The study, published in the open-access journal Discover Geoscience, analysed twenty sampling sites spaced five to ten kilometres apart along the shoreline. Sediment was collected during the pre-monsoon season using a Peterson grab sampler, a timing chosen deliberately because pre-monsoon conditions reveal sediment texture and ecological patterns most clearly and because metal concentrations tend to peak in this season relative to monsoon and post-monsoon periods. Each roughly two-kilogram sample was cleared of shells and litter, air-dried, oven-dried to a stable weight and prepared for a suite of analytical techniques that together paint a comprehensive portrait of the coastal geochemistry.

The physical characterisation alone yielded striking results. Grain size analysis by mechanical sieving showed that the sediments are overwhelmingly fine-grained, classified predominantly as silty clay loam. Sand content ranged from a mere 0.30 percent to 9.18 percent, while silt dominated at 28.12 to 84.97 percent and clay ranged from 13.97 to 71.01 percent. The pH measurements told a story of gentle alkalinity: most sites fell in the very slightly alkaline range of 7.1 to 7.5, with only a handful of mildly acidic readings near 6.6 to 6.9 and no strongly acidic or strongly alkaline samples anywhere. Electrical conductivity values between 0.20 and 0.82 dS/m confirmed non-saline conditions with limited ionic activity, reflecting the local geochemical and hydrodynamic conditions of this monsoon-battered coast.

For the geochemical work, the team turned to energy-dispersive X-ray fluorescence, a non-destructive spectrometric technique that quantifies elemental concentrations with the help of certified reference materials such as IAEA-433 and NIST-2709a. Eleven elements were measured: vanadium, chromium, manganese, iron, copper, zinc, barium, aluminium, zirconium, arsenic and lead. Their abundance followed a clear hierarchy, with aluminium and iron at the top, followed by zirconium, manganese, barium, vanadium, chromium, zinc, copper, lead and finally arsenic at the lowest concentrations. Aluminium and iron dominate because they occur naturally at high levels in sediments, but the enrichment patterns of the trace metals point to something more troubling: anthropogenic inputs from wastewater discharge, aquaculture and shipping, alongside industrial, agricultural and vehicular sources.

The radiological measurements revealed why this coast has fascinated radioecologists for decades. Using a 3-by-3-inch NaI(Tl) scintillation detector shielded by four inches of lead on each side, which suppresses background by roughly 95 percent, the researchers counted each sample for 20,000 seconds after a four-week sealing period to allow the uranium-238 and thorium-238 decay chains to reach secular equilibrium. The mean activity concentrations of uranium-238, thorium-232 and potassium-40 all exceeded the global average values of 35, 30 and 400 Bq per kilogram respectively. The culprit is mineralogy: monazite, a phosphate mineral packed with thorium and lesser amounts of uranium, accumulates in these beach sands alongside zircon, garnet, ilmenite, rutile and apatite, driven shoreward by the net movement of heavy minerals in the wave-dominated coastal zone.

Magnetic susceptibility added a third dimension to the picture. Measured with a Bartington MS2B dual-frequency meter at low frequency of 0.47 kilohertz and high frequency of 4.7 kilohertz, with five readings per sample averaged at each frequency, the technique tracks the concentration of magnetic mineral grains in the sediment. The difference between the low- and high-frequency readings, expressed as frequency-dependent susceptibility, serves as a proxy for fine-grained magnetic particles. Together with the radiochemical and geochemical data, these measurements fed into a statistical framework built on Pearson correlation, factor analysis and hierarchical cluster analysis conducted in SPSS, an approach the authors argue should become a model for integrated sediment assessment worldwide.

The statistical engine of the study produced some of its most intriguing findings. For the magnetic parameters, factor analysis identified two components explaining 61.71 percent of total variance, with the first factor loading positively on clay percentage and both susceptibility measures. Correlation analysis reinforced the pattern: high-frequency susceptibility rose with clay content and fell with sand, silt, pH and conductivity, indicating that magnetic properties strengthen as the fine fraction increases. For heavy metals, two principal components accounted for about 56 percent of the variance, with the first dominated by vanadium, zirconium, arsenic, zinc, iron and manganese in a signature the authors attribute to anthropogenic pollution, and the second capturing sediment texture and physicochemical conditions through silt, pH, conductivity and aluminium. Notably, most metals correlated positively with clay and pH, confirming that clay particles, with their enormous specific surface area, are the preferred adsorption substrate for trace metals.

