Bioaccumulation of Metals in Clarias gariepinus from Earthen Ponds and Associated Human Health Risk in Effurun, Delta State, Nigeria

Abstract

In aquaculture systems, especially earthen ponds supplied by natural water bodies, fish are continuously exposed to fluctuating environmental conditions and potential pollutant inputs from surrounding anthropogenic activities. This study evaluated the bioaccumulation and human health risks associated with toxic metals in Clarias gariepinus cultured in earthen ponds in Effurun, Delta State, Nigeria. Fifteen fish were reared for six months, after which muscle tissues were analysed using inductively coupled plasma optical emission spectrometry (ICP-OES). Human health risk was assessed using established exposure models, including estimated daily intake (EDI), target hazard quotient (THQ), hazard index (HI), and carcinogenic risk (CR). Descriptive statistics, including mean, standard deviation, and range, were used to describe variability in metal concentrations. The toxic metals recorded in fish muscle included lead (0.1021 mg/kg), cadmium (0.0558 mg/kg), arsenic (0.0349 mg/kg), chromium (0.1462 mg/kg), nickel (0.0754 mg/kg), thallium (0.0246 mg/kg), antimony (0.0358 mg/kg), silver (0.0156 mg/kg), and beryllium (0.0032 mg/kg). Corresponding pond water concentrations ranged from 0.03 mg/L (Pb) to 0.32 mg/L (Cd), with several metals exceeding permissible environmental limits. Bioaccumulation factor (BAF) analysis showed elevated accumulation for lead (3.40), silver (1.56), chromium (1.33), antimony (1.19), and arsenic (1.16), whereas cadmium (0.17) and thallium (0.49) exhibited lower accumulation levels. BAF values for nickel and beryllium were not computed because their water concentrations were non-detectable. Human health risk assessment indicated estimated daily intake values ranging from 0.000001 to 0.000063 mg/kg/day. Hazard quotient values for lead (0.109393), chromium (0.062657), arsenic (0.049857), and cadmium (0.047829) remained below unity, indicating low non-carcinogenic risk. However, carcinogenic risk values for arsenic (2.2 × 10⁻⁵) and chromium (3.1 × 10⁻⁵) suggested potential long-term health concerns. The findings highlight the presence of toxic metals in aquaculture systems and their implications for food safety.