Iodine-129 in seawater offshore Fukushima: distribution, inorganic speciation, sources, and budget

Comparison of dissolved iodine measurements in seawater between inductively coupled plasma mass spectrometry and voltammetry

Two analytical methods, inductively coupled plasma mass spectrometry (ICP-MS) combined with high-performance liquid chromatography (HPLC) and voltammetry (VM), for three chemical species of dissolved iodine (iodide, iodate, and total dissolved iodine: TDI) were compared for dozens of coastal seawater samples owing to the compatibility of data between both methods. The median differences in the measured concentrations of TDI, total inorganic dissolved iodine (TII, the sum of iodide and iodate), and iodate between ICP-MS and VM were equivalent to 9.2, 13, and 14%, respectively. These differences were within the ranges that could be explained by the repeated-measurement precision of each measurement method for TDI, TII, and iodate. The difference for iodide was 19%, which was larger than the value based on the repeated-measurement precision for both methods. This is considered to be caused by the chemical instability and lower concentrations of iodide compared to other iodine species in seawater, in addition to the heterogeneity of natural samples. Finally, both methods provided reasonable measurement values for the iodine concentration in natural seawater samples.

Dielectric barrier discharge-induced chemical vapor generation for highly sensitive analysis of iodine in seawater by ICP-MS

BACKGROUND

The accurate determination of iodine in seawater is essential to understanding its impact on the environment and human health. Inductively coupled plasma mass spectrometry (ICP-MS) is a widely used technique for elemental analysis due to its high sensitivity, speed, and low limit of detection (LOD). However, its capability in the detection of iodine in complex matrix samples is still limited by the low sample introduction efficiency of pneumatic nebulization and the high ionization energy of iodine. Dielectric barrier discharge microplasma-induced vapor generation (DBD-μPIVG) is a sample introduction technique that has been widely coupled with atomic spectrometry due to its high vapor generation efficiency, rapid reaction speed, high anti-interference capability, and environmental friendliness.

RESULTS

A new method was developed for the rapid and sensitive determination of iodine using DBD-μPIVG coupled with ICP-MS. The DBD-μPIVG sample introduction technique can convert both iodide and iodate to their volatiles with a vapor generation efficiency of 70 %. The experimental conditions were optimized in detail, and the LOD for iodine was 0.04 μg L-1, which was lower compared to pneumatic nebulization and comparable to that after the extraction treatment. The relative standard deviation (RSD) obtained after 11 replicate determinations was 2.4%. Furthermore, the potential mechanism and anti-interference performance of the proposed method were also carefully investigated.

SIGNIFICANCE

Compared to other analytical methods for iodine analysis, this approach is environmentally friendly, exhibits high anti-interference capability and enables accurate determination of iodine in complex matrix samples. The high vapor generation efficiency of DBD-μPIVG improves the sensitivity for iodine detection and expands the applicable elemental range of DBD-μPIVG. Finally, the proposed method was successfully applied to analyze the iodine content in seawater samples obtained from the Chinese coastal waters and retains great potential for assessing the distribution of iodine in different sea areas.

Records of the riverine discharge of 129I in riverbank sediment after the Fukushima accident

Although 129I discharge from watersheds is fundamental for assessing long-term radiation effects on aquatic ecosystems, 129I originating from the Fukushima nuclear accident is yet be evaluated. This study investigated the transport behavior of 129I by riverbank surveys conducted from 2013 to 2015 in a watershed where the 129I/137Cs activity ratio is low in the mountainous area and high in the plain as of 2011. Until 2015, the 129I/137Cs activity ratio of the levee crown in the studied watershed was similar to that of the surrounding area in 2011. However, the 129I/137Cs ratios of the surface riverbank sediments were all low, indicating that radionuclides transported from the mountainous area were deposited on the riverbank in the plain. The vertical distribution of the 129I/137Cs ratio in the riverbank sediments indicated that some 129I and 137Cs deposited during the accident remained in the lower layers, but most were eroded immediately after the accident. Based on the 129I/137Cs ratios of sediments deposited on the riverbank, which remained constant until 2015 after the accident, the amount of 129I discharged to the ocean was determined from the previously evaluated 137Cs discharge. It was calculated that 1.8 × 105 Bq and 1.2 × 107 Bq of 129I were discharged with sediment from the studied watershed and the contaminated river watersheds (Abukuma River and Fukushima coastal rivers, including the study river), respectively. This amount of 129I was 0.3% of the 129I released from the Fukushima Dai-ichi Nuclear Power Plant into the ocean immediately after the accident. Furthermore, a comparison of the 129I/137Cs ratio showed that the continuous 129I and 137Cs discharge from the river contribute little to their amount in the seafloor sediments along the Fukushima coast.

Unraveling the mechanism of iodate adsorption by anthocyanin-rich fruit waste as green adsorbents for Applications of radioactive iodine remediation in water environment

In aquatic settings, radioactive iodine from nuclear waste can exist as iodate (IO3-). This study explored the efficiency and mechanism of IO3- adsorption by minimally modified anthocyanin-based adsorbents. Pomegranate peels and mangosteen pericarps were selected from an initial screening test and could remove over 70% of 10 mg/L IO3-. The adsorbents yielded adsorption capacity (q) of 9.59 mg/g and 2.31 mg/g, respectively, at room temperature. At 5 °C, q values increased to 14.5 and 5.13 mg/g, respectively. Pomegranate peels showed superior performance, with approximately 4 times the anthocyanin content of mangosteen pericarps. Both adsorbents took 120 min to reach adsorption equilibrium, and no desorption was observed after 8 days (I-131 half-time). Confirmation of physisorption was indicated by the fit of the pseudo-first-order reaction model, negative entropy (exothermic), and negative activation energy (Arrhenius equation). IO3- inclusion was confirmed through adsorbent surface modifications in scanning electron microscope images, the increased iodine content post-adsorption in energy-dispersive X-ray spectroscopy analysis, and alterations in peaks corresponding to anthocyanin-related functional groups in Fourier transform infrared spectroscopy analysis. X-ray absorption near-edge spectroscopy at 4564.54 eV showed that iodine was retained in the form of IO3-. Through the computational analysis, electrostatic forces, hydrogen bonds, and π-halogen interactions were deduced as mechanisms of IO3- adsorption by anthocyanin-based adsorbents. Anthocyanin-rich fruit wastes emerged as sustainable materials for eliminating IO3- from water.

