Heavy Metal Bioaccumulation and Health Risk Assessment of Nile Tilapia in the Hadejia-Nguru Wetlands, Nigeria

Abstract

The Hadejia-Nguru Wetlands, a vital but ecologically sensitive ecosystem in northeastern Nigeria, is increasingly threatened by anthropogenic activities. This study assessed the bioaccumulation of copper (Cu) and lithium (Li) in water and the economically important fish species, Nile Tilapia (Oreochromis niloticus), to evaluate potential risks to aquatic biota and human consumers. Water and fish (n=96) samples were collected bi-weekly over an eight-week period (March–April 2024) from three distinct sites (Dogon-kuka, Garbi, and Gada). Physico-chemical parameters (temperature, pH, dissolved oxygen) were measured in situ. Metal concentrations in water, fish muscle, and gill tissues were determined using Atomic Absorption Spectroscopy (AAS) after acid digestion. Data were analyzed using one-way ANOVA. Physico-chemical parameters were stable across sites, with no significant differences (P > 0.05). However, mean copper concentration in water from Garbi (1.13 ± 0.10 mg/L) exceeded the WHO permissible limit of 1.0 mg/L. Bioaccumulation patterns were tissue- and site-specific. The highest copper concentration in fish muscle was recorded at Gada (21.85 ± 0.74 mg/kg), while the gills showed the highest accumulation at Garbi (36.9 ± 11.3 mg/kg). Both values significantly exceeded (P < 0.05) the WHO/FEPA recommended limit of 2.0 mg/kg for human consumption. Lithium levels in fish tissues were below the WHO limit (1.0 mg/kg), though measurable accumulation was observed. This study reveals significant copper contamination in the edible muscle of O. niloticus from the Hadejia-Nguru Wetlands, posing a substantial public health risk. These findings underscore the critical need for continuous environmental monitoring and the implementation of stringent pollution control policies to protect both the wetland ecosystem and the health of communities reliant on it.