Assessment of Heavy Metal Contamination in Fish and Water from the Asa River, Kwara State

The Asa River in Kwara State, North Central Nigeria, receives wastewater from industrial, agricultural, and domestic sources that may elevate heavy metal concentrations in its water and aquatic fauna. This study assesses the concentrations of lead, cadmium, copper, zinc, and iron in water and selected fish species from three sampling stations along the Asa River in Ilorin. Water and fish tissue samples were collected monthly over six months during the dry season and analysed by atomic absorption spectrophotometry. Fish species sampled included Clarias gariepinus, Oreochromis niloticus, and Synodontis clarias, collected using gillnets from local fishers. Results showed that lead concentrations in surface water at Station 1, located near an industrial effluent discharge point, exceeded the WHO guideline of 0.01 mg/L in all sampling months. Cadmium was detected above acceptable limits in 40% of fish muscle tissue samples from the same station. Zinc and iron were within safe limits across all stations. The bioaccumulation factor for lead was highest in Clarias gariepinus, indicating a greater tissue accumulation tendency in this species. The study documents a spatial gradient in heavy metal contamination consistent with upstream industrial discharges and recommends regular biomonitoring of the Asa River fishery by the Kwara State Environmental Protection Agency to safeguard public health and aquatic ecosystem integrity.

Keywords: heavy metals, fish contamination, Asa River, bioaccumulation, Kwara State