Gross Alpha and Gross Beta Radioactivity and Annual Effective Dose from Surface-Water Consumption in Oil-Producing Communities of Delta State, Nigeria
Sanda Yusuf Sadau *
Department of Natural and Physical Science, Science Directorate, National Agency for Science and Engineering Infrastructure (NASENI) HQ, FCT Abuja, Nigeria.
N. Rabiu
Department of Physics, Ahmadu Bello University, Zaria, Nigeria.
N. N. Garba
Department of Physics, Ahmadu Bello University, Zaria, Nigeria.
Suleiman Bello
Department of Physics, Umar Musa Yar'adua University, Katsina, Nigeria.
Ishaya Iliyasu
Department of Physics with Electronics, Nuhu Bamalli Polytechnic, Zaria, Nigeria.
*Author to whom correspondence should be addressed.
Abstract
The presence of naturally occurring radioactive material in surface water may constitute a radiological health concern where such water is used for domestic purposes. This study investigated gross alpha and gross beta activity concentrations and the resulting annual effective doses associated with surface-water consumption in the Apkai and Umusedege oil-producing communities of Ndokwa East and Ndokwa West Local Government Areas, Delta State, Nigeria. Surface-water samples were collected from nine locations—five in Apkai and four in Umusedege—together with groundwater controls, and gross alpha and beta activities were measured using a desktop MPC 2000-DP proportional counter following evaporation and preparation on stainless-steel planchettes; the counter was calibrated against ²³⁹Pu and ⁹⁰Sr standard sources. Mean gross alpha and beta activity concentrations were 1184 and 2164 mBq/L, respectively, with ranges of 122–3160 and 301–6145 mBq/L; the highest values for both parameters occurred at K-APK. Most sampling locations exceeded the 500 mBq/L gross-alpha and 1000 mBq/L gross-beta screening levels adopted in this study, with mean concentrations approximately 2.37 and 2.16 times those levels, respectively. Mean annual effective doses from ingestion were 2.154, 1.133 and 0.566 mSv/year (gross alpha) and 4.087, 2.106 and 1.053 mSv/year (gross beta) for adults, children and infants, respectively; each of these six mean values exceeded the 0.1 mSv/year reference level, and gross beta consistently contributed approximately 1.9 times the dose of gross alpha across all three population groups. Comparison with other Nigerian studies showed that the present mean activities exceeded values reported for Ado-Ekiti, Kano and Kaduna, but remained below the substantially higher values reported for an earlier Delta State investigation. The results indicate elevated gross alpha and beta radioactivity in portions of the investigated surface-water system, identify K-APK as a priority location for further radionuclide-specific investigation, and demonstrate the continued need for radiological monitoring of water resources in this oil-producing environment.
Keywords: Gross alpha, gross beta, surface water, annual effective dose, natural radioactivity, NORM, radiological risk