Microbial Transformation of Iodine: From Radioisotopes to Iodine Deficiency

Changes in 129I concentration of soil samples after thermal drying

To precisely evaluate the concentration of iodine-129 (129I) in soil samples, changes in this concentration after thermal drying under several temperature conditions were investigated. The soil sample used in this study was collected from a site located near a nuclear fuel reprocessing plant, which atmospherically released 129I in a test operation in 2006-2008, resulting in the soil sample containing higher 129I concentrations than their natural levels. Thermal drying was conducted from 60°C to 110°C and compared with lyophilization result, showing that the 129I concentration in the soil sample was statistically comparable among all the drying treatments.

Dissimilatory Iodate-Reducing Microorganisms Contribute to the Enrichment of Iodine in Groundwater

Iodate reduction by dissimilatory iodate-reducing microorganisms (DIRMs) plays a crucial role in the biogeochemical cycling of iodine on Earth. However, the occurrence and distribution of DIRMs in iodine-rich groundwater remain unclear. In this study, we isolated the dissimilatory iodate-reducing bacteriumAzonexus hydrophilusstrain NCP973 from a geogenic high-iodine groundwater of China for the first time. The analysis of genome, transcriptome, and heterologous expression revealed that strain NCP973 uses the dissimilatory iodate-reducing enzyme IdrABP1P2 to reduce dissolved or in situ sediment-bound iodate to iodide. The location of IdrABP1P2 in the conjugative plasmid of strain NCP973 implies that IdrABP1P2 could be spread by horizontal gene transfer and allow the recipient microorganisms to participate in the enrichment of iodide in aquifers. Based on the global iodine-rich groundwater metagenomes and genomes, the identification of idrA showed that phylogenetically diverse DIRMs are widely distributed not only in geogenic high-iodine groundwater of China but also in radionuclide-contaminated groundwater of USA as well as in subsurface cavern waters in Germany and Italy. Moreover, the abundance of idrA was found to be higher in groundwater with a relatively high iodine content. Collectively, these results suggest that terrestrial iodine-affected groundwater systems are another important habitat for DIRMs in addition to marine environments, and their activity in aquifers triggers the mobilization and enrichment of iodine in groundwater worldwide.

Challenges in radioecology following the new trends in UAE's agriculture and environmental changes: a review

The development of the nuclear industry in the countries of the Arabian Gulf demands an investigation of its potential impact on the environment and human activities. It should involve routine monitoring of radionuclide from existing nuclear facilities as well as modelling of accidental release of radioactivity. Agriculture is usually considered the human activity which is the most endangered with radioactive pollution. Although the traditional concept of low-developed agriculture in the United Arab Emirates has been already described from a radioecological point of view, herein, the recent trends of agriculture are recorded. Due to climatic changes and population increase, the use of saline lands will be more pressing. Apart from it, the risk assessment for nuclear events, which was formed mainly for temperate zones, neglected another aspect of arid zones which is underground water reservoirs refilled with episodic heavy rains. The sandy or saline soils are not an effective barrier for the migration of radionuclide deposited in topsoil. A hypersaline environment could prevent the adsorption of radionuclide on soil particles and allow their high bioavailability for halophyte plants. The new principal challenges in radioecological research in arid zones are impacts on (i) saline agriculture, (ii) underground water reservoirs, and (iii) proposal for countermeasures in order to minimise the impact of radioactive contamination.

Iodate reduction by marine aerobic bacteria

Iodate reductase (Idr) gene cluster (idrABP1P2 ) is involved in bacterial iodate (IO3 -) respiration under anaerobic conditions. Putative idr gene clusters are present in both anaerobic and aerobic bacteria; however, the specific physiological roles of idr genes in aerobic bacteria remain unclear. Therefore, in this study, three marine aerobic bacteria with putative idr gene clusters (Roseovarius azorensis, Notoacmeibacter marinus, and Aliiroseovarius sediminilitoris) were grown in the presence of iodate to determine whether they can reduce iodate to iodide (I-). All tested bacteria almost completely reduced 2 mM iodate under static conditions but only reduced 0.1-0.5 mM iodate under shaking conditions. Moreover, the washed cell suspension of R. azorensis reduced iodate only when the cells were pre-grown statically in the presence of iodate. Transcriptional analysis revealed that the expression levels of idrA, idrB, idrP1 , and idrP2 genes were upregulated in R. azorensis when the cells were grown statically in the presence of iodate. Specifically, idrA expression was induced by 0.1 μM iodate and was up to 14-fold higher compared to that of the non-iodate control. These results suggest that marine aerobic bacteria reduce iodate under oxygen-limited conditions, and that this capacity is induced by environmentally relevant levels of iodate in seawater. Our results suggest that marine aerobic bacteria contribute to iodide production in marine surface waters, thereby affecting the global iodine cycling and ozone budget.

Suppressing the Shuttle Effect of Aqueous Zinc-Iodine Batteries: Progress and Prospects

Aqueous zinc-iodine batteries are considered to be one of the most promising devices for future electrical energy storage due to their low cost, high safety, high theoretical specific capacity, and multivalent properties. However, the shuttle effect currently faced by zinc-iodine batteries causes the loss of cathode active material and corrosion of the zinc anodes, limiting the large-scale application of zinc-iodine batteries. In this paper, the electrochemical processes of iodine conversion and the zinc anode, as well as the induced mechanism of the shuttle effect, are introduced from the basic configuration of the aqueous zinc-iodine battery. Then, the inhibition strategy of the shuttle effect is summarized from four aspects: the design of cathode materials, electrolyte regulation, the modification of the separator, and anode protection. Finally, the current status of aqueous zinc-iodine batteries is analyzed and recommendations and perspectives are presented. This review is expected to deepen the understanding of aqueous zinc-iodide batteries and is expected to guide the design of high-performance aqueous zinc-iodide batteries.

