River Water Near Tanzanian Uranium Project Carries Radiation Doses Above WHO Guidelines

Untreated water from parts of the Likuyu River in southern Tanzania may expose people who drink it to radiation doses well above international safety guidelines, according to a new study published in Environmental Monitoring and Assessment. A team led by Charles D. Kadala sampled water and sediment at five sites along a 22.7-kilometre stretch of the river during the rainy season, collecting triplicate samples at each location. The researchers measured three naturally occurring radionuclides — radium-226, thorium-232, and potassium-40 — using high-purity germanium gamma spectrometry, a technique sensitive enough to detect the faint gamma emissions these isotopes release as they decay.

The results revealed striking spatial variation. Site A recorded the highest radium-226 activity concentration in water at 2.71 ± 0.33 becquerels per litre, while Site C showed an elevated potassium-40 level of 120.06 ± 1.62 becquerels per litre. When the researchers converted these concentrations into annual ingestion doses, Sites A and C stood out: 0.743 ± 0.109 and 0.623 ± 0.007 millisieverts per year respectively, both exceeding the World Health Organisation's total indicative dose criterion of 0.1 millisievert per year for drinking water.

The health implications extend beyond the dose figures themselves. The corresponding excess lifetime cancer risk values at these two sites were calculated at 28.6 × 10⁻⁴ and 23.97 × 10⁻⁴, both far above the tolerable risk level of 1 × 10⁻⁴ set by the International Commission on Radiological Protection. In practical terms, a person drinking untreated water from these locations over a lifetime would carry a substantially elevated estimated probability of developing radiation-associated cancer compared with the accepted benchmark.

Sediments told a different story. Although radionuclide enrichment appeared locally at Sites B and D, every radiological index computed for the sediment samples remained within safety limits. Radium equivalent activity ranged from 150.8 to 247.4 becquerels per kilogram, annual effective doses from sediments fell between 0.090 and 0.139 millisieverts per year, and both the external and internal hazard indices stayed below the threshold value of 1.

This contrast suggests that the primary exposure pathway of concern is ingestion of water rather than external exposure from riverbank sediments. To probe the origins of the contamination, the team applied Principal Component Analysis to the dataset. The analysis revealed co-enrichment of uranium-series and thorium-series radionuclides alongside potassium-driven inputs, a pattern the authors interpret as evidence of lithogenic and mineralogical control.

The study addresses a notable gap. By establishing baseline concentrations and dose estimates for the Likuyu River, the research provides reference data against which future monitoring — including any potential influence from mining operations upstream — can be judged. The authors caution that their findings apply to untreated river water and to the rainy-season conditions under which sampling occurred.

Communities relying on the river without treatment may face a significant radiological health risk at the affected sites, while sediment exposure remains within regulatory thresholds. The team frames the work as a foundation for ongoing surveillance and for water safety initiatives in uranium-affected agro-mining regions of East Africa, where the intersection of mineral wealth, agriculture, and untreated water supplies makes radiological monitoring an emerging public health priority.

Subject of Research: Natural radionuclide contamination and radiological risk assessment in the Likuyu River system, southern Tanzania

Article Title: Risk from natural radionuclides in the Likuyu River system, Tanzania: implications for radiological safety in a uranium-rich geological setting

Article References: Kadala, C. D., Rwiza, M. J., Mwaijengo, G. N., Sawe, S. F., & Mataba, G. R. (2026). Risk from natural radionuclides in the Likuyu River system, Tanzania: implications for radiological safety in a uranium-rich geological setting. Environmental Monitoring and Assessment, 198(11), Article 1251. https://doi.org/10.1007/s10661-026-16109-z

Image Credits: AI Generated

DOI: 10.1007/s10661-026-16109-z

Keywords: radionuclides, uranium, Tanzania, Likuyu River, radiological risk, drinking water, gamma spectrometry, radium-226, WHO guidelines, excess lifetime cancer risk, sediment, Mkuju River Uranium Project