Reconstructing atmospheric 129I deposition over 170 years with the varved sediment in the Sihailongwan Maar Lake, northeast China

Long-term deposition of atmospheric radioactive iodine-129 (129I) is important for assessing the impact of human nuclear activities (HNAs), but still not well understood in East Asia. In this study, we quantitatively reconstructed the deposition history of airborne 129I using varved sediment from Sihailongwan Maar Lake (SHLW) in northeast China. Our results revealed significant increases in 129I concentrations and 129I/127I atomic ratios since the 1950s, indicating the influence of HNAs on the environment and marking the onset of the Anthropocene. The variation of 129I in the investigated site can be primarily attributed to the global fallout of ANWT as well as nuclear fuel reprocessing in Europe, Russia and the USA. Notably, neither the Chernobyl nor the Fukushima nuclear accidents have had any discernable impact on the SHLW Lake. Over the past 170 years (1846-2021), the reconstructed fluxes indicate a rapid increase in 129I deposition from the early 1950s until the 1970s followed by dramatic changes thereafter. The measured 129I fluxes range between (1.26-349) × 109 atoms m-2 yr-1 in the SHLW Lake, which are consistent with similar latitude zones across East Asia, but differ significantly from those observed in high-elevation glaciers within the Northern Hemisphere due to prevailing atmospheric circulation patterns. The total 129I inventory was calculated to be 11.9 × 1012 atoms m-2, with natural and anthropogenic 129I accounting for 2.86 % and 97.1 %, respectively, suggesting an overwhelming artificial contribution. The reconstructed fluxes and inventory of atmospheric 129I deposition quantitatively distinguish the natural and artificial contributions, and provide a novel insight into the historical environmental impact of HNAs in East Asia and the characteristics of the Anthropocene.

Level, distribution and sources of Np, Pu and Am isotopes in Peter the Great Bay of Japan sea

Transuranium elements such as Np, Pu and Am, are considered to be the most important radioactive elements in view of their biological toxicity and environmental impact. Concentrations of 237Np, Pu isotopes and 241Am in two sediment cores collected from Peter the Great Bay of Japan Sea were determined using radiochemical separation combined with inductively coupled plasma mass spectrometry (ICP-MS) measurement. The 239,240Pu and 241Am concentrations in all sediment samples range from 0.01 Bq/kg to 2.02 Bq/kg and from 0.01 Bq/kg to 1.11 Bq/kg, respectively, which are comparable to reported values in the investigated area. The average atomic ratios of 240Pu/239Pu (0.20 ± 0.02 and 0.21 ± 0.01) and 241Am/239+240Pu activity ratios (3.32 ± 2.76 and 0.45 ± 0.17) in the two sediment cores indicated that the sources of Pu and Am in this area are global fallout and the Pacific Proving Grounds through the movement of prevailing ocean currents, and no measurable release of Np, Pu and Am from the local K-431 nuclear submarine incident was observed. The extremely low 237Np/239Pu atomic ratios ((2.0-2.5) × 10-4) in this area are mainly attributed to the discrepancy of their different chemical behaviors in the ocean due to the relatively higher solubility of 237Np compared to particle active plutonium isotopes. It was estimated using two end members model that 23% ± 6% of transuranium radionuclides originated from the Pacific Proving Grounds tests, and the rest (ca. 77%) from global fallout.

Transfer of 129I to freshwater fish species within Fukushima and Chernobyl exclusion zones

Unique data is reported on the transfer of 129I iodine from freshwaters to fish as well as the internal distribution within fish from the Fukushima and Chernobyl exclusion zones (ChEZ). Samples of water, sediments and fish were collected in the contaminated ponds Inkyozaka and Suzuuchi, and in the less contaminated Abukuma river in Fukushima, as well as in the contaminated Glubokoye lake and in the less contaminated Starukha lake in ChEZ. In water, 129I was mainly present as low molecular mass (LMM) and negatively charged species, while a minor fraction was associated with colloidal fraction, most probably organic material in water. The sediment-water 129I apparent distribution coefficients, Kd, ranged from 225 to 329 L/kg, equal that of stable iodine, but did not correlate with 129I/127I ratio or 129I/137Cs ratio as the environmental distribution of radioactive iodine was different from that of stable iodine and radioactive cesium. Concentration ratios (CR) of 129I in muscle of freshwater fish ranged from 85 to 544 across waterbodies with limited water exchange, similar in Fukushima and Chernobyl, but varied with respect to fish species. Thus, this is the first results on the transfer of 129I to freshwater fish, showing that the CR for freshwater fish is higher than CR reported for marine fish. Concentrations of 129I in fish muscle were, however, lower than in the intestinal content, indicating the influence of more contaminated dietary ingredients probably of terrestrial origin based due to δ13C signal on as well as of biodilution. The present results highlighted also that the radiation dose in fish was highly inhomogeneously distributed. Based on the present 129I/127I atomic ratio of 10-5 in the most contaminated fish in the ponds in Fukushima and Glubokoye lake in Chernobyl, however, a radiation dose of 10 μSv/y would not pose any harm to the fish population.

Microbial involvement in iodine cycle: mechanisms and potential applications

Stable iodine isotopes are essential for humans as they are necessary for producing thyroid gland hormones. However, there are hazardous radioactive iodine isotopes that are emitted into the environment through radioactive waste generated by nuclear power plants, nuclear weapon tests, and medical practice. Due to the biophilic character of iodine radionuclides and their enormous biomagnification potential, their elimination from contaminated environments is essential to prevent the spread of radioactive pollution in ecosystems. Since microorganisms play a vital role in controlling iodine cycling and fate in the environment, they also can be efficiently utilized in solving the issue of contamination spread. Thus, this paper summarizes all known on microbial processes that are involved in iodine transformation to highlight their prospects in remediation of the sites contaminated with radioactive iodine isotopes.

Synthesis of Tröger's base-based [3]arenes for efficient iodine adsorption

Enantiomers of Tröger's base-based [3]arenes R6N-E[3] and S6N-E[3] were synthesized successfully as two optically pure Tröger's base-based macrocycles in which three Tröger's base subunits were incorporated. Among these Tröger's base-based[3]arenes, M[3] showed high absorption of iodine up to 4.02 g g-1 in vapor.