Bacterial Sulfate Reduction Facilitates Iodine Mobilization in the Deep Confined Aquifer of the North China Plain

Bacterial sulfate reduction plays a crucial role in the mobilization of toxic substances in aquifers. However, the role of bacterial sulfate reduction on iodine mobilization in geogenic high-iodine groundwater systems has been unexplored. In this study, the enrichment of groundwater δ34SSO4 (15.56 to 69.31‰) and its significantly positive correlation with iodide and total iodine concentrations in deep groundwater samples of the North China Plain suggested that bacterial sulfate reduction participates in the mobilization of groundwater iodine. Similar significantly positive correlations were further observed between the concentrations of iodide and total iodine and the relative abundance of the dsrB gene by qPCR, as well as the composition and abundance of sulfate-reducing bacteria (SRB) predicted from 16S rRNA gene high-throughput sequencing data. Subsequent batch culture experiments by the SRB Desulfovibrio sp. B304 demonstrated that SRB could facilitate iodine mobilization through the enzyme-driven biotic and sulfide-driven abiotic reduction of iodate to iodide. In addition, the dehalogenation of organoiodine compounds by SRB and the reductive dissolution of iodine-bearing iron minerals by biogenic sulfide could liberate bound or adsorbed iodine into groundwater. The role of bacterial sulfate reduction in iodine mobilization revealed in this study provides new insights into our understanding of iodide enrichment in iodine-rich aquifers worldwide.

Discriminating two bacteria via laser-induced breakdown spectroscopy and artificial neural network

Rapid and successful clinical diagnosis and bacterial infection treatment depend on accurate identification and differentiation between different pathogenic bacterial species. A lot of efforts have been made to utilize modern techniques which avoid the laborious work and time-consuming of conventional methods to fulfill this task. Among such techniques, laser-induced breakdown spectroscopy (LIBS) can tell much about bacterial identity and functionality. In the present study, a sensitivity-improved version of LIBS, i.e. nano-enhanced LIBS (NELIBS), has been used to discriminate between two different bacteria (Pseudomonas aeruginosa and Proteus mirabilis) belonging to different taxonomic orders. Biogenic silver nanoparticles (AgNPs) are sprinkled onto the samples' surface to have better discrimination capability of the technique. The obtained spectroscopic results of the NELIBS approach revealed superior differentiation between the two bacterial species compared to the results of the conventional LIBS. Identification of each bacterial species has been achieved in light of the presence of spectral lines of certain elements. On the other hand, the discrimination was successful by comparing the intensity of the spectral lines in the spectra of the two bacteria. In addition, an artificial neural network (ANN) model has been created to assess the variation between the two data sets, affecting the differentiation process. The results revealed that NELIBS provides higher sensitivity and more intense spectral lines with increased detectable elements. The ANN results showed that the accuracy rates are 88% and 92% for LIBS and NELIBS, respectively. In the present work, it has been demonstrated that NELIBS combined with ANN successfully differentiated between both bacteria rapidly with high precision compared to conventional microbiological discrimination techniques and with minimum sample preparation.

A review of iodine in plants with biofortification: Uptake, accumulation, transportation, function, and toxicity

Iodine deficiency can cause thyroid disease, a serious health problem that has been affecting humans since several years. The biofortification of plants with iodine is an effective strategy for regulating iodine content in humans. In addition, radioiodine released into the atmosphere may contaminate terrestrial ecosystem along with dry or wet deposition and its accumulation in plants may cause exposure risks to humans via food chain. Recent progress in understanding the mechanisms related to iodine uptake, elementary speciation, dynamic transportation, nutritional role, and toxicity in plants is reviewed here. First, we introduced the iodine cycle in a marine-atmosphere-land system. The content and speciation of iodine in plants under natural conditions and biofortification backgrounds were also analyzed. We then discussed the mechanisms of iodine uptake and efflux by plants. The promotion or inhibition effects of iodine on plant growth were also investigated. Finally, the participation of radioiodine in plant growth and its safety risks along the food chain were evaluated. Furthermore, future challenges and opportunities for understanding the participation of iodine in plants have been outlined.

MnO2-Induced Oxidation of Iodide in Frozen Solution

Metal oxides play a critical role in the abiotic transformation of iodine species in natural environments. In this study, we investigated iodide oxidation by manganese dioxides (β-MnO₂, γ-MnO₂, and δ-MnO₂) in frozen and aqueous solutions. The heterogeneous reaction produced reactive iodine (RI) in the frozen phase, and the subsequent thawing of the frozen sample induced the gradual transformation of in situ-formed RI to iodate or iodide, depending on the types of manganese dioxides. The freezing-enhanced production of RI was observed over the pH range of 5.0-9.0, but it decreased with increasing pH. Fulvic acid (FA) can be iodinated by I^-/MnO₂ in aqueous and frozen solutions. About 0.8-8.4% of iodide was transformed to organoiodine compounds (OICs) at pH 6.0-7.8 in aqueous solution, while higher yields (10.4-17.8%) of OICs were obtained in frozen solution. Most OICs generated in the frozen phase contained one iodine atom and were lignin-like compounds according to Fourier transform ion cyclotron resonance/mass spectrometry analysis. This study uncovers a previously unrecognized production pathway of OICs under neutral conditions in frozen environments.