The radionuclide statistics told a subtly different story. Principal component analysis revealed two components explaining 71.66 percent of variance, with the first dominated by uranium-238, thorium-232 and potassium-40, indicating a geogenic rather than anthropogenic source. Clay percentage showed a significant positive association with all three radionuclides, while sand and silt correlated negatively, and the clay correlations were considerably stronger. The message is consistent: activity concentrations climb as particle size decreases, because the heavy radioactive minerals are concentrated in the finer fractions. Intriguingly, pH and electrical conductivity showed little influence on radionuclide levels, and cluster analysis separated the radionuclides into a group distinct from the physicochemical parameters, underscoring that geology, not sediment chemistry, governs the distribution of natural radioactivity here. A negative loading for pH in the factor model did suggest, however, that radionuclide mobility may increase under acidic conditions.

Descriptive statistics added texture to the narrative. Most variables displayed strong positive skewness, with sharp right tails for sand, clay, frequency-dependent susceptibility, vanadium, iron, chromium, zinc, zirconium, arsenic, thorium-232 and potassium-40, signalling localised enrichment hotspots and high-value outliers scattered along the coast. Silt, by contrast, skewed negatively, while pH and lead were nearly symmetrical. Overall, the skewness and kurtosis coefficients deviated substantially from those of a normal distribution, pointing toward log-normal behaviour that reflects sediment heterogeneity and the patchwork of local geochemical processes operating along this dynamic shoreline.

The authors conclude that clay and silt percentages emerge as the master variables controlling the concentrations of the studied parameters, and that the combination of spectroscopic techniques with multivariate statistics offers a powerful, transferable methodology for disentangling natural from human influences in coastal sediments. In a region where monazite-rich black sands have shaped both the environment and the lives of coastal communities, understanding how grain size, pH and conductivity modulate the behaviour of radionuclides and heavy metals is more than an academic exercise. It provides environmental managers with a practical tool for monitoring pollution from agricultural runoff, industrial waste and urban encroachment, and offers future researchers a tested framework for assessing environmental quality on one of the most naturally radioactive coastlines on Earth.

Subject of Research: Influence of sediment physicochemical properties on natural radionuclides, heavy metals and magnetic susceptibility in Kerala coast beach sediments.

Article Title: Influence of physicochemical properties on natural radionuclides, heavy metal, and magnetic susceptibility in the sediment of Kerala Coast with statistical approach

Article References: Kiruba, T., Jayaprakash, P., Raju, K., Venkatamuthukumar, J., Ravi, A., & Ravisankar, R. (2026). Influence of physicochemical properties on natural radionuclides, heavy metal, and magnetic susceptibility in the sediment of Kerala Coast with statistical approach. Discover Geoscience, 4(1), Article 374. https://doi.org/10.1007/s44288-026-00753-6

Image Credits: AI Generated

DOI: 10.1007/s44288-026-00753-6

Keywords: Kerala coast, natural radionuclides, heavy metals, magnetic susceptibility, monazite, sediment texture, high background radiation area, gamma-ray spectrometry, EDXRF, multivariate analysis, clay content, geochemistry

The team, led by Xuan-Quang Nguyen of Dong Nai Technology University and Trung-Tien Chu of VNU School of Interdisciplinary Sciences and Arts, together with Van-Hao Duong and Thanh-Xuan Pham-Thi, found striking differences between the isotopes. Potassium-40 dominated every sample by a wide margin, with mean activity concentrations of 101 plus or minus 8.6 becquerels per kilogram, ranging from 65 to 169 becquerels per kilogram. This was expected, since potassium is an essential element that fish regulate biologically regardless of environmental conditions, and its radioactive isotope makes up a fixed fraction of all natural potassium. Polonium-210 followed at 11.8 plus or minus 0.9 becquerels per kilogram, lead-210 at 9.1 plus or minus 1.7, radium-226 at 7.69 plus or minus 1.04, and radium-228 at just 1.22 plus or minus 0.2 becquerels per kilogram, with some measurements falling below detection limits.

