Determination of Naturally Occurring Radioactive Materials and Radiological Hazard of Sachet Water from Mubi North and South Local Government Metropolis, Adamawa State, Nigeria

Abstract

Sachet water, widely known as “pure water,” is the predominant drinking water source for communities in Mubi North and South Local Government Areas (LGAs), Adamawa State, Nigeria. Despite its pervasive consumption, its radiological safety has received little systematic investigation. This study quantified activity concentrations of naturally occurring radioactive materials (NORM) Potassium-40 (K-40), Uranium-238 (U-238), and Thorium-232 (Th-232) in fifteen sachet water brands using gamma-ray spectrometry with a NaI(Tl) detector. Radiological hazard indices radium equivalent activity (Raeq), external hazard index (Hex), internal hazard index (Hin), absorbed dose rate (D), annual effective dose equivalent (AEDE), and excess lifetime cancer risk (ELCR) were derived. Measured concentrations spanned 36.08–98.91 Bq/L for K-40 (mean: 64.54 ± 19.38 Bq/L), 13.14–24.33 Bq/L for U-238 (mean: 17.20 ± 3.85 Bq/L), and 15.01–48.84 Bq/L for Th-232 (mean: 29.22 ± 9.32 Bq/L). K-40 remained within WHO guidelines; however, U-238 and Th-232 exceeded the WHO gross-alpha screening level of 0.5 Bq/L and the 0.1 mSv/y reference dose level in all 15 samples, indicating that full ingestion-dose assessment is required. One-way ANOVA confirmed highly significant inter-radionuclide differences (F = 57.12, p < 0.0001). External hazard indices (Raeq, Hex, Hin, D) remained within UNSCEAR/ICRP/OECD thresholds. Th-232 was the principal hazard driver, showing the strongest correlations with Raeq (r = 0.959) and D (r = 0.952). The universal exceedance of U-238 and Th-232 screening levels is attributed to geogenic enrichment from the regional Precambrian basement geology. Systematic radiological monitoring and regulatory enforcement are urgently recommended.