Pollution level of toxic heavy metals (As, Hg, Pb, Cd and Cu) in well water and stream water in relation with traditional gold mining activities in Bero Woreda, Bench Maji Zone, Southwest Ethiopia

Abstract

The study was undertaken basically to assess the status of drinking water quality in relation with traditional gold mining activities at the gold mining areas of Bero Woreda, Bench Maji Zone, South West Ethiopia. Prior to sampling deliberate observation was made & site specific data were taken from each site. A total of 6 water samples (4 well water samples & 2 stream water samples (for reference)) were collected in February, 2011 from 3 gold mining kebeles (Sholla, Gabissa & Seyali). Field measurements of water quality indicator parameters: Temperature (24–28 0C), pH (7.02–8.1), Electrical conductivity (927–1726 µS/cm) & Turbidity (28–230 NTU) were measured & TDS (593–1105 mg/l) was calculated from the measured EC value of the samples. All the samples were analyzed for the toxic heavy metals: As, Hg, Cd, Pb & Cu following the recommended standard procedures. The heavy metals (As & Hg) were analyzed using hydride AAS method & the heavy metals (Cd, Pb & Cu) & major cation (Ca2+ & Mg2+) were analyzed using Flame AAS method. From the analyses the following analytical results in (mg/l): As (0.00091–0.0031), Hg (0.00011– 0.00199), Cu (0.159) only at one well sample site, Pb & Cd below the detection limit (0.0001 mg/l) of the instrument, calcium (114.4 – 292.2) & magnesium (99.2–191.5) were obtained. The major ions in mg/l: sulphate (1.02–80), chloride (7.4–88.3) & bicarbonate (314.5–594.5) were obtained. As, Hg, SO4 2-, Cl- , pH & turbidity were found higher in stream water samples & also As, Hg, SO4 -2, Cl- , pH , HCO3 - , EC & turbidity were found higher in downstream than upstream water samples. The physicochemical parameters mercury, temperature, turbidity, electrical conductivity (EC), bicarbonate & TDS were found in 66.7%, 100%, 100%, 100%, 50% & 100% of the water samples in the study area respectively. These parameters were also found in 50%, 100%, 100%, 100%, 75% & 100% of the well water samples respectively higher than the WHO (1993), EU (1998) & ES (2001) recommended maximum desirable limits set for drinking water