These differences are not random. Each radionuclide behaves according to its own chemistry in aquatic systems. Polonium-210, a highly radiotoxic alpha emitter from the uranium-238 decay chain, is known to bind strongly to proteins and organic matter, making it particularly prone to bioaccumulation in fish tissue. Lead-210, its precursor in the same decay chain, behaves differently, attaching to particles and sediments. Radium isotopes, chemical analogs of calcium, tend to concentrate in bone and calcified structures. Potassium-40, as an essential element analog, is homeostatically controlled. The Red River itself carries a heavy sediment load shaped by decades of dam construction and land-use change in its watershed, and earlier work by some of the same authors documented elevated natural radioactivity in the river’s surface sediments, providing a plausible source term for the isotopes measured in fish.

One of the most intriguing findings concerns fish biology. The researchers observed a negative correlation between radium-226 concentrations and body weight, suggesting that smaller fish accumulate proportionally more of this isotope than larger individuals. This morphological influence on radioactivity absorption has practical implications for monitoring programs, which often assume that radionuclide concentrations scale simply with size or trophic position. If body weight systematically modulates uptake, then sampling strategies that ignore biological characteristics could misestimate the radiological burden carried by a fish population, and by extension the dose delivered to human consumers who prefer particular size classes.

To translate these measurements into human health terms, the team calculated annual effective doses from fish consumption. The average annual effective dose came to 0.105 millisieverts per year, with individual values ranging from 0.030 to 0.247 millisieverts per year. These figures sit comfortably below internationally recognized safety thresholds, which typically allow on the order of 1 millisievert per year of additional exposure from all practices combined. Lifetime cancer risk estimates ranged from 1.4 times ten to the minus seven to 7.7 times ten to the minus seven, well within the acceptable limits used by radiological protection agencies worldwide. In plain terms, an ordinary consumer of Red River fish faces a negligible incremental cancer risk from natural radioactivity in the fish they eat.

The story is more nuanced for the fish themselves. Using the ERICA Tool, a widely adopted software framework for assessing ionizing radiation doses to wildlife, the researchers estimated total dose rates to the fish ranging from 0.2 to 10.4 micrograys per hour, with a mean of 3.0 micrograys per hour. Most species fell well below the screening threshold of 10 micrograys per hour, indicating negligible ecological risk. But one species, the Zig-zag eel, exceeded that threshold, signaling a potential radiological concern for this species specifically. The result highlights that ecological risk from natural radionuclides is not distributed evenly across a food web; species-specific feeding habits, habitat use, and physiology can push individual species over protective screening levels even when the community as a whole appears safe.

The Zig-zag eel finding deserves careful interpretation. Screening thresholds in tools like ERICA are deliberately conservative, designed to flag cases that warrant more detailed investigation rather than to declare harm definitively. Exceeding the threshold does not mean the eel population is being damaged, but it does mean the species merits closer study, including tissue-specific dose modeling and, ideally, biological endpoints such as reproductive success. For a river basin that supports intensive fishing and aquaculture, identifying which species sit closest to ecological limits is a valuable early-warning capability.

The study also fills an important regional data gap. Vietnam’s Red River basin is home to tens of millions of people, and fish from the river and its delta contribute substantially to local protein intake. Yet systematic measurements of natural radionuclides in the basin’s freshwater biota have been scarce, with prior work focusing mainly on sediments, soils, and thermal waters. By establishing baseline activity concentrations across ten commercially and nutritionally important species, the researchers have created a reference point against which future changes, whether from industrial development, mining activity in the geologically radioactive highlands upstream, or shifts in sediment dynamics caused by dams, can be detected and evaluated.

Methodologically, the work demonstrates the value of combining direct radiometric measurement with biological covariates and dual risk frameworks, one for humans and one for wildlife. The inter-isotope variability observed, spanning nearly two orders of magnitude between radium-228 and potassium-40, underscores why single-isotope assessments can be misleading. Polonium-210, for example, typically contributes the dominant share of internal dose from fish consumption even when potassium-40 dominates total activity, because polonium’s alpha radiation carries far higher radiotoxicity per unit of activity. Comprehensive multi-isotope datasets like this one allow risk assessors to weight each nuclide appropriately rather than relying on activity totals alone.

