澜沧江河床沉积物重金属污染评价

河床沉积物是河流水体与泥沙环境中重金属的主要积存载体,能反映水环境的重金属污染状况。本文选取澜沧江为对象,通过对澜沧江干流西藏和云南境内22个河段的河床沉积物重金属测定分析,得到了8种主要的重金属元素(Cr、Mn、Ni、Zn、As、Pb、Cu和Co)的含量,并采用沉积物富集系数法与地质积累指数法分别对所测得沉积物的重金属污染程度进行了评价。结果表明:①澜沧江干流大部分河段污染情况并不明显,但在中游的旧州和功果桥河段,因该区域的地质金属背景值和支流沘江流域铅锌矿开采,地表的重金属元素被雨水冲刷到该河段,导致沉积物重金属富集现象明显,出现了轻度到较强度污染;②澜沧江流域受人为干扰的区域集中于中游与下游,部分河段(功果桥附近)Cu、Pb和Zn等元素呈轻度或偏中度污染;③大坝对河流的阻隔效应使得干流沉积物重金属污染呈现片段化分布,河流沿岸城市化等人类活动对附近河段沉积物重金属污染状况也有较明显的影响。

Assessment of heavy metal pollution of bed sediment in the Lancang River

Bed sediment is the main carrier of heavy metals in rivers. Its heavy metal content is an important indicator of heavy metal pollution in the water environment. This study investigates heavy metal contents of bed sediments along the mainstream of the Lancang River in Yunnan and Tibet and assesses their pollution risks. In recent years, the accumulation of heavy metals in the aquatic system of the Lancang River has become a problem. With increasing industrialization of the region, water quality of the Lancang River is in general declining and sediments in many river segments contain a high concentration of heavy metals that is higher than the background values. As an international river, Lancang river's water quality affects the relationship of the riparian countries. This article focuses on the following three aspects of heavy metal pollution in the river: the distribution of heavy metals in the sediments of the river basin; the enrichment factors of heavy metal pollutants at the sampling sites along the main river stream; and geoaccumulation of heavy metals in bed sediments. This study uses 22 sediment samples collected from different control sites in the river basin. These samples were analyzed using X-ray fluorescence (XRF) analysis at the laboratory of Yunnan University for the content of eight heavy metals (Cr. Mn, Ni, Zn, As, Pb, Cu, and Co). Background values of these heavy metals used in the assessment of river sediment pollution came from the database of background of elements in soils of China. Two assessment methods (sediment enrichment factor and geoaccumulation index) were employed to evaluate the severity of contamination of various heavy metals in the river. The results of these assessments show that (1) the average concentration of the heavy metals in most parts of the main river stream is at the safe level, but the concentration is high in the middle reach of the river between Jiuzhou and Gongguo Bridge, due to the high geological background and Zn-Pb mining in the Bijiang River basin; (2) the result of sediment enrichment factor analysis indicates that anthropogenic influences concentrate mainly in the middle and lower reaches of the river. Geoaccumulation index analysis also shows that Cu, Pb, Zn contents of the sediments are higher in the transitional area between the middle and lower reaches of the river; (3) dams block the transportation of sediments and make heavy metal pollution of sediments discontinuous along the river. Human activities such as urbanizaion also have a clear impact on the heavy metal pollution of the nearby river sediments. Urban development, mining, and dam building have played a significant role in heavy metal pollution of the Lancang River. A comprehensive investigation of heavy metal pollution should be performed in the middle reache area where the concentration of heavy metals is at a high level.