Transmission of SARS-CoV-2 in children aged 0 to 19 years in childcare facilities and schools after their reopening in May 2020, Baden-Württemberg, Germany.

We investigated data from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infected 0-19 year olds, who attended schools/childcare facilities, to assess their role in SARS-CoV-2 transmission after these establishments' reopening in May 2020 in Baden-Württemberg, Germany. Child-to-child transmission in schools/childcare facilities appeared very uncommon. We anticipate that, with face mask use and frequent ventilation of rooms, transmission rates in schools/childcare facilities would remain low in the next term, even if classes' group sizes were increased.

Human pregnancy is accompanied by modifications in B cell development and immunoglobulin profile.

Though human pregnancy success has been classically linked with a shift into a Th2 immunoglobulin producing cell response, a clear picture concerning B cell development and immunoglobulin profile during human pregnancy is missing. We analyzed in this work the dynamic of different B cell populations in peripheral blood of pregnant women on the first, second and third trimester of pregnancy. As control, age-matched non-pregnant fertile women were included. Additionally, we quantified the levels of immunoglobulin (IgG1, IgG2, IgG3, IgG4, IgM, IgA and IgE) in the serum of pregnant and non-pregnant women. We observed a significant decrease in the percentages of transitional B cells in peripheral blood of pregnant women as compared to non-pregnant control women. Besides, percentages of naïve as well as switched and non-switched memory B cells in peripheral blood of pregnant women were similar to those in non-pregnant control women. Interestingly, although we did not observe differences in the activation status of B cells as well as in the percentages of plasma cells between pregnant and non-pregnant women, we observed significantly higher levels of IgM, IgA, IgG3, more likely natural antibodies, as well IgG4 in serum of pregnant women compared to non-pregnant age matched control women.

[Acute, bilateral visual loss in a patient with IgA glomerulonephritis]. / Akute, bilaterale Visusminderung bei einem Patienten mit IgA-Glomerulonephritis.

We report on a 30-year-old male patient presenting with acute bilateral loss of vision. Fundus examination showed bilateral retinal hemorrhages, cotton-wool spots, macular edema and optic disk hyperemia. The blood pressure was elevated. The patient was referred to the emergency department with the diagnosis of severe stage IV hypertensive retinopathy. Further examination revealed a previously unknown IgA glomerulonephritis with terminal renal failure and secondary blood pressure derailment. Hypertensive retinopathy can be a first sign of acute renal failure. In cases of hypertensive retinopathy the differential diagnosis including systematic screening is of utmost importance.

Expression analysis of cannabinoid receptors 1 and 2 in B cells during pregnancy and their role on cytokine production.

The endocannabinoid system consists in a family of lipids that binds to and activates cannabinoid receptors. There are two receptors so far described, the cannabinoid receptor 1 (CB1) and 2 (CB2). In the context of pregnancy, the endocannabinoid system was shown participates in different key aspects of reproductive events. B-lymphocytes are pleiotropic cells belonging to the adaptive arm of the immune system. Besides immunoglobulin production, B-lymphocytes were recently shown to be actively involved in antigen presentation as well as cytokine production, thus playing a central role in immunity. In this study we first aimed to characterize the expression of CB1 and CB2 receptors in B cells during pregnancy and then analyze the impact of their activation in term of cytokine production by B cells from pregnant and non-pregnant mice. We observed that the expression of CB1 and CB2 receptors in B-lymphocytes is differentially regulated during pregnancy. While CB2 expression is down regulated CB1 is augmented in B-lymphocytes of pregnant mice. Additionally, the treatment of activated B-lymphocytes with specific CB1 and CB2 agonists, showed a different response in term of cytokine production. Particularly, CB1 against boosted the production of the anti-inflammatory cytokine IL-10 by activated B-lymphocytes from pregnant mice.

Dysautonomia in prodromal α-synucleinopathy: peripheral versus central autonomic degeneration.

