Radiological risk assessment due to naturally occurring radionuclides in water and fish from gold mining-impacted regions in northern Tanzania

Abstract

Many households in gold-mining regions of northern Tanzania have limited access to safe and reliable drinking water and rely on surface water, groundwater, and locally caught fish as key drinking-water and dietary sources, yet the radiological safety of these sources remains uncertain. This study evaluated age-dependent radiological risks from ingestion of naturally occurring radionuclides ( 234 U, 238 U, 226 Ra, 210 Po, 210 Pb) in multiple water sources and in fish tissues (bones, gills and flesh) of African lungfish ( Protopterus aethiopicus ), Nile tilapia ( Oreochromis niloticus ) and African Catfish ( Clarias gariepinus ). Activity concentrations were determined by radiochemical separation followed by alpha spectrometry and gas-flow proportional counting. Annual effective dose (AED) and excess lifetime cancer risk (ELCR) were estimated using age-specific water and fish consumption rates. Groundwater, particularly from shallow wells, produced the highest exposures, with a maximum AED for a 5-year-old child, dominated by 234 U, exceeding both the World Health Organization (WHO) screening level (0.1 mSv/y) and the International Commission on Radiological Protection (ICRP) public dose reference level (1 mSv/y). Fish consumption was the dominant pathway, with African lungfish consistently yielding the highest AEDs, followed by Tilapia and Catfish. The dose contributions were dominated by 210 Pb (75% −96%) and 210 Po (4% - 25%), while 234 U, 238 U, and 226 Ra contributed <1%. The estimated ELCRs associated with consumption of all fish species, exceeded the USEPA acceptable risk range (10 −6 – 10 −4 ). Elevated 234 U/ 238 U activity ratios (>1) indicated preferential mobilisation of 234 U via alpha-recoil, while low 210 Po/ 210 Pb ratios (<1) confirmed 210 Pb predominance. These findings underscore the need for continued radiological monitoring and targeted mitigation to protect vulnerable communities.