To study the geogenic processes of naturally occurring radioactive materials' (NORMs') distribution, a transboundary Himalayan river (Punarbhaba) is chosen due to its trivial anthropogenic impacts. In explaining the genesis of radionuclides, transition elements (Sc, Ti, V, and Fe), rare-earth-elements (REEs: La, Eu, Ce, Yb, Sm, and Lu), Ta, Hf, Th, and U were analysed in 30 riverbed sediments collected from the Bangladeshi portion of the river. Elemental abundances and NORMs' activity were measured by neutron activation analysis and HPGe-gamma-spectrometry, respectively. Average_n=30 radioactivity concentrations of ²²⁶Ra (68.4 Bq kg⁻¹), ²³²Th (85.7 Bq kg⁻¹), and ⁴⁰K (918 Bq kg⁻¹) were 2.0–2.3-fold higher, which show elevated results compared to the corresponding world mean values. Additionally, mean-REE abundances were 1.02–1.38-times higher than those of crustal origin. Elevated (relative to earth-crust) ratios of Th/U (=3.95 ± 1.84) and ²³²Th/⁴⁰K and statistical demonstrations invoke Th-dominant heavy minerals, indicating the role of kaolinite clay mineral abundance/granitic presence. However, Th/Yb, La/V, Hf/Sc, and Th/Sc ratios reveal the presence of felsic abundances, hydrodynamic sorting, and recycling of sedimentary minerals. Geo-environmental indices demonstrated the enrichment of chemical elements in heavy minerals, whereas radiological indices presented ionizing radiation concerns, e.g., the average absorbed-gamma-dose rate (123.1 nGy h⁻¹) was 2.24-fold higher compared to the threshold value which might cause chronic health impacts depending on the degree of exposure. The mean excess lifetime cancer risk value for carcinogen exposure was 5.29 × 10⁻⁴ S v⁻¹, which is ∼2-times greater than the suggested threshold. Therefore, plausible extraction of heavy minerals and using residues as building materials can alleviate the two-reconciling problems: (1) radiological risk management and (2) fluvial navigability.

中文翻译：

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河流沉积物中环境放射性水平升高：起源和健康风险评估

为了研究自然产生的放射性物质（NORM）分布的地质过程，选择了一条跨境喜马拉雅河流（Punarbhaba），因为它的人为影响微不足道。在解释放射性核素、过渡元素（Sc、Ti、V 和 Fe）、稀土元素（REE：La、Eu、Ce、Yb、Sm 和 Lu）、Ta、Hf、Th 和 U 的成因时对从孟加拉河段收集的 30 个河床沉积物进行了分析。元素丰度和 NORM 活性分别通过中子活化分析和 HPGe-gamma 能谱测定来测量。²²⁶ Ra (68.4 Bq kg ⁻¹ )、²³² Th (85.7 Bq kg ⁻¹ ) 和⁴⁰ K (918 Bq kg ⁻¹ ) 的平均_{n =30}放射性浓度高出 2.0–2.3 倍，这表明结果较高到相应的世界平均值。此外，平均稀土元素丰度比地壳起源的稀土丰度高 1.02-1.38 倍。 Th/U (= 3.95 ± 1.84) 和²³² Th/ ⁴⁰ K比率升高（相对于地壳）以及统计论证表明以 Th 为主的重矿物，表明高岭石粘土矿物丰度/花岗岩存在的作用。然而，Th/Yb、La/V、Hf/Sc 和 Th/Sc 比率揭示了长英质丰度、水动力分选和沉积矿物的循环利用。地质环境指数表明重矿物中化学元素富集，而放射学指数则提出了电离辐射问题，例如，平均吸收伽马剂量率（123.1 nGy h ^-1）比阈值高2.24倍。根据接触程度，可能会造成慢性健康影响。致癌物质暴露的平均超额终生癌症风险值为 5.29 × 10 ^-4 S v ^-1，比建议阈值高约 2 倍。因此，合理提取重矿物并将残留物用作建筑材料可以缓解两个协调问题：（1）放射性风险管理和（2）河流通航性。