Reconstruction of the Sources and Their Contributions to 129I in Northern Xinjiang, China

Anthropogenic ¹²⁹I, as a long-lived fission product and volatile radionuclide, can be used to investigate dispersion of air masses and the deposition of atmospheric pollution. Surface soil and soil core samples were collected from Northern Xinjiang and analyzed for ¹²⁷I and ¹²⁹I. The results show that ¹²⁹I/¹²⁷I atomic ratios in surface soil are inhomogeneous with a range of (2.07-106) × 10^-9, and the maximum values in each soil core occurred at surface-subsurface layers (0-15 cm) at undisturbed sites. The dominant source of ¹²⁹I in Northern Xinjiang is European nuclear fuel reprocessing plant (NFRP) releases, accounting for at least 70% of the total inventory; less than 20% of ¹²⁹I originates from the global fallout of atmospheric nuclear weapons tests; less than 10% comes from the regional deposition of nuclear weapons tests at the Semipalatinsk site; and the regional deposition from the nuclear weapons tests at the Lop Nor site is insignificant. The European NFRP-derived ¹²⁹I was transported to Northern Xinjiang via long-distance atmospheric dispersion with the westerlies through Northern Eurasia. The distribution of ¹²⁹I in the surface soil in Northern Xinjiang is mainly controlled by topography, wind fields, land utilization, and vegetation coverage.

Status report of the first AMS laboratory in the Czech Republic at the Nuclear Physics Institute, Řež

The first accelerator mass spectrometry (AMS) laboratory in the Czech Republic has been established and put into routine operation in February 2022. Here we briefly describe the facilities available, namely a 300 kV multi-isotope low-energy AMS system (MILEA) capable of determination 10Be, 14C, 26Al, 41Ca, 129I, isotopes of U, especially 236U, Pu and other actinoids, and accessories for 14C measurements, which include a gas interface system, a preparative gas chromatography system for compound-specific radiocarbon dating analysis, and an isotope-ratio mass spectrometer. The first results achieved for separation and measurement of the above radionuclides (except for 41Ca) are also reported, with the main focus on 14C measurements. A specimen breakdown of 729 graphitised samples analysed for 14C so far is presented, as well as a proof of measurement stability of the MILEA system obtained by analysis of radiocarbon standards and analytical blanks. For the other radionuclides, well proven or novel procedures for sample preparation and measurement are presented.

Effect of different synthesis methodologies on the adsorption of iodine

Radioactive nuclides such as cesium, ruthenium, and iodine are difficult to remove in radioactive wastewater, which could be removed by coprecipitation of special chemical precipitants. In this study, dynamic Cu/Ag-mordenite (Cu/Ag-MOR) material was synthesized to be treated as the precipitant to selectively adsorb the iodine ion (I^-) through controlled chemisorption combined with physical adsorption. XRD, XPS, and FTIR characterization demonstrated the successful modification of the MOR carrier surface by Cu/Ag particles and the high selectivity of the active component Cu (I) on the dynamic Cu/Ag-MOR material. SEM, TEM, and BET methods were used to characterize the Cu/Ag-MOR material, demonstrating these results: the MOR carried a stable porous structure, which allowed the silver to be well dispersed on its surface. The silver improved the copper distribution by being well-coated by the copper species. Furthermore, the analysis of the factors influencing the chemical plating of copper showed that the pH, the concentration of EDTA-2Na and the temperature all influenced the deposition rate of Cu₂O. The activation energy for Cu₂O deposition in dynamic Cu/Ag-MOR was 20.31 kJ/mol. The highest removal of I^- in the presence of dynamic Cu/Ag-MOR could reach 99.1% in the adsorption tests. The adsorption kinetics was under a proposed second-order model, with chemisorption being the controlling step of the reaction. The adsorption/desorption experiments demonstrated the reusability of the nano-sorbent. It was also demonstrated that dynamic Cu/Ag-MOR materials showed good applicability in complex situations where multiple pollutants co-exist.

Visualized electrochemiluminescence iodine sensor based on polymer dots with Co-reactive group for real-time monitoring system

Trace iodine (I₂) radioisotopes are commonly regarded as an indicator in nuclear security early warnings. Herein, we develop a visualized I₂ real-time monitoring system using electrochemiluminescence (ECL) imaging technology for the first time. In detail, the polymers based on poly [(9,9-dioctylfluorene-alkenyl-2,7-diyl)-alt-co-(1,4-benzo-{2,1',3}-thiadiazole)] are synthesized for iodine detection. An ultra-low limit of detection (0.01 ppt) to iodine can be achieved by adding the modification ratio of tertiary amine onto PFBT as a co-reactive group, which is the lowest detection limit in known iodine vapor sensors. This result can be attributed to the co-reactive group poisoning response mechanism. Considering to the strong ECL behavior of this polymer dots, P-3 Pdots with ultra-low detection limit for iodine is combined with ECL imaging technology to realize the visualized rapid I₂ vapor response with high selectivity. ECL imaging component based on ITO electrode can make iodine monitoring system more convenient and suitable for real-time detection in early warning of nuclear emergency. The detection result cannot be affected by vapor of organic compounds, humidity and temperature, indicating a good selectivity to iodine. This work provides a strategy for nuclear emergency early warning, showing its significance in environmental and nuclear security fields.

Improvement of the Stability of IO3--, SeO32--, and SeO42--Coprecipitated Barite after Treatment with Phosphate

Coprecipitation of radionuclides with barite has been studied to remove radionuclides from radioactive liquid waste because of its excellent removal efficiency; however, little information exists concerning the stability of the ions coprecipitated with barite. This study systematically investigated the stability of iodate, selenite, and selenate coprecipitated with barite via leaching tests. These oxyanions were gradually leached from the oxyanion-bearing barite into ultrapure water over time. Leaching of the oxyanions significantly increased in leaching solutions containing NaCl (pH 5.3), NaNO₃ (pH 5.9), and Na₂SO₄ (pH 5.7). Conversely, leaching of the oxyanions was suppressed in KH₂PO₄ solution (pH 8.5), indicating that phosphate stabilized the oxyanion-bearing barite. The effect of phosphate treatment on oxyanion-bearing barite was further investigated. The results showed that the barite surface was modified with phosphate, and a thin surface layer of a barium phosphate-like structure was formed. The amount of oxyanions leached from the phosphate-treated samples into leaching solutions containing NaCl or NaNO₃ was much lower than the amounts leached from the untreated barite samples into ultrapure water. The barite coprecipitation combined with subsequent phosphate treatment may be a promising method to efficiently remove iodate, selenite, and selenate from wastewater and stabilize them as barite coprecipitates.

