Heavy metal accumulation in catfish species (<i>Malapterurus electricus, Chrysichthys nigrodigitatus</i> and <i>Synodontis clarias</i>) inhabiting the Lekki Lagoon, Lagos, Nigeria

Abstract

The concentration of heavy metals; Lead, Nickel, Zinc and Iron in surface waters and sediment as well as in liver of catfish species; Malapterurus (=Erpetoichthys) electricus, Chrysichthys nigrodigitatus and Synodontis clarias collected from Lekki Lagoon were investigated. Heavy metal concentrations were determined in water, sediment, liver of fish species using Atomic Absorption Spectrophotometer. Higher concentrations of heavy metals were detected in sediment as compared to concentrations detected in surface water. The trend of metal concentrations in surface water was; Zn > Ni > Fe < Pb, and sediment was; Ni > Zn > Fe > Pb. M. electricus had the highest concentrations of hepatic lead, iron and nickel; Pb (0.98±0.79 mg kg^-1), Fe (24.54±55.07 mg kg^-1), Zn (6.83±8.20 mg kg^-1), Ni (3.42±6.26 mg kg^-1) as compared to the other species; S. clarias which had, Pb (0.02±0.04 mg kg^-1), Fe (0.61±0.21 mg kg^-1), Zn (0.38 ± 0.20 mg kg^-1), Ni (0.04±0.01 mg kg^-1) and C. nigrodigitatus which had the Pb (0.01±0.04 mg kg^-1), Fe (5.58±5.38 mg kg-1), Zn (29.81±25.10 mg kg^-1), Ni (0.68±0.75). S. clarias showed the lowest accumulation efficiency of heavy metals form surface water and sediment as compared to bio-accumulation factors recorded for M. electricus and C. nigrodigitatus. M. electricus and S. clarias had similar trend in hepatic metal concentrations; Fe > Zn > Ni > Pb while C. nigrodigitatus had; Zn > Fe > Ni > Pb. The difference in trend could be attributed to bioavailability, intrinsic fish processes, and trophic structure variation. Concentrations of the heavy metals analyzed in the edible fish species were above the safe limits recommended by FEPA and WHO (Pb, 0.01 mg kg-1, Ni, 0.02 mg kg^-1, Fe, 0.2 mg kg^-1, Zn, 3.0 mg kg^-1). Therefore measures should be taken to monitor the Lekki lagoon for heavy metals pollution. Use of multiple indicator species in bio-monitoring should be encouraged and M. electricus which has shown better bio-indicator capability according to results obtained from this study should be considered a preferred fish model in bio-monitoring program.