Radiocesium is an especially difficult analytical target because cesium-137 has a half-life of 30.2 years and cesium-134 has a half-life of 2.06 years, yet both can occur at extremely low concentrations in seawater. Major sources include fallout from atmospheric nuclear weapons tests, accidental releases such as Chernobyl and Fukushima, and authorized discharges from nuclear-fuel reprocessing plants. Before Fukushima, the review estimates that global fallout, local fallout and reprocessing discharges contributed approximately 69%, 24% and 7%, respectively, of global cesium-137 inputs. The 2011 Fukushima accident released about 19–25 petabecquerels of cesium-137, with approximately 15–20 petabecquerels entering the ocean. Detection therefore depends on concentrating cesium from tens or even thousands of litres of seawater into a compact medium that can be measured reliably.

Ammonium phosphomolybdate, or AMP, remains one of the two established analytical workhorses. It is a heteropolyacid salt built around a negatively charged Keggin framework, commonly written as (NH4)3PMo12O40·nH2O, whose interstitial ammonium ions can exchange with dissolved Cs+. The large, weakly hydrated Cs+ ion preferentially occupies bridging oxygen sites in the framework, allowing the exchange of Cs+ for NH4+ even in acidic media. A silica-based AMP exchanger has adsorbed cesium across nitric acid concentrations of 0.001–3 mol L−1. Conventional AMP coprecipitation is mature and permits chemical-recovery correction: reported precipitate yields for 20-litre seawater tests exceeded 97%, and radiochemical yields of 96.1–100.1% were obtained in separate 137Cs-spiked 5-litre samples. Its main burdens are transportation of large water volumes, acidification, bulky containers, slow settling, filtration and approximately a week of pretreatment.

Immobilizing AMP in polyacrylonitrile, or PAN, converts the fragile powder into a usable column medium. One Fukushima seawater study used 5 mL of AMP–PAN resin to process 20 litres at 35–40 mL min−1 and reported chemical recovery of 93.5% ± 5% across 55 samples; direct gamma spectrometry then reduced processing from several days to several hours. A 25 mL column processed about 100 litres at 240–320 mL min−1 in roughly six hours, but its six recoveries averaged 88.1% ± 3.3% and fell as flow increased. These results illustrate the central compromise: faster columns increase throughput but reduce contact time and recovery, while specialized resin remains comparatively expensive. Composite AMP systems—including granular and mesoporous forms, magnetic particles and graphene-oxide membranes—are promising, but most have not yet been systematically validated for trace radiocesium in large volumes of low-activity natural seawater.

Ferrocyanides offer the other established route. Copper ferrocyanide and potassium nickel hexacyanoferrate contain negatively charged Prussian-blue-type frameworks whose interstitial sodium or potassium can be replaced by Cs+. The ion sheds part of its hydration shell to enter the structure, where the framework charge, cyanide-bridge environment and exchange sites stabilize it. Copper ferrocyanide cartridges can enrich seawater in the field: a paired system processed 800–5,000 litres at 4–6 L min−1, and the activity ratio in the second cartridge was used to detect breakthrough. The recommended ratio was below roughly 0.2–0.3 for about 1,000 litres and 5 g of adsorbent; ratios reached 0.5–0.8 near 2,000 litres and 0.6–0.9 in five of six samples at 4,000–5,000 litres, making correction increasingly unreliable. Later nonwoven cartridges could be counted directly: 20 litres at 0.5 L min−1 took 40 minutes, with field recovery above 93%, although raising the flow to 2.5 L min−1 lowered recovery to 84–86%.

For accident-contaminated water, zeolites have the advantage of an established engineering role, relatively low raw-material cost and a framework that can exchange Cs+ with sodium, potassium, calcium and other cations. Following Fukushima, herschelite-packed KURION columns provided principal upstream cesium removal, while the parallel SARRY system used IONSIV IE-96 chabazite followed by IE-911 crystalline silicotitanate. Their advantages come with a major constraint: sea salts compete strongly for the same exchange sites. The capacity of KURION herschelite in 3.4 wt% sea-salt solution was approximately one-tenth of its capacity in pure water, and salinity also reduced the effective volume treated by a dynamic bed. Low-silica Na-CHA has separately removed more than 99% of ppt-level cesium-137 in actual nuclear-power-plant wastewater, but such treatment evidence does not establish the material as a principal tracer for quantitative seawater analysis.

