SPATIALLY RESOLVED COMPOSITE RADIOLOGICAL AND HEAVY METAL RISK ASSESSMENT AROUND THE ARIARIA MUNICIPAL WASTE DUMPSITE: BUFFER ZONE HAZARD MAPPING AND POPULATION EXPOSURE ANALYSIS IN NIGERIA

Municipal waste dumpsites in low- and middle-income countries are often unlined and poorly regulated, releasing a complex mixture of heavy metals and naturally occurring radionuclides into surrounding environments. Conventional risk assessments typically evaluate these hazards independently, thereby underestimating cumulative exposure and associated health risks. There is an urgent need for spatially explicit, integrated risk mapping approaches to inform effective intervention strategies. A field-based assessment was conducted around the ariaria dumpsite, Nigeria, using three concentric buffer zones (0–100 m, 100–300 m, and 300–500 m). Data collection included (i) in situ background ionizing radiation (BIR) measurements (n = 120) using a calibrated dosimeter, (ii) soil sampling (n = 45) for heavy metal analysis (Pb, Cd, Cr, As, Ni) via ICP-MS, and (iii) groundwater sampling (n = 15). Radiological indices (AEDE, ELCR) and toxicological indices (HQ, HI, CR) were computed. Spatial distributions were generated using ordinary kriging, and a Composite Risk Index (CRI = normalized AEDE + normalized HI + normalized CR) was developed. Population exposure was estimated through GIS-based overlay with high-resolution census data. BIR decreased from 0.21 µSv/h (0-100 m) to 0.09 µSv/h (300-500 m), while Pb concentrations declined from 85 mg/kg to 22 mg/kg, indicating consistent spatial attenuation. The CRI exceeded unity up to ~250 m from the dumpsite. Within the 0–100 m zone, approximately 1,250 residents are exposed to CRI > 1, corresponding to ELCR > 10⁻⁴ and HI >1. A significant spatial correlation between radiological and toxicological hazards (R² = 0.68, p < 0.01) suggests common waste sources. It was concluded that integrated spatial risk assessment reveals that single-hazard approaches underestimate environmental exposure. Similarly, the buffer zone framework provides actionable guidance for resettlement and remediation, while the composite mapping approach offers a transferable tool for global dumpsite risk evaluation.