Assessment of Selected Metals and Polycyclic Aromatic Hydrocarbons in the Gills and Muscles of Oreochromis Niloticus from Oyorokoto River, Andoni, Rivers State, Nigeria

Abstract

Aquatic organisms such as tilapia fish are broadly consumed due to their nutritional value; however, their tendency to bioaccumulate environmental contaminants raises serious food safety concerns. This study investigated the metal and polycyclic aromatic hydrocarbon (PAH) concentrations in the muscles and gills of tilapia (Oreochromis sp.) obtained from the Oyorokoto River (n=18). Fish samples were collected from local fishermen, rinsed, placed in pre-cleaned polyethylene bags, and oven-dried prior to laboratory analysis. Selected metals and PAHs were quantified using atomic absorption spectrophotometry and gas chromatography-mass spectrometry, respectively. In the gills, the concentrations (mg/kg wet weight) of copper (187.05± 1.12), iron (160.75 ± 2.84), lead (284.00 ± 3.15), chromium (146.35 ± 1.06), nickel (69.55 ± 1.42), cadmium (97.65 ± 0.88), and zinc (275.10 ±1.75) exceeded WHO permissible limits, except magnesium (351.00 ± 0.00), which remained within guideline values. In the muscles, copper (58.75 ± 0.94), lead (128.00 ± 2.06), chromium (36.95 ± 0.78), nickel (32.95 ± 1.25), cadmium (98.00 ± 1.14), and zinc (186.71 ± 1.52) also exceeded permissible limits, whereas iron (59.75±0.00) and magnesium (308.55 ± 0.00) were within acceptable ranges. Sixteen PAHs were detected, including carcinogenic compounds. Phenanthrene showed the lowest concentration (0.03 ± 0.01 ppm), while chrysene recorded the highest (0.36 ± 0.04 ppm), and all PAH concentrations surpassed WHO guideline values. The findings reveal significant contamination and bioaccumulation of toxic metals and PAHs in tilapia from the Oyorokoto River, indicating they are unsafe for human consumption. These contaminants pose substantial public health risks, including metal poisoning and elevated cancer risk. Immediate environmental remediation and targeted public health interventions are strongly recommended.