Assessment of Natural Radionuclides, Soil-to-Plant Transfer and Radiological Significance of a Municipal Waste Dumpsite in Kaura Namoda, Zamfara State, Nigeria

Abstract

This study investigated the occurrence of natural radionuclides in soil and vegetation at a municipal waste dumpsite in Kaura Namoda, Zamfara State, Nigeria, with emphasis on soil-to-plant transfer and radiological significance. Soil and corresponding plant samples collected from six sampling locations were analysed for ⁴⁰K, ²²⁶Ra, and ²³²Th using NaI(Tl) gamma-ray spectrometry. Soil-to-plant transfer factors (TFs) were determined from the activity concentrations in paired soil and plant samples. The absorbed dose rate (D_air), annual effective dose equivalent (AEDE), radium equivalent activity (Ra_eq), external hazard index (H_ex), and excess lifetime cancer risk (ELCR) were also evaluated. Mean soil activity concentrations were 237.46, 51.01, and 159.03 Bqkg⁻¹ for ⁴⁰K, ²²⁶Ra, and ²³²Th, respectively, while corresponding mean plant activities were 216.54, 37.48, and 82.97 Bqkg⁻¹, respectively. The mean TFs were 1.80 for ⁴⁰K, 0.79 for ²²⁶Ra, and 0.80 for ²³²Th, indicating comparatively greater transfer of ⁴⁰K into vegetation. Mean D_air, AEDE, Ra_eq, H_ex, and ELCR were 131.61 nGyh⁻¹, 0.16 mSv y⁻¹, 295.28 Bqkg⁻¹, 0.80, and 0.42 × 10⁻³, respectively. KRN 01 recorded the highest radiological values, including a D_air of 278.68 nGyh⁻¹, a Ra_eq of 625.13 Bqkg⁻¹, an H_ex of 1.69, and an ELCR of 0.89 × 10⁻³. Although the site-wide mean Ra_eq and H_ex were below their conventional reference levels, the elevated values at KRN 01 demonstrate considerable spatial variability within the dumpsite. The findings confirm measurable transfer of natural radionuclides from soil to vegetation and provide baseline information for continued environmental monitoring and prudent management of agricultural activities within and around the dumpsite.