Pollution assessment of the lower basin of Lakes Kainji/Jebba, Nigeria: heavy metal status of the waters, sediments and fishes.

The objective of this investigation was to examine the heavy metal status of the lower basin of Kainji dam (used for hydroelectricity generation), which includes Lakes Kainji/Jebba, Nigeria, and the potential for human exposure to heavy metals from eating fish caught in the lakes. Water, sediments and fish were sampled from the lakes and evaluated for As, Cu, Co, Cr, Fe, Hg, Mn, Ni, Pb, Sb, Ti, V and Zn using the EDXRF technique. Fe and Mn were found to be present at high mean concentrations in the water (13 and 9 microg L(-1)), sediment (7,092 and 376 microg g(-1)) and fish (11.4 and 4.6 microg g(-1)) samples. Sb (3.2 microg L(-1)), Ti (4.1 mug L(-1)), Cr (2.2 microg L(-1)), Co (1.2 microg L(-1)), Cu (1.3 microg L(-1)) and Pb (1.2 microg L(-1)) in the water samples and Sb (29 microg g(-1)), Ti (27 microg g(-1)), V (27 microg g(-1)), Cr (27 microg g(-1)), Co (40 microg g(-1)), Ni (33 microg g(-1)), Cu (25 microg g(-1)), Zn (59 microg g(-1)) and Pb (19 microg g(-1)) in the sediment samples were found to be of medium mean concentrations. The other metals were present at trace levels (<1 microg), including As and Hg in the fish and sediment samples. There was an appreciable increase in metal concentrations in going from the water to the sediment samples. The probable source of the pollutants is anthropogenic, arising from agricultural activities, corrosion/abrasion of the ferrous steel material and additives in the lubricants and insulation used for auxiliary services on the turbine floor of the dam constructed on the lakes. However, natural geological sourcing from the underlying lake rock cannot be totally ignored, particularly the high levels of Fe and Mn in the sediment samples. The potential risk for human exposure to these metals emanates from the fish caught in the lakes and subsequently consumed, as there are already significant levels of these metals in the two fish species analysed, Tilapia (Oreochromis niloticus) and Chrysicthys (Chrysicthys auratus).