Spatial distribution and radiological risk assessment of natural radionuclides in sediments from Kayamkulam Estuary, Kerala

The prevalence and spatial dispersal of primordial radionuclides in natural high background radiation areas (NHBRAs) require systematic environmental and health safety assessment monitoring, with estuarine environments serving as crucial indicators of radionuclide behavior and distribution patterns. This study investigates the spatial distribution of primordial radionuclides ( 238 U, 40 K, and 232 Th) within the sedimentary matrices of Kayamkulam Estuary, Kerala, an NHBRA region proximate to the well-documented Chavara region. Sediment samples were collected from ten locations using systematic random sampling techniques, and radionuclide concentrations were analyzed using a 3″ × 3″ NaI (Tl) scintillation detector coupled with a multi-channel analyzer. Activity concentrations exhibited significant spatial heterogeneity, with mean values of 343.8 Bq/kg for 238 U (range: 111–1834 Bq/kg), 583.9 Bq/kg for 232 Th (range: 118–3511 Bq/kg), and 910.2 Bq/kg for 40 K (range: 592–2599 Bq/kg), substantially exceeding global average values. Radiological risk assessment revealed elevated parameters, with mean radium equivalent activity of 1248.9 Bq/kg, absorbed dose rate of 549.7 nGy/h, and annual effective dose equivalent of 0.67 mSv/y. The mean gamma index of 4.37 and external hazard index of 3.37 exceeded recommended safety thresholds. Geochemical analyses indicated predominantly oxidizing conditions, with Th/U ratios ranging from 3.18 to 6.86. The study provides crucial insights into radionuclide behavior in estuarine environments, emphasizing the interplay of natural geological factors and potential anthropogenic influences, while highlighting the necessity for continuous surveillance and strategic management to alleviate prospective environmental and health hazards. • Activity concentration of primordial radionuclides was associated in the sediments of the Kayamkulam estuary. • Significant elevation in the activity concentration as well as elemental concentration in the sediments. • Ecological risk parameters were well above the world permissible limits. • Spacial heterogeneity can be attributed to its proximity to mining activities and natural background radiation area of Chavara.