Long-term environmental risks of the Baltic Sea's "memory effect" revealed by ocean modeling and observation of reprocessing-derived radiotracers

Although previous research indicated that the Baltic Sea has a strong "memory effect" for trapping pollutants/nutrients, the associated environmental risks are not well understood due to the knowledge gaps in the long-term hydrodynamics-driven exchange of pollutants/nutrients between the North Sea and the Baltic Sea. In this work, we exploited ⁹⁹Tc and ¹²⁹I released from the two European nuclear reprocessing plants as oceanic tracers and pollutant proxies, and performed a five-decade hindcast simulation to quantitatively estimate the fluxes and timescales of marine transport of pollutants/nutrients in the North-Baltic Sea. Modeling results underline two potential environmental risks of the Baltic Sea's "memory effect": (1) ∼26 years of environmental half-life for any existing water-soluble pollutants/nutrients in the Baltic Sea driven by its hydrodynamics; (2) the Baltic Sea as a pollutant reservoir continuously exporting 3 % of contaminations per year to the downstream areas after any pollution event. Our findings provide fundamental knowledge for understanding the long-term hydrodynamics-driven pollutant/nutrient transport in the North-Baltic Sea, facilitating the future regional management of the marine environment.

Highly Sensitive Adsorption and Detection of Iodide in Aqueous Solution by a Post-Synthesized Zirconium-Organic Framework

Effective methods of detection and removal of iodide ions (I^-) from radioactive wastewater are urgently needed and developing them remains a great challenge. In this work, an Ag⁺ decorated stable nano-MOF UiO-66-(COOH)₂ was developed for the I^- to simultaneously capture and sense in aqueous solution. Due to the uncoordinated carboxylate groups on the UiO-66-(COOH)₂ framework, Ag⁺ was successfully incorporated into the MOF and enhanced the intrinsic fluorescence of MOF. After adding iodide ions, Ag⁺ would be produced, following the formation of AgI. As a result, Ag⁺@UiO-66-(COOH)₂ can be utilized for the removal of I^- in aqueous solution, even in the presence of other common ionic ions (NO₂^-, NO₃^-, F^-, SO₄^2-). The removal capacity as high as 235.5 mg/g was calculated by Langmuir model; moreover, the fluorescence of Ag⁺@UiO-66-(COOH)₂ gradually decreases with the deposition of AgI, which can be quantitatively depicted by a linear equation. The limit of detection toward I^- is calculated to be 0.58 ppm.

127I and 129I species in the English Channel and its adjacent areas: Uncovering impact on the isotopes marine pathways

Radioactive iodine-129 has been released from the La Hague nuclear fuel reprocessing facility (NRF) into the English Channel, but the distribution and transformation of the isotope species, and environmental consequences have not been fully characterized in the Channel. Here we present data on iodine isotopes (¹²⁹I and ¹²⁷I) species in surface water of the English Channel and the southern Celtic Sea. Compared to ¹²⁷I species, the concentrations of ¹²⁹I^- and ¹²⁹IO₃^- show more variations, but iodate is the major species for both ¹²⁹I and ¹²⁷I. Our data provide new information regarding iodide-iodate inter-conversion showing that water dilution and mixing are the main factors affecting the ¹²⁷I and ¹²⁹I species distribution in the Channel. Some reduction of iodate occurs within the English Channel and mainly in the west part because of biotic processes. The ¹²⁹I species transformation is overall insignificant, especially in the eastern Channel, where a constant value of ¹²⁹IO₃^-/¹²⁹I is observed, which might characterize the La Hague wastewater signal. In the Celtic Sea, oxidation of iodide can be traced by ¹²⁷I and ¹²⁹I species. On a larger scale, ¹²⁹I generally experienced an oxidation process in the Atlantic Ocean, while in the coast of shallow shelf seas, new produced ¹²⁹I^- can be identified, especially in the German Bight and the Baltic Sea. The data of ¹²⁹I species in the English Channel can provide estimate of redox rates in a much broader marine areas if the transit time of ¹²⁹I from La Hague is well-defined. Furthermore, estimate of inventories for ¹²⁹I and its species in the Channel, and fluxes of ¹²⁹I species from the English Channel to the North Sea add important information to the geochemical cycle of ¹²⁹I.

Speciation analysis of both inorganic and organic 129I in seawater and its application in the study of the marine iodine cycle

A complete protocol is presented for the speciation analysis of ¹²⁹I for both inorganic and organic iodine in seawater using coprecipitation and solid-phase extraction (SPE) combined with accelerator mass spectrometry (AMS). By modifying the iodide separation process and adding a crossover removal step, the improved coprecipitation method significantly reduces the cross-contamination of iodide and iodate to less than 0.05% in the speciation analysis of inorganic ¹²⁹I, with the separation efficiencies of about 95% and 93% for iodide and iodate, respectively. The SPE-DOI method for the dissolved organic ¹²⁹I (DO¹²⁹I) analysis was developed, whereby we report the first direct observation of DO¹²⁹I/DO¹²⁷I atom ratios in seawater in this paper. ¹²⁹I species in seawater from Tokyo Bay were analysed. The ¹²⁹I results demonstrated that our protocol for speciation analysis of ¹²⁹I is reliable and provided new insights into understanding the iodine cycle.

TEMPORAL VARIATION OF POST-ACCIDENT 129I IN ATMOSPHERIC PARTICULATE MATTER COLLECTED FROM AN EVACUATED AREA OF FUKUSHIMA PREFECTURE, JAPAN

To understand the behavior of atmospheric 129I that originated from the Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident, activity concentrations of 129I in samples of atmospheric particulate matter (PM), comprising coarse (>1.1 μm) and fine (<1.1 μm) fractions (separated using a single stage impactor), were measured on a nearly monthly basis from October 2012 to October 2014 at a site in an area evacuated after the FDNPP accident. Total atmospheric 129I activity concentrations in PM at the site ranged between 0.15 and 2.17 nBq m-3. Specific activity concentration of 129I in total atmospheric PM ranged between 40.8 and 336 mBq kg-1, with a mean and standard deviation of 142 and 77.6 mBq kg-1, respectively. The specific activity in PM tended to be higher than not only the background values reported from soil collected before the FDNPP accident but also than those reported from the contaminated soil after the accident (range: 1.6-57 mBq kg-1; mean and standard deviation: 10.6 and 12.3 mBq kg-1, respectively). Total 129I/127I atomic ratios in PM ranged from 2.0 × 10-8 to 59.8 × 10-8, with a mean and standard deviation of 15.0 × 10-8 and 14.4 × 10-8, respectively. These ratios were generally lower than those of the contaminated soil collected after the FDNPP accident (range: 4.9 × 10-8-443 × 10-8; mean and standard deviation: 74.2 × 10-8 and 85.4 × 10-8, respectively). The 129I concentration and 129I/127I atomic ratio in atmospheric PM showed different characteristics from that of contaminated soils, suggesting that the presence of other atmospheric PMs plays a more important role as the host for 129I.

