Anthropogenic drivers of pollutant presence and composition in first-order streams of the Ona River System, Ibadan, Nigeria

Urbanization exerts profound effects on freshwater quality, yet its influence in rapidly developing regions remains undercharacterized. This study assessed physicochemical parameters, heavy metals, and microplastic contamination across eight urban rivers in southwestern Nigeria while examining correlations with land-use indicators, including population density and built infrastructure. Results revealed significant spatial variation in pollutant concentrations, with Gege River exhibiting the highest levels of lead (2.13 mg L−1), cadmium (2.08 mg L−1), and arsenic (2.11 mg L−1). Microplastics were present at all sites, peaking at Alaro River (53 particles). Statistical analysis demonstrated strong positive correlations between heavy metals and urban development metrics (e.g., Cd and population, r = 0.760, p < 0.001), underscoring anthropogenic drivers of water pollution. Microplastic levels correlated moderately with population density and land use. These findings highlight the urgent need for integrated land and water management strategies in urban catchments to mitigate the impacts of unchecked development on aquatic ecosystems.