Bibliometric insights into the evolution of uranium contamination reduction research topics: Focus on microbial reduction of uranium.

Confronting the threat of environment uranium pollution, decades of research have yielded advanced and significant findings in uranium bioremediation, resulting in the accumulation of tremendous amount of high-quality literature. In this study, we analyzed over 10,000 uranium reduction-related papers published from 1990 to the present in the Web of Science based on bibliometrics, and revealed some critical information on knowledge structure, thematic evolution and additional attention. Methods including contribution comparison, co-occurrence and temporal evolution analysis are applied. The results of the distribution and impact analysis of authors, sources, and journals indicated that the United States is a leader in this field of research and China is on the rise. The top keywords remained stable, primarily focused on chemicals (uranium, iron, plutonium, nitrat, carbon), characters (divers, surfac, speciat), and microbiology (microbial commun, cytochrome, extracellular polymeric subst). Keywords related to new strains, reduction mechanisms and product characteristics demonstrated the strongest uptrend, while some keywords related to mechanism and performance were clearly emerging in the past 5 years. Furthermore, the evolution of the thematic progression can be categorized into three stages, commencing with the discovery of the enzymatic reduction of hexavalent uranium to tetravalent uranium, developing in the groundwater remediation process at uranium-contaminated sites, and delving into the research on microbial reduction mechanisms of uranium. For future research, enhancing the understanding of mechanisms, improving uranium removal performance, and exploring practical applications can be considered. This study provides unique insights into microbial uranium reduction research, providing valuable references for related studies in this field.

Seaward alteration of arsenic mobilization mechanisms based on fine-scale measurements in Pearl River estuarine sediments.

Identification of key As mobilization processes in estuarine sediments is challenging due to the transitional hydrodynamic condition and the technical restriction of obtaining fine-scale results. Herein, high-resolution (µm to mm) and in situ profiling of As with associated elements (Fe, Mn, and S) by the diffusive gradients in thin-film (DGT) technique were applied and coupled with pore water and solid phase analysis as well as microbial high-throughput sequencing, to ascertain the driving mechanisms of As mobilization in the sediments of Pearl River Estuary (PRE). Significant diffusion fluxes of As from sediment to water were observed, particularly in the upper estuary. With the seaward increase of salinity, the driving mechanism of As mobilization gradually shifted from microbial-induced dissimilatory Fe reduction to saltwater-induced ion exchange. Correspondingly, the dominant Fe-reducing bacteria (FeRB) in sediments changed from the genera Clostridium_sensu_stricto_1 and Bacillus to Ferrimonas and Deferribacter. The presence of dissolved sulfide in deeper sediments contributes to As removal through the formation of As-S precipitates as supported by theoretical calculations. Fine-scale findings revealed seaward changes of As mobilization mechanism in the sediments of a human-impacted estuary and may benefit the understanding of As biogeochemical behavior in estuaries worldwide.

A Prussian blue analog-based copper-aluminum layered double hydroxide for cesium removal from water: fabrication, density functional theory-based molecular modeling, and the adsorption mechanism.

A new type of adsorbent, a Prussian blue analog-based copper-aluminum layered double hydroxide (PBA@CuAl-LDH), was successfully synthesized using a one-step method for the removal of radioactive Cs+ from wastewater. The adsorption performance, characteristics and the underlying adsorption mechanism of PBA@CuAl-LDH were systematically examined. The results showed that PBA@CuAl-LDH exhibited excellent adsorption performance, with a maximum adsorption capacity of 109.2 mg g-1. Over 85% of PBA@CuAl-LDH can be recycled, and the material exhibited only a 6.6% loss in adsorption performance. The adsorption process was well-fitted using the pseudo-second-order kinetic model and the Freundlich isotherm model, revealing the surface heterogeneity of the composite adsorbent. A molecular model of PBA@CuAl-LDH was constructed by combining density functional theory and multiple instrumental characterization techniques. Our results indicate that PBA crystals can be generated between layers and on the surface. Ion exchange was revealed as the main adsorption mechanism of Cs+ by PBA@CuAl-LDH. Specifically, the interstitial spaces of the PBA crystals generated between the layers and on the surface played an important role in ion exchange. These findings provide concrete theoretical support for radioactive pollution control and have significant value in directing the fabrication of cesium removal materials and their future engineering application.

