Assessment of natural radioactivity with radiological hazards and spatial distribution of radionuclides in soils, sediments from coastal and non-coastal regions of southeastern Bangladesh.

This study investigates the distribution of natural radioactivity and associated radiological hazard indices in 50 soil and sediment samples collected from coastal and non-coastal regions of southeastern Bangladesh. The concentrations of naturally occurring radionuclides 226Ra, 232Th, and 40K were measured using a high purity germanium (HPGe) detector-based gamma spectrometry system. The activity concentrations of 226Ra, 232Th, and 40K in the collected samples ranged from 10.0 ± 3.2 to 85.9 ± 9.3 Bq kg-1, 12.1 ± 3.5 to 92.3 ± 9.6 Bq kg-1, and 199.0 ± 14.1 to 809.9 ± 28.5 Bq kg-1, respectively. Higher levels were typically seen in coastal regions like Teknaf, Cox's Bazar, and Chakaria. To assess the radiological risks posed by these radionuclides, key radiological hazard parameters were calculated; absorbed dose rate (ADR) varied from 29.9 ± 4.7 to 114.2 ± 11.0 nGy h-1; annual effective dose equivalent (AEDE) varied from (3.7 ± 0.6) × 10-2 to (14.0 ± 1.3) × 10-2 mSv year-1, External Hazard Index (Hex) and Internal Hazard Index (Hin) hazard values varied from (1.7 ± 0.3) × 10-1 to (6.8 ± 0.7) × 10-1 and (2.0 ± 0.4) × 10-1 to (9.4 ± 0.9) × 10-1; radium equivalent activity (Raeq) ranged from 61.2 ± 10.3 to 251.6 ± 24.6 Bq kg-1; gamma representative index (Iγ) varied from (2.4 ± 0.4) × 10-1 to (8.9 ± 0.9) × 10-1. The measured excess lifetime cancer risk (ELCR) ranged from (1.3 ± 0.2) × 10-4 to (4.9 ± 0.5) × 10-4, and annual gonadal dose equivalent (AGDE) varied from 214.6 ± 32.6 to 791.6 ± 75.4. Radiological hazard indices were generally higher in the coastal region, particularly at Teknaf and Cox's Bazar, although all mean hazard indices remained within internationally accepted safety limits. Although a few coastal locations exhibited relatively elevated ELCR values, the overall mean ELCR remained within internationally reported reference levels. This study, based on HPGe, provides key data on natural radioactivity and its spatial distribution, which supports safe soil and sediment use and future radiological monitoring.