Tissue-Specific Bioaccumulation of Zinc, Lead, Copper, Cadmium and Manganese in Clarias gariepinus from Lake Alau, Northeastern Nigeria

Abstract

Heavy metal contamination of freshwater ecosystems poses significant ecological and public health concerns due to the persistence, toxicity, and bioaccumulative nature of these pollutants. This study investigated the tissue-specific bioaccumulation of zinc (Zn), lead (Pb), copper (Cu), cadmium (Cd), and manganese (Mn) in the gills, liver, and muscle tissues of Clarias gariepinus collected from Lake Alau, Borno State, Nigeria, between January 2025 and June 2026. Fish samples were obtained monthly from artisanal fishermen, and heavy metal concentrations were determined using Flame Atomic Absorption Spectrophotometry (FAAS) following acid digestion. The data were analyzed using descriptive statistics and one-way analysis of variance (ANOVA) at a significance level of P < 0.05. Results revealed significant tissue-specific variations in metal accumulation, with the liver recording the highest concentrations, followed by the gills and muscles (Liver > Gills > Muscle). The overall order of metal abundance was Zn > Mn > Cu > Cd > Pb. Mean concentrations (mg kg⁻¹ wet weight) in liver tissues were Zn (0.49 ± 0.05), Pb (0.30 ± 0.03), Cu (0.45 ± 0.05), Cd (0.31 ± 0.03), and Mn (0.46 ± 0.05). Zinc was the predominant essential metal, whereas lead and cadmium concentrations in the edible muscle tissues exceeded the permissible limits recommended by WHO/FAO, indicating potential health risks associated with fish consumption. One-way ANOVA showed significant differences (P < 0.001) among tissues for all metals analyzed. The findings demonstrate that C. gariepinus is an effective bioindicator of heavy metal pollution in Lake Alau and suggest that anthropogenic activities within the lake catchment contribute to metal contamination. Continuous environmental monitoring and effective pollution control measures are therefore recommended to safeguard aquatic ecosystem health and protect consumers from heavy metal exposure.