Fabrication of Oriented MOF-Based Mixed Matrix Membrane via Ion-Induced Synchronous Synthesis.

Developing a facile strategy for constructing oriented mixed matrix membranes (MMMs) with uniformly dispersed and high-loading metal-organic frameworks (MOFs) is a crucial scientific challenge in probing the enhanced capability and potential applications of MOF-polymer MMMs. Herein, a novel synchronous synthetic method for constructing oriented CuBDC/poly(m-phenylenediamine) (CuBDC/PmPD) MMM with uniform MOF dispersion at high loading at the air-solution interface via the dual function of metal ions is reported. The resulting MMM exhibits excellent separation performance in ion sieving and seawater desalination due to the structural integrity of the proposed membrane and the highly interconnected channels created through the oriented distribution of MOF in a polymer matrix. Such a cutting-edge approach may provide promising insights into the development of advanced MMMs with optimized structure and superior performances.

Ultrafast and Scalable Fabrication of Coordination Polymer Films on Network Substrates via Thermal Current-Induced Dewetting.

Coordination polymers are among the most favored active materials by researchers due to their broad application prospects. However, most of them are usually difficult to directly process into applicable devices because of their unsatisfied processability. One process of great concern for researchers is the in situ preparation of the coordination polymer on the applicable substrate, especially for the favored network substrates with good mechanical properties and 3D porous structure, which could provide obvious convenience and facilitation in the application process. Herein, we present an ultrafast and scalable thermal current-induced dewetting strategy to obtain uniform coordination polymer film in situ on network substrates, which could enable unprecedented convenience to obtain directly usable coordination polymer composites such as practical catalytic electrodes with excellent electrocatalytic performance. The proposed thermal current-induced dewetting method provides a highly adaptable and efficient practical production approach to integrate coordination polymer materials with network substrates and also provides new inspiration for understanding and applying the dewetting process on complex 3D network substrates.

Combination of Sequencing Batch Operation and A/O Process to Achieve Partial Mainstream Anammox: Pilot-Scale Demonstration and Microbial Ecological Mechanism.

In this study, sequencing batch operation was successfully combined with a pilot-scale anaerobic biofilm-modified anaerobic/aerobic membrane bioreactor to achieve anaerobic ammonium oxidation (anammox) without inoculation of anammox aggregates for municipal wastewater treatment. Both total nitrogen and phosphorus removal efficiencies of the reactor reached up to 80% in the 250-day operation, with effluent concentrations of 4.95 mg-N/L and 0.48 mg-P/L. In situ enrichment of anammox bacteria with a maximum relative abundance of 7.86% was observed in the anaerobic biofilm, contributing to 18.81% of nitrogen removal, with denitrification being the primary removal pathway (38.41%). Denitrifying phosphorus removal (DPR) (40.54%) and aerobic phosphorus uptake (48.40%) played comparable roles in phosphorus removal. Metagenomic sequencing results showed that the biofilm contained significantly lower abundances of NO-reducing functional genes than the bulk sludge (p < 0.01), favoring anammox catabolism in the former. Interactions between the anammox bacteria and flanking community were dominated by cooperation behaviors (e.g., nitrite supply, amino acids/vitamins exchange) in the anaerobic biofilm community network. Moreover, the hydrolytic/fermentative bacteria and endogenous heterotrophic bacteria (Dechloromonas, Candidatus competibacter) were substantially enriched under sequencing batch operation, which could alleviate the inhibition of anammox bacteria by complex organics. Overall, this study provides a feasible and promising strategy for substantially enriching anammox bacteria and achieving partial mainstream anammox as well as DPR.

AP2XII-1 is a negative regulator of merogony and presexual commitment in Toxoplasma gondii.

IMPORTANCE: Sexual development is vital for the transmission, genetic hybridization, and population evolution of apicomplexan pathogens, which include several clinically relevant parasites, such as Plasmodium, Eimeria, and Toxoplasma gondii. Previous studies have demonstrated different morphological characteristics and division patterns between asexual and sexual stages of the parasites. However, the primary regulation is poorly understood. A transition from the asexual to the sexual stage is supposedly triggered/accompanied by rewiring of gene expression and controlled by transcription factors and chromatin modulators. Herein, we discovered a tachyzoite-specific transcriptional factor AP2XII-1, which represses the presexual development in the asexual tachyzoite stage of T. gondii. Conditional knockdown of AP2XII-1 perturbs tachyzoite proliferation by endodyogeny and drives a transition to a morphologically and transcriptionally distinct merozoite stage. The results also suggest a hierarchical transcriptional regulation of sexual development by AP2 factors and provide a path to culturing merozoites and controlling inter-host transmission of T. gondii.

