Assessment of Natural Radioactivity and Radiological Hazards in Abiotic and Biogenic Marine Matrices of St. Martin’s Island, Bangladesh

This study presents an integrated assessment of natural radioactivity and associated radiological hazards in coastal sediments and marine biogenic materials from St. Martin’s Island, the only coral island in Bangladesh. Activity concentrations of 226Ra, 232Th, and 40K (Bq/kg) showed clear matrix-dependent variations, with mean values of 19 ± 1, 31 ± 3, and 320 ± 22 in sands; 20 ± 1, 26 ± 2, and 273 ± 17 in rocks; 10 ± 1, 12 ± 1, and 150 ± 10 in coral skeletons; and 10 ± 1, 9 ± 1, and 110 ± 8 in seashells, respectively. Some of the sediment samples exhibited activity concentrations exceeding global average values, whereas all coral and seashell samples remained well below these reference levels. All evaluated radiological hazard indices were significantly lower than internationally recommended limits, indicating negligible radiological risk for residents, visitors, and associated personnel. This study provides the most comprehensive radiological baseline to date for St. Martin’s Island by offering the first integrated comparison of abiotic (sand and rock) and biogenic (coral skeletons and seashells) marine matrices in the coastal environment. These findings establish a comprehensive radiological baseline that will support future environmental monitoring programs and radiological safety assessments in Bangladesh, particularly for coastal regions where natural and anthropogenic influences may evolve over time.