Determination of radon-222 activity concentrations in groundwater sources at Felele campus, Federal University Lokoja, Kogi state, Nigeria

Abstract

This study investigates the activity concentrations of radon-222 in groundwater sources within Felele Campus, Federal University Lokoja, Kogi State, Nigeria, and evaluates the associated radiological health risks to the university community. Ten groundwater samples comprising five boreholes and five hand-dug wells were collected and analysed using a Packard Tri-Carb 1000TR liquid scintillation counter at the Centre for Energy Research and Training, Ahmadu Bello University, Zaria. The annual effective doses due to ingestion of radon-laden water were calculated for adult residents using established dose conversion factors, with a daily water intake of two litres per day explicitly assumed based on World Health Organization reference values. Radon concentrations in borehole water samples ranged from 11.02 to 15.51 Bq/L, with a mean of 13.96 plus or minus 2.16 Bq/L, and eighty per cent exceeding the United States Environmental Protection Agency maximum contaminant level of 11.1 Bq/L. Well water samples showed concentrations ranging from 7.48 to 11.14 Bq/L, with a mean of 9.65 plus or minus 1.44 Bq/L, and sixty per cent falling below international safety thresholds. The corresponding annual effective doses ranged from 0.080 to 0.113 mSv per year for boreholes and 0.055 to 0.081 mSv per year for wells. The mean annual effective dose for borehole water marginally exceeded the World Health Organization recommended reference level of 0.1 mSv per year, while well water samples remained below this threshold. The elevated radon levels in borehole water are attributed to the underlying Precambrian basement geology, characterised by granitic rocks containing uranium-bearing minerals. While well water sources appear safe for consumption, borehole water requires treatment through aeration or granular activated carbon filtration before use. This study provides baseline data for radon levels in the area and underscores the need for regular monitoring of groundwater quality in university campuses reliant on underground water sources.