Radiological risk assessment due to naturally occurring radionuclides in water and fish from gold mining-impacted regions in northern Tanzania.
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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 (234U, 238U, 226Ra, 210Po, 210Pb) 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 234U, 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 210Pb (75% -96%) and 210Po (4% - 25%), while 234U, 238U, and 226Ra contributed <1%. The estimated ELCRs associated with consumption of all fish species, exceeded the USEPA acceptable risk range (10-6 - 10-4). Elevated 234U/238U activity ratios (>1) indicated preferential mobilisation of 234U via alpha-recoil, while low 210Po/210Pb ratios (<1) confirmed 210Pb predominance. These findings underscore the need for continued radiological monitoring and targeted mitigation to protect vulnerable communities.