BACKGROUND AND PURPOSE: There is an urgent need for early predictive markers for the course of disease in prodromal α-synucleinopathies such as idiopathic rapid eye movement (REM) sleep behaviour disorder. Autonomic cardiac/vascular dysfunction is a prominent feature in advanced α-synucleinopathies, but its diagnostic value as an early neurodegenerative marker remains unclear. The latter may be complicated since synuclein-mediated neurodegeneration may involve central and peripheral components of the autonomic nervous system. METHODS: The diagnostic value of autonomic symptoms and central and peripheral autonomic markers of blood pressure and heart rate regulation were prospectively evaluated in 20 subjects with idiopathic REM sleep behaviour disorder and 20 age-matched healthy controls. RESULTS: Although subjects with REM sleep behaviour disorder showed no clinical autonomic symptoms, blood pressure (P ≤ 0.035) and heart rate response (P ≤ 0.065) were slightly diminished during orthostatic challenge. Autonomic dysregulation was distinctively reflected in lower resting heart rate (all components, P ≤ 0.05) and blood pressure variability (low frequency component, P ≤ 0.024) indicating peripheral cardiac/vascular denervation. In contrast, baroreflex sensitivity and central cardiac autonomic outflow (sympathovagal balance) were well preserved indicating intact central autonomic regulation. Heart rate variability [very low frequency component, receiver operating characteristic (ROC) area under the curve (AUC) 0.80, P ≤ 0.001] and blood pressure variability (low frequency component ROC AUC 0.73, P ≤ 0.01) but not baroreflex sensitivity and sympathovagal balance showed an excellent diagnostic accuracy in identifying subjects with REM sleep behaviour disorder and healthy controls. CONCLUSIONS: Cardiac/vascular dysfunction in prodromal α-synucleinopathy arises from peripheral rather than from central autonomic degeneration. Autonomic indices encoded in heart rate and blood pressure variability are precise functional markers of early synuclein-mediated neurodegeneration.

Multivariate regression approaches for surrogate-based diffeomorphic estimation of respiratory motion in radiation therapy.

Breathing-induced location uncertainties of internal structures are still a relevant issue in the radiation therapy of thoracic and abdominal tumours. Motion compensation approaches like gating or tumour tracking are usually driven by low-dimensional breathing signals, which are acquired in real-time during the treatment. These signals are only surrogates of the internal motion of target structures and organs at risk, and, consequently, appropriate models are needed to establish correspondence between the acquired signals and the sought internal motion patterns. In this work, we present a diffeomorphic framework for correspondence modelling based on the Log-Euclidean framework and multivariate regression. Within the framework, we systematically compare standard and subspace regression approaches (principal component regression, partial least squares, canonical correlation analysis) for different types of common breathing signals (1D: spirometry, abdominal belt, diaphragm tracking; multi-dimensional: skin surface tracking). Experiments are based on 4D CT and 4D MRI data sets and cover intra- and inter-cycle as well as intra- and inter-session motion variations. Only small differences in internal motion estimation accuracy are observed between the 1D surrogates. Increasing the surrogate dimensionality, however, improved the accuracy significantly; this is shown for both 2D signals, which consist of a common 1D signal and its time derivative, and high-dimensional signals containing the motion of many skin surface points. Eventually, comparing the standard and subspace regression variants when applied to the high-dimensional breathing signals, only small differences in terms of motion estimation accuracy are found.

[Seasonal and pandemic influenza vaccination: coverage and attitude among private physicians in Germany]. / Saisonale und pandemische Influenzaimpfung: Impfquoten und Einstellung niedergelassener Ärzte in Deutschland.

BACKGROUND: General practitioners serve as important multipliers for seasonal influenza vaccination in risk groups such as elderly or chronically ill persons, for whom vaccination is recommended in Germany by the Standing Committee on Vaccination (STIKO). Moreover, physicians are a target group for influenza vaccination themselves. METHODS: Data from 1 590 telephone interviews were analysed. The study population comprised private physicians from 4 different disciplines (general and internal medicine, gynaecology, paediatrics). We assessed seasonal and pandemic vaccination coverage, attitudes and informational needs related to vaccination in general, and opinions about the pandemic situation 2009. RESULTS: Of the interviewed physicians, 61% stated that they have been vaccinated against seasonal influenza regularly. Main reasons for not/only occasionally having received a flu shot were: the belief that seasonal influenza vaccination is not necessary for them (78%) or having forgotten about the vaccination (28%). The interviewed physicians expressed a great demand for active information on STIKO recommendations and certain aspects of the seasonal influenza vaccination. There was a significant association between physicians' own influenza vaccination status and the provision of vaccination information materials, utilisation of a data management system for the vaccination of patients, and active vaccination reminders in the physicians' office. In 2009/10, almost 60% had received a pandemic influenza A(H1N1) vaccination. A major barrier to vaccine uptake was the mistrust in the safety of H1N1 vaccines (stated by 54% of non-vaccinees). Information for the public and physicians by the German public health authorities during the pandemic was rather critically appraised by the respondents. CONCLUSION: Compared to other subgroups of health-care workers, among private physicians seasonal and pandemic vaccine uptake was rather high. The physicians' need for more information on vaccination topics can be met by intensified publishing and communication activities of STIKO and by using existing physician-information channels.