Spatial-Temporal Analysis of Factors Influencing the Median Urine Iodine Concentration of 8-10-year-old Children in Xinjiang, China 25 Years after Implementation of the Salt Iodization Policy

The iodine status of children has improved and stabilized since China implemented salt iodization measures 25 years ago, but routine monitoring of iodine cannot reflect regional factors that influence the iodine level in children. Therefore, we conducted a regional spatial-temporal analysis of children's median urinary iodine concentration (MUIC) and searched for possible factors that might affect children's iodine levels by mining monitoring data. We analyzed data from Xinjiang collected as part of the "Iodine Deficiency Disease National Monitoring Program" from 2017 to 2020. The study population consisted of 76,268 children who participated in the study. We used global autocorrelation analysis to determine whether the MUIC of children was spatially clustered, local autocorrelation analysis to identify specific clustering areas, local cold and hot spot analysis to verify the reliability of the local autocorrelation results, and a spatial lag model to identify factors affecting the children's MUIC. The MUIC values were 217.70, 227.00, 230.67, and 230.67 µg/L in 2017, 2018, 2019, and 2020, respectively. Global autocorrelation analysis showed that the MUIC of all children in the study was significantly related to region (Z scores all > 1.96, P values all < 0.05) from 2017 to 2020. Partial auto-correlation analysis showed that counties with clusters of high values were mostly concentrated in the southwestern region of Xinjiang, whereas counties with clusters of low values were located in the northern part of Xinjiang. Partial cold spot and hot spot analysis showed the same trend, and there are more overlapping districts and counties in 4 years. Three-dimensional trend analysis indicated that children from the western part of Xinjiang had high levels of urinary iodine. According to spatial lag model, urine iodine concentration level is positively correlated with thyroid volume, average salary, and urbanization rate classification. The MUIC of 8-10-year-old children in Xinjiang was spatially clustered and related to geographic region. Our results show that spatial analysis of survey data combined with geographic technology and public health data can accurately identify areas with abnormal iodine concentrations in children. Additionally, understanding the factors that influence iodine levels in the human population is conducive to improving monitoring methods.

Microbial Contributions to Iodide Enrichment in Deep Groundwater in the North China Plain

Microorganisms play crucial roles in the global iodine cycling through iodine oxidation, reduction, volatilization, and deiodination. In contrast to iodate formation in radionuclide-contaminated groundwater by the iodine-oxidizing bacteria, microbial contribution to the formation of high level of iodide in geogenic high iodine groundwater is poorly understood. In this study, our results of comparative metagenomic analyses of deep groundwater with typical high iodide concentrations in the North China Plain revealed the existence of putative dissimilatory iodate-reducing idrABP1P2 gene clusters in groundwater. Heterologous expression and characterization of an identified idrABP1P2 gene cluster confirmed its functional role in iodate reduction. Thus, microbial dissimilatory iodate reduction could contribute to iodide formation in geogenic high iodine groundwater. In addition, the identified iron-reducing, sulfur-reducing, sulfur-oxidizing, and dehalogenating bacteria in the groundwater could contribute to the release and production of iodide through the reductive dissolution of iron minerals, abiotic iodate reduction of derived ferrous iron and sulfide, and dehalogenation of organic iodine, respectively. These microbially mediated iodate reduction and organic iodine dehalogenation processes may also result in the transformation among iodine species and iodide enrichment in other geogenic iodine-rich groundwater systems worldwide.

Spatiotemporal Variability of Groundwater Iodine in the Northern Arid Basins: Significance for Safe Water Supply

The genesis of geogenic iodine (I)-contaminated groundwater poses a significant threat to long-term water exploitation. Safe and sustainable water supply, particularly in the northern arid basins, demands a quantitative prediction of the high variability of I distribution over hydrogeological timescales. Here, bioenergetics-informed reactive transport modeling was combined with high-resolution molecular characterization of fueling organic matter to decipher the time-controlled interactions between vertical flow and (bio)geochemical processes in I transport within the Datong aquifers. The declining reactivities of I-bearing organic matter and Fe oxides in the 15-40 m depth decreased the rate of I release, while a growing number of pore volumes flushed through the aquifers to leach out I^- and organic I. This removal effect is compensated by the desorption of I^- from Fe oxides and secondary FeS generated from the concurrent reduction of Fe oxides and SO₄^2-. Consequently, peak concentrations of groundwater I^- may have appeared, depending upon the vertical recharge rate, at the first several pore volumes flushed through the aquifers. The current vertical distributions of the various I species likely represent a quasi-steady state between I mobilization and leaching. These new mechanistic insights into the dynamic hydrogeological-(bio)geochemical processes support secure groundwater use in the I-affected northern arid basins.