DISTRIBUTION OF IODINE-127 IN MARINE ORGANISMS FROM COASTAL WATERS AROUND AOMORI, JAPAN

We measured the concentrations and determined the distribution of the stable isotope 127I in the marine organisms. Marine fish were collected from the Pacific Ocean near Aomori, Japan. The mean 127I concentrations in the muscle of marine fish ranged from 0.67 μg g-1-wet weight (ww) in cherry salmon to 0.84 μg g-1-ww in fat greenling. Among the tissues measured, the muscle showed the lowest levels of 127I in all fish species. The highest 127I concentration in the tissues of marine fish was observed in the ovary of fat greenling. The mean 127I concentration in the of Japanese scallop ranged from 0.06 μg g-1-ww in adductor muscle to 5.49 μg g-1-ww in mid-gut gland. The 127I concentrations in seaweeds were 67 μg g-1-dry weight (dw) in sea lettuce and 1783 μg g-1-dw in kombu. Thus, the distribution of 127I concentration in marine organisms varied considerably depending on the tissue.

Distribution of Anthropogenic 129I in the Western South China Sea and Its Application for Tracing the Sources and Movement of Pollution

Anthropogenic ¹²⁹I has been dispersed all over the world and could be utilized as an oceanographic tracer based on its conservative nature in the ocean. The first datasets of ¹²⁹I and ¹²⁷I were obtained by analysis of seawater of 36 water columns collected in the western South China Sea during August-September 2018. The measured ¹²⁹I concentrations decreased with depth from (0.93-1.61) × 10⁷ atoms/L in the upper 200 m to (0.04-0.14) × 10⁷ atoms/L at 1500 m, indicating a clear anthropogenic source in the upper layer, mainly originated from the global fallout. The riverine input of the deposited ¹²⁹I on the catchment area of the Mekong River is an important source besides the direct deposition in the seas. The water mass with high ¹²⁹I from the Mekong River water moves to the east at 11°N by the North Nansha Current in the surface layer (2-25 m). The exponentially decreasing ¹²⁹I level with depth indicates that the vertical dispersion of ¹²⁹I from the upper to the lower layer was mainly through slow diffusion, and the deep water at more than 1500 m was not significantly contaminated by the upper layer water at least in the past 70 years.

Microplastics as vectors of radioiodine in the marine environment: A study on sorption and interaction mechanism

Radioiodine is one of the long-lived fission products and also an important radionuclide released during nuclear accidents, which generates interest in its environmental fate. Its sorption has been studied in a wide range of materials, but no equivalent study exists for microplastics, an emerging environmental vector. Weathering and biofilm formation on microplastics can enhance radioiodine sorption. For the first time, we're reporting how radioiodine interacts with different types of polyethylene derived microplastics (pristine, irradiated, and biofilm developed microplastics). This study revealed that exposure to radiation and the marine environment significantly alters the physico-chemical properties of microplastics. In particular, in marine-exposed samples, a signature of biofilm development was detected. Speciation study indicates that iodine exists in the iodide form in the studied marine environment. The study revealed that, iodide ions attach to biofilm-developed microplastics via electrostatic, ion-dipole, pore filling, and van der Waals interactions. Pore filling, ion-dipole, and van der Waals interactions may cause iodide binding to irradiated microplastics, whereas pore-filling and van der Waals interactions cause iodide binding to pristine microplastics. The distribution coefficient (K_d) of iodine on microplastics is positively correlated with biofilm biomass, which signifies the role of biofilm in radioiodine uptake. The K_d indicates microplastics are potential iodide accumulators and could be a possible vector in the marine system.

Selective removal of radioactive iodine from water using reusable Fe@Pt adsorbents

Environmental damage from serious nuclear accidents should be urgently restored, which needs the removal of radioactive species. Radioactive iodine isotopes are particularly problematic for human health because they are released in large amounts and retain radioactivity for a substantial time. Herein, we prepare platinum-coated iron nanoparticles (Fe@Pt) as a highly selective and reusable adsorbent for iodine species, i.e., iodide (I^-), iodine (I₂), and methyl iodide (CH₃I). Fe@Pt selectively separates iodine species from seawater and groundwater with a removal efficiency ≥ 99.8%. The maximum adsorption capacity for the iodine atom of all three iodine species was determined to be 25 mg/g. The magnetic properties of Fe@Pt allow for the facile recovery and reuse of Fe@Pt, which remains stable with high efficiency (97.5%) over 100 uses without structural and functional degradation in liquid media. Practical application to the removal of radioactive ¹²⁹I and feasibility for scale-up using a 20 L system demonstrate that Fe@Pt can function as a reusable adsorbent for the selective removal of iodine species. This systematic procedure is a standard protocol for designing highly active adsorbents for the clean separation and removal of various chemical species dissolved in wastewater.