Shifts in the high-resolution spatial distribution of dissolved N2O and the underlying microbial communities and processes in the Pearl River Estuary.

Estuaries are significant sources of the ozone-depleting greenhouse gas N2O. However, owing to large spatial heterogeneity and discrete measurements, N2O emissions from estuaries are considerably uncertain. Microbial processes are disputed in terms of the dominant N2O production under severe human disturbance. Herein, combining real-time and high-resolution measurements with bioinformatics analysis, we accurately mapped the consecutive two-dimensional N2O distribution in the Pearl River Estuary (PRE), China, and revealed its underlying microbial mechanisms. Both the horizontal and vertical distributions of N2O concentrations varied greatly at fine scales. Supersaturated N2O concentrations (9.1 to 132.2 nmol/L) in the surface water decreased along the estuarine salinity gradient, with several emission hotspots scattering upstream. The vertical N2O distribution showed marked differences from complete mixing upstream to incomplete mixing downstream, with constant or changeable concentrations with increasing depth. Furthermore, spatially varied denitrifying and nitrifying microorganisms controlled the N2O production and distribution in the PRE, with denitrification playing the dominant role. The nirK-type and nirS-type denitrifying bacteria were the primary producers of N2O in the water and sediment columns, respectively. In addition, substrate concentration (NO3- and DOC) regulated N2O production by affecting key microbial processes, while physical influences (water-mass mixing and salt wedges) reshaped N2O distribution. With these information, a conceptual model of estuarine N2O production and distribution was constructed to generalize the possible biochemical processes under environmental constraints, which could provide insights into the N2O biogeochemical cycle and emission mitigation from a mechanistic perspective.

Self-Catalysis Transformation of Metal-Organic Coordination Polymers.

Designing a multidimensional transformation of metal-organic coordination polymers (MOPs) is highly attractive yet very challenging. Herein, by combining the dynamicity of the coordination bond with the controllability of the chemical reaction, the concept of self-catalysis transformation of MOPs is first proposed. It uses the metal in MOPs as the catalyst to catalyze the chemical reaction of the ligand in the frameworks, simultaneously changing the coordination environment of the metal and the structure of the ligand, resulting in the controllable multidimensional transformation in the morphology and structure of MOPs. The self-catalysis transformation of MOPs can be triggered by heat or light, and crystals with various morphologies and structures can be obtained. Significantly, because the self-catalysis reaction is constraint in the framework, the products at different transformation processes are relatively stable. Monitoring and characterizing the transformation of MOPs give evidences for the exploration of the self-catalysis reaction, and a plausible transformation mechanism is proposed and proved. It can be foreseen that this novel self-catalysis transformation strategy might open up a new direction for the diverse development of MOPs and provide a powerful tool for the study of organic reaction mechanism.

Microbial community assembly responses to polycyclic aromatic hydrocarbon contamination across water and sediment habitats in the Pearl River Estuary.

Along with rapid urbanization and intensive human activities, polycyclic aromatic hydrocarbon (PAH) pollution in the Pearl River Estuary (PRE) and its effects on the microbial community have attracted extensive attention. However, the potential and mechanism of microbial degradation of PAHs across water and sediment habitats remain obscure. Herein, the estuarine microbial community structure, function, assembly process and co-occurrence patterns impacted by PAHs were comprehensively analyzed using environmental DNA-based approaches. The contamination and distribution of PAHs were jointly affected by anthropogenic and natural factors. Some of the keystone taxa were identified as PAH-degrading bacteria (i.e., genera Defluviimonas, Mycobacterium, families 67-14, Rhodobacteraceae, Microbacteriaceae and order Gaiellales in water) or biomarkers (i.e., Gaiellales in sediment) that were significantly correlated with PAH levels. The proportion of deterministic process in the high PAH-polluted water (76%) was much higher than that in the low pollution area (7%), confirming the significant effect of PAHs on the microbial community assembly. In sediment, the communities with high phylogenetic diversity demonstrated a great extent of niche differentiation, exhibited a stronger response to environmental variables and were strongly influenced by deterministic processes (40%). Overall, deterministic and stochastic processes are closely related to the distribution and mass transfer of pollutants, and substantially affect the biological aggregation and interspecies interaction within communities in the habitats.