Iodate respiration by Azoarcus sp. DN11 and its potential use for removal of radioiodine from contaminated aquifers

Azoarcus sp. DN11 was previously isolated from gasoline-contaminated groundwater as an anaerobic benzene-degrading bacterium. Genome analysis of strain DN11 revealed that it contained a putative idr gene cluster (idrABP₁P₂ ), which was recently found to be involved in bacterial iodate (IO₃ ^-) respiration. In this study, we determined if strain DN11 performed iodate respiration and assessed its potential use to remove and sequester radioactive iodine (¹²⁹I) from subsurface contaminated aquifers. Strain DN11 coupled acetate oxidation to iodate reduction and grew anaerobically with iodate as the sole electron acceptor. The respiratory iodate reductase (Idr) activity of strain DN11 was visualized on non-denaturing gel electrophoresis, and liquid chromatography-tandem mass spectrometry analysis of the active band suggested the involvement of IdrA, IdrP₁, and IdrP₂ in iodate respiration. The transcriptomic analysis also showed that idrA, idrP₁ , and idrP₂ expression was upregulated under iodate-respiring conditions. After the growth of strain DN11 on iodate, silver-impregnated zeolite was added to the spent medium to remove iodide from the aqueous phase. In the presence of 200 μM iodate as the electron acceptor, more than 98% of iodine was successfully removed from the aqueous phase. These results suggest that strain DN11 is potentially helpful for bioaugmentation of ¹²⁹I-contaminated subsurface aquifers.

SOIL-SOIL SOLUTION DISTRIBUTION COEFFICIENT OF RADIOIODINE IN SURFACE SOILS AROUND SPENT NUCLEAR FUEL REPROCESSING PLANT IN ROKKASHO, JAPAN

The soil-soil solution distribution coefficient (Kd) of radioiodine in soil samples with various total carbon (TC) contents was measured in a batch sorption experiment using 125I tracer spiked as I-. The log values of Kd-125I and TC concentration in low-TC soils (< 10g kg-1) were positively correlated, whereas those of Kd-125I in TC rich soils (> 10 g kg-1) and dissolved organic carbon (DOC) in liquid phase were negatively correlated. The proportion of 125I in the < 3 kDa fraction in the liquid phase is negatively correlated with the log of DOC, implying that 125I is primarily combined with high-molecular-weight organic matter in soil solutions rich in DOC. The results suggest that Kd-125I in soil with high soil organic material (SOM) content is governed by DOC via the combination of 125I and DOC. In contrast, Kd-125I in soils with a low SOM content was governed by SOM because the anion exchange capacity of SOM was vital for the sorption of 125I-.

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.

1H-13C heteronuclear single quantum coherence NMR evidence for iodination of natural organic matter influencing organo-iodine mobility in the environment

The complex biogeochemical behavior of iodine (I) isotopes and their interaction with natural organic matter (NOM) pose a challenge for transport models. Here, we present results from iodination experiments with humic acid (HA) and fulvic acid (FA) using ¹H-¹³C heteronuclear single quantum coherence (HSQC) nuclear magnetic resonance (NMR) spectroscopy. Even though not a quantitative approach, ¹H-¹³C HSQC NMR corroborated that iodination of NOM occurs primarily through aromatic electrophilic substitution of proton by I, and also revealed how iodination chemically alters HA and FA in a manner that potentially affects the mobility of iodinated NOM in the environment. Three types of iodination experiments were conducted with HA and FA: a) non-enzymatic iodination by IO₃^- (pH 3) and I^- (pH 4 and 7), b) addition of lactoperoxidase to promote I^--iodination in the presence of the co-substrate, H₂O₂ (pH 7), and c) addition of laccase for facilitating I^--iodination in the presence of O₂, with or without a mediator (pH 4). When mediators or H₂O₂ were present, extracellular oxidases and peroxidases enhanced I^- incorporation into NOM by between 54% and 3400%. Iodination of HA, which was less than that of FA, enhanced HA's stability (inferred from increases in aliphatic compounds, decreases in carbohydrate moieties, and thus increased molecular hydrophobicity) yet reduced HA's tendency to incorporate more iodine. As such, HA is expected to act more as a sink for iodine in the environment. In contrast, iodination of FA appeared to generate additional iodine binding sites, which resulted in greater iodine uptake capability and enhanced mobility (inferred from decreases in aliphatic compounds, increases in carbohydrates, and thus decreases in molecular hydrophobicity). These results indicate that certain NOM moieties may enhance while others may inhibit radioiodine mobility in the aqueous environment.

Factors controlling iodine enrichment in a coastal plain aquifer in the North Jiangsu Yishusi Plain, China

Iodine is an essential micronutrient in the human diet and an appropriate human iodine intake level is important for population health. Excessive iodine intake is often associated with high iodine groundwater which serves as an important drinking water source in many regions. This study aims to identify the source and key hydrogeochemical processes for iodine accumulation and mobility in the groundwaters of the Northern Jiangsu Yishusi Plain. Combined hydrogeochemical and statistical analyses, specifically random forest modeling and factor analysis, were used to explore the mechanisms affecting the spatial distribution of iodine. The concentration of iodine in the investigated groundwaters was found to vary widely and to range between 4.8 and 4750 μg/L, with 48.9% of the total samples (674) exceeding the threshold value of 100 μg/L for toxic exposure, as defined by the Chinese high‑iodine standard guideline. High iodine concentrations are shown to mainly occur in the marine plain and the shallow aquifer associated with the floodplains of the Old Yellow River. The marine or lagoons-facies sediments were identified as the most plausible iodine source. In addition, mixing of groundwater with paleo-seawater might also have played a role in the coastal area. In contrast, the flood sediments of the Old Yellow River are shown to be an unlikely source. However, they serve as a cover layer that favored the development of reducing hydrogeochemical conditions that can trigger iodine mobilization via the reductive dissolution of iron oxides and the degradation of organic matter. Slow groundwater flow rates also appear to favor iodine release from sediments.

