空间分布特征研究

The Space Distribution Characteristics Study of Rare Earth Elements in the Surface Soil of Urban Areas in Beijing

土壤稀土元素作为反映土壤污染的指标之一,识别其空间分布特征及来源对于客观评价城市表层土壤污染水平、制定治理方案具有重要意义。为研究北京市区表层土壤稀土元素的空间分布特征,于2014年3月15日系统采集46个表层土样,并用电感耦合等离子体质谱仪测定10种稀土元素(La、Ce、Pr、Nd、Sm、Eu、Gd、Tb、Dy和Sc)的含量。采用统计分析和地统计方法对北京市区表层土壤稀土元素的变化趋势及空间分布进行研究,并对表层土壤和大气降尘中稀土元素进行Pearson相关性分析,结果表明,(1)北京市区表层土壤呈轻稀土富集型,稀土元素主要污染点位于海淀区周家巷桥和西直门外大街采样点,表层土壤与大气降尘中的稀土元素相关系数介于0.873~0.946之间,相关性显著。总体上,北京市区表层土壤稀土元素污染较轻。(2)各采样点δCe和δEu的变化范围分别为0.85~0.98和0.63~0.82,说明稀土元素Ce无显著异常,稀土元素Eu负异常,亏损较大。(3)大部分稀土元素(La、Ce、Nd、Sm、Gd、Eu和Dy)在东西方向和南北方向均呈现先减少后增加的趋势,最低值出现在东西方向和南北方向的中心位置。(4)富集因子表明北京市区表层土壤中各稀土元素受人为因素影响较小,为弱污染。主成分分析结果表明,煤炭燃烧和汽车尾气的排放,煤炭燃烧、工业生产和农业化肥的使用可能分别是四环线内、外各稀土元素的主要人为来源。

Rare earth elements, as a crucial indicator for soil pollution, play a significant roles for both evaluating the level of soil pollution objectively and developing controlling program to identify spatial distribution characteristics and provenances. In order to study spatial distribution characteristics of rare earth elements in the surface soil of urban areas in Beijing, forty-six surface soil samples were obtained by systematic collection on March 15th, 2014 and ten rare earth elements （La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Sc） were measured by ICP-MS. Statistical analysis and Geostatistical methods were both used on variation trend and space distribution of those rare earth elements for the surface soil in Beijing, and the correlation of rare earth elements in topsoil and atmospheric precipitation were analyzed. The results show that, （1） The surface soil of Beijing was enriched-type of light rare earth. The main pollution points of the rare earth elements were the sampling points of Zhoujiaxiang Bridge and Xizhimen Street in Haidian district. The correlation coefficients of rare earth elements in topsoil and atmospheric precipitation ranged from 0.873 to0.946, and the correlation was significant. In general, the pollution of rare earth elements in the surface soil was light in Beijing. （2） The variation range of delta Ce and delta Eu was 0.85~0.98 and 0.63~0.82 on sampling points, respectively. There were nosignificant differences in Ce in different sampling point. The rare earth element of Eu was negative anomaly, and was much lower than the standard value. （3） Most of the rare earth elements （La, Ce, Nd, Sm, Gd, Eu and Dy） declined at first and then increased in east-west and north-south direction, the lowest contents of rare earth elements were located in the east-west and north-south center of the study area. （4） By enrichment factor method, we concluded that the surface soil was less polluted and affected by human factors in urban areas of Beijing. The principal component analysis results indicated that coal combustion and the use of automobile exhaust emissions, coal combustion, industrial production and the agricultural fertilizer might be the main artificial sources on rare earth elements inside and outside the fourth ring line.