Geochemical distribution of arsenic, antimony and mercury in surface waters and bedsediments from Aq-Darreh river and the impacts of mining activities on surface water qualityin Takab-NW Iran

Aq-Darreh mining district is located in the Aq-Darreh river watershed. The water and river-bedsediments of this area are very polluted due to the severe weathering and erosion of waste piles ofAq-Darreh Bala abandoned Sb mine and Aq-Darreh Au deposit. The concentration of As and Sb inwater of Aq-Darreh river ranges from 3.2 to159 μg/l and 1.32 to 54.00 μg/l respectively. Also theamount 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 differentrock units of Aq-Darreh river watershed and water and bed sediments samples of Aq-Darreh riverand its tributaries indicate that geochemical background of this area, and also mining activities areresponsible for these high concentrations of toxic elements. Based on mathematical calculations,the proportion of different sources of toxic elements in water samples, including naturalcontamination and anthropogenic sources are measured to be 5 % and 95 % for As and 87 % and13 % for Sb respectively. These proportions have also been calculated for the river-bed sedimentsas follows: 88 % and 12 % for As, 80 % and 20 % for Sb and 43 % and 57 % for Hg. According tothe analytical results (As, Sb and Hg concentrations) and their comparison to world river averagevalues it is concluded that Aq-Darreh river is amongst the very polluted water bodies of the world.

Keywords:

Environmental geochemistry , water pollution , river-bed sediment contamination , Aq- Darreh mining district , Takab , NW Iran