ASSESSMENT OF HEAVY METALS, PHYSICOCHEMICAL PROPERTIES IN WATER AND PROXIMATE COMPOSITION OF FISH FROM OYAN AND ASEJIRE DAMS.

The bioaccumulation of nutrients and contaminants in fish and water indicates environmental conditions and seasonal changes that directly affects food quality and public health. This study evaluated seasonal changes in water quality and heavy metal contamination in Oyan and Asejire Dams, Nigeria, focusing on environmental health and food safety. Water and fish samples (tilapia from Oyan, catfish from Asejire) were collected in wet and dry seasons and analyzed for physicochemical parameters (pH, EC, TDS, alkalinity, hardness), nutrients (nitrate, phosphate, sulfate), proximate composition (protein, ash, fat, moisture and carbohydrate) and selected heavy metals using standard methods. Statistical tools (descriptive stats, Pearson correlations, PCA) were used to interpret results. Marked seasonal differences were observed. Oyan Dam was acidic in the wet season (mean pH 5.66), with high nitrate (up to 39.26 mg/L) and phosphate (mean 1.01 mg/L), while dry season pH rose to 7.87. Asejire Dam had higher ionic strength and elevated nitrate (mean 13.8 mg/L) in the dry season. Notably, iron levels in Oyan’s wet-season water (mean 2.60 mg/L; max 10.38 mg/L) exceeded safety guidelines, though other metal concentrations remained low. Fish showed substantial protein, ash, and lipid contents, though clarification is needed on whether values are wet or dry weight. Most heavy metal residues in fish were within safe limits, except for lead in wet season tilapia (0.215 mg/kg), which exceeded FAO’s 0.2 mg/kg limit but stayed below WHO’s 0.5 mg/kg guideline. The study emphasizes the role of seasonal variation in influencing nutrient levels and metal bioaccumulation, highlighting the need for ongoing monitoring, pollution source control, and ecological risk assessments to protect aquatic life and public health.

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Proximate composition, Oyan Dam, Asejire Dam, Bioaccumulation, Biomagnification, Metals.

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This research holds significant local relevance for both environmental management and public health within Ogun and Oyo States, Nigeria. The Oyan and Asejire dams serve as key sources of water supply, aquaculture, and livelihood for surrounding communities. By assessing heavy metal concentrations and the nutritional quality of fish, this study provides valuable information on the safety of fish consumed locally, helping to protect residents from potential toxic metal exposure — especially lead, which was found to approach unsafe levels during the dry season. The findings can guide local regulatory agencies such as the Ogun and Oyo State Environmental Protection Agencies, as well as NAFDAC and SON, in setting or enforcing limits for fish safety and water pollution control. Furthermore, the data can assist local fish farmers and fishermen in adopting better water management and pollution-prevention practices. Beyond health and environmental protection, the research also contributes to food security and economic stability by ensuring that fish from these dams remain a safe, nutritious, and marketable protein source for the local population.

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