Iodate Reduction by Shewanella oneidensis Requires Genes Encoding an Extracellular Dimethylsulfoxide Reductase

Microbial iodate (IO3 -) reduction is a major component of the iodine biogeochemical reaction network in anaerobic marine basins and radioactive iodine-contaminated subsurface environments. Alternative iodine remediation technologies include microbial reduction of IO3 - to iodide (I-) and microbial methylation of I- to volatile gases. The metal reduction pathway is required for anaerobic IO3 - respiration by the gammaproteobacterium Shewanella oneidensis. However, the terminal IO3 - reductase and additional enzymes involved in the S. oneidensis IO3 - electron transport chain have not yet been identified. In this study, gene deletion mutants deficient in four extracellular electron conduits (EECs; ΔmtrA, ΔmtrA-ΔmtrDEF, ΔmtrA-ΔdmsEF, ΔmtrA-ΔSO4360) and DMSO reductase (ΔdmsB) of S. oneidensis were constructed and examined for anaerobic IO3 - reduction activity with either 20 mM lactate or formate as an electron donor. IO3 - reduction rate experiments were conducted under anaerobic conditions in defined minimal medium amended with 250 μM IO3 - as anaerobic electron acceptor. Only the ΔmtrA mutant displayed a severe deficiency in IO3 - reduction activity with lactate as the electron donor, which suggested that the EEC-associated decaheme cytochrome was required for lactate-dependent IO3 - reduction. The ΔmtrA-ΔdmsEF triple mutant displayed a severe deficiency in IO3 - reduction activity with formate as the electron donor, whereas ΔmtrA-ΔmtrDEF and ΔmtrA-ΔSO4360 retained moderate IO3 - reduction activity, which suggested that the EEC-associated dimethylsulfoxide (DMSO) reductase membrane-spanning protein DmsE, but not MtrA, was required for formate-dependent IO3 - reduction. Furthermore, gene deletion mutant ΔdmsB (deficient in the extracellular terminal DMSO reductase protein DmsB) and wild-type cells grown with tungsten replacing molybdenum (a required co-factor for DmsA catalytic activity) in defined growth medium were unable to reduce IO3 - with either lactate or formate as the electron donor, which indicated that the DmsAB complex functions as an extracellular IO3 - terminal reductase for both electron donors. Results of this study provide complementary genetic and phenotypic evidence that the extracellular DMSO reductase complex DmsAB of S. oneidensis displays broad substrate specificity and reduces IO3 - as an alternate terminal electron acceptor.

Ultralow-cost portable device for cesium detection via perovskite fluorescence

Public anxiety and concern from cesium pollution in oceans have been back on the agenda since tons of nuclear waste water were announced to be poured into oceans. Cesium ion can easily enter organisms and bioaccumulate in animals and plants, thus its harm is chronic to humans through food chains. Here we showed a kind of hybrid ionic liquid membrane (HILM) for detection of cesium ion in seawater through CsPbBr₃ perovskite fluorescence. With sustainability in mind, HILM was built frugally. The lowest cost of HILM is below 3 cents per piece. The HILM can detect cesium ion quickly with eye-readable fluorescence signal. Ultracheap, portable, easy-to-use on-site detection device could offer benefit for personal security and applications in environment science and ecology in the future decades.

Facile synthesis of novel Bi0-SBA-15 adsorbents by an improved impregnation reduction method for highly efficient capture of iodine gas

Development of high efficient adsorbents to capture iodine is of great significance for the active development of nuclear power. Herein, Bi⁰-SBA-15 was firstly synthesized and applied for capture of iodine gas. Bi⁰-SBA-15 materials were prepared by an improved impregnation reduction method. The benefit of this method was that the Bi⁰ nanoparticles with flocculent and spherical morphologies were loaded on the surface of SBA-15, which provide abundant active sites for iodine and improve the utilization rate of active sites, so as to attain a record high capture capacity (up to 925 mg/g within 60 min) and high stablitiy (91.2%) at 200 °C. The results demonstrated that the loading of Bi⁰ on the surface showed a significant impact on the structure of Bi⁰-SBA-15 and did greatly enhance the iodine capture. Furthermore, the high iodine capture capacity mainly derived from the chemical adsorption in the stable form of BiI₃. The obtained Bi⁰-SBA-15 materials exhibited excellent aqueous and irradiation stability. Thus, the results indicated that the new and highly efficient Bi⁰-SBA-15 was a potential radioactive iodine gas capture material.

Radiochemical analysis of the drain water sampled at the exhaust stack shared by Units 1 and 2 of the Fukushima Daiichi Nuclear Power Station

Radioactive gas of Unit 1 of the Fukushima Daiichi Nuclear Power Station was released from the exhaust stack shared by Units 1 and 2 through the venting line on March 12th, 2011. In the present study, radiochemical analysis of drain water sampled at the drain pit of the exhaust stack was conducted to study radionuclides released during venting of the Unit 1. Not only volatile ¹²⁹I, ¹³⁴Cs and ¹³⁷Cs but also ⁶⁰Co, ⁹⁰Sr, ¹²⁵Sb and Unit 1-originated stable Mo isotopes were detected. Although Unit 1-originated stable Mo isotopes were clearly detected, their amounts were quite low compared to Cs, suggesting that the formation of Cs₂MoO₄ was suppressed under the accident condition. Approximately 90% of iodine existed as I⁻ and 10% as IO₃⁻ in November 2020. Furthermore, larger amount of ¹²⁹I than ¹³⁷Cs was observed, suggesting major chemical form of ¹³¹I was molecular iodine rather than CsI at the accident time. The ¹³⁴Cs/¹³⁷Cs radioactivity ratio decay-corrected to March 11th, 2011 was 0.86, supported the results that Unit 1 originated radiocesium in environment has smaller ¹³⁴Cs/¹³⁷Cs radioactivity ratio than Unit 2 and 3 originated radiocesium.

Magnetic chitosan microspheres: An efficient and recyclable adsorbent for the removal of iodide from simulated nuclear wastewater

The efficient and recyclable magnetic chitosan microspheres (MCMs) were successfully synthesized to remove iodide from nuclear wastewater and characterized through XRD, FTIR, SEM, EDS, VSM, TGA and XPS. The characterization results indicated that the MCMs exhibited smooth spherical morphology and good magnetic properties. The removal potential of MCMs was investigated for iodide (I^-) anions at different conditions. From pH 3 to pH 9, MCMs performed the high I^- removal efficiency (>90%). The maximum I^- removal capacity of MCMs was up to 0.8087 mmol g^-1 at 298 K, well-fitting with the pseudo-second-order and Sips models. Furthermore, the I^- removal efficiency of MCMs still maintained more than 91% after five adsorption-desorption cycles, performing good regeneration and reusability. This study is expected to prompt the MCMs to become an efficient and recyclable biosorbent for iodide removal from nuclear wastewater.

