Spatio-Temporal Assessment of Heavy Metal Contamination and Associated Human Health and Ecological Risks in the Ona River, Ibadan, Nigeria

Abstract

Freshwater rivers are critical for human livelihoods, agriculture, industry, and ecosystem services, yet they face increasing pressure from urbanization, industrialization, and agricultural runoff. The Ona River in Ibadan, Nigeria, serves multiple domestic, industrial, and ecological functions but is increasingly compromised by anthropogenic inputs, including industrial effluents, untreated sewage, and urban runoff. This study assessed spatio-temporal variations in heavy metal concentrations along the Ona River at three sampling stations during wet and dry seasons. Water samples were analyzed for potentially toxic elements (Fe, Zn, Cu, Cr, As, Cd, Ni, Pb, and Mn) using Atomic Absorption Spectrophotometry, and pollution indices (Geo-accumulation Index, Enrichment Factor, Contamination Factor, Pollution Load Index) and health risk assessments (carcinogenic and non-carcinogenic) were computed. Results indicated seasonal variations, with higher concentrations of Cr, Pb, Cd, and Ni during the dry season exceeding WHO and Nigerian drinking water standards at certain sites. Pollution indices and health risk metrics revealed moderate to high contamination levels, particularly near industrial and urban discharge points. The findings highlight significant ecological and public health risks, emphasizing the urgent need for targeted pollution management strategies to safeguard water quality and community well-being.