Distribution of Heavy Metals In Sediments of Mwanza Gulf of Lake Victoria, Tanzania

Abstract

A study was conducted in February - April 2000 with the aim of determination of heavy metal concentrations in lake sediment at areas, which were considered as point- and non-point sources. A trend of heavy metal variation in sediment with increasing distance towards the lake from the point- and non-point sources was also investigated. Samples were analyzed for Cd, Cr, Cu, Pb, Hg and Zn by AAS. The highest concentrations (ppm) for Cu (26.1 ± 4.8), Hg (0.2 ± 0.05), Pb (30.7 ± 5.6) and Zn (45.4 ± 13.1) were found at approximately 25 m from the shoreline. Generally, heavy metals concentration in the sediment decreased with increasing distance from the point sources towards the lake except for Cd and Cr whose highest concentrations were found at approximately 2000 m from the shoreline. Sediment samples which were collected at the shores within the urban area of Mwanza showed elevated levels of Pb (54.6 ± 11.1 ppm) and Zn (83.7 ± 21.5 ppm). However, the highest concentrations of Cd (7.0 ± 0.2 ppm), Cr (12. 9 ± 1.0 ppm) and Hg (2.8 ± 0.8 ppm) were recorded at sampling stations, which were adjacent to river mouths. In this study, it was concluded that, urban areas contain high levels of heavy metals due to pollution generating activities, which are taking place in these areas. However, more researches on factors influencing the accumulation of heavy metals in the aquatic systems including the chemical make-up of the sampling stations are emphasized