Immobile crystallization of radioactive iodide by redox transformation of a low crystalline copper phase

Here we show an innovative way to effectively scavenge highly mobile radioiodide and to dramatically reduce its waste volume through a spontaneous phase transformation. Under an anaerobic condition, as metallic copper (II) was favorably associated with bicarbonate (HCO₃^-) in solution, a cupriferous carbonate compound (malachite) quickly formed, which was redox-sensitive and transformable to a compact crystal of CuI (marshite). The formation of CuI crystal was principally led by the spontaneous Cu-I redox reaction centering around the copper phase over the presence of sulfate (SO₄^2-). The completely transformed CuI crystal was poorly soluble in water and grew to large microcrystals (∼μm) via a remarkable selectivity for I^-. Interestingly, this redox-induced iodide crystallization was rather promoted over the existence of anionic competitors (e.g., HCO₃^- and SO₄^2-), which usually exist in wastewater and natural water. Unlike the conventional methods, these competing anions positively behaved in our system by supporting that the initial malachite was more apt to be reactive to largely attract highly mobile I^-. Under practical environments with various anions, such a selective I^- uptake and fixation within a compact crystalline space will be a promising way to effectively remove I^- in a great capacity.

Concentration factors and biological half-lives for the dynamic modelling of radionuclide transfers to marine biota in the English Channel

The biokinetics of radionuclide transfers to biota in the marine environment can be modelled using two parameters, specific to both each element/radionuclide and biota. The Concentration Factor (CF) reflects the ratio between the activity concentrations in the biota and the surrounding seawater in steady state. The biological half-life (tb_1/2) characterizes depuration kinetics for the radionuclide from the biota. While recommended CF values can be found in the literature, no guidelines actually exist for tb_1/2 values. We used available time-series activity concentration measurements in biota in the English Channel, where controlled amounts of liquid radioactive waste are discharged by the ORANO La Hague reprocessing plant. We calculated the corresponding time-series activity concentrations in seawater for each biota dataset using an extensively-validated hydrodynamic model. We derived the values of CF and tb_1/2 from seawater and biota data, to model radionuclide transfers between the two compartments. To assess the performance of the model, we analyzed the residual between observed and calculated levels in the biota. Datasets for macroalgae, mollusks, crustaceans and fish yielded parameters (CF, tb_1/2) for H-3 (as body water and as organically bound tritium), C-14, Sb-125, Cs-137, I-129, Mn-54, Co-60, Zn-65 and Ru-106. After discussing the results and qualifying the model's reliability, we proposed recommendations for CF and tb_1/2 for the purposes of the operational modelling of radionuclide transfers to biota in the marine environment.

Porous ZIF-8@polyacrylonitrile composite beads for iodine capture

The safe and effective capture and storage of iodine from nuclear waste is of great significance in industry. This article reports the preparation of a series of millimeter-sized ZIF-8@polyacrylonitrile composite beads with high specific surface area and porosity by the phase inversion method for iodine capture. The composite beads showed a higher capture capacity (4150 mg g⁻¹) under excess iodine vapor. The amount of iodine adsorbed in the organic solution is also as high as 643 mg g⁻¹, and the adsorption conforms to the Freundlich isotherm and the pseudo-second-order kinetic model. Moreover, composite beads also exhibit higher thermal stability (310 °C). Therefore, ZIF-8@polyacrylonitrile composite beads show great potential as a material for capturing and temporarily storing radioactive iodine.

This article reports the preparation of a series of millimeter-sized ZIF-8@polyacrylonitrile composite beads with high specific surface area and porosity by the phase inversion method for iodine capture.

Records of iodine isotopes (129I, 127I) in the Barkol peat bog from northwest China and their sources, transport and preservation

The research on geochemical behaviors of iodine is significant for deep understanding of the source and distribution of iodine on the earth. However, as one of the most important sources, the ocean emissions and relative transport pathways of iodine, as well as the preservation after deposition are still not well known, especially in the arid areas of central Asia. A peat sediment core collected nearby Barkol Lake from northwest China was analyzed for iodine isotopes (¹²⁷I and ¹²⁹I). The observed high ¹²⁷I concentration in the top 2 cm indicated a significant accumulation of iodine in the surface oxic conditions due to the continuous sources of incompletely decomposed organic matter. Dissociation of iodine into pore waters occurred once the anoxic conditions established beneath the surface by a serial reduction reaction during the degradation of organic matter. The temporal variation of anthropogenic ¹²⁹I in the peat sediment recorded its sources and transport pathways. Besides the global fallout ¹²⁹I during late 1950s and early 1960s, the significantly increased air releases from the European nuclear fuel reprocessing plants during 1975-1997 and the increased marine discharges since 1990s contributed the major portion of ¹²⁹I in the peat core. The major transport pathway of ¹²⁹I from the Europe was through Westerlies following the re-emission of the marine discharged ¹²⁹I to the atmosphere, indicating a clearly ocean emitted iodine in the concerned central Asia.

Evaluation of radioiodine (129I) dissolution from sediment of a brackish lake beside a spent nuclear fuel reprocessing plant in Japan

Dissolution fluxes of stable (¹²⁷I) and radioactive (¹²⁹I) isotopes of iodine from a brackish lake sediment beside a spent nuclear fuel reprocessing plant in Japan were evaluated through two kinds of experiments: incubation using a sediment core sample for 24 h, and observation of ¹²⁷I and ¹²⁹I concentrations in sedimentary pore water. For ¹²⁷I, the dissolution flux evaluated in the incubation experiment was comparable with that obtained from the vertical gradient of ¹²⁷I concentration in pore water in the observation experiment. This suggests that degradation of organic matter in the surface sediment is an important source of dissolved ¹²⁷I found in the water. For ¹²⁹I, the dissolution flux estimated in the incubation experiment showed negative values, indicating the transfer of ¹²⁹I to the sediment from the overlying water (i.e., absorption). Moreover, the flux evaluated from the observation experiment was positive. This result suggests that degradation of organic matter in the surface sediment is scarcely important to the supply of ¹²⁹I from the sediment to the water in the studied lake. The dissolution flux of ¹²⁹I estimated in the observation experiment was smaller than the absorption flux of ¹²⁹I in the incubation experiment. This potentially indicates that the dissolution of sedimentary ¹²⁹I does not significantly change ¹²⁹I concentrations in the water and sediment of the lake. This hypothesis was consistent with previous research conducted for the studied lake.

