贵州万山废弃矿区小流域系统沉积物及悬浮物重金属的空间分布特征

The Spatial Distribution Characteristics of Heavy Metals in River Sediments and Suspended Matter in Small Tributaries of the Abandoned Wanshan Mercury Mines,Guizhou Province

废弃矿山虽已不再开采,但废弃矿坑、旧冶炼场地、埋填的尾矿坝受雨水淋滤仍可通过地表径流对下游地区造成污染。研究废弃矿山水系沉积物及悬浮物中重金属的沿河道分布及相互关系具有重要的现实意义。本文以贵州万山汞矿区下溪河小流域系统作为研究区域,对沉积物及悬浮物中重金属元素进行初步调查,为监测和污染耕地进行修复提供基础资料。通过湿法消解的前处理方法,利用电感耦合等离子体质谱和原子荧光光谱法测定了沉积物及悬浮物样品中Cr、Ni、Cu、Cd、Pb、As、Hg、Zn、Co含量,查明污染现状及空间分布特征,以获取矿区污染物向下游迁移、扩散的信息。结果表明:沉积物中Hg含量范围为0.10~16.0μg/g(干重),平均值为5.79μg/g,是《国家土壤环境质量标准》二级土壤Hg限值的几十倍;Cd在部分站点超标;Ni、Cu、Co含量平均值均不超标;Hg和Cd的变异系数较大,显示空间分布不均的特征。沉积物中Hg为高潜在生态风险级别。研究区沉积物及悬浮物中的Hg浓度与河段的水动力条件有关,最大值出现在河道宽阔、水流平缓的站点。由于万山汞矿早已停止开采和冶炼,本研究提出,自然条件下废弃矿区的风化淋滤引起颗粒物输送是造成河流下游Hg和Cd污染的原因。

BACKGROUND: Although abandoned mines are no longer exploited, waste mines, old smelting sites and buried tailings can still pollute downstream areas through rainwater leaching and surface runoff. The study on the distribution and relationship of heavy metals in sediments and suspended particulate matter(SPM) along rivers in abandoned mines has important significance. OBJECTIVES: To preliminarily investigate heavy metals in river sediments and SPM in Wanshan Mercury Mines, and provide basic information for monitoring and remediation of contaminated cultivated land. METHODS: The contents of Cr, Ni, Cu, Cd, Pb, As, Hg, Zn and Co in sediments and SPM samples were determined by Inductively Coupled Plasma-Mass Spectrometry(ICP-MS) and Atomic Fluorescence Spectrometry(AFS) with wet digestion pretreatment. The pollution status and spatial distribution characteristics were identified in order to obtain information of pollutant migration and diffusion downstream. RESULTS: The total mercury content(Hg) in sediments ranged from 0.10 to 16.0μg/g(dry weight), averaging 5.79μg/g, which was ten times higher than the Hg limit of the Class Ⅱ soil environmental quality standard of China. The average contents of Ni, Cu and Co were not higher than the standard. The variation coefficients of Hg and Cd were large, indicating the heterogeneously spatial distribution of Hg and Cd. Mercury in sediments reached a high potential ecological risk level. CONCLUSIONS: The Hg in sediments and SPM in the study area are related to the hydrodynamic conditions, and the maximum values occurred at the sites with broad river channel and low flow rate. As the mining and smelting of Wanshan Mercury Mine has been stopped for a long time, the weathering and leaching of the abandoned mining area under natural conditions will cause Hg and Cd pollution in the lower reaches of the river.