Radiological Risk Assessment and Groundwater Vulnerability from Municipal Solid-Waste Dumpsites in Uyo and Eket, Akwa Ibom State, Nigeria

Abstract

Open municipal solid-waste (MSW) dumpsites in Uyo and Eket, Akwa Ibom State, southeastern Nigeria, constitute long-term sources of chronic low-level radiological exposure through the accumulation of naturally occurring radioactive materials (NORMs) and technologically enhanced NORMs (TENORMs). This study integrates in situ gamma surveys, laboratory gamma spectrometry, radiological hazard-index calculations, a detailed assessment of NORM sources in the waste stream, and analysis of leachate radionuclide migration to evaluate health risks and groundwater vulnerability within the highly permeable Benin Formation. Field dose rates ranged from 0.18–0.45 µSv h⁻¹ at Eket and 0.10–0.54 µSv h⁻¹ at Uyo, both substantially above local background (≈0.03–0.04 µSv h⁻¹). Laboratory analysis of solid waste samples yielded activity concentrations of ⁴⁰K (211–546 Bq kg⁻¹), ²³⁸U (6–38 Bq kg⁻¹) and ²³²Th (9–22 Bq kg⁻¹). Principal NORM/TENORM sources identified include construction debris (especially asphalt and ceramics), electronic waste, ash from open burning, medical residues and residual fertilisers. Absorbed dose rates, annual effective doses (AED) and excess lifetime cancer risk (ELCR) were computed using UNSCEAR and ICRP conversion factors. Although most indices remain below thresholds for acute hazard, the persistent elevation above background, combined with shallow unconfined aquifers, high rainfall (>2 000 mm a⁻¹), absence of engineered liners and documented leachate plumes, creates a realistic pathway for radionuclide migration into groundwater. Site-specific contrasts show more localised anomalies at Eket and broader diffuse enhancement at Uyo. The findings provide essential baseline data for radiological protection, groundwater safeguarding and evidence-based waste-management policy in the Niger Delta.