Radium in marine sediments and offshore NORM/TENORM: a framework for environmental radiological protection,...

Radium isotopes are central to marine radioecology and environmental radiological protection because they connect natural decay series, sediment-water exchange, offshore oil and gas naturally occurring radioactive material (NORM), technologically enhanced NORM and exposure of humans and non-human biota. Marine sediments are often described as radionuclide repositories, yet for radium they may function as reactive interfaces where activity is generated, adsorbed, coprecipitated, remobilised, buried, resuspended or incorporated into low-solubility sulfate phases such as radiobarite. This review develops a framework-guided synthesis of²²⁶Ra and²²⁸Ra in marine sediments, produced water, NORM scale, oily sludge, sediment-water exchange, analytical methods and radiological risk assessment. The proposed framework organises the evidence into five domains: source terms, host phases, mobility processes, analytical observability and exposure relevance. Recent studies show that produced-water radium can precipitate as micron-sized radiobarite or radiostrontiobarite particles, radium-bearing barite scales may preserve strong mineralogical control over solubility and release and ecological dose assessment depends on exposure geometry, partitioning assumptions, mineral incorporation, progeny ingrowth, sediment mixing depth and organism occupancy. Bulk activity concentration alone is therefore insufficient for interpreting radiological significance. Future monitoring should integrate²²⁶Ra and²²⁸Ra activity, isotope ratios, porewater measurements, Ba-Sr-Ca-SO₄chemistry, mineralogical characterisation, phase-specific activity, leaching tests, site-specificK_dvalues and tiered dose modelling. By reframing marine sediments as active radium reaction zones, this review provides a practical basis for improved monitoring, offshore NORM management and environmental radiation protection.