Quantification of NORM concentrations and radiological risk indices in southern Tanzanian natural gas operations

Naturally occurring radioactive materials (NORMs) associated with natural gas production may pose radiological risks to workers and the environment if present at elevated levels. This study presents the first comprehensive radiological assessment of NORMs using representative samples of soils (n = 27), produced water (n = 15), wastewater (n = 6), treated water (n = 3) and gas condensates (n = 9) collected from the Mnazi Bay, Msimbati, and Madimba Natural Gas Processing Plant, Tanzania. Collected samples were analyzed by using high-purity germanium (HPGe) detector. Soil samples exhibited mean activity concentrations of 13.12 Bq kg −1 for 226 Ra, 14.50 Bq kg −1 for 232 Th, and 816.3 Bq kg −1 for 40 K, while the corresponding mean absorbed dose rate, annual effective dose (AED), and excess lifetime cancer risk (ELCR) were 48.85 nGy h −1 , 0.01368 mSv y −1 , and 2.74 × 10 −5 , respectively. Mean radium equivalent activity (Raeq) in soils was 96.70 Bq kg −1 , which is well below the recommended limit of 370 Bq kg −1 , while the mean annual gonadal dose equivalent (AGDE) (357.44 μSv y −1 ) exceeded the reference value of 300 μSv y −1 . In produced water, wastewater, and gas condensates, radionuclide activities and hazard indices were several orders of magnitude below internationally accepted safety limits. Wastewater treatment significantly reduced radionuclide concentrations and corresponding radiological hazards. Comparison with published data from other oil and gas producing countries indicated generally lower radionuclide concentrations in the Tanzanian facilities. These findings provide baseline data for environmental radiation monitoring and support the development of national guidelines for NORM management in Tanzania's expanding natural gas industry.