Au Nanoparticles@UiO-66 Composite Film-Coated Carbon Cloth Substrate for High-Performance H2O2 Electrochemical Sensing.

Due to the strong oxidizability of H2O2, rapid, accurate, sensitive, and stable sensors of hydrogen peroxide (H2O2) have attracted wide attention in the chemical industry, food, medicine, household detergents, and environmental monitoring fields. Here, a high-performance H2O2 electrochemical sensing platform is proposed based on an Au nanoparticles@UiO-66 film coated on a carbon cloth (CC) electrode (Au NPs@UiO-66/CC electrode). The Au NPs@UiO-66/CC electrode was prepared through solvothermal growth of a UiO-66 film on a functionalized three-dimensional CC electrode, followed by in situ deposition of Au NPs into the UiO-66 film under a periodic galvanostatic pulse current. The in situ preparation strategy greatly improves the electrical interaction between Au NPs@UiO-66 and the CC substrate without sacrificing the electrochemical activity of the Au NPs@UiO-66/CC electrode. Meanwhile, thanks to the high specific surface area of the three-dimensional Au NPs@UiO-66/CC electrode, the optimized Au NPs@UiO-66/CC electrode illustrates excellent electrochemical detection capability for H2O2 with an extensive linear range (0.1-21 mM), high sensitivity (1048.01 µA mM-1 cm-2), and lower limit of detection [0.033 µM (S/N = 3)] and limit of quantification [0.109 µM (S/N = 3)]. At the same time, the encapsulated structure of Au NPs in the UiO-66 film also endows the composite electrode with specific sensing performance owing to the regular opening channels of the UiO-66 films that prevent large-size interferents from reacting to the electrochemically active Au NPs. Together with all these advantages, the proposed sensing platform would exhibit great potential for electrochemical sensors and bioelectronics.

Preparation of One-Dimensional Hollow Metal-Organic Frameworks via the Marangoni Effect.

The fabrication of one-dimensional hollow metal-organic frameworks (1D HMOFs) has attracted considerable attention for the catalysis and separation because of their large surface areas and short and continuous axial diffusion pathways. However, the fabrication of 1D HMOFs requires the use of a sacrificial template and multiple steps, limiting their potential applications. This study proposes a novel Marangoni-assisted method to synthesize 1D HMOFs. Using this method, the MOF crystals can undergo heterogeneous nucleation and growth, affording a morphology self-regulation process under kinetic control and forming tubular 1D HMOFs in one step without requiring additional treatment. This method is expected to open new avenues for synthesizing 1D HMOFs.

The effect of microplastics on the depuration of hydrophobic organic contaminants in Daphnia magna: A quantitative model analysis.

Microplastics are emerging pollutants that can absorb large amounts of hydrophobic organic contaminants (HOCs). However, no biodynamic model has yet been proposed to estimate their effects on HOC depuration in aquatic organisms, where the HOC concentrations are time-varying. In this work, a microplastic-inclusive biodynamic model was developed to estimate the depuration of HOCs via ingestion of microplastics. Several key parameters of the model were redefined to determine the dynamic HOC concentrations. Through the parameterized model, the relative contributions of dermal and intestinal pathways can be distinguished. Moreover, the model was verified and the vector effect of microplastics was confirmed by studying the depuration of polychlorinated biphenyl (PCB) in Daphnia magna (D. magna) with different sizes of polystyrene (PS) microplastics. The results showed that microplastics contributed to the elimination kinetics of PCBs because of the fugacity gradient between the ingested microplastics and the biota lipids, especially for the less hydrophobic PCBs. The intestinal elimination pathway via microplastics would promote overall PCB elimination, contributing 37-41 % and 29-35 % to the total flux in the 100 nm and 2 µm polystyrene (PS) microplastic suspensions, respectively. Furthermore, the contribution of microplastic uptake to total HOC elimination increased with decreasing microplastic size in water, suggesting that microplastics may protect organisms from HOC risks. In conclusion, this work demonstrated that the proposed biodynamic model is capable of estimating the dynamic depuration of HOCs for aquatic organisms. The results can shed light on a better understanding of the vector effects of microplastics.

