Assessment of Heavy Metal Contamination and its Associated Human Health Risks in the Nun River, Bayelsa State, Nigeria

Abstract

Surface waters in the Niger Delta remain critical sources of domestic water supply but are increasingly degraded by anthropogenic contamination. This study assessed heavy-metal contamination in the Nun River, Bayelsa State, Nigeria, and evaluated associated human health risks. Surface water samples were collected from upstream, midstream, and downstream sections using a triplicate sampling design. Physicochemical parameters were measured in situ, while heavy-metal concentrations were determined following acid digestion using Atomic Absorption Spectrophotometry. Contamination levels and health risks were evaluated using contamination factors and USEPA-based exposure models. Results indicate slightly acidic to near-neutral water conditions, elevated turbidity, and reduced dissolved oxygen, reflecting organic and particulate loading. Aluminium and arsenic exceeded recommended guideline limits at several locations, while manganese approached permissible levels downstream. Contamination factor analysis identified arsenic and vanadium as the most critical pollutants, indicating considerable anthropogenic enrichment. Health risk assessment revealed significant non-carcinogenic risk to children from arsenic exposure, suggesting a high probability of adverse health effects under long-term consumption, while mercury posed a potential risk. Estimated carcinogenic risks for arsenic and mercury were within acceptable thresholds but consistently higher for children than adults. The heavy-metal contamination of the Nun River poses meaningful environmental and public health concerns, particularly for vulnerable populations. These findings highlight the urgent need for routine monitoring, exposure reduction strategies, and improved water resource management to protect river-dependent communities in the Niger Delta.