Evaluation of Radon-222 concentration and its associated risks in groundwater sources of communities around selected mining sites in Sierra Leone

Abstract

Radon-222 in groundwater poses significant health risks through ingestion and inhalation, being the second leading cause of lung cancer deaths in the U.S., with 21,000 fatalities annually. This study evaluated radon-222 levels and associated risks in groundwater near mining sites in Sierra Leone during the rainy season. Fifteen samples from each site – Koidu, Yengema and Marampa, were analyzed using a calibrated DURRIDGE RAD-7 detector. Risks were calculated for infants, children and adults, including annual effective doses, Excess lifetime cancer risks and Lung Cancer Cases per million people per year. The results showed that Radon-222 concentrations in the groundwater samples ranged from 5.07 to 41.63 Bq/l with an average value of 19.10 Bq/l. The total annual effective doses varied from 65.53 to 590.49 (μSv/y), highest in infants. Excess lifetime cancer risks ranged from 0.0002 to 0.0021, with infants at the greatest risk. Lung cancer incidence was approximately 0.0009 per million people per year. Importantly, all samples remained below WHO and EU limits of 100 Bq/l, indicating compliance with international safety guidelines and no immediate health risk. However, 87.5% of samples exceeded USEPA's more stringent maximum contaminant level of 11.1 Bq/l. This discrepancy reflects differing regulatory philosophies : USEPA's precautionary approach versus WHO/EU's risk-based thresholds. While the water meets international standards for safe consumption, the exceedance of USEPA standards suggests potential long-term health concerns warranting continued monitoring, particularly for vulnerable populations such as infants and children. Simple, low-cost mitigation measures such as aeration, storage (allowing radon to decay/escape) and ventilation during water use are recommended where concentrations approach upper limits. Highlights 1. This study evaluated 222Rn levels and associated risks in groundwater near mining sites in Sierra Leone during the rainy season. 2. Fifteen samples from each site – Koidu, Yengema and Marampa, were analyzed using a calibrated DURRIDGE RAD-7 detector. 3. Risks were calculated for infants, children and adults, including annual effective doses, Excess lifetime cancer risks and Lung Cancer Cases per million people per year. 4. Calculations reveal that the total annual effective doses varied from 65.53 to 590.49 (µSv/y), highest in infants. 5. Elevated 222Rn levels indicate potential long-term health risks for inhabitants, especially infants and children.