Crystalline silicotitanates and layered titanates are tailored more explicitly to high-loading treatment streams. In H-CST, Cs+ enters eight-membered-ring channels and replaces H+, with local oxygen coordination helping stabilize the exchanged structure. Layered titanates instead exchange sodium, potassium or hydrogen from interlayers, while surface hydroxyls and sheet edges may also participate. TAM-5 separated ppm-level Cs+ at pH above 14 and sodium concentrations above 5 mol L−1. H-CTO nanosheets reached a reported maximum capacity of 329 mg g−1 and could be regenerated with 0.2 mol L−1 HCl, while a hydrophilic HTO-3 material reached 360 mg g−1 and equilibrium in about two hours. Titanium-based ion sieves and electrically controlled titanosilicate electrodes offer still more specialized routes, including preselected binding sites and potential-controlled intercalation and release, but many nanstructured forms remain difficult to shape and recover.

Metal sulfides and ion-imprinted materials provide another route to selective capture in hostile matrices. Layered sulfides combine exchange of interlayer cations with strong Cs···S interactions at polarizable sulfur sites. The layered Ti/Sn material KTSS reached equilibrium in about one minute and had a maximum capacity of 450.12 mg g−1. FJSM-KCGTS was built with Cs+ as a template, activated with K+ after template removal, and retained more than 99% removal in actual industrial wastewater containing 137Cs; its capacity in spiked seawater was 206.44 mg g−1. It also retained more than 99.5% removal after 100 or 200 kGy gamma irradiation and more than 98.97% after three regenerations with 1 mol L−1 ammonium chloride. These are encouraging treatment results, but most seawater experiments used elevated stable-Cs spikes and therefore do not demonstrate quantitative recovery of trace 137Cs from natural seawater.

The frontier in analytical enrichment is increasingly molecular. Metal-organic frameworks can bind Cs+ through framework counterions, sulfonic or carboxylic groups, and crown-ether cavities that mimic the ion’s preferred coordination environment. ZJU-X102 incorporates a 24-crown-8 unit and has a reported maximum capacity of 121 mg g−1, while an anionic indium-based layered framework reached 297.67 mg g−1 and a cesium/strontium separation factor of about 320. An NH2-MIL-125(Ti)@ZIF-8 heterostructure reported 392.62 mg g−1 capacity by adding interfacial sites. Immobilized macrocycles are more selective still: a calixarene resin had a Cs+ selectivity coefficient above 300 in nitric-acid feed and retained performance after 500 kGy irradiation. Their narrow recognition cavities suit small-volume enrichment or fine separation, but costly synthesis, ligand loss, salt tolerance and competition from potassium limit seawater use.

The review’s practical conclusion is that no material yet wins every category. AMP and ferrocyanide systems have the clearest foundation for quantitative seawater analysis, yet acidification, column breakthrough, flow sensitivity and cost remain important limitations. Zeolites and crystalline silicotitanates have demonstrated fixed-bed treatment of accident-contaminated water, but seawater salts reduce uptake and effective bed volume. Emerging materials should therefore be judged by the application they are intended to serve. Analytical candidates need validation in low-activity natural seawater for overall recovery, blanks, usable flow rates and maximum treatable volume. Treatment candidates require dynamic breakthrough, service life, radiation stability, leaching and safe immobilization data. Cold-sintered Cs-AMP and thermally converted Cs-zeolite also show how adsorption can be linked to waste-volume reduction and final disposal, but no laboratory capacity result or stable-Cs spike substitutes for sustained, trace-level field validation.