129I/127I and Δ14C records in a modern coral from Rowley Shoals off northwestern Australia reflect the 20th-century human nuclear activities and ocean/atmosphere circulations

Radionuclides produced by 20th-century human nuclear activities from 1945 (e.g., atmospheric nuclear explosions and nuclear-fuel reprocessing) made significant impacts on earth's surface environments. Long-lived shallow-water corals living in tropical/subtropical seas incorporate the anthropogenically-produced radionuclides, including ¹²⁹I and ¹⁴C, into their skeletons, and provide time series records of the impacts of nuclear activities. Here, we present ¹²⁹I/¹²⁷I and Δ¹⁴C time series records of an annually-banded modern coral skeleton from Rowley Shoals, off the northwestern coast of Australia, in the far eastern Indian Ocean. The ¹²⁹I/¹²⁷I and Δ¹⁴C records, covering the period 1930s-1990s, exhibit distinct increases caused by the nuclear activities, and their increasing profiles are clearly different from each other. The first distinct ¹²⁹I/¹²⁷I increase occurs from 1955 to 1959, followed by a decrease in 1960-1963. The increase is probably due to US atmospheric nuclear explosions in Bikini and Eniwetok Atolls in 1954, 1956 and 1958. The ¹²⁹I produced in those nuclear tests would be transported by the North Equatorial Current, a portion of which passes through the Indonesian Throughflow and then reaches Rowley Shoals. This initial increase from 1955 is, however, absent in the Δ¹⁴C record, which shows a distinct increase from 1959 and its peak around the mid-1970s, followed by a gradual decrease. This absence and the 4-year-delayed Δ¹⁴C increase are likely due to dilution of explosion-produced ¹⁴C with natural carbon (by seawater mixing and air-sea gas exchange) being much more intense than that of explosion-produced ¹²⁹I with natural iodine (by the same processes), suggesting that the ¹²⁹I/¹²⁷I ratio is a more conservative anthropogenic tracer in surface ocean waters, as compared to Δ¹⁴C. The second ¹²⁹I/¹²⁷I increase is contemporaneous with a rapid Δ¹⁴C increase during 1964-1967, followed by a rapid ¹²⁹I/¹²⁷I decrease in 1968-1969; the increases can be ascribed to very large atmospheric nuclear explosions conducted in the former Soviet Union in 1961-1962. The third ¹²⁹I/¹²⁷I increase appears between 1969/1970 and 1992, which can be attributed to airborne ¹²⁹I released from nuclear-fuel reprocessing facilities in Europe, the former Soviet Union and the US. The coral ¹²⁹I/¹²⁷I and Δ¹⁴C time series records, combined with previous studies, enhance our understanding of the behavior of anthropogenic ¹²⁹I and ¹⁴C in the global ocean and atmosphere.

A Carbazole-Functionalized Porous Aromatic Framework for Enhancing Volatile Iodine Capture via Lewis Electron Pairing

Nitrogen-rich porous networks with additional polarity and basicity may serve as effective adsorbents for the Lewis electron pairing of iodine molecules. Herein a carbazole-functionalized porous aromatic framework (PAF) was synthesized through a Sonogashira-Hagihara cross-coupling polymerization of 1,3,5-triethynylbenzene and 2,7-dibromocarbazole building monomers. The resulting solid with a high nitrogen content incorporated the Lewis electron pairing effect into a π-conjugated nano-cavity, leading to an ultrahigh binding capability for iodine molecules. The iodine uptake per specific surface area was ~8 mg m-2 which achieved the highest level among all reported I2 adsorbents, surpassing that of the pure biphenyl-based PAF sample by ca. 30 times. Our study illustrated a new possibility for introducing electron-rich building units into the design and synthesis of porous adsorbents for effective capture and removal of volatile iodine from nuclear waste and leakage.

Microbial Community Composition Correlates with Metal Sorption in an Ombrotrophic Boreal Bog: Implications for Radionuclide Retention

Microbial communities throughout the 6.5 m depth profile of a boreal ombrotrophic bog were characterized using amplicon sequencing of archaeal, fungal, and bacterial marker genes. Microbial populations and their relationship to oxic and anoxic batch sorption of radionuclides (using radioactive tracers of I, Se, Cs, Ni, and Ag) and the prevailing metal concentrations in the natural bog was investigated. The majority of the detected archaea belonged to the Crenarchaeota, Halobacterota, and Thermoplasmatota, whereas the fungal communities consisted of Ascomycota, Basidiomycota, and unclassified fungi. The bacterial communities consisted mostly of Acidobacteriota, Proteobacteria, and Chloroflexi. The occurrence of several microbial genera were found to statistically significantly correlate with metal concentrations as well as with Se, Cs, I, and Ag batch sorption data. We suggest that the metal concentrations of peat, gyttja, and clay layers affect the composition of the microbial populations in these nutrient-low conditions and that particularly parts of the bacterial and archaeal communities tolerate high concentrations of potentially toxic metals and may concurrently contribute to the total retention of metals and radionuclides in this ombrotrophic environment. In addition, the varying metal concentrations together with chemical, mineralogical, and physical factors may contribute to the shape of the total archaeal and bacterial populations and most probably shifts the populations for more metal resistant genera.

