Heavy metal discharge into Lake Victoria : a study of the Ugandan cities of Kampala, Jinja and Entebbe
Abstract: Water samples from different sampling sites located in the Ugandan cities of Kampala, Jinja and Entebbe as well as the remote Ssese Islands, were analyzed for concentrations of Cd, Cr, Cu, Ni, Pb and Zn. Both Kampala and Jinja have large industrial areas while Entebbe has Uganda's largest airport. Household and industrial wastes are discharged into Lake Victoria largely untreated. The objectives of this study were to: 1) evaluate concentrations of the metals in discharge from the selected sites; 2) determine whether or not wetlands impacted on the magnitude of metal discharge into the lake, 3) determine and assess heavy metal levels in drinking and irrigation water; 4) evaluate heavy metal related risks for humans and the environment. The discharges from the cities contained rather high concentrations of Cd, Cu, Pb and Zn in comparison with Swedish environmental guidelines. In Kampala and Jinja, samples were taken before and after water had passed through areas of wetland. The results show a reduction of these metals as the water passed through these areas. The reduction was especially noticeable in Kampala, where metal concentrations were reduced by up to 99%. The concentrations of all metals but Ni were alarming in Lugogo and Mpanga along Nakivubo channel (running through central and industrial areas in Kampala), these sites also being used for household farming. Some of the results from Jinja could be explained by the former Cu mine at Kilembe. The activity at the airport of Entebbe seemed to cause heavy metal pollution in nearby waters. Areas of special concern regarding the environment were all sites along Nakivubo channel, especially since the concentrations of Cd, Pb and Zn were high already at its emergence point in Makerere. In Jinja and Entebbe, all sites had Cd- and Zn concentrations exceeding the given guideline for sub-lethal or chronic effects. The expected result of lower concentrations in water outside Kalangala of Ssese Islands than outside Kampala, Jinja and Entebbe was not confirmed. The finding that the Ssese Islands had higher concentrations of Pb and Cr than 55% of the sampling sites in the cities was most surprising. Only 45% of the city sites had lower Cu concentrations than the Ssese Islands. The high concentration of Pb at Ssese Islands is alarming. The concentration was above the Swedish environmental guideline used, and there were no point sources of this metal on the island. Possible sources are therefore transport via air and/or water from the riparian countries as well as unauthorized dumping of wastes. The results from all sampling sites were compared with WHO's guidelines for drinking water. Only the Kampala sites Makerere, Lugogo and Mpanga exceeded the guidelines for Pb. Similarly, Cd and Ni concentrations at Makerere and Lugogo exceeded the guidelines. Concentrations of Pb and Cd were high at the majority of the sites. This is alarming since these metals are among the most hazardous to humans and the environment. Reduced discharge of the other metals is also important since low concentrations can accumulate and have negative longterm effects. The importance of wetlands as a purifying media must be recognized and protected. Efforts should also be put into limiting the sources of metals since treatment always means that it will end up somewhere else. Conversion to unleaded petrol as well as proper maintenance of dumping sites could lead to reduced metal leakage and decreased unlawful dumping in the lake. Implementation and enforcement of environmental legislation are most important.
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