Determination of Natural Uranium and Thorium Levels in Environmental Matrices Surrounding Uranium Mining Sites via ICP-MS

Abstract

The link between energy use and environmental health is crucial, yet the role of thorium near uranium deposits remains poorly understood despite known issues with nuclear power. In this context, this study determines the concentration of natural thorium in environmental matrices around a uranium mining site andexplores the distribution of natural uranium and thorium radionuclides in ore from the Cachoeira and Engenho mines in Brazil, as well as in aqueous and soil samples, using ICP-MS. Despite distinct ore fingerprints, the Engenho mine exhibits a lower uranium-to-thorium ratio than the Cachoeira mine. However, thorium levels from both mines are significantly lower than those reported in the literature, where concentrations exceed 150 Bq.kg^-1. Conversely, thorium levels in aqueous samples from both mines are significantly higher than literature values, suggesting that uranium concentrations in these sites could be influenced by hydrological and geological conditions. The range of thorium levels in Cachoeira mine is 1.27 x 10⁴ to 1.8 x 10³ Bq.L^-1, but in Engenho mine, the values are 2.41 x 10⁴ to 3.69 x 10³ Bq.L^-1. The agricultural crop soil values, such as bean, corn, cassava, and prickly pear, are lower than the literature estimates, suggesting little to no input from nearby mines. The range of thorium activity in agricultural soil was 90.97 to 99.42 Bq.kg^-1, which is higher than the values reported in literature in areas without uranium mining (28 ± 39 Bq.kg^-1). Understanding the geographic variability of these radionuclides informs health policies and supports sustainable mining practices, promoting environmental and community safety.