Radon-222 Concentration, Exhalation Rates, And Health Risks in Okaba/Okobo Coal Mining Soils, Nigeria: Implications for Environmental Quality Management

Abstract

Radon-222, the second leading cause of lung cancer, is enhanced by mining activities. This study assessed radon concentrations, exhalation rates, and health risks in soils from the Okaba coal mining area in Nigeria. Forty composite samples from mining zones, residential areas, agricultural fields, and control sites were analyzed using a RAD7 detector and NaI(Tl) gamma spectrometry. Radon concentrations ranged from 52.3 to 912.6 Bq m⁻³ (mean: 338.7), with highest values in mine pits and waste dumps. Exhalation rates ranged from 3.2–36.9 Bq m⁻² h⁻¹ (mean: 15.3). Radium-226 ranged from 9.6–110.2 Bq kg⁻¹ (mean: 50.4). The mean annual effective dose was 8.53 mSv y⁻¹, exceeding the 1 mSv y⁻¹ ICRP limit. The excess lifetime cancer risk was 42.6 × 10⁻³. All samples exceeded the WHO action level (100 Bq m⁻³). Strong correlation existed between ²²⁶Ra and exhalation rates (r = 0.88). These findings support risk-based zoning and NORM-specific regulations