Radon-222 is a chemically inert noble gas produced continuously in the decay chain of uranium-238, which occurs naturally in rocks and soils. Because it is a gas, radon can migrate through fractures, faults, and porous formations, dissolving in groundwater along the way. When that water is drawn to the surface and consumed, the gas can deliver a radiation dose in two distinct ways: through ingestion, when radon dissolved in water passes through the digestive tract, and through inhalation, when radon degasses from water during showering, cooking, or other household activities and is breathed into the lungs. Inhaled radon and its short-lived progeny are the second leading cause of lung cancer after tobacco smoking in many countries, making accurate assessments of exposure a public health priority worldwide.

The measurement campaign in Kribi relied on a RAD7 electronic radon detector, an instrument that uses a passivated implanted planar silicon detector to capture alpha particles emitted by radon and its decay products. Water samples were collected from a range of drinking water sources across the study area, each reflecting the local geological conditions of its catchment. The concentrations recorded spanned a wide range, from as low as 0.07 becquerels per liter to a maximum of 11.42 becquerels per liter, with a geometric mean of 0.81 becquerels per liter. Nearly all of the measured values fell below the reference levels established by the United States Environmental Protection Agency, which recommends an action threshold of 11.1 becquerels per liter, and the World Health Organization, which suggests 100 becquerels per liter as a guideline for drinking water. This pattern suggests that for the average resident of Kribi, the radon burden in the water supply is unlikely to pose a significant radiological hazard under normal consumption habits.

Converting concentration measurements into meaningful estimates of radiation dose requires careful accounting of how much water different age groups consume and how their bodies absorb or retain radon. The researchers calculated annual effective doses for three categories: infants, children, and adults. For ingestion, the dose estimates were 10.19 microsieverts for infants, 4.35 microsieverts for children, and 3.10 microsieverts for adults per year. These figures reflect the fact that infants, despite consuming less water by volume than adults, receive proportionally higher doses because of their smaller body mass and the higher sensitivity of developing tissues to ionizing radiation. For inhalation, the doses were more evenly distributed across age groups: 7.48 microsieverts for infants, 7.03 microsieverts for children, and 6.42 microsieverts for adults. All of these values remained well below the WHO reference limits, which cap the acceptable annual effective dose at 100 microsieverts for adults and 200 microsieverts for children, suggesting that the combined ingestion and inhalation pathways in Kribi do not currently represent a significant health concern.

What makes the study particularly interesting from a geological perspective is its investigation of how lithology, the physical character of the underlying rock layers, and proximity to volcanic faults influence radon behavior. Statistical tests comparing radon concentrations across different lithological units and across different water source types produced p-values greater than 0.05, meaning no statistically significant differences emerged. This finding is notable because it challenges the assumption that rock type alone can predict radon levels in groundwater. Instead, the researchers found that both lithological setting and water source type together shape radon concentrations in this particular coastal environment, highlighting the complexity of radon migration through heterogeneous geological terrain.

Proximity to the Kribi volcanic fault did appear to play a role, but not in a simple or uniform way. Some locations situated near the fault exhibited elevated radon concentrations in their water supplies, consistent with the idea that fault zones serve as preferential pathways for radon-rich fluids rising from deeper in the crust. However, other locations equally close to the fault showed comparatively low concentrations. This inconsistent pattern suggests that factors beyond fault proximity alone are at work, possibly including local variations in rock uranium content, aquifer permeability, water residence time, and the degree of fracturing at specific sites. The study’s authors emphasize that these local factors may collectively override any simple relationship between distance from a fault and radon concentration, complicating efforts to predict exposure based on geological maps alone.

One of the most striking results of the investigation was the strong statistical correlation between radon concentrations in drinking water and radon concentrations in soil gas measured at the same locations. The correlation coefficient of r = 0.78, with a p-value below 0.001, indicates a robust association that is extremely unlikely to have arisen by chance. This relationship points to a common geogenic source for radon in both media, meaning that the uranium-bearing minerals in the underlying bedrock are simultaneously releasing radon into the soil atmosphere and into the groundwater. The finding has practical implications because it suggests that soil gas radon measurements, which are relatively quick and inexpensive to perform, could serve as a useful screening tool for identifying areas where groundwater radon concentrations might be elevated. This correlation also underscores the influence of broader environmental characteristics, including soil permeability, moisture content, and structural geology, on the diffusion and transport of radon through the subsurface.

The Kribi study adds to a growing body of research from Cameroon and other African nations examining natural radiation exposure in settings where uranium-bearing rocks, volcanic activity, and extensive fault networks create conditions favorable for radon accumulation. Earlier investigations in the Adamawa region, the Poli uranium-bearing area, the bauxite-rich zones of western Cameroon, and the coastal Bakassi Peninsula have all documented elevated radon in various environmental compartments. What distinguishes the current study is its focus on a tropical coastal aquifer system, an environment where the interaction between saline intrusion, weathered basement rocks, and fractured volcanic formations creates a distinct geochemical setting that has been underrepresented in the global radon literature. By providing baseline data for Kribi, the researchers have established a reference point that can inform future monitoring programs and public health interventions across similar tropical coastal environments elsewhere in West and Central Africa.

The implications of this research extend beyond academic interest. In many rural and peri-urban communities across sub-Saharan Africa, groundwater from wells, boreholes, and springs constitutes the primary source of drinking water, and the geological conditions controlling radon transport are rarely mapped in detail. The Kribi findings suggest that blanket assumptions about radon risk, whether based on rock type, fault proximity, or water source category, may be misleading without site-specific measurement. The strong water-to-soil-gas correlation offers a pragmatic approach for resource-limited settings: a rapid soil gas survey could help prioritize water sources for more expensive and time-consuming water sampling and dose assessment. As climate change, population growth, and urbanization place increasing pressure on coastal aquifers worldwide, understanding the geological controls on naturally occurring radionuclides in drinking water will become ever more important for protecting public health in vulnerable communities.

Subject of Research: Assessment of age-dependent radiological health risks from radon-222 in drinking water and soil gas in a volcanic fault region of Kribi, Cameroon

Article Title: Age-dependent health risks assessment due to 222Rn in drinking water depending on lithology and volcanic faults

Article References: Juste, B. N., Dieu Souffit, G., Joseph Emmanuel, N. N. I., François, K., Modibo, O. B., Saïdou, & Motapon, O. (2026). Age-dependent health risks assessment due to 222Rn in drinking water depending on lithology and volcanic faults. Environmental Geochemistry and Health, 48(14), Article 585. https://doi.org/10.1007/s10653-026-03432-0

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03432-0

Keywords: radon-222, drinking water, soil gas, volcanic fault, lithology, Kribi Cameroon, annual effective dose, ingestion dose, inhalation dose, groundwater, radiological risk, tropical coastal aquifer