Seasonal Dynamics of Heavy Metals in Water and Clarias gariepinus Organs from Lake Geriyo: Implications for Environmental and Human Health

Abstract

Freshwater ecosystems worldwide are contaminated by heavy metals from industrial, agricultural, and domestic activities, which threaten aquatic biodiversity and human health through bioaccumulation in fish. Lake Geriyo, a key reservoir in northeastern Nigeria, supports local fisheries and irrigation but is exposed to anthropogenic pollutants. This study examined seasonal dynamics of zinc (Zn), copper (Cu), iron (Fe), and manganese (Mn) in lake water and organs (gills and muscle tissue) of the catfish Clarias gariepinus from October 2017 to March 2019. Triplicate samples were collected monthly from three sites (lower: Station A; upper: Station B; middle: Station C) during wet (May–October) and dry (November–April) seasons. Water and tissue samples were digested with HNO₃-HClO₄ and analyzed using atomic absorption spectrophotometry. In water, Fe concentrations were highest in the wet season (6.07 ± 1.74 mg/l), exceeding the FAO/WHO (2011) limit of 0.3 mg/l, while Zn (0.11 ± 0.12 mg/l wet; 0.06 ± 0.08 mg/l dry), Cu (0.03 ± 0.02 mg/l wet; 0.11 ± 0.31 mg/l dry), and Mn (0.08 ± 0.03 mg/l wet; 0.02 ± 0.02 mg/l dry) remained compliant. In C. gariepinus gills and muscle, all metals were below Codex limits (Zn: 50 mg/kg; Cu: 30 mg/kg; Fe: 100 mg/kg; Mn: 0.5 mg/kg), with dry season levels generally higher than wet season levels (e.g., Zn in gills: 0.76 ± 0.56 mg/kg dry compared to 0.40 ± 0.57 mg/kg wet). No significant spatial variations occurred (p > 0.05). These findings indicate low human health risks from fish consumption but highlight seasonal Fe enrichment in aquatic environments, which may cause ecological stress. Recommendations include runoff management and regular monitoring to safeguard environmental and public health, aligning with SDGs 3 and 6.