Aspects of heavy metal pollution in Mwanza gulf of lake Victoria, Tanzania

The aim of this study was to investigate heavy metal concentrations in suspended particulate matter (SPM), sediment and fish tissues found in Mwanza Gulf in the Tanzania portion of Lake Victoria. Samples were analyzed for Cd, Cr, Cu, Pb, Hg and Zn by AAS. The highest concentrations (ppm) of Cd (0.2 ± 0.04), Cr (35.3 ± 6.5), Cu (3.0 ± 1.3), Pb (4.5 ± 0.7) and Zn (7.2 ± 1.7) were recorded in SPM sampled closer to the shore. Stations that were far from the shoreline had relatively low concentrations. The highest concentrations (ppm) for the sediment samples 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 metal concentrations in the sediment decreased with increasing distance from the shoreline except for Cd and Cr whose high 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 ± 2.1 ppm), Cr (12. 9 ± 1.0 ppm) and Hg (2.8 ± 0.8 ppm) were recorded at sampling stations that were adjacent to river mouths. Similarly, for SPM stations, which were within the urban area, had high concentrations of the analyzed heavy metals with the exception of Cu and Cd that showed high levels at stations adjacent to the river mouths and fish landing beaches respectively. The Friedman comparison test showed a significant difference in the concentration of heavy metals in SPM and sediment between the sampling areas as well as within a sampling area with increasing distance from the shoreline. Heavy metal concentration in fish tissues was highest in the liver, relatively low in gills and scales and lowest in muscle. Heavy metal concentrations in tissues of different size groups of fish were also statistically different. A positive correlation was found between the concentrations of some analyzed heavy metals in fish liver, muscle and sediment. This study shows that Mwanza Gulf of Lake Victoria is contaminated with heavy metals, these findings call for urgent measures to rectify the situation