heavy metals in lake George,uganda,with relation to metal concentrations in tissues of common fish species.

摘要

The northern end of Lake George,Uganda,and its associated wetlands receive localized metal pollution from a former copper mine and tailings left after metal extraction.The aim of this study was to determine(i) whether the heavy metals are a threat to the major commercial fish species and (ii) whether consumption of the fish threatens human health.Concentrations of copper,zinc,cobalt and nickel in detrital sediments,plankton,and five fish species form sites in lake George,the Kazinga Chennel and lake Edward (which are inter-connected)were determiend using atomic absorption spectroscopy.The deterital sediments of Hamukungu Bay,Lake George,had average concnetrations (mug/g dry weight)of 96.3 zinc,270.4 copper,57.4 cobalt and 42.8 nickel.There were no significant differences between the Hamukungu Bay and the North lake George site of Bushatu:both receive inflows from the mining activities.Concnetrations of copper and zinc were signficantly higher than background values from the mining activities.Concentratons of copper and zinc were significantly higher than background with a gradient form the source of poluutionin northern lake George,along the Kazinga Channel to Lake Edward.The liver tissues of fish had markedly higher concentrations of copper and zinc than flesh.Concentrations of copperand nickel were relatively low.The highest mean concentrations of metals in liver tissue occured in oreochromis leucostictus(189.0mug/g Cu) and Bagrus docmac(187.5mug/g Zn)whilst the lowest occurred in Oreochromis niloticus(15.3mug/g and 78.2mug/g dry weight copper and zinc,respectively).Hwever,O.Niloticus contained the highest concentratiosn of cobalt (11.2mug/g) and nickel(3.8mug/g).Liver Somatic Indices(LSI) of the fish species from the dirrerent sites indicated a reductionfLSI in thosefish from the most contaminated zones of abnormalities linked to the heavy metal pollution.The flesh had only low concentrationsof metals;well withi international guidelines for consumptions.A personwould haveto consume 9 kg of fresh flesh of Clariassp.and 65 kg of O.leucostictus daily to exceedthe WHO recommended intake for copperand even more for other metals.Thisimplies that currently methal pollution in Lake george presents an ecological rather than a human health concern.