Natural radioactivity and heavy mineral enrichment in coastal sediments from North Chennai to Pondicherry: implications for environmental and public health risk

Understanding natural sources of radiation in coastal environments is essential for evaluating environmental quality and radiological conditions. This study investigates the relationship between heavy mineral enrichment and natural radioactivity in coastal sediments along the North Chennai–Pondicherry shoreline, southeastern India. Twenty-one sediment samples were analyzed using NaI(Tl) γ-ray spectrometry to quantify the activity concentrations of 238U,232Th, and 40K. Mean activity concentrations were 48 Bq kg−1 (238U), 34 Bq kg−1 (232Th), and 568 Bq kg−1 (40K), with thorium showing the strongest statistical association with the evaluated radiological parameters. Radium equivalent activity (140 Bq kg−1), absorbed dose rate (66 nGy h−1), and annual effective dose (0.08 mSv y−1) remained within internationally accepted reference values, whereas the annual gonadal dose equivalent (469 μSv y−1) exceeded the commonly cited reference level of 300 μSv y−1, indicating localized radiological enrichment. Heavy mineral characterization revealed an assemblage dominated by zircon (18.12%), ilmenite (13.74%), garnet (13.45%), tourmaline (12.86%), and rutile (11.99%), with monazite accounting for 3.64%. Spatial distribution analysis demonstrated a clear association between monazite-rich zones and elevated 232Th concentrations, highlighting the influence of mineralogical composition and coastal sediment sorting processes on radionuclide distribution. Multivariate statistical analyses revealed strong relationships between 232Th and the radiological indices, suggesting a predominantly geogenic origin of the observed radiological variability. These findings establish a radiological baseline for the North Chennai–Pondicherry coastline and provide new insights into the role of heavy minerals in controlling natural radionuclide distribution. The study offers a scientific basis for future environmental monitoring, radiological assessment, and sustainable management of placer mineral-rich coastal environments.