Estimation of Radiological Hazard in the Water of Okaba and Okobo Coalfields and their Environs in Ankpa, Kogi State, Nigeria

Abstract

This study evaluates the radiological hazard associated with natural radionuclides (238U, 232Th, and 40K) in water samples collected from the Okaba and Okobo coalfields and their environs in Ankpa, Kogi State, Nigeria. Water samples from various sources were analyzed, yielding activity concentrations of 238U from 44.23 to 172.62 Bq L⁻¹, 232Th from 21.66 to 99.20 Bq L⁻¹, and 40K from 101.72 to 987.24 Bq L⁻¹. These values were employed to compute the radium equivalent activity (Raeq), external (Hex) and internal (Hin) hazard indices, as well as the outdoor and indoor gamma dose rates. The mean Raeq value of 573.87 Bq L⁻¹ far exceeds the recommended safety threshold of 370 Bq L⁻¹, highlighting a significant radiological risk. Although the Hex values (ranging from 0.421 to 0.987) indicate that external gamma exposure may be within acceptable limits, the elevated indoor absorbed dose rates and annual effective dose equivalents for infants, children, and adults clearly surpass international safety guidelines. These findings suggest that the high radioactivity levels are influenced by geological heterogeneities, mining, and farming activities in the region. The study underscores the urgent need for enhanced regulatory oversight and continuous environmental monitoring to mitigate potential adverse health impacts due to long-term exposure to contaminated drinking water.