Heavy Metal Bioaccumulation and Histopathological Studies of Fish Tissues from Ose River, Ondo State, Nigeria

The exposure of the aquatic ecosystem to heavy metal from both natural and anthropogenic activities are on the rise and have harmful health effects on all aquatic organisms and human. This study assessed the concentrations of heavy metals (Fe, Pb, Cd, Cr, As and Zn) in surface water, sediments and fish tissues of Ose River and examined the histopathological changes of the tissues of two fish species (Mormyrus rume and Clarias garienpinus). Surface water, sediments and fish samples were collected and procured from Ose River in Ondo State, Nigeria from February to April 2021. Heavy metal digestions were done in the laboratory using HNO3/HCl while the concentrations were determined using Atomic Absorption Spectrometer. Histopathological alterations in the fish tissues were also assessed. Bioaccumulation factor (BAF), ecological risk index and potential ecological risk level were used to assess the investigated metal concentrations. In the surface water, the concentration of Cd (0.010–0.030 mg/l) and As (0.010–0.05 mg/l) exceeded the WHO limits of 0.01mg/l respectively while Fe, Pb, Cr and Zn were within the limits. In the sediments, all metals exceeded the limits except Pb and As. The concentrations of Pb (0.30±0.000–4.12±0.030 mg/l), Zn (9.970±0.010–30.77±0.023 mg/l), Cd (0.026±0.002–0.331±0.004 mg/l) and Cr (ND-0.331±0.004 mg/l) in the fish tissues were seen to be higher than the permissible limits of 0.5 mg/l, 5 mg/l, 0.005 mgl and 0.05-0.15 mg/l respectively. The BAF showed no probability. The alterations observed in the kidneys of the fish were cholestasis, necrosis, loss of glomeruli structure and tubular necrosis. While the gills showed congestion of the central veins and interlamellae hyperplasia caused by the presence of a monogenean parasite. The livers however revealed loss of hepatocytes nuclei, necrosis in hepatocytes and lymphocytic infiltrate. The study showed that the study site was polluted with heavy metals and may pose serious health issues to fishers, those using the water and people feeding on fish from the river. This study therefore suggests good indicators for bio-monitoring of heavy metals in Ose River. Seeing that the site was polluted with heavy metals hence, a more comprehensive assessment of the river is recommended.