Toxic Metal Residues in Gills and Muscles of Freshwater Fishes: Implications for Chronic Noncarcinogenic Risk Assessment

Abstract

We determined the concentrations of metals in gills and muscles of fish species from Ezu River and associated noncarcinogenic risk from the exposure. The following fish species; Clarias gariepinus, Trachurus trachurus, Parachana africana and Heterotis niloticus were collected from potential contamination hotspots of the river and analysed for zinc (Zn), arsenic (As), mercury (Hg), copper (Cu), cadmium (Cd) and lead (Pb). Concentrations of the metals ranged between Cu: 0.01-0.03 mg kg^-1, Cd: 0.02-0.12 mg kg^-1, Zn: 0.13-0.22 mg kg^-1, Hg: 0.02-0.07 mg kg^-1, As: 0.02-0.25 mg kg^-1, and Pb: 0.01-0.03 mg kg^-1, and Cu: 0.01-0.02 mg kg^-1, Cd: 0.02-0.2 mg kg^-1, Zn: 0.10-0.27 mg kg^-1, Hg: 0.01-0.07 mg kg^-1, As: 0.08-0.45 mg kg^-1 and Pb: 0.01-0.02 mg kg^-1 in gills and muscles, respectively. Zn and As were higher in the muscles and gills of the sampled fish species. Concentrations of Cu, Hg Cd, and Pb appeared similar in both the gills and muscles. Metal concentration gradient across hotspots was evident in all the sections of the river. Ugbenu and Ugbene had high concentrations of Zn and As with the concentration of As being above limit by the Codex (FAO/WHO). The noncarcinogenic risk evaluation showed negligible effects from oral exposure to the metals examined. While the risk of health impact from oral exposure is negligible under the conditions of current study, the elevated levels of the heavy metals in the examined fish species are indicative of metal enrichment of the river and thus call for a regulatory control to safeguard the aquatic resources of the river.