Fabrication of a self-standing supramolecular membrane by a "soft spray" technique.

We report a one-step method to fabricate a free-standing supramolecular membrane composed of melamine and barbituric acid coordinated with silver nitrate (Mba-Ag) at the gas/liquid interface by a soft spray technique. MBa-Ag exhibits a folded two-dimensional layered morphology and thickness of 4.5 µm. The shortwave IR transmittance of MBa-Ag is as high as 95%, which is much higher than the transmittance of UV and visible light, and has the potential for electromagnetic wave transmission.

The positive roles of influent species immigration in mitigating membrane fouling in membrane bioreactors treating municipal wastewater.

The influence of influent species immigration (ISI) on membrane fouling behaviors of membrane bioreactors (MBRs) treating municipal wastewater remains elusive, leading to an incomprehensive understanding of fouling ecology in MBRs. To address this issue, two anoxic/aerobic MBRs, which were fed with raw (named MBR-C) and sterilized (MBR-E) municipal wastewater, were operated. Compared with the MBR-E, the average fouling rate of the MBR-C was lowered by 30% over the long-term operation. In addition, the MBR-E sludge had significantly higher unified membrane fouling index and biofilm formation potential than the MBR-C sludge. Considerably larger flocs size and lower soluble microbial products (SMP) concentrations were observed in the MBR-C than in the MBR-E. Moreover, the 16S rRNA gene sequencing results showed that highly diverse and abundant populations responsible for floc-forming, hydrolysis/fermentation and SMP degradation readily inhabited the influent, shaping a unique microbial niche. Based on species mass balance-based assessment, most of these populations were nongrowing and their relative abundances were higher in the MBR-C than in the MBR-E. This suggested an important contribution of the ISI on the assemblage of these bacteria, thus supporting the increased flocs size and lowered SMP concentrations in the MBR-C. Moreover, the SMP-degrading related bacteria and functional pathways played a more crucial role in the MBR-C ecosystem as revealed by the bacterial co-occurrence network and Picrust2 analysis. Taken together, this study reveals the positive role of ISI in fouling mitigation and highlights the necessity for incorporating influent wastewater communities for fouling control in MBR plants.

Rapid metabolic reprogramming mediated by the AMP-activated protein kinase during the lytic cycle of Toxoplasma gondii.

The ubiquitous pathogen Toxoplasma gondii has a complex lifestyle with different metabolic activities at different stages that are intimately linked to the parasitic environments. Here we identified the eukaryotic regulator of cellular homeostasis AMP-activated protein kinase (AMPK) in Toxoplasma and discovered its role in metabolic programming during parasite's lytic cycle. The catalytic subunit AMPKα is quickly phosphorylated after the release of intracellular parasites to extracellular environments, driving energy-producing catabolism to power parasite motility and invasion into host cells. Once inside host cells, AMPKα phosphorylation is reduced to basal level to promote a balance between energy production and biomass synthesis, allowing robust parasite replication. AMPKγ depletion abolishes AMPKα phosphorylation and suppresses parasite growth, which can be partially rescued by overexpressing wildtype AMPKα but not the phosphorylation mutants. Thus, through the cyclic reprogramming by AMPK, the parasites' metabolic needs at each stage are satisfied and the lytic cycle progresses robustly.

Spatiotemporal dynamics and anthropologically dominated drivers of chlorophyll-a, TN and TP concentrations in the Pearl River Estuary based on retrieval algorithm and random forest regression.

