Geochemical distribution of arsenic, antimony and mercury in surface waters and bed sediments from Aq-Darreh river, Takab, northwest Iran

Aq-Darreh mining district is located in the Aq-Darreh River watershed. The water and river-bed sediments of this area are much polluted due to the severe weathering and erosion of waste piles of Aq-Darreh Bala abandoned Sb mine and Aq-Darreh Au deposit. The concentration of As and Sb in water of Aq-Darreh River ranges from 3.2 to159 μg/l and 1.32 to 54.00 μg/l, respectively. Also the amount of As, Sb and Hg in the Aq-Darreh river-bed sediments ranges from 38.6 to 1087.4 mg/kg (As), 1.87 to 93 mg/kg (Sb) and 0.096 to 23.7 mg/kg (Hg). Detailed chemical analyses of water and bed sediments samples of Aq-Darreh River and its distributaries indicate that geochemical background of this area, and also mining activities are responsible for these high concentrations of toxic elements. According to the analytical results (As, Sb and Hg concentrations) and their comparison to world river average values, it is concluded that Aq-Darreh River is amongst the very polluted water bodies of the world.