Crystal and Electronic Structures of A2NaIO6 Periodate Double Perovskites (A = Sr, Ca, Ba): Candidate Wasteforms for I-129 Immobilization

The synthesis, structure, and thermal stability of the periodate double perovskites A₂NaIO₆ (A= Ba, Sr, Ca) were investigated in the context of potential application for the immobilization of radioiodine. A combination of X-ray diffraction and neutron diffraction, Raman spectroscopy, and DFT simulations were applied to determine accurate crystal structures of these compounds and understand their relative stability. The compounds were found to exhibit rock-salt ordering of Na and I on the perovskite B-site; Ba₂NaIO₆ was found to adopt the Fm-3m aristotype structure, whereas Sr₂NaIO₆ and Ca₂NaIO₆ adopt the P2₁/n hettotype structure, characterized by cooperative octahedral tilting. DFT simulations determined the Fm-3m and P2₁/n structures of Ba₂NaIO₆ to be energetically degenerate at room temperature, whereas diffraction and spectroscopy data evidence only the presence of the Fm-3m phase at room temperature, which may imply an incipient phase transition for this compound. The periodate double perovskites were found to exhibit remarkable thermal stability, with Ba₂NaIO₆ only decomposing above 1050 °C in air, which is apparently the highest recorded decomposition temperature so far recorded for any iodine bearing compound. As such, these compounds offer some potential for application in the immobilization of iodine-129, from nuclear fuel reprocessing, with an iodine incorporation rate of 25-40 wt%. The synthesis of these compounds, elaborated here, is also compatible with both current conventional and future advanced processes for iodine recovery from the dissolver off-gas.

Natural organic matter-enhanced transportation of iodine in groundwater in the Datong Basin: Impact of irrigation activities

Local residents in the Datong Basin of northern China are exposed to groundwater with elevated iodine concentrations. Natural organic matter (NOM) has been linked to the heterogeneous distribution of elevated iodine in groundwater used for irrigation purposes, but little is known about the effects of hydrologic fluctuations and NOM characteristics on the transport and enrichment of iodine in the groundwater. Cl/Br molar ratios in Datong Basin groundwater range widely from 133 to 2099. A rapid increase in Cl/Br molar ratio with increasing Cl content indicates hydrologic fluctuations from the upper groundwater to the deeper aquifer due to large-scale irrigation activities in the Basin. A two end-member model of groundwater δ²H and δ¹⁸O values suggests the contribution of upper water recharging groundwater ranges from 20.7 to 49.5%. This vertical recharge process predominantly controls iodine enrichment and distribution in the groundwater. Additionally, the correlation between DOC concentration and δ¹⁸O signatures indicates considerable fresh organic matter is imported into the aquifer during the vertical recharge process. Iodine mobilization is likely promoted by young carbon transported to the deeper aquifer in the organo‑iodine form. Excitation-emission matrix (EEM) results indicate humic-like substances dominate NOM in the groundwater. Evidence from a PARAFAC model suggests organic matter in groundwater samples is associated with microbially-mediated degradation processes in an anaerobic environment. The drawdown migration of organic matter from the upper soil/sediments or surface could provide an extra energy source that promotes microbial activity. Buried sedimentary iodine coupled with anaerobic microbial respiration of subsurface organic carbon within the aquifer could lead to the release of iodine into the groundwater. These findings pave the way for a more comprehensive assessment of the susceptibility of drinking water aquifers, thereby supporting the management of groundwater resources.

Use of Antimicrobial-Impregnated Incise Drapes to Prevent Periprosthetic Joint Infection in Primary Total Joint Arthroplasty: A Retrospective Analysis of 9774 Cases

BACKGROUND

Antimicrobial-impregnated incise drapes are often used despite any literature that demonstrates a reduction in the rate of periprosthetic joint infection (PJI). The aim of this study is to compare the efficacy of antimicrobial-impregnated incise drapes with nonantimicrobial-impregnated incise drapes for the prevention of PJI in patients undergoing total joint arthroplasty (TJA).

METHODS

A retrospective study of 9774 primary TJAs from 2000 to 2012 was performed. Patients who received an antimicrobial-impregnated incise drape (n = 5241) were compared with patients who received a nonantimicrobial-impregnated incise drape (n = 4533). The decision to use an antimicrobial drape was based on the surgeon's discretion. Patients who developed PJI within 1 year after index surgery were identified. Multivariate logistic regression analysis and sensitivity analysis using propensity score matching were performed to control for potential confounders.

RESULTS

The overall PJI rate was 1.14% (60 of 5241) for patients who received an antimicrobial-impregnated incise drape compared with 1.26% (57 of 4533) for those with a nonantimicrobial-impregnated incise drape. There was no difference in the PJI rate between patients with an antimicrobial-impregnated incise drape and those who received nonantimicrobial-impregnated incise drape in the univariate (odds ratio [OR] = 0.91; 95% confidence interval [CI] = 0.63-1.30), multivariate (adjusted OR = 0.92; 95% CI, 0.63-1.34), or propensity score matching analysis (OR = 0.84; 95% CI = 0.52-1.35).

CONCLUSION

Despite the increasing adoption of the use of antimicrobial-impregnated incise drapes in our institute, this study suggests that antimicrobial-impregnated incise drapes do not reduce PJI in patients undergoing primary TJAs.

