Microplastics Contamination of Surface Water and Selected Fish Species in Ovia River, Southern Nigeria

This study examines microplastic contamination of surface water and two fish species (Notopterus afer and Heterobranchus bidorsalis) in Ovia River, Southern Nigeria, utilizing Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR), and Energy Dispersive X-ray Spectroscopy (EDX) to assess particle size distribution (PSD), polymer composition, and elemental contamination. The results showed that polyvinyl alcohol (PVA; 31%) and nylon (28%) were the dominant polymers in surface water. Other prominent polymers recorded were polypropylene (PP) and low-density polyethylene (LDPE), accounting for 5% each, with smaller amounts of polyethylene terephthalate (PET), cellophane, and polyurethane. In the fish species, the dominant polymers were LDPE (32%) and PP (31%), followed by PVA (16%), PET (16%), and cellophane (5%). However, H. bidorsalis exhibited a more diverse and complex microplastic polymer profile than N. afer. The SEM analysis of surface water and fish samples showed spatial variations in the mean microplastic particle size. The mean particle size in surface water samples was highest in station 2 (4.02 ± 4.25 µm), station 1 (3.60 ± 3.38 µm), station 4 (2.72 ± 2.20 µm), and station 3 (2.25 ± 2.21 µm), respectively. The fish species exhibited a similar trend for N. afer (3.11 ± 1.59 µm) and H. bidorsalis (3.07 ± 1.84 µm). The elemental composition using the energy-dispersive X-ray spectroscopy (EDX) in surface water and fish species identified Cl, N, Na, C, Ca, Mg, Si, P, K, Al, Fe, S, Ti, Ag, and Mn as additives to microplastics with high-intensity peaks of chlorine and carbon. Overall, the Ovia River ecosystem is moderately polluted with microplastics, and there is evidence of bioaccumulation in the two commonly consumed fish species.