Abstract:
This study was conducted to assess heavy metal contamination (Hg, Fe, Ni, As, Mn, Pb, Cd, Zn)
in water and sediment samples from the Birim River in the Akyem Abuakwa Area. Water and
sediment samples were taken from ten different Sites within the Akyem Abuakwa area in
September 2015 (wet season) and January 2016 (dry season). Heavy metal concentrations were
determined using atomic absorption spectrophotometer (AAS) equipped with cold vapour
(CVAAS) for total mercury. In the wet season, mean concentrations of heavy metals in the water
samples were 0.47 µg/L (Hg), 1.75 mg/L(Fe), 0.03 mg/L (Ni), 0.01 mg/L (As) , 0.40 mg/L (Mn),
0.02 mg/L (Pb), 0.02 mg/L (Cd) and 0.18 mg/L (Zn) while in the dry season, the mean
concentrations were 0.34 µg/L (Hg), 1.28 mg/L (Fe), 0.05 mg/L (Ni), 0.01 mg/L (As) , 0.44 mg/L
(Mn), 0.01 mg/L (Pb), 0.01 mg/L (Cd) and 0.38 mg/L (Zn). Levels of heavy metals (As, Ni, Pb,)
were below the WHO guideline values for drinking water while metals such as (Hg, Mn, Fe, Cd)
were all above the EPA and WHO recommended safety guideline limit for drinking water. All the
metal concentrations in the sediment were higher than that of the water samples in both dry and
wet seasons. The concentrations of all the metals studied were below USEPA guideline values.
Results of Pollution Indices computed namely, contamination factors (Cf), Geo-Accumulation
Index (I-Geo) Pollution load Index showed no pollution for all metals studied except mercury and
iron which showed moderate pollution. There was no correlation between the pH and heavy
metals in the water samples. However the metal concentrations in the river sediments showed a
significant difference with pH.
Ions in the water (K+, Na+, SO42-, PO43- and NO3-) showed seasonal variations. Also physic-
chemical parameters such as total dissolved solids, total suspended solids, total alkalinity, total
hardness, electrical conductivity and temperature showed seasonal variations in their
concentration levels. The high levels of metals such as Mn, Fe, Cd and Hg indicates that artisanal
gold mining has adverse impact on the Birim River.
Keywords: Birim River, water, sediment, heavy metals, seasonal variation, Contamination
factors, Geo- Accumulation Index, Pollution load Index
