Oguttu, H.W.

National Agricultural Research Organisation (NARO), Fisheries Resources Research Institute (FIRRI), P.O. Box 343, Jinja, Uganda. E-mail:firi@infocom.co.ug

Sources and levels of heavy metal pollutants from Jinja Town into Napoleon Gulf, Lake Victoria and their potential impacts to aquatic resources

Heavy metal pollutants entering aquatic ecosystems from urban sources world over occur in low concentrations normally from nanogram to microgram per litre level. The paper highlights the results of a one-year study (1997/1998) of point sources in the industrial sector of Jinja Town. Industrial point sources were sampled based on a simple random methodology. Heavy metal effluents were collected at point source outflows using clean/sterilized syringes with a rope tied on a metal pipe for support or from discharge pipes using clean/sterilized water sample bottles. Samples were acid digested and taken on ice to Geology Department, Makerere University for Atomic Absorption Spectrophotometric analysis (AAS). A leather Industry (tannery), discharged a mean concentration of 264.4±27.7 mg l-1 of very highly toxic Chromium (VI) exceeding the maximum permissible effluent limits of 0.05 mg l-1 Chromium (VI) by approximately 5280 times. Two metallurgy point sources indicated high Chromium (VI) above maximum permissible limits with means of 0.15±0.01 mg l-1 and 0.26±0.01 mg l-1 from scrap and steel metal inputs respectively. Copper, Lead, Nickel, Cadmium and Manganese concentrations from municipal lagoon outflows, fish filleting and food processing plants were below maximum permissible limits. With time, these toxic heavy metals are likely to enter the food chain and bioaccumulate into other biota including fish. This may cause poisoning at higher trophic levels including serious cumulative effects to fish eating aquatic organisms. The study proposes efficient on-site pretreatment and monitoring of industrial effluents from "hot spots" to non-critical levels prior to final discharge through lagoons into Napoleon Gulf, Lake Victoria