Evaluation of heavy metal pollution and its ecological risk in one river reach of a gold mine in Inner Mongolia, Northern China

Abstract

The spatial distribution characteristics of As, Cu, Hg, Pb, Zn and pH were analyzed by measuring the contents of several heavy metals in surface and profile sediment, in one river reach of a gold mine, Inner Mongolia. The results indicated that heavy metal pollution had less and less effect on river reach with the distance from the gold mine, and the effect nearly disappeared when falling into the Zhaosu River. In vertical profile, there was a trend that the contents of heavy metals gradually decreased with the depth increasing. The river reach in the gold mine was contaminated more seriously by As and Hg, for which As contents exceeded the national soil quality standard of grade III, and the contents of Cu, Pb and Zn all didn't exceed it. The evaluation results by Hakanaon risk index method indicated that the ecological risk for Hg and As were higher, reaching up to grade C, while the risk for Cu, Pb and Zn were low. The comprehensive ecological risk of heavy metals reached up to grade III in the junction of river and valley and near the mining site, while the grades were A and B in two sampling sites of Zhaosu River. It was believed that mining activities and adsorption by clay minerals were primary controls for ecological impact of As and Hg.