Mechanism of elevated radioactivity in Teesta river basin from Bangladesh: Radiochemical characterization, provenance and associated hazards

Abstract

This work presents a river basin (Teesta River, Bangladesh) which possesses significantly higher radioactivity compared to other freshwater basins around the globe. A total of thirty sediment samples were collected to determine the naturally occurring radionuclides (²²⁶Ra, ²³²Th, and ⁴ K)and elemental abundances using the HPGe gamma spectrometry and instrumental neutron activation analysis (INAA), respectively. To understand the provenance of higher radioactivity, the compositional elements (Sc, Ti, V, Fe, La, Ce, Sm, Eu, Dy, Yb, Lu, Hf, Ta, Th, and U) of heavy minerals are thoroughly studied, where ∑REEs (rare earth elements), Hf, Ta, Th, and U are ∼2 times higher than the crustal values with negative Ce and Eu anomalies. Mechanism to co-occurrence among radioactivity concentrations and REEs has been explored in this work. Enrichment of light rare earth elements ( × 2.01 UCC) and thorium ( × 2.8 UCC), and Th/U (=5.54 ± 1.05), ²³²Th/⁴ K ratio and statistical analyses demonstrate the presence of heavy minerals with monazite predominance. Accumulations of these minerals are most likely due to the fluvial suspended sediments transported by the hydrodynamic forces from up-stream. Elemental ratios including La/V, Th/Yb, Th/Sc, and Hf/Sc confirm the dominance of felsic-source over the mafic-components and the source of sediment has experienced major recycling and sorting during transportation. Evaluation of radiological risks invokes ionizing radiation related hazards to the local inhabitants and the householders residing in the buildings comprised with sandy river sediments. However, minute probability of REEs, Th, and U entrance to the human body through food chain can cause trivial health risks.

Keywords: Bangladesh; Co-distribution; Elemental distribution; Provenance; Radioactivity concentrations; Risk assessment; Teesta river basin.