First probabilistic radiological risk appraisal of Bay of Bengal beach sands: Explicit spatial hot-spot analysis

Coastal beach pollution caused by primordial radionuclides has emerged as a global environmental concern. This study presents the first integrated probabilistic-spatial framework for assessing radiological risk in the Bay of Bengal (BoB) beach sands. Twenty-two surface sediment samples (10-15 cm depth) from Darianagar, Himchari, and Nidania beaches along the BoB were analyzed using HPGe gamma spectrometry. Geometric mean (range) activity concentrations (Bq kg^-1) were 77.6 (15.1-1914.3) for ²²⁶Ra, 123.1 (8.12-1847.3) for ²³²Th, and 312.8 (122.4-562) for ⁴⁰K, exceeding global averages for ²²⁶Ra and ²³²Th by factors of 2.2 and 4.1 times, respectively. Principal component analysis (PCA) identified natural mineralogical controls, primarily monazite and K-feldspar rather than distinct anthropogenic sources, while Monte Carlo simulations revealed 95th-percentile radiological indices (Raeq, D_out, ELCR) exceeding international safety thresholds (8.5 × 10^-4 to 23.3 × 10^-4). Deterministic calculations yielded mean values higher than probabilistic medians, reflecting right-skewness. All radionuclide concentrations followed lognormal distributions, indicating significant spatial variability. Sensitivity analysis showed ²³²Th (∼75 %) as the primary contributors to total radiological risk. GIS-based spatial modeling delineated localized high-risk hotspots requiring restricted access, hazard signage, and periodic radiological monitoring. This study establishes benchmark data and a transferable methodological framework for coastal radiation surveillance and sustainable management, supporting evidence-based regulation of BoB and similar global beach systems.