Subject of Research: Materials for enriching radioactive cesium isotopes from seawater and treating nuclear-polluted water

Article Title: Materials used for enriching radioactive cesium isotopes from seawater

Article References: Ling, C., Qian, S., Zhang, K., Zhu, S., Gu, Y., Ma, Z., & Ren, Y. (2026). Materials used for enriching radioactive cesium isotopes from seawater. Frontiers in Marine Science, 13, Article 1996662. https://doi.org/10.3389/fmars.2026.1996662

Image Credits: AI Generated

DOI: 10.3389/fmars.2026.1996662

Keywords: radiocesium, cesium enrichment, seawater analysis, nuclear wastewater, adsorption materials, ammonium phosphomolybdate, ferrocyanides, zeolites, metal-organic frameworks, water treatment, Materials, used

Rather than identifying one universally effective treatment, the review argues that countermeasures should be matched to local soil mineralogy, crop species, potassium status and contamination level. The first barrier is the soil itself. Cesium reaches plant roots through the dissolved soil pool because it behaves as a potassium analogue, but its persistence depends strongly on the minerals present.

Cesium-137 binds preferentially to frayed-edge sites within micaceous and illitic clay minerals, which can trap it for long periods. Catchment-scale modeling indicates that about 95% of cesium-137 in undisturbed soils remains strongly bound within the top 2 cm, while much of the remainder is concentrated in clay-sized particles and the upper 5 cm rooting zone. Total clay content alone, however, is a poor guide to crop contamination.

A survey of 925 farmland soils across northeastern Japan found a radiocesium interception potential of 1,693 ± 1,404 mmol kg−1, with a range of 73–12,700 mmol kg−1; vermiculite and illite were the principal mineralogical predictors. Sands, peats and highly weathered tropical soils lack these strong fixation sites, making exchangeable potassium and other competing cations more influential. Organic matter presents a different hazard.

It can retain cesium through cation exchange, but that association is comparatively non-specific and the cesium remains available for root uptake. Fukushima studies also indicate that abundant organic matter can physically obstruct clay sites responsible for stronger fixation. The distinction between total contamination and root-accessible contamination therefore matters when selecting a remedy.

A field with a large total inventory may present a modest bioavailable pool if its clay minerals immobilize cesium, whereas a field with less total contamination can sustain uptake when much of the inventory is exchangeable or organically bound. The review cautions against treating interception potential as a universal value or assuming that a countermeasure effective in one landscape will transfer directly to another. At the root surface, potassium transporters become unintended gateways.

Cesium and potassium have similar hydrated ionic radii and charge densities, so plants equipped to acquire scarce potassium also import cesium. In rice, the high-affinity transporter OsHAK1 is estimated to mediate 80–90% of total cesium uptake when active, with channels such as OsAKT1 and voltage-insensitive cation channels providing secondary routes. A comparable pattern occurs in Arabidopsis, where AtHAK5 drives high-affinity uptake and is strongly induced when internal potassium falls below a critical threshold.

That response can create a hazardous feedback: potassium-deficient plants activate the same transport systems that inadvertently admit radiocesium. Potassium fertilization therefore has a dual function. Raising exchangeable potassium competitively discourages cesium at transporter binding sites, but it also reduces the low-potassium signaling that induces the principal uptake genes.

This cascade passes through a calcium-signaling network in which sensors CBL1 and CBL9 activate kinases including CIPK23. CIPK23 phosphorylates HAK5 and AKT1, while structural studies show how phosphorylation changes AKT1 from a two-fold to a four-fold symmetric configuration associated with channel opening. Japanese field guidance cited by the review recommends maintaining exchangeable potassium near 200 mg kg−1, equivalent to approximately 0.25–0.33 g K₂O kg−1, to keep the soil-solution cesium-to-potassium ratio low.

Basal applications before sowing also outperform later top-dressing in buckwheat because radiocesium uptake is concentrated during early vegetative growth. Nevertheless, required rates differ among soils, and repeated heavy inputs can be costly and complicate broader nutrient management. Stopping cesium at the roots is only part of the task, because food safety ultimately depends on what reaches leaves, husks and grain.

