Spatial distribution of heavy metal concentrations and pollution assessment in the bed loads of the Lancang River System

Mining-induced heavy metal pollution in river system is one of the main environmental problems in the process of watershed development and resource utilization. This research investigated that the bed loads of the mainstream and its 11 tributaries in the Lancang River, aiming to examine the spatial distribution of heavy metal contents (Cu, As, Pb, Zn and Cr), as well as to assess the heavy metal contamination status with the methods of Single Factor Index and Potential Ecological Risk Index. The results are shown as follows: (1) Heavy metal contents in sediments present a decreasing trend from upstream to downstream of the Lancang River system, while the heavy metal contents contained in the tributaries' bed sands are distinctly different. (2) The results of Single Factor Index indicate that sands at the Jiuzhou are seriously contaminated by As and Pb due to their high regional geological background. The two tributaries, the Heihui and Mengjia rivers, have been heavily polluted by As and Cu respectively. Especially, the single factor indexes of Pb and As are the highest with massive pollution in the Bijiang River. The other sampling sites, except for a few heavy metal elements with moderate pollution, present a pollution-free status in the main stream and tributaries. (3) The results of Potential Ecological Risk Index suggest that potential ecological risk factors ( E i r ) of the mainstream at Jiuzhou with As and the Bijiang tributary with Pb are relatively high, while the values in the other samples are below 40, and risk indices for all the tributaries investigated are less than 150, so the potential ecological risk of heavy metals is significantly low. Thus this work devotes to inspect and evaluate the spatial distribution of heavy metals in the bed loads throughout the river system of the Lancang River, in association with analyses of the pollution sources of the main stream from tributaries. So our conclusions could provide a scientific reference for pollution control during the basin development.