Assessment of Heavy Metal Concentrations in Water, Sediment and Water Hyacinth of the Inner Murchison Bay, Lake Victoria

Abstract

This study assessed heavy metal pollution in the Inner Murchison Bay within Lake Victoria region. The assessment was based on determination of concentrations of heavy metals in water, sediment and water hyacinth (Eichhornia crassipes). The Bay is the abstraction point of water supplied in Kampala City and metropolitan areas. It is also the recipient of partially treated and untreated wastewater from the City. There is a potential for continuous deterioration of the Bay’s water quality due to anthropogenic activities carried out in its catchment. Twelve sampling locations that are representative of the Bay were used to gather samples of water, sediment, and water hyacinth based on cross-sectional study. Atomic Absorption Spectrophotometer (AAS) analysis was performed on the samples to ascertain their lead (Pb), cadmium (Cd), and mercury (Hg) concentrations. Results showed that the concentration of Pb and Cd in water was above the permissible limits set by WHO and NEMA (Pb:0.01ppm and Cd:0.003) at all sites. In sediment, Pb was below the LEL (31.0) while Cd exceeded both the LEL (0.60) and TEL (0.99) signifying that the values of Pb and Cd were permissible as per the sediment assessment guidelines Contamination Factor and Pollution Load Index indicated moderate pollution of the sediment with Pb and Cd (CF>1, PLI>1). The values of Bio-concentration factor for water hyacinths were above 1 indicating that the plants were able to take up Pb and Cd from water. Mercury (Hg) was below the detectable levels in all the samples. Pb and Cd are from agricultural fertilizers, industrial effluent, urban runoff, wastewater effluent, navigation and recreational activities carried out in the catchment of the Bay. Evidence of concentration of heavy metals in water, sediment and water hyacinth indicates pollution of the Bay by heavy metals thus continuous monitoring of the Bay’s state is crucial. Key words: Inner Murchison Bay, Heavy Metals, Contamination Factor, Pollution Load Index, Water hyacinth, Bio-concentration Factor, Lowest Element Level (LEL), Threshold Element Level (TEL), Probable Effect Concentration (PEC) and Severe Effect Level (SEL)