Environmental radioactivity in marine food webs of the Tamil Nadu coast: sources, transfer pathways and radiological implications

Seafood constitutes a major pathway for the transfer of naturally occurring and anthropogenic radionuclides from marine ecosystems to humans. The Tamil Nadu coast, spanning the Bay of Bengal, Palk Bay, Gulf of Mannar and the Indian Ocean, supports intensive fisheries, aquaculture and seafood consumption while encompassing nuclear installations, mineral-rich coastal sediments, major ports, estuaries, industrial zones and riverine inputs that collectively influence marine radioactivity. This review critically synthesises current knowledge of radionuclides in marine fish, crustaceans, molluscs, seaweeds and other edible organisms along the Tamil Nadu coast, with emphasis on their sources, environmental behaviour, bioaccumulation, trophic transfer and implications for seafood safety. Naturally occurring and cosmogenic radionuclides (^210Po, ^210Pb, ^226Ra, ^228Ra, ^238U, ^232Th, ^40K and ^14C), together with surveillance-relevant anthropogenic radionuclides (^137Cs, ^134Cs, ^90Sr, ^3H, ^99Tc and plutonium isotopes), are evaluated with respect to environmental sources, sediment interactions, tissue-specific accumulation, spatial variability and radiological significance. Under normal/background conditions, across Tamil Nadu studies that quantified radionuclide ingestion dose, ^210Po ^210Po frequently represented the largest contributor among the radionuclides assessed, although the magnitude of exposure varied substantially with seafood group, tissue selection, processing state and consumption assumptions. Anthropogenic radionuclides were less extensively characterised and generally contributed smaller reported doses in the available surveillance studies; however, their relative radiological importance may increase substantially following accidental or off-normal releases. Comparability among studies remains constrained by differences in sampling design, target species, tissue selection, analytical methods, reporting basis, detection limits, seafood-consumption data and dose-assessment assumptions. This review therefore emphasises the need for harmonised, long-term radioecological monitoring integrating seawater, sediments, plankton, representative marine biota and commercially important seafood, together with robust QA/QC, whole organism ecological dose assessment and category-specific probabilistic dietary exposure modelling. Establishing spatially and temporally resolved baseline datasets will strengthen seafood-safety assessments, improve source attribution, support rapid evaluation of accidental releases and provide a more robust basis for environmental protection and coastal management along the Tamil Nadu coast.