Effective removal of iodate by coprecipitation with barite: Behavior and mechanism

Radioactive iodine (¹²⁹I) is of great concern owing to its high mobility in the environment and long-term radiotoxicity. However, there is a lack of effective techniques for removing iodate (IO₃^-) from aqueous solution. This study aims to develop a new technique for removing radioactive iodate from contaminated solution by using barite (BaSO₄). We examined the coprecipitation mechanism of iodate by barite at the molecular level to determine the optimum conditions for iodate removal. Results showed that iodate was effectively removed from the aqueous solution by coprecipitation even in the presence of competitive anions. Based on comparison of our method with previous techniques, the iodate removal efficiency by barite was determined to be about two orders of magnitude greater than that by hydrotalcite-like layered double hydroxide at 10 mmol L^-1 Cl^-. Extended X-ray absorption fine structure analysis indicated that the incorporated iodate was strongly bound to the crystal lattice of barite by substituting the sulfate site in the structure when the iodine concentration was low. The charge compensation problem from the IO₃^- substitution in the SO₄^2- site was achieved by the substitution of Na⁺-IO₃^- pairs at the nearest Ba²⁺ site. Given the high removal efficiency and strong binding of iodate to barite, coprecipitation with barite is a promising tool for removing radioactive iodate from various aqueous solutions contaminated with iodate.

Use of thermal treatment with CaCl2 and CaO to remove 137Cs in the soil collected from the area near the Fukushima Daiichi Nuclear Power Plant

A massive amount of soils and inflammable materials of plants etc. contaminated by radiocesium are generated from decontamination work in the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident affected area. In present study, the removal experiments of ¹³⁷Cs in a soil collected from the FDNPP accident affected area were carried out in a lab-scale electrical heating horizontal furnace through thermal treatment with CaCl₂ addition over a temperature of 900 - 1300 °C. The results indicated that the average radioactive concentration of ¹³⁷Cs in the soil was 52.8 Bq/g. The removal ratio of ¹³⁷Cs in the soil treated at 1300 °C was 96.3 % when 20 % CaCl₂ was added. The addition of CaCl₂ and CaO mixture exhibited a synergistic effect on the removal of ¹³⁷Cs, relative to the addition of CaCl₂ alone. Accordingly, the addition of CaCl₂ or its mixture with CaO during thermal treatment is suggested to remove ¹³⁷Cs in the soil collected from the FDNPP accident affected area. Additionally, segregation of the soil sample to fine and coarse fraction and then treated individually are also recommended.

Distribution and Evolution of Fukushima Dai-ichi derived 137Cs, 90Sr, and 129I in Surface Seawater off the Coast of Japan

The Fukushima Dai-ichi Nuclear Power Plants (FDNPPs) accident in 2011 led to an unprecedented release of radionuclides into the environment. Particularly important are ⁹⁰Sr and ¹³⁷Cs due to their known health detriments and long half-lives (T_1/2 ≈ 30 y) relative to ecological systems. These radionuclides can be combined with the longer-lived ¹²⁹I (T_1/2 = 15.7 My) to trace hydrologic, atmospheric, oceanic, and geochemical processes. This study seeks to evaluate ¹³⁷Cs, ⁹⁰Sr, and ¹²⁹I concentrations in seawater off the coast of Japan, reconcile the sources of contaminated waters, and assess the application of ¹³⁷Cs/⁹⁰Sr, ¹²⁹I/¹³⁷Cs, and ¹²⁹I/⁹⁰Sr as oceanic tracers. We present new data from October 2015 and November 2016 off the coast of Japan, with observed concentrations reaching up to 198 ± 4 Bq·m^-3 for ¹³⁷Cs, 9.1 ± 0.7 Bq·m^-3 for ⁹⁰Sr, and (114 ± 2) × 10^-5 Bq·m^-3 for ¹²⁹I. The utilization of activity ratios suggests a variety of sources, including sporadic and independent releases of radiocontaminants. Though overall concentrations are decreasing, concentrations are still elevated compared to pre-accident levels. In addition, Japan's Environment Minister has suggested that stored water from the FDNPPs may be released into the environment and thus continued efforts to understand the fate and distribution of these radionuclides is warranted.

Circulation of Circumpolar Deep Water and marine environment traced by 127I and 129I speciation in the Amundsen Sea Polynya, Antarctica

The long-lived anthropogenic ¹²⁹I released from human nuclear activities has been widely employed as an effective oceanographic tracer to investigate circulation of water masses in marine environment. Depth profiles of seawater collected from the Amundsen Sea Polynya, Antarctica were analyzed for total ¹²⁹I and ¹²⁷I, as well as their species of iodide and iodate. The measured ¹²⁹I concentrations ((1.15-3.43) × 10⁶ atoms/L) and ¹²⁹I/¹²⁷I atomic ratios ((0.53-1.19) × 10^-11) indicate that anthropogenic ¹²⁹I has not only reached the Antarctic surface marine environment but also the deep water due to a strong vertical mixing of water masses. The Circumpolar Deep Water (CDW) flowed southward along continental shelf towards the ice shelf zone (74.25°S) at a depth of 1025 m and then migrated upward and northward to the polynya and finally to the sea ice zone (71.95°S). The maximum upwelling depth of the CDW was around 200 m in the polynya. The source of ¹²⁹I^- in the polynya is predominantly the intrusion of source waters rather than the in-situ reduction of iodate by phytoplankton, implying a considerably slow reduction process of iodate to iodide in this region.

Iodine effective diffusion coefficients through volcanic rock: Influence of iodine speciation and rock geochemistry

Accurate prediction of the subsurface transport of iodine species is important for the assessment of long-term nuclear waste repository performance, as well as monitoring compliance with the Comprehensive Nuclear-Test-Ban Treaty, given that radioiodine decays into radioxenon. However, the transport of iodine through intact geologic media is not well understood, compromising our ability to assess risk associated with radioiodine migration. The current study's goal is to quantify the matrix diffusion of iodine species through saturated volcanic rock, with particular attention paid to the redox environment and potential speciation changes. Diffusion experiments were run for iodide through lithophysae-rich lava, lithophysae-poor lava, and welded tuff, whereas iodate diffusion was studied through welded tuff. Iodine transport was compared with a conservative tracer, HDO, and effective diffusion coefficients were calculated. Likely due to a combination of size and anion exclusion effects, iodine species diffused more slowly than the conservative tracer through all rock types tested. Furthermore, oxidation of iodide to iodate was observed in the lithophysae-poor lava, affecting transport. Results provide much needed data for subsurface transport models that predict radioiodine migration from underground sources, and indicate the pressing need for geochemical and redox interactions to be incorporated into these models.