Evaluation of Radionuclide Concentrations and Radiological Health Risks in Groundwater of the Groot-Aub Aquifer System, Namibia

Abstract

Primordial radionuclides (226Ra, 232Th, and 40K) occur naturally in varying concentrations within environmental media. Anthropogenic activities that disturb the Earth’s crust, such as drilling and mining, have the potential to alter the concentrations of these radionuclides in environmental compartments, including water and soil. Through various exposure pathways, naturally occurring radionuclides contribute to the radiation dose received by humans on a daily basis. The Groot-Aub settlement, located in central Namibia, relies heavily on groundwater as its primary water source. To meet increasing water demand, several boreholes have been drilled in the area over recent years. This situation necessitated the present study, which aimed to evaluate the concentrations of naturally occurring radionuclides (226Ra, 232Th, and 40K) and assess the associated radiological health risks in groundwater from the study area. A total of ten boreholes were sampled and analyzed for radionuclide activity concentrations using a high-purity germanium (HPGe) gamma-ray detector. The results reveal mean activity concentrations of 11.77 ± 0.86 Bq L−1, 6.24 ± 1.97 Bq L−1, and 780.30 ± 12.17 Bq L−1 for 226Ra, 232Th, and 40K, respectively. These mean values exceed the guidance levels established under the International Drinking Water Guidelines. The mean total annual effective ingestion dose (AEID) values for the four age groups are observed in the following order: children < teenagers < infants < adults (≤1 year, 1–12 years, 12–17 years, and >17 years, respectively). The mean total AEID for the adult age group is slightly higher than the worldwide Individual Dose Criterion (IDC) of 0.1 mSv y−1, whereas the corresponding values for the other three age groups remain within the recommended limit. Furthermore, the mean values of the hazard indices (Hex, Hin, Iα, and Iγ), as well as the mean absorbed dose rate (D), are all within their respective permissible limits. In addition, the mean annual gonadal equivalent dose (AGED) is 307.45 ± 11.26 μSv y−1, exceeding the globally recommended permissible limit. The mean excess lifetime cancer risk (ELCR) values range from 5.73 × 10−5 for the child age group to 1.26 × 10−3 for the adult age group. Only the mean ELCR value for adults exceeds the worldwide permissible limit, while the values for the remaining age groups are within acceptable levels. With the exception of the adult age group, the findings indicate that groundwater consumption in Groot-Aub is, on average, radiologically safe. However, the elevated AEID, AGED, and ELCR values observed for the adult age group suggest a potential risk of adverse radiological health effects, arising from the lifelong ingestion of radionuclides in groundwater and the cumulative effects of long-term radiation exposure. Consequently, periodic radiological monitoring of groundwater quality in the study area is recommended, together with appropriate mitigation and regulatory measures where necessary, to ensure the continued protection of public health.

The authors' abstract, as published at the source. Water, 2026 · DOI ↗