Prof. M. O. Omoigberale

Microplastics have become an emerging pollutant of concern in aquatic environments due to their persistence, potential toxicity, and ability to bioaccumulate in aquatic organisms. However, limited information exists on the extent of microplastics contamination in Nigerian freshwater systems, especially in the Ovia River. This study aims to assess microplastics contamination in surface water and some fish species (Notoptera's afar and Heterotriches BI dorsalis) of the Ovia River in Benin City, Nigeria, with the goal of determining pollution levels, potential sources, and associated health risks. Data were generated through the collection of water and fish samples from four stations along the river from January to June, 2024. Physicochemical parameters of the water were measured using standard procedures, and microplastics were extracted from both water and fish digestive tracts using density separation and wet peroxide oxidation methods. Polymer types were identified using Fourier Transform Infrared Spectroscopy (FTIR), while elemental composition was analyzed using Energy Dispersive X-ray Spectroscopy (EDX). Particle size distribution was examined using Scanning Electron Microscopy (SEM), and ImageJ software was used for image analysis. Pollution indices such as Water Quality Index (WQI), Contamination Factor (CF), and Carcinogenic and Non-carcinogenic Risk Indices (CDI, HQ, HI, CR) were also applied. The analysis of physicochemical parameters in the Ovia River revealed generally acceptable
levels with no significant differences (P > 0.05) across the study stations, except for copper, chromium, and manganese which showed significant variation (P < 0.05). Heavy metal concentrations were ranked: Fe > Zn > Cr > Cu >Mn > Ni > Pb, while arsenic and vanadium were below detection limits. Water Quality Index (WQI) and Comprehensive Pollution Index (CPI) classified Station 1 as having good water quality, while others were rated poor. Health risk assessment using Chronic Daily Intake (CDI) identified iron as the most prominent exposure risk. SEM revealed spatial variation in microplastic particle sizes in both water and fish, with the
highest mean sizes observed in station 2 and in Notoptera's afar respectively. Polymer analysis identified polyvinyl alcohol and nylon as the dominant microplastics in surface water, while LDPE (Low-density polyethylene) and polypropylene were most prevalent in fish samples. However, Heterotriches BI dorsalis exhibited a more diverse and complex microplastics polymer profile, indicating greater ingestion and exposure compared to Notoptera's afar. The xxii elemental composition in water and fish samples 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 fish, necessitating urgent environmental management strategies. xxiv