Investigating the contamination of soils and water by cyanide and mercury in mining :

Abstract

Physico-chemical quality of ground and surface waters from Tiira mines and its environs was conducted between January, 2017 and April, 2017. This study was undertaken to determine whether physical, chemical and trace metal contamination of water sources in Tiira mines is as a result of mining or geochemical and biochemical processes within the environment. Levels of trace metals (mercury) physical parameters (pH, Total Dissolved Solids (TDS), E-C and Temperature) and chemical parameters (Alkalinity, and CN) in water resources were determined. Water samples were collected from 8 sampling points including stream, 2 boreholes and 2 hands dug wells for water quality tests. The results showed that groundwater (pH range 5.70-7.44) was slightly acidic (low pH) compared to surface water (pH range 6.60 - 7.80 pH units). Groundwater electrical conductivity ranged from 350 to 857 NS/cm whereas that of surface water ranged from 451 to 777 PS/cm. Mining contaminants detected in water samples in this study were As (ranging from values <0.0001 to 0.0027 mg/l), CN (minimum and maximum) concentrations of 0.0001 and 0.0026 mg/l respectively).the relationship chemical and physical parameters in ground and surface water showed that there was a strong negative correlation (r = - 0.911) with significance between TI)S concentration and temperature in groundwater samples. A weak positive correlation (r = 0.124) was however observed between these variables in surface water samples. The correlation matrix showed a significant correlation (r =-0.866) for TDS and Temperature concentrations in groundwater samples. TDS and Temperature concentrations in surface water exhibited a moderate positive correlation with no significance (r =- 0.309).PH and CN concentration in surface water correlated negatively with significance (r -0.325) implying both variables decreased together. Water and sediment samples of the River were analyzed for various parameters and compared with Environmental Protection Agency (EPA) and WHO permissible guidelines for drinking water. The water quality parameters included PH, EC Total Dissolved Solids (TDS), Total Suspended Solids (TSS), temperature, Total suspended solids (TSS) True Colour, CN and Hg concentrations. Metals (such as Mercury) in the water samples and the river sediments were determined using atomic absorption spectrophotometer (AAS) using AAS 220 model. The result of the study revealed that, the mean values for true colour and total suspended solids of the river water at the various sampling sites exceeded EPA permissible level for drinking water. However, pH, total dissolved solid and E.C were below acceptable levels. The concentrations of CN and Hg recorded in the River water and sediments were also below EPA and WHO standards, rendering the water unsafe for domestic use. The study revealed that Small Scale Mining activities in the area have impacted on the water quality of River Namukobe and the soils in the mining concession considering the higher levels of True colour, Total Suspended cyanide and Mercury which exceeded the EPA and WHO Levels at the leachate points.