Seasonal dynamics of microplastic pollution and trace element bioaccumulation in aquatic food webs of the Itu river, Nigeria

Microplastic pollution has emerged as a critical environmental issue because of its persistence, capacity to transport toxic contaminants, and potential risks to aquatic ecosystems and human health. This study investigated the seasonal dynamics of microplastic pollution and trace element bioaccumulation in aquatic food webs of the Itu river, Nigeria. Representative fish and shellfish samples, together with surface water, were collected during the wet and dry seasons. Microplastics were extracted using alkaline digestion and density separation, identified by stereomicroscopy, and polymer composition was confirmed using Fourier Transform Infrared Spectroscopy (FTIR-ATR). Heavy metal concentrations were determined by atomic absorption spectrophotometry, while bioconcentration factors (BCFs) were calculated to evaluate metal transfer from water to aquatic organisms. Microplastics were detected in all sampled species, with fibres and fragments being the dominant morphotypes. Wet-season samples generally exhibited greater microplastic abundance and polymer diversity than dry-season samples, reflecting enhanced hydrological transport during periods of increased rainfall. Polyethylene and polypropylene were the predominant polymers identified. Although cadmium, zinc, chromium, and mercury exhibited comparatively higher transfer factors than other metals, all calculated BCF values remained below 1000, indicating no evidence of significant bioaccumulation. Correlation and hierarchical cluster analyses revealed complex relationships between microplastic abundance and trace element concentrations, suggesting multiple contamination sources and transport pathways. These findings demonstrate that seasonal processes strongly influence microplastic distribution and associated trace element dynamics in the Itu River and underscore the need for improved waste management and long-term monitoring to safeguard aquatic ecosystems and seafood quality. .