A novel dimethylsulfoxide reductase family of molybdenum enzyme, Idr, is involved in iodate respiration by Pseudomonas sp. SCT

Pseudomonas sp. strain SCT is capable of using iodate (IO₃ ^- ) as a terminal electron acceptor for anaerobic respiration. A possible key enzyme, periplasmic iodate reductase (Idr), was visualized by active staining on non-denaturing gel electrophoresis. Liquid chromatography-tandem mass spectrometry analysis revealed that at least four proteins, designated as IdrA, IdrB, IdrP₁ , and IdrP₂ , were involved in Idr. IdrA and IdrB were homologues of catalytic and electron transfer subunits of respiratory arsenite oxidase (Aio); however, IdrA defined a novel clade within the dimethylsulfoxide (DMSO) reductase family. IdrP₁ and IdrP₂ were closely related to each other and distantly related to cytochrome c peroxidase. The idr genes (idrABP ₁ P ₂ ) formed an operon-like structure, and their transcription was upregulated under iodate-respiring conditions. Comparative proteomic analysis also revealed that Idr proteins and high affinity terminal oxidases (Cbb₃ and Cyd), various H₂ O₂ scavengers, and chlorite (ClO₂ ^- ) dismutase-like proteins were expressed specifically or abundantly under iodate-respiring conditions. These results suggest that Idr is a respiratory iodate reductase, and that both O₂ and H₂ O₂ are formed as by-products of iodate respiration. We propose an electron transport chain model of strain SCT, in which iodate, H₂ O₂ , and O₂ are used as terminal electron acceptors.

Emergence and fate of volatile iodinated organic compounds during biological treatment of oil and gas produced water

Oil and gas (O&G) production in the United States is expected to grow at a substantial rate over the coming decades. Environmental sustainability related to water consumption during O&G extraction can be addressed through treatment and reuse of water returning to the surface after well completion. Water quality is an important factor in reuse applications, and specific treatment technologies must be utilized to remove different contaminants. Among others, biological active filtration can remove dissolved organic matter as a pre-treatment for surface discharge or to facilitate reuse in such applications as hydraulic fracturing, dust suppression, road stabilization, and crop irrigation. Yet, the formation of byproducts during treatment of O&G wastewater remains a concern when evaluating reuse applications. In this study, we investigated the previously unnoticed biotic formation of iodinated organic compounds (IOCs) such as triiodomethane during biological treatment of O&G wastewater for beneficial reuse. Iodide and several IOCs were quantified in O&G produced water before and after treatment in biological active filters filled with different media types over 13 weeks of operation. While iodide and total IOCs were measured at concentrations <53 mg/L and 147 μg/L, respectively, before biological treatment, total IOCs were measured at concentrations close to 4 mg/L after biological treatment. Triiodomethane was the IOC that was predominantly present. IOC formation had a negative strong correlation (r = -0.7 to -0.8, p < 0.05, n = 9) with iodide concentration in the treated O&G wastewater, indicating that iodide introduced to the biological active filter system was utilized in various reactions, including biologically mediated halogenation of organic matter. Additionally, iodide-oxidizing bacteria augmented in the treated produced water pointed towards potential negative environmental implications when releasing biologically treated halide-rich wastewater effluents to the aquatic environment.

Microbial Methylation of Iodide in Unconfined Aquifer Sediments at the Hanford Site, USA

Incomplete knowledge of environmental transformation reactions limits our ability to accurately inventory and predictably model the fate of radioiodine. The most prevalent chemical species of iodine include iodate (IO3 -), iodide (I-), and organo-iodine. The emission of gaseous species could be a loss or flux term but these processes have not previously been investigated at radioiodine-impacted sites. We examined iodide methylation and volatilization for Hanford Site sediments from three different locations under native and organic substrate amended conditions at three iodide concentrations. Aqueous and gaseous sampling revealed methyl-iodide to be the only iodinated compound produced under biotic conditions. No abiotic transformations of iodide were measured. Methyl-iodide was produced by 52 out of 54 microcosms, regardless of prior exposure to iodine contamination or the experimental concentration. Interestingly, iodide volatilization activity was consistently higher under native (oligotrophic) Hanford sediment conditions. Carbon and nutrients were not only unnecessary for microbial activation, but supplementation resulted in >three-fold reduction in methyl-iodide formation. This investigation not only demonstrates the potential for iodine volatilization in deep, oligotrophic subsurface sediments at a nuclear waste site, but also emphasizes an important role for biotic methylation pathways to the long-term management and monitoring of radioiodine in the environment.

SPECIATION OF IODINE IN SOIL SOLUTION IN FOREST AND GRASSLAND SOILS IN ROKKASHO, JAPAN

The behaviour of I in soil depends on its chemical form in soil solution. Stable I (127I) in the soil solution under actual soil conditions was investigated as a natural analogue of long-lived radioiodine (129I). Soil samples were collected at 5-cm depth intervals down to 20 cm from forests and grasslands in Rokkasho, where the Japanese first commercial nuclear fuel reprocessing plant is located, and the soil solution was extracted by centrifugation. Almost half of total I in the soil solution was iodide, and the other half was dissolved organic I (DOI), with iodate under the detection limit. The proportion of DOI in total I at 0-5 cm depth was larger than the proportions at 5-20 cm depth. The concentration of DOI was positively correlated with that of DOC in the soil solution, suggesting that the behaviour of DOI in the surface soil is affected by labile organic matter dynamics.

