Abstract

The activity levels of ⁴⁰K, ²³⁸U, and ²³²Th radionuclides in soil and associated radiological risk in rice field 1 and field 2 located in Ezillo, Ebonyi State, Nigeria were investigated in this study. Topsoil soil samples at depths 0–4 cm and 4–8 cm were collected before planting (BP), after planting (AP) and during harvesting (DH) stages. The activities of the radionuclides in the soil were measured by gamma spectrometric technique employing NaI(TI) detector. The results indicate that the activity concentrations of the radionuclides in the paddy fields, in all stages and depths, are higher than those obtained from the control site. The activity concentrations of the radionuclides across the farming stages indicated this order of DH > AP > BP for ²³⁸U in both fields at both depths; DH > BP > AP at both depths in field 1 and at depth 4–8 cm in field 2 and DH > AP > BP at depth 0–4 cm in field 2 for ²³²Th; while for ⁴⁰K, the orders are DH > BP > AP at depth 0–4 and DH > AP > BP at depth 4–8 cm in field 1 and AP > DH > BP at both depths in field 2. The radionuclides activities in both fields indicate this order ⁴⁰K > ²³⁸U > ²³²Th in all the stages and depths. The mean activities of the radionuclides determined before and after planting stages in both fields and at both depths were below UNSCEAR world average levels of 420 (⁴⁰K), 33 (²³⁸U), and 45 (²³²Th) Bqkg⁻¹. Only ⁴⁰k has a value below the world average during harvesting. The values of the examined radiological risk indices in the paddy fields in all the stages and depths were all higher than those of the control site. All the risk indices across the farming stages indicate that DH > AP > BP in both fields. Only the risk indices estimated during harvesting were higher than the respective permissible limit. The risk assessment shows that while the radiation doses from ²³²Th, ²³⁸U and ⁴⁰K before and after planting stages do not constitute any threat to the farmers at this present moment, those during the harvesting stages present some levels of threat.

摘要

本研究调查了位于尼日利亚埃博尼州 Ezillo 的稻田 1 和稻田 2 土壤中⁴⁰ K、²³⁸ U 和²³² Th 放射性核素的活度水平及相关的放射性风险。在种植前 (BP)、种植后 (AP) 和收获 (DH) 阶段收集 0-4 cm 和 4-8 cm 深度的表土土壤样品。土壤中放射性核素的活度通过伽马能谱技术采用 NaI(TI) 检测器进行测量。结果表明，稻田各阶段、各深度的放射性核素活度浓度均高于对照地。整个耕作阶段放射性核素的活度浓度表明，DH > AP > BP 的顺序为^{在两个深度的两个场中均为238} U；DH > BP > AP 在视野 1 的两个深度和视野 2 的深度 4-8 cm 处，DH > AP > BP 在视野 2 的深度 0-4 cm 处，持续²³² Th；而对于⁴⁰ K，顺序是 DH > BP > AP 在深度 0-4 和 DH > AP > BP 在深度 4-8 cm 场 1 和 AP > DH > BP 在场 2 的两个深度。两个字段都表明在所有阶段和深度中这个顺序为⁴⁰ K > ²³⁸ U > ^{232 Th。}在两个田间和两个深度的种植阶段前后测定的放射性核素的平均活度均低于 UNSCEAR 世界平均水平 420 ( ⁴⁰ K)、33 ( ²³⁸ U)、^-1。在收获期间，只有⁴⁰ k 的值低于世界平均水平。各阶段和深度的水田放射风险指数值均高于对照点。整个耕作阶段的所有风险指数表明，两个田间的 DH > AP > BP。只有在收获期间估计的风险指数高于相应的允许限值。风险评估表明，虽然目前种植阶段前后的²³² Th、²³⁸ U 和^{40 K 辐射剂量对农民没有任何威胁，但收获阶段的辐射剂量存在一定程度的威胁。}