For the public, the bottom line is reassuring: eating fish from the Red River does not pose a meaningful radiological health risk under current conditions. For scientists and regulators, the study offers something equally valuable, a rigorous baseline and a demonstration that fish biology matters in radiological monitoring. As radiation monitoring programs expand across Southeast Asia’s river systems, the Red River work suggests that the most informative datasets will be those that record not just what is in the water and sediment, but how the size, species, and ecology of the fish themselves shape the journey of natural radioactivity through the food web.

Subject of Research: Natural radionuclide accumulation in freshwater fish from the Red River, Vietnam, and its implications for human and ecological radiological risk

Article Title: Natural Radionuclides in Selected Freshwater Fishes from the Red River (Vietnam): Influence of Biological Characteristic and Implication for Human Health Risk

Article References: Nguyen, X.-Q., Duong, V.-H., Pham-Thi, T.-X., & Chu, T.-T. (2026). Natural Radionuclides in Selected Freshwater Fishes from the Red River (Vietnam): Influence of Biological Characteristic and Implication for Human Health Risk. Archives of Environmental Contamination and Toxicology, 91(2), Article 17. https://doi.org/10.1007/s00244-026-01217-1

Image Credits: AI Generated

DOI: 10.1007/s00244-026-01217-1

Keywords: natural radionuclides, Red River Vietnam, freshwater fish, polonium-210, potassium-40, radium-226, radiological risk assessment, ERICA Tool, food safety, annual effective dose, Zig-zag eel, radiation monitoring

The research, conducted by Blessing N. Ben-Festus and Festus Ben of the Centre for Advanced Materials Research and Development at Federal Polytechnic Ede in Nigeria, with Ben also affiliated with the Centre for Nanoengineering and Advanced Materials at the University of Johannesburg, focused on sediments within a tropical river estuarine system in southwestern Nigeria. The fieldwork was carried out in a waterway shaped by seasonal rainfall and runoff, artisanal and urban pressures, and the steady downstream delivery of weathered material from the surrounding landscape. Regions of this kind are often underrepresented in global radiological databases, which historically have emphasized temperate environments, making the new dataset a valuable reference point not only for Nigeria but for comparative assessments of depositional environments worldwide.

Technically, the study relied on gamma-ray spectrometry, the workhorse technique of environmental radiochemistry. Sediment samples collected from the estuary were prepared, sealed to allow radioactive equilibrium to be established, and then quantified using a calibrated sodium iodide detector, a scintillation-based instrument that records the characteristic gamma-ray energies emitted by decaying nuclides. Sodium iodide spectrometers are prized in field-adjacent laboratories for their high detection efficiency and relatively low cost, although they demand careful energy and efficiency calibration to resolve the photopeaks of interest. The authors followed established calibration practice, drawing on the well-documented performance characteristics of 3-inch by 3-inch NaI(Tl) detectors, to convert counts into activity concentrations expressed in becquerels per kilogram, a unit that describes the number of radioactive decays per second in each kilogram of dry sediment.

The measured activity concentrations told a consistent story. Potassium-40, the primordial isotope that has persisted since the formation of the Earth and pervades virtually all crustal material, averaged 490.50 plus or minus 7.66 becquerels per kilogram across the samples. Uranium-238, the head of the uranium decay series, averaged just 5.67 plus or minus 0.20 becquerels per kilogram, and thorium-232, the progenitor of the thorium series, registered 4.81 plus or minus 0.26 becquerels per kilogram. Benchmarked against the reference values published by the United Nations Scientific Committee on the Effects of Atomic Radiation, the potassium result ran about 16.79 percent above the global average, a modest elevation the authors attribute to the potassium-rich minerals weathered from the catchment’s bedrock and soils. By contrast, the uranium and thorium figures sat far below the corresponding global thresholds, at 82.82 percent and 89.31 percent below them, respectively, underscoring how strongly the local geology, rather than industrial contamination, controls the radiological signature of these deposits.

