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The quality of water and sediments from a marginally-studied river was investigated with respect to As, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn
including their fractionation behavior and environmental risk. Samples were collected along the Kou River that flows across two districts in
the Manyara region of Tanzania. The leaching behavior of Fe was studied using sequential extraction fractionation and kinetics approach. The
Kou water failed to meet the irrigation, aquatic, and biological life standards with respect to one of more trace metallic elements (TMEs). Fe
concentration in the river water ranged from 4.1 to 5.38 mg/L, exceeding all the three standards. Six pollution indices were applied to assess
the contamination and ecological risks of the nine trace metallic elements in the sediments. Overall, the metals were found to moderately
contaminate the sediments. Cr, Fe, and Mn fell under the ‘severely polluted’ sediment quality class. Fe was the only metal that was found to
significantly pollute both the river water and sediments. The Fe fractions in the sediments were in the order of residuals.Fe-Mn bound.or ganic bound.carbonate bound.water soluble.ion exchangeable; 7.8% of the total Fe content was bioavailable with a low potential to leach
from the sediments. Under natural conditions, the sharpest release of the non-residual mobile fractions of Fe were identified to occur within
the first 24 hours with the maximum Fe leached being 0.14% on the 12th day. None of the metals in the sediments were found with a poten tial to pose ecological risk |
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