Concentrations of heavy metals and related trace elements in some Ethiopian rift-valley lakes and their in-flows

Concentrations of heavy metals commonly known to impact the environment and other related trace elements were quantified in the water bodies of nine Ethiopian rift-valley lakes and six rivers ( their inflows) as well as in effluents from two factories. In about half of the samples the concentrations of As was 10 - 700 mug l(-1) and Se, ranged from 10 to 28 mug l(-1), were much higher than the maximum permissible level (MPL) according to international standards for drinking water. Mercury ( Hg) was detected in four lakes and one river with high values ranging from 2 to 165 mug l(-1). Concentrations of Mo in three soda lakes were as high as 544 - 2590 mug l(-1). Iron (Fe) was found in high concentrations (567 - 4969 mug l(-1)) in three lakes, which are known to be discolored from inorganic colloids. Levels of Cd, Pb, and Cr ranged between 5 and 9, 12 and 20 and 104 and 121 mug l(-1), respectively. The rest of the heavy metals analyzed, Ba, Cu, Mn, Ni and Zn, were either not detected in the samples or were found in much lower concentrations than the MPL for drinking water. Effluent from a tannery contained about 15, 141, 523, and 19 mug l(-1) of As, Cr, Fe, and Se, respectively, and effluent from a textile factory contained high concentrations of As (10.6), Hg (3.8) and Se (20) mug l(-1). Compared to more industrialized regions and other African lakes the concentrations of heavy metals in Ethiopian rift-valley lakes ( with the exception of the soda lakes) and their inflows were low.