The review identifies xylem loading as a distinct regulatory bottleneck. In Arabidopsis, disabling the stelar potassium outward-rectifier SKOR sharply reduced cesium movement from roots to shoots while leaving a disproportionate share in roots. Cryo-electron microscopy revealed unusual two-fold cytoplasmic symmetry in SKOR, unlike the four-fold arrangement of the inward-rectifying channel AKT1, helping explain how outward transport is achieved.

The rice orthologue OsK5.2 likewise participates in xylem potassium release. These results identify a second line of defense in which a crop might retain radiocesium in roots while limiting its delivery to harvestable tissues. Structural mutations, chemical inhibitors and breeding targets emerge from this mechanism, but their effects on potassium nutrition, yield and grain quality remain to be established.

Sodium provides a more surprising control point. Rice lacking the transporter OsHKT2;1, which admits sodium under potassium starvation, accumulated more cesium in shoots than wild-type plants rather than less. Isotope tracing revealed a negative relationship between internal sodium accumulation and cesium translocation, indicating that sodium taken up through OsHKT2;1 suppresses cesium loading into the xylem.

When sodium uptake was restricted, the plants compensated by transporting more cesium upward. The pattern was reproduced over three seasons, from 2019 to 2021, in a contaminated Fukushima paddy field, where mutants accumulated significantly more cesium in shoots, husks and brown rice. The same antagonism helps explain the low-radiocesium rice mutant lcs1, in which loss of the OsSOS2 kinase disrupts sodium extrusion and alters expression of several cesium- and potassium-transport genes.

These observations do not justify adding salt to crops: excess salinity suppresses yields, and the lcs1 mutation increases sensitivity to sodium chloride under experimental conditions. Genetic engineering can act more directly. CRISPR-Cas9 inactivation of OsHAK1 produced rice that, when grown in heavily contaminated Fukushima soil, showed more than a 60-fold reduction in shoot cesium-137 and an approximately 30-fold reduction in root retention compared with wild-type plants.

Grain concentrations fell within regulatory limits, while the edited lines maintained comparable vegetative growth, biomass and yield under standard potassium regimes. The lcs1 mutant produced grain cesium roughly 50% below standard cultivars in reported tests. Disruption of SKOR or components of the calcium-signaling network may provide further routes to reducing translocation, but their agronomic performance has not yet been established.

Regulatory treatment also differs sharply: Japan’s Site-Directed Nuclease-1 framework exempts foreign-DNA-free edits from genetically modified organism rules, whereas the European Union classifies equivalent edits as GMOs. A gene can therefore be an effective biochemical target without being an immediately deployable product. Soil amendments and biological partnerships broaden the available options, but their evidence is less uniform.

Porous biochar can sorb cesium through its internal micropores and negatively charged functional groups, and greenhouse trials have reported large reductions in plant tissue when it is combined with adequate potassium. Its performance varies with feedstock, soil mineralogy, competing ions and ageing, and direct field evidence from Fukushima remains limited. Zeolite and vermiculite can transiently reduce exchangeable cesium in low-retention soils, yet aging tests show that their durable contribution is small where native clay already fixes cesium strongly.

Legume root nodules can retain cesium, and soybean nodule number is inversely associated with shoot cesium after accounting for soil potassium, but this observational relationship does not establish causation. Arbuscular mycorrhizal fungi are less predictable: depending on the host–fungus pairing and environmental conditions, they can decrease, leave unchanged or increase radionuclide transfer, so they cannot be treated as universal biological filters. The practical future is integrated rather than single-factor.

Potassium management remains the most widely applicable intervention, particularly in sandy or low-retention soils, but its application rate should be calibrated locally. Physical removal, clean-soil replacement and plough-layer inversion can reduce near-surface contamination quickly, yet they damage soil structure, remove organic matter and create large volumes of contaminated material requiring secure management. For perennial crops, dormant-season bark washing and removal of contaminated branches can address direct atmospheric deposition that root-based measures cannot.

The review’s principal research priority is multi-season, multi-site evaluation of edited cultivars, exchangeable-potassium regimes and amendments across contrasting mineralogies and cropping systems. Such trials must measure more than grain cesium: yield, potassium and sodium status, soil nitrogen, nutrient availability, amendment persistence and practical implementation constraints also need quantification. The accumulated evidence supports a move beyond indiscriminate fertilization toward coordinated management in which soil physics, transporter biology and crop genetics form parts of one food-safety system.

