Integrated Environmental Hazard and Human Health Risk Evaluation of Water Resources in the Okaba Coal Mining Region

Abstract

This study evaluated radiological contamination in water sources near the Okaba coal mining area, Ankpa, Kogi State, Nigeria. Twenty-four water samples were collected from streams, rivers, and boreholes adjacent to mining operations during October–December 2024. Activity concentrations of naturally occurring radionuclides (²³⁸U, ²³²Th, and ⁴⁰K) were determined using high-purity germanium (HPGe) gamma spectrometry. Measured ²³⁸U activities ranged from 44.24 ± 0.33 to 172.67 ± 2.39 Bq L⁻¹ (mean: 104.80 Bq L⁻¹), ²³²Th from 21.66 ± 0.03 to 99.20 ± 0.91 Bq L⁻¹ (mean: 51.49 Bq L⁻¹),  and ⁴⁰K from 101.72 ± 0.18 to 987.24 ± 4.32 Bq L⁻¹ (mean: 719.64 Bq L⁻¹). The mean radium equivalent activity  (573.87 Bq L⁻¹) exceeded recommended limits. Average outdoor and indoor absorbed dose rates (109.53 and  210.63 nGy h⁻¹) surpassed global reference values by factors of 1.86 and 2.51. Estimated annual effective ingestion  doses for infants, children, and adults (means: 6.88, 4.59, and 3.15 mSv y⁻¹) substantially exceeded WHO guidelines.  Excess lifetime cancer risk values ranged from 12.57 × 10⁻³ (adults) to 27.45 × 10⁻³ (infants), markedly above benchmarks. These results demonstrate that coal mining activities have significantly enhanced natural radioactivity in local water resources, necessitating immediate regulatory intervention.