Iodine speciation in a silver-amended cementitious system

Silver-impregnated zeolite (AgIZ) has been used for removing radioiodine from contaminated groundwater and nuclear waste streams and the worldwide inventory of such secondary waste is rapidly increasing. The objective of this study was to 1) quantify the effectiveness of two grout waste forms for disposing of the used AgIZ, and 2) determine the I speciation leached from AgIZ encapsulated in grout. A 60-day kinetics batch experiment demonstrated that AgIZ encapsulated in slag-free grout was extremely effective at immobilizing I and Ag, a potential non-radioactive carcinogen. However, AgIZ encapsulated in slag-containing grout, the most common type of grout used for low-level radioactive waste disposal, was entirely ineffective at immobilizing I. While the slag-free grout with AgIZ released only 3.3 μg/L I_total into the contact solution, the slag-containing grout released 19,269 μg/L I_total. Based on thermodynamic calculations, the strongly reducing conditions of the slag-containing system (Eh was -392 mV) promoted the reductive dissolution of the AgI, forming Ag⁰_(aq) and releasing iodide (I^-) into the aqueous phase. The slag-free grout system was maintained under more oxidizing conditions (Eh was 439 mV) and a minimal amount of I was released from the grout. In both grout systems, the aqueous I, originally added to the AgZ as iodide, was composed primarily of iodide and org-I, and essentially no iodate was detected. More organo-I was detected in the slag-free than the slag-containing grout system because the high redox potential of the former system was more conducive to the formation of oxidized I species, such as I₂, which may be intermediates in the covalent bonding of I with organic C in grout. Iodine K-edge XANES analysis indicated that I existed exclusively as silver iodide in both AgIZ-grout samples. Together, these results indicate that subsurface grout disposal of AgIZ waste should be done under oxidizing conditions and that radioiodide released from AgIZ can undergo speciation transformations that have important implications on subsequent mobility and estimated risk.

Direct quantification of inorganic iodine in seawater by mixed-mode liquid chromatography-electrospray ionization-mass spectrometry

Atmospheric iodine plays a relevant role in climate change. Bearing in mind that most of this iodine comes from the oceans, analytical methods capable of determining iodine in a challenging matrix as seawater are necessary. In this work, the first method capable of direct determination of total inorganic iodine in seawater at subnanomolar level based on mixed-mode liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS) without any sample treatment is presented. Analytical characteristics of the developed method were studied in terms of linear range, limits of detection and quantification, precision, trueness, matrix effect, and robustness. The detection limit for iodide was as low as 0.16 nM, injecting 5 μL of seawater without any sample treatment and the working linear range of four orders of magnitude was wide enough to cover the broad concentration range observed in seawater samples. Average values for repeatability and intermediate precision were 4.1% and 8.1%, respectively. The suitability of the method was demonstrated through its application to the analysis of several types of samples, including seawater samples taken at different locations along the Spanish Mediterranean coast and some domestic iodized salts. According to the results obtained, the method developed is rapid, easy to apply and to be automated, avoids sample treatment and requires only few microliters of sample. Furthermore, it has a low detection limit and allows the quantification of inorganic iodine over a wide concentration range.

Role of fungal laccase in iodide oxidation in soils

Previously, we hypothesized that microbial laccase oxidizes iodide (I^-) in soils to molecular iodine (I₂) or hypoiodous acid (HIO), both of which are easily incorporated into natural soil organic matter, and thus plays a role in iodine sorption on soils. In this study, soil iodide oxidase activity was determined by a colorimetric assay to evaluate if laccase is responsible for iodide oxidation in soils. Three types of Japanese soil showed significant iodide oxidase activities (0.751-2.87 mU g soil^-1) at pH 4.0, which decreased with increasing pH, until it was no longer detected at pH 5.5. The activity was inhibited strongly by autoclaving or by the addition of common laccase inhibitors. Similar tendency of inhibition was observed in soil laccase activity, which was determined with 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) as a substrate. Significant positive correlations (R² values of 0.855-0.896) between iodide oxidase activity and laccase activity were observed in two of three soils. Commercially available fungal laccases showed only very low iodide oxidase activities (4.68-18.0 mU mg^-1), but enhanced activities of 102-739 mU mg^-1 were observed in the presence of redox mediators. Finally, we successfully isolated fungal strains with iodide-oxidizing phenotype in the presence of redox mediators. Polyacrylamide gel electrophoresis of the culture supernatant of Scytalidium sp. strain UMS and subsequent active stain revealed that the fungal laccase actually oxidized iodide in the presence of redox mediators. These results suggest that at least part of iodide in soils is oxidized by fungal laccase through the laccase-mediator system.

A Simple Compartment Model for the Dynamical Behavior of Medically Derived 131I in a Municipal Wastewater Treatment Plant

A compartmental model for the reactive flow of the radioisotope ¹³¹I, frequently introduced into the sewer system at varying concentrations through radiotherapy of thyroid diseases, has been developed for an existing municipal wastewater treatment plant (WWTP). It includes the transition of activity from dissolved to suspended particulate and colloid matter, and the separation of phases in sedimentation basins. It has been parametrized by experimental data obtained at key locations in the plant, and validated by measured time series of activity concentration of inflow and outflow. It can be used to predict concentrations at various locations in the WWTP, including outflow and primary sludge. It can also be reparameterized to be applied to other WWTPs based on activated sludge systems. In principle, a modification for the simulation of other nuclides is possible as well. As radioisotopes of iodine form an important part of accidental releases from nuclear power plants, they are monitored, and their environmental behavior is predicted by models. The present work can contribute to these efforts by improving predictions of radioiodine transport in the public sewer system.