Raw concentrations, however, are only the starting point of a radiological risk assessment. Because potassium-40, uranium-238 and thorium-232 differ in the energy and intensity of the gamma radiation they emit, regulators and researchers combine them into derived indices that better approximate real-world exposure. The study calculated the radium equivalent activity, a composite quantity that weights the three nuclides according to their relative gamma dose contributions, and obtained a mean value of 50.32 becquerels per kilogram, well under the widely cited 370 becquerels per kilogram ceiling that marks the threshold above which structural or land-use restrictions might be considered. This single number already suggests that neither beachcombers nor construction workers handling dredged sediment would encounter unusual radiation fields at the site.

The dose-based indicators reinforce that conclusion. The absorbed gamma dose rate in air at one meter above the sediment surface averaged 26.13 nanogray per hour, translating into an annual effective dose of roughly 0.03 millisievert per year for a member of the public spending typical time near or on the sediments. For context, the global average outdoor terrestrial dose attributable to natural radionuclides is generally estimated at around 0.07 millisievert per year, meaning the Nigerian estuary delivers less than half of that conventional background. The team also evaluated the annual gonadal dose, a quantity used to approximate the genetically significant dose to reproductive organs, obtaining 191.64 microsieverts per year, again comfortably below the internationally recognized screening level of about 300 microsieverts per year. Taken together, these parameters indicate that external exposure pathways linked to the estuary’s sediments pose no significant radiological risk to the surrounding communities.

The findings matter for reasons that extend beyond a single river. Sediments are the memory of a river system: they trap not only radionuclides but also heavy metals, nutrients and pollutants, and their radioactive inventory reflects the interplay of bedrock composition, weathering intensity, grain-size sorting and hydrodynamic energy. In tropical climates, intense rainfall and episodic flooding periodically resuspend and redistribute these deposits, meaning that a baseline established today is the essential yardstick against which future disturbance, whether from mining, dredging, dam construction or land-use change, can be judged. Comparable investigations along the Arvand River in Iran, the Pashur River in Bangladesh, the Ravi River in Pakistan and the coastal wetlands of southern Taiwan have revealed that fluvial radioactivity can vary enormously with geology, and in some industrialized estuaries technogenic nuclides from mining discharges or phosphogypsum releases dominate the picture. Against that backdrop, the low uranium and thorium readings in this Nigerian system signal an environment whose radiological profile remains essentially natural.

The study also contributes methodological value to the radiological sciences. Gamma spectrometry with sodium iodide detectors requires meticulous attention to detection efficiency, coincidence summing effects and source-to-detector geometry, and the growing literature on detector calibration offers practical guidance for laboratories working with modest infrastructure. By demonstrating that credible, standards-aligned hazard assessments can be produced with such instrumentation, the research lowers the barrier for similar monitoring programs in other data-poor tropical basins. The authors acknowledge research assistants Miss Daud Ajarat Olaide and Mr. Adeyeni Tunmise Afolabi for their contributions during the field study, and the work was funded by the Centre for Advanced Materials Research and Development, highlighting the role of institutionally supported, locally grounded science in filling global environmental data gaps.

Looking ahead, the researchers position their dataset as a foundation for longitudinal monitoring. Natural radioactivity is not static: sediments are eroded, redeposited and chemically transformed, and the same estuary measured after a decade of accelerated development could present a different signature. The measured values, now archived in the peer-reviewed literature and available upon reasonable request, give regulators in Osun State and beyond a defensible pre-disturbance benchmark. They also give residents a rare piece of quantified good news: the muds beneath their river, far from being a hidden radiological hazard, are among the quieter sediments on the planet, holding only a whisper of the uranium and thorium that Earth’s crust normally carries, and a dose burden that any international safety authority would judge unremarkable.

Subject of Research: Measurement of natural radionuclide activity concentrations and radiological hazard indices in sediments of a tropical river estuarine system

Article Title: Sediment-associated natural radionuclide and radiological risk indicators in a tropical river estuarine system

Article References: Ben-Festus, B. N., & Ben, F. (2026). Sediment-associated natural radionuclide and radiological risk indicators in a tropical river estuarine system. Environmental Monitoring and Assessment, 198(10), Article 1069. https://doi.org/10.1007/s10661-026-15895-w

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15895-w

Keywords: natural radionuclides, gamma spectrometry, estuarine sediments, radiological risk, potassium-40, uranium-238, thorium-232, tropical river, environmental monitoring, radiation dose, Nigeria, radium equivalent activity