Subject of Research: Molecular, agronomic and ecological strategies for reducing radiocesium uptake and translocation in crops

Article Title: Suppressing radiocesium uptake and root-to-shoot translocation in crops: Molecular, agronomic, and ecological strategies

Article References: Rahman, I., Khan, B. M., Hossen, I., & Rahman, Z. (2026). Suppressing radiocesium uptake and root-to-shoot translocation in crops: Molecular, agronomic, and ecological strategies. Environmental Geochemistry and Health, 48(16), Article 648. https://doi.org/10.1007/s10653-026-03520-1

Image Credits: AI Generated

DOI: 10.1007/s10653-026-03520-1

Keywords: radiocesium contamination, cesium-137, crop food safety, soil mineralogy, potassium fertilization, plant ion transporters, xylem transport, genome editing, agricultural remediation, Suppressing, radiocesium, uptake

Cesium-137 is a particularly stubborn contaminant. Because the element binds tightly to soil particles and barely migrates downward, it lingers in the top layers of fields and forests where crops and wildlife are most exposed. Its radioactive half-life of roughly thirty years means that contaminated land remains a concern for generations. Among the group I alkali metals, cesium is also the most biologically toxic; even non-radioactive cesium, when accumulated in large amounts, stunts the growth of plants and other organisms. After Fukushima, the standard response was to strip away the contaminated surface layer of soil, an approach that proved enormously expensive and labor-intensive, generating mountains of waste that still await disposal.

Phytoremediation, the use of plants to extract contaminants from soil, has long been touted as a greener alternative. The catch is that most plants absorb cesium poorly, limiting how much of the element they can remove per growing season. Quinoa, the South American pseudo-cereal that has become a global superfood, stands out as an exception. Certain quinoa cultivars grow to around two meters tall and produce substantial biomass, and the species is a halophyte, a plant adapted to salty conditions. Previous work by the same research group showed that applying an appropriate amount of sodium chloride enhances quinoa’s aboveground growth and increases its cesium uptake, making the crop a leading candidate for cesium removal from polluted fields.

Quinoa’s leaves are also studded with epidermal bladder cells, translucent balloon-like structures on the leaf surface that have long been credited with boosting salt tolerance by sequestering excess ions. Earlier measurements showed that cesium concentrations in these bladder cells exceed those in the leaf cells themselves, leading researchers to consider the bladders the key sites of cesium accumulation. But a critical question remained: when soil cesium levels climb high enough to poison the plant, does quinoa still grow, and do the bladder cells keep working? Answering that question was the central aim of the new study, led by Katsunori Isobe with colleagues Yuta Oku and Masao Higo.

The team ran four pot experiments in 2023 using the quinoa variety CICA-127, grown in Wagner pots filled with 2.5 kilograms of Andosol field soil. In the first experiment, they applied cesium chloride at rates ranging from 0.3 to 1.0 grams per pot. Growth declined steadily as cesium doses rose: plant height dropped significantly at 0.5 grams and above, while leaf area and the fresh and dry weights of the aboveground parts fell significantly at the highest dose. Severely stressed plants showed chlorosis spreading from the older basal leaves, and under the harshest treatment the leaves senesced prematurely, leaving too little tissue to even measure cesium content. The message was clear: high soil cesium can shut quinoa down entirely.

The second experiment probed where the cesium and potassium ended up inside the leaves. The researchers brushed the epidermal bladder cells off the leaf surfaces and analyzed the two compartments separately by atomic absorption spectrophotometry. Cesium content rose in both compartments as cesium chloride application increased, and in every treatment the bladder cells held significantly more cesium than the leaf cells. Potassium followed the same pattern, concentrating in the bladders. Crucially, however, potassium levels in the leaf cells did not decline when cesium was applied, which ruled out a long-standing assumption: the growth inhibition caused by cesium was not simply a matter of potassium deficiency, since the plants’ leaf cells retained their potassium even as growth stalled.

