Seasonal Dynamics of Heavy Metals in Water and Heterotisniloticus Organs from Lake Geriyo, Yola, Adamawa StateNigeria: Implications for Environmental and HumanHealth

Abstract

Seasonal fluctuations significantly influence heavy metal concentrations and bioaccumulation in
aquatic ecosystems. This study investigated the levels of Zn, Cu, Fe, and Mn in water and organs (gills
and muscle tissue) of H. niloticus from Lake Geriyo, northeastern Nigeria, across wet and dry seasons.
Monthly triplicate samples were collected from three sites between October 2017 and March 2019,
digested with HNO₃-HClO₄ mixture, and analysed by atomic absorption spectrophotometry. Results
revealed significantly higher Zn, Fe, and Mn concentrations in water during the wet season due to
surface runoff, while Cu levels were elevated in the dry season due to evaporative concentration (p <
0.05). In H. niloticus, dry-season accumulation of all four metals was higher in both gills and muscle
tissue, with gills showing greater concentrations than muscle. All measured concentrations remained
well below FAO/WHO permissible limits for water and fish, and Pb and Cd were not detected. Although
human health risk appears minimal, the consistent dry-season accumulation suggests potential sublethal effects on fish physiology. Continuous seasonal monitoring, catchment runoff management, and
predictive modelling are recommended to safeguard the lake’s fisheries and support Sustainable
Development Goals 3 and 6.