Integrated segmentation and non-linear registration for organ segmentation and motion field estimation in 4D CT data.

OBJECTIVES: The development of spatiotemporal tomographic imaging techniques allows the application of novel techniques for diagnosis and therapy in the medical routine. However, in consequence to the increasing amount of image data automatic methods for segmentation and motion estimation are required. In adaptive radiation therapy, registration techniques are used for the estimation of respiration-induced motion of pre-segmented organs. In this paper, a variational approach for the simultaneous computation of segmentations and a dense non-linear registration of the 3D images of the sequence is presented. METHODS: In the presented approach, a variational region-based level set segmentation of the structures of interest is combined with a diffusive registration of the spatial images of the sequence. We integrate both parts by defining a new energy term, which allows us to incorporate mutual prior information in order to improve the segmentation as well as the registration quality. RESULTS: The presented approach was utilized for the segmentation of the liver and the simultaneous estimation of its respiration-induced motion based on four-dimensional thoracic CT images. For the considered patients, we were able to improve the results of the segmentation and the motion estimation, compared to the conventional uncoupled methods. CONCLUSIONS: Applied in the field of radiation therapy of thoracic tumors, the presented integrated approach turns out to be useful for simultaneous segmentation and registration by improving the results compared to the application of the methods independently.

Computation of a probabilistic statistical shape model in a maximum-a-posteriori framework.

OBJECTIVES: When analyzing shapes and shape variabilities, the first step is bringing those shapes into correspondence. This is a fundamental problem even when solved by manually determining exact correspondences such as landmarks. We developed a method to represent a mean shape and a variability model for a training data set based on probabilistic correspondence computed between the observations. METHODS: First, the observations are matched on each other with an affine transformation found by the Expectation-Maximization Iterative-Closest-Points (EM-ICP) registration. We then propose a maximum-a-posteriori (MAP) framework in order to compute the statistical shape model (SSM) parameters which result in an optimal adaptation of the model to the observations. The optimization of the MAP explanation is realized with respect to the observation parameters and the generative model parameters in a global criterion and leads to very efficient and closed-form solutions for (almost) all parameters. RESULTS: We compared our probabilistic SSM to a SSM based on one-to-one correspondences and the PCA (classical SSM). Experiments on synthetic data served to test the performances on non-convex shapes (15 training shapes) which have proved difficult in terms of proper correspondence determination. We then computed the SSMs for real putamen data (21 training shapes). The evaluation was done by measuring the generalization ability as well as the specificity of both SSMs and showed that especially shape detail differences are better modeled by the probabilistic SSM (Hausdorff distance in generalization ability Re approximately 25% smaller). CONCLUSIONS: The experimental outcome shows the efficiency and advantages of the new approach as the probabilistic SSM performs better in modeling shape details and differences.

Medical image computing for computer-supported diagnostics and therapy. Advances and perspectives.

OBJECTIVES: Medical image computing has become one of the most challenging fields in medical informatics. In image-based diagnostics of the future software assistance will become more and more important, and image analysis systems integrating advanced image computing methods are needed to extract quantitative image parameters to characterize the state and changes of image structures of interest (e.g. tumors, organs, vessels, bones etc.) in a reproducible and objective way. Furthermore, in the field of software-assisted and navigated surgery medical image computing methods play a key role and have opened up new perspectives for patient treatment. However, further developments are needed to increase the grade of automation, accuracy, reproducibility and robustness. Moreover, the systems developed have to be integrated into the clinical workflow. METHODS: For the development of advanced image computing systems methods of different scientific fields have to be adapted and used in combination. The principal methodologies in medical image computing are the following: image segmentation, image registration, image analysis for quantification and computer assisted image interpretation, modeling and simulation as well as visualization and virtual reality. Especially, model-based image computing techniques open up new perspectives for prediction of organ changes and risk analysis of patients and will gain importance in diagnostic and therapy of the future. RESULTS: From a methodical point of view the authors identify the following future trends and perspectives in medical image computing: development of optimized application-specific systems and integration into the clinical workflow, enhanced computational models for image analysis and virtual reality training systems, integration of different image computing methods, further integration of multimodal image data and biosignals and advanced methods for 4D medical image computing. CONCLUSIONS: The development of image analysis systems for diagnostic support or operation planning is a complex interdisciplinary process. Image computing methods enable new insights into the patient's image data and have the future potential to improve medical diagnostics and patient treatment.