Estimation of large-scale and high-precision water quality parameters is critical in explaining the spatiotemporal dynamics and the driving factors of water quality variability, especially in areas with environmental complexity (e.g., crisscrossing waterways, high flood risk in rainy season and seawater invasion). Thus, in this study, a retrieval algorithm was developed to predict chlorophyll-a (Chl-a), total nitrogen (TN) and total phosphorus (TP) concentrations in the Pearl River Estuary (PRE) based on a large amount of in situ measurements and Landsat 8 remote sensing images. Random Forest (RF) machine learning was conducted to identify the relationship between environmental indicators (pH, turbidity, conductivity, total dissolved solids and water temperature), Chl-a, TN and TP. The results showed that the NIR/R Binomial algorithm for Chl-a estimation presented appreciable reliability with R2 of 0.7429, root mean square error (RMSE) of 1.2089 and mean absolute percent error (MAPE) of 15.33%. The water quality variation in the PRE showed a characteristic of overall improvement and regional deterioration with average concentrations of 7.28 µg/L, 1.15 mg/L and 0.12 mg/L for Chl-a, TN, and TP respectively. Turbidity and pH were identified as the most important indicators to explain Chl-a (52.86%, 39.91%), TN (52.38%, 40.57%) and TP (55.23%, 40.03%) variation. Agricultural pollution was the main pollution source due to the intensive application of fertilizer and increased field size. Besides, land use patterns (e.g., increasing farmland but decreasing forest) greatly influenced water quality from 2010 to 2020. Moreover, light limitation caused by high turbidity reduced the algae productivity and further lowered the Chl-a concentration. The driving factors for regional water quality variations were anthropologically dominated and supplemented by climate change. This study improved the monitoring accuracy of regional water environment and provided quantitative early warning of water pollution events for environmental practitioners, so as to achieve long-term monitoring, precise pollution management and efficient water resources management.

In situ fabrication of bendable epitaxial metal-organic framework films via spraying.

Epitaxial metal-organic framework (MOF) films have shown huge potential for use in separation applications. Herein, bendable epitaxial MOF films are fabricated via spraying. The synthesized MOF films show excellent oil-in-water emulsion separation performance even after being bent for multiple times at high curvatures.

A portable and miniaturized lab-on-fiber sensor based on a responsive Fabry-Perot resonance cavity for the detection of thiocyanate.

Thiocyanate (SCN-) detection is highly significant because of the toxicity of SCN-. Herein, a portable and miniaturized lab-on-fiber (LOF) sensor is reported for the detection of SCN- through integrating a Fabry-Perot (F-P) optical resonance cavity based on anionic-responsive metal-insulator-metal (MIM) onto an optical fiber tip. The responsive MIM optical resonance cavity is constructed with an intermediate cationic polymer brush layer (poly[2-(methacryloyloxy)ethyl] trimethylammonium chloride, PMETAC) and two silver layers via a facile in situ "layer-by-layer" construction method. When the fabricated LOF sensor was immersed in SCN- solutions, an obvious reflection dip shift can be observed, which is feasible for the quantitative detection of SCN-. What's more, the fabricated LOF sensor exhibits outstanding selectivity and anti-interference against other interfering anions. Furthermore, the fabricated LOF sensor also displays other excellent advantages endowed by the polymer brush film, such as a fast response rate and outstanding reproducibility. Therefore, it is believed that the fabricated miniaturized LOF sensor would show great potential as a portable sensor in future applications, such as environmental monitoring and clinical diagnosis.

Research on the remediation of cesium pollution by adsorption: Insights from bibliometric analysis.

While nuclear energy with zero carbon emissions will continue to occupy an indispensable position in future scenarios for power generation, the proper disposal of nuclear waste is still highly challenging in many countries. Adsorption is currently one of the primary methods used for removal of cesium from wastewater. However, no available literature has systematically summarized advances and outlooks on the adsorptive removal of cesium, and research issues such as relevant adsorption mechanisms remain largely unexplored. In this study, a bibliometric analysis was used to quantitatively analyze 10141 publications in the Web of Science Core Collection that were published from 1900 to 2022. Current publication trends and active countries, most influential authors and institutions, journal distribution, and research hotspots and trends were reviewed and summarized. The results for the conceptual structure and evolution of investigations in this field showed three distinct periods of rapid development in recent decades. The first period concerned the scope, degree, and influences of pollution by cesium and the development of natural adsorbents. The second period included the exploration and verification of adsorption mechanisms, the fabrication and optimization of new materials, and the application of density functional theory for chemical calculations. The third period involved the development of more advanced biodegradable, nanoscale and synthetic materials with great potential for use as adsorbents as well as advances in engineering applications. Notably, the study showed that it is necessary to further enhance application-driven laboratory investigations. Future directions for research were proposed, such as the investigation of complex adsorption mechanisms, development of new materials, and engineering applications of materials developed in the laboratory. The findings will provide valuable insights and serve as a reference for researchers and policymakers as they address the adsorptive remediation of cases of pollution by cesium.