Abstract

The study assessed the physicochemical parameters of the water and concentrations of

Cd, Co, Cr, Cu, Pb and Zn in the water, sediments and organs (bones, brain and flesh) of

Clarias gariepinus, Oreochromis niloticus and Synodontis nigrita obtained from River

Niger, River Benue (close to their confluence) and after the confluence point at Lokoja,

Nigeria during the months of March, June, September and December 2013. By using

standard procedures, the chemical oxygen demand, dissolved oxygen, turbidity,

biological oxygen demand, total dissolved solids, total hardness, conductivity and pH of

the water were determined. The ranges of these parameters were 98.25 - 141.73 mg/L,

2.26 - 14.39 mg/L, 5.33 - 23.13 NTU, 5.56 - 15.59 mg/L, 457.91 - 781 mg/L, 48.85 -

245.83 mg/L, 65.61 - 233.39 µs/cm and 6.77 - 8.07 respectively. All the parameters were

above the acceptable limits set by World Health Organisation (WHO), except pH. The

concentrations (mg/L) of Cd, Co, Cr, Cu, Pb and Zn in the water samples were in the

range of 0.0082 - 0.0276, 0.0042 - 0.0279, 0.0480 - 0.1391, 0.0979 - 1.8037, 0.0003 -

0.0047 and 0.7671 - 2.8510 respectively. Only Pb and Zn were in levels within the

permissible limit set by WHO and the concentrations recorded between the rivers and

across sampling periods were significantly different. The concentrations of Cd, Co, Cr,

Cu, Pb and Zn in the sediments were in the range of 0.2026 - 2.0203, 2.1567 - 20.5421,

13.1767 - 33.0976, 7.0832 - 23.4040, 0.1054 - 2.5593 and 12.9263 - 32.8418 mg/kg

respectively. The mean concentration of Cd in the sediment was above the ISQG (Interim

Freshwater Standard Quality Guidelines) limit of 0.6000 mg/kg. The pollution load index

for the heavy metals indicates low to moderate pollution state of the sediments while the

geoaccumulation index for Cd, Co, Cr, Cu, Pb and Zn also suggest low to moderate

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