Geochemical Behavior of Radium in Groundwater Systems

Radium is introduced into groundwater through the decay of uranium and thorium in aquifer minerals and is subject to a range of geochemical processes that determine its mobility, speciation and concentration. In oxic, neutral to alkaline waters, Ra2+ commonly co-precipitates with barite (BaSO4) or adheres to mineral surfaces via adsorption onto clays, iron oxides and organic matter. Under reducing or sulphate-depleted conditions, desorption is enhanced and barite dissolution can release significant quantities of dissolved radium. The extent of alpha-recoil—a process by which daughter radionuclides are physically ejected from mineral lattices—also influences the short-term release of 224Ra and 223Ra. Key controls on radium behaviour include pH, redox potential, the concentrations of competing cations (notably Ba2+, Ca2+ and Sr2+) and anions such as SO42–. Geochemical modelling and field data together reveal that groundwater residence time, flow path length and mineralogy govern radium activity concentrations, which frequently exceed drinking-water guidelines in fractured crystalline or carbonate aquifers. Understanding these processes is essential for assessing radiological health risks, guiding water-treatment strategies and informing resource management in regions reliant on groundwater for domestic and agricultural supply.

Research from Nature Portfolio

A comprehensive study of the Nubian Sandstone Aquifer System revealed elevated 226Ra and 228Ra activities well above international drinking-water limits, with combined concentrations reaching over 4 Bq L–1 in some wells. Analysis showed positive correlations between dissolved radium and barium, and inverse correlations with sulphate, indicating that both barite precipitation and microbial sulphate reduction strongly modulate dissolved radium levels. Barite approaches saturation in many samples, suggesting active co-precipitation removes radium from solution, while alpha-recoil and slow mineral dissolution supply fresh Ra. These findings emphasize the need for targeted mitigation—such as controlled sulphate dosing or ion-exchange treatment—to reduce radium uptake by millions of users dependent on this transboundary resource.

Geochemical Behavior of Radium in Groundwater Systems publication trend

The graph below shows the total number of articles in geochemical behavior of radium in groundwater systems across all publications each year (not limited to Nature Index journals).

Technical terms

Aquifer: A geological formation capable of storing and transmitting significant quantities of groundwater.

Activity concentration: The radioactivity of a radionuclide per unit volume of water, typically expressed in becquerels per litre (Bq L–1).

Alpha-recoil: The physical ejection of a daughter radionuclide from a mineral surface following alpha decay.

Adsorption/desorption: The reversible attachment/detachment of dissolved species to solid surfaces.

Barite co-precipitation: The simultaneous precipitation of radium with barium sulphate (BaSO4), removing Ra from solution.

Redox potential: A measure of the tendency of a chemical environment to acquire or lose electrons, influencing element speciation.

References

1. 222Rn and 226Ra concentrations in selected shallow circulation groundwaters from the Fore-Sudetic Monocline area. Environmental Geochemistry and Health (2023).
2. Water–rock interactions in the Bruchsal geothermal system by U–Th series radionuclides. Geothermal Energy (2020).
3. Elevated radium levels in Nubian Aquifer groundwater of Northeastern Africa. Scientific Reports (2021).
4. Chemical composition, radioactive and stable isotopes in several selected thermal waters in North Vietnam. Ecological Indicators (2022).