Natural radionuclides in flood-affected rice agroecosystems: distribution patterns, transfer dynamics, and radiological implications

Abstract

This study assessed the redistribution of natural radionuclides and associated radiological risks in flood-affected rice agroecosystems of Hadejia, Jigawa State, Nigeria. Radiation surveys and sample collection were conducted shortly after floodwater recession. A total of 50 soil and rice samples were analyzed using gamma spectrometry. The mean activity concentrations of ²²⁶Ra, ²³²Th, and ⁴⁰K were 11.58 ± 0.41, 16.32 ± 1.28, and 470.24 ± 25.13 Bq/kg in soil, and 2.01 ± 0.15, 2.24 ± 0.17, and 130.22 ± 2.19 Bq/kg in rice, respectively. The corresponding radiological indices due to soil exposure were below world averages and recommended safety limits. Soil-to-rice transfer factors followed the order ⁴⁰K (0.30) > ²²⁶Ra (0.18) > ²³²Th (0.17), consistent with the existing literature. The annual effective dose from rice consumption (0.06 ± 0.01 mSv/y) was below the public dose constraint of 0.3 mSv/y. Regression analysis showed strong dependence of ²²⁶Ra uptake on soil concentration (R² = 0.815), weak correlation for ²³²Th (R² = 0.304), and no significant relationship for ⁴⁰K (R² = 0.006). Spatial and normalized analyses revealed localized hotspots linked to flood-induced sediment deposition. The radiological risk was low, although continued monitoring is recommended.