Occurrence and distribution of microplastics in water, sediment, and aquatic insects of the Owena River, Osun state, Nigeria

Microplastic pollution in freshwater ecosystems poses a growing threat to biodiversity and human health. Microplastics (0.5-5 mm), derived from the degradation of larger plastics or manufactured as microbeads, can accumulate in aquatic organisms and serve as indicators of ecosystem health. This study investigated the abundance, shapes, and colors of microplastics in water, sediment, and aquatic insects from the Owena River, Osun State, Nigeria, to assess spatial trends and ecological implications. Monthly sampling was carried out between July 2024 and June 2025 across the up, middle, and down sections of the river. Aquatic insects were identified to order level, while microplastics were visually identified under a stereomicroscope without spectroscopic confirmation. Results revealed widespread microplastic contamination, with concentrations increasing from the up section towards the down section in both water and sediment. Fragments were the most abundant shape, and black particles dominated color composition. Hemiptera and Odonata were the most represented insect orders, indicating potential bioaccumulation pathways within the aquatic food web. This study provides the first report of microplastic occurrence in aquatic insects of the Owena River, Nigeria, and underscores the urgent need for improved plastic waste management to safeguard freshwater biodiversity and ecosystem health.