With the toxicity confirmed and its mechanism still murky, the team turned to the salt question. In the third and fourth experiments, they applied sodium chloride alone, cesium chloride alone, and the two together. Sodium chloride by itself actually promoted growth, with leaf area and fresh weight significantly exceeding the untreated controls. More remarkably, when cesium chloride and sodium chloride were applied together, the growth suppression vanished: plants receiving both chemicals grew as well as, or better than, untreated controls, with significant differences recorded in plant height, leaf area, and fresh and dry weights compared with plants receiving cesium alone. The salt had neutralized the poison.

The elemental analysis made the result even more intriguing. The researchers had expected that if sodium chloride rescued growth, it might do so by blocking cesium uptake, diluting the toxin in the leaves. Instead, cesium content in the leaf cells was similar to, or even higher than, that in plants treated with cesium chloride alone. In other words, the leaves carried a cesium load that should have been toxic, yet the plants thrived. The authors propose two possible explanations: either the accumulated cesium no longer inhibited growth once sodium was present, or sodium itself acted as a growth promoter. Because no potassium fertilizer was used in any experiment, absorbed sodium may have partially substituted for potassium in maintaining cellular turgor and enzyme activity, a substitution documented in other halophytes. Studies in ice plants and Arabidopsis have similarly shown that modest salt applications stimulate growth, whether by boosting antioxidants and beneficial metabolites or by enhancing sulfur, zinc, and copper uptake and photosynthesis.

The bladder cell story took an unexpected turn as well. Under sodium chloride treatment, sodium content was higher in the leaf cells than in the bladder cells, the reverse of the pattern seen without added salt. This indicates that quinoa does not actively shuttle sodium from leaf cells into the bladders even when internal sodium rises, echoing recent findings that bladder-cell-free quinoa mutants tolerate salinity surprisingly well. The bladders, it seems, are not the salt-tolerance workhorses they were assumed to be. Yet they do concentrate cesium and potassium far above leaf-cell levels under all conditions, suggesting they function instead as organs for detoxifying and excreting cesium specifically. For phytoremediation, that is arguably the more valuable job.

Taken together, the results sketch a practical roadmap. Quinoa can be classified as a cesium-accumulating plant, consistent with broader surveys showing that members of the Amaranthaceae family possess preferential cesium uptake and high translocation efficiency. By pairing the crop with sodium chloride amendment, farmers and remediation teams could harvest more biomass from cesium-contaminated fields, and each kilogram of that biomass would carry a heavier cesium burden, even where soil contamination is severe enough to stunt untreated plants. The approach avoids the genetic modification and ammonium fertilizers explored in earlier studies on rice and Arabidopsis, relying instead on a cheap, widely available compound. The authors caution that the precise physiological role of sodium inside quinoa remains unresolved, and further work is needed to pin down how it alleviates cesium’s multifactorial damage, which modern research links to disrupted signaling, oxidative stress, and protein-folding problems rather than simple potassium starvation. Still, the core demonstration stands: with a handful of salt, one of the world’s most resilient crops becomes an even more effective vacuum for one of the world’s most persistent pollutants, bringing plant-based cleanup of radiocesium-contaminated land a decisive step closer to reality.

Subject of Research: Sodium chloride enhancement of cesium uptake and growth in quinoa under cesium stress for phytoremediation

Article Title: Application of sodium chloride improves quinoa (Chenopodium quinoa Willd.) growth and cesium accumulation under cesium stress

Article References: Isobe, K., Oku, Y., & Higo, M. (2026). Application of sodium chloride improves quinoa (Chenopodium quinoa Willd.) growth and cesium accumulation under cesium stress. Discover Plants, 3(1), Article 399. https://doi.org/10.1007/s44372-026-00882-9

Image Credits: AI Generated

DOI: 10.1007/s44372-026-00882-9

Keywords: quinoa, cesium, sodium chloride, phytoremediation, epidermal bladder cells, halophyte, radiocesium, Fukushima, soil contamination, potassium, plant physiology, Discover Plants