Preparation and characterisation of raw chars and physically activated carbons derived from marine Posidonia oceanica (L.) fibres.

Industrial valorisation of low cost and renewable biomass as raw precursor of activated carbon for environmental applications is an interesting alternative to costly commercial activated carbons. In this study, the possible use of Mediterranean, Posidonia oceanica fibrous biomass, as a precursor for chars and physically activated carbons, is investigated. Firstly, the raw marine material was chemically and biochemically characterised throughout dry-basis elemental, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis. Then, several P. oceanica chars were prepared and characterised under different pyrolysis times and temperatures. In addition, physically activated carbons (PACs) were produced via water steam flow under various activation periods. The results showed that the pyrolysis induces the creation of pores at different levels with respect to the involved temperature. Thereafter, the physical activation tends to enhance the development of the porous structure. In that issue, the performed Brunauer-Emmett-Teller (BET) and Barrett-Joiner-Halenda (BJH) analysis revealed that the prepared PACs have a mainly mesoporous inner morphology with a varying fraction of micropores.

Fat properties during homogenization, spray-drying, and storage affect the physical properties of dairy powders.

Changes in fat properties were studied before, during, and after the drying process (including during storage) to determine the consequences on powder physical properties. Several methods were combined to characterize changes in fat structure and thermal properties as well as the physical properties of powders. Emulsion droplet size and droplet aggregation depended on the homogenizing pressures and were also affected by spray atomization. Aggregation was usually greater after spray atomization, resulting in greater viscosities. These processes did not have the same consequences on the stability of fat in the powders. The quantification of free fat is a pertinent indicator of fat instability in the powders. Confocal laser scanning microscopy permitted the characterization of the structure of fat in situ in the powders. Powders from unhomogenized emulsions showed greater free fat content. Surface fat was always overrepresented, regardless of the composition and process parameters. Differential scanning calorimetry melting experiments showed that fat was partially crystallized in situ in the powders stored at 20 degrees C, and that it was unstable on a molecular scale. Thermal profiles were also related to the supramolecular structure of fat in the powder particle matrix. Powder physical properties depended on both composition and process conditions. The free fat content seemed to have a greater influence than surface fat on powder physical properties, except for wettability. This study clearly showed that an understanding of fat behavior is essential for controlling and improving the physical properties of fat-filled dairy powders and their overall quality.

Motion artifact reducing reconstruction of 4D CT image data for the analysis of respiratory dynamics.

OBJECTIVES: Respiratory motion represents a major problem in radiotherapy of thoracic and abdominal tumors. Methods for compensation require comprehensive knowledge of underlying dynamics. Therefore, 4D (= 3D + t) CT data can be helpful. But modern CT scanners cannot scan a large region of interest simultaneously. So patients have to be scanned in segments. Commonly used approaches for reconstructing the data segments into 4D CT images cause motion artifacts. In order to reduce the artifacts, a new method for 4D CT reconstruction is presented. The resulting data sets are used to analyze respiratory motion. METHODS: Spatiotemporal CT image sequences of lung cancer patients were acquired using a multi-slice CT in cine mode during free breathing. 4D CT reconstruction was done by optical flow based temporal interpolation. The resulting 4D image data were compared with data generated by the commonly used nearest neighbor reconstruction. Subsequent motion analysis is mainly concerned with tumor mobility. RESULTS: The presented optical flow-based method enables the reconstruction of 3D CT images at arbitrarily chosen points of the patient's breathing cycle. A considerable reduction of motion artifacts has been proven in eight patient data sets. Motion analysis showed that tumor mobility differs strongly between the patients. CONCLUSIONS: Due to the proved reduction of motion artifacts, the optical flow-based 4D CT reconstruction offers the possibility of high-quality motion analysis. Because the method is based on an interpolation scheme, it additionally has the potential to enable the reconstruction of 4D CT data from a lesser number of scans.

Structure-preserving interpolation of temporal and spatial image sequences using an optical flow-based method.

OBJECTIVES: Modern tomographic imaging devices enable the acquisition of spatial and temporal image sequences. But, the spatial and temporal resolution of such devices is limited and therefore image interpolation techniques are needed to represent images at a desired level of discretization. This paper presents a method for structure-preserving interpolation between neighboring slices in temporal or spatial image sequences. METHODS: In a first step, the spatiotemporal velocity field between image slices is determined using an optical flow-based registration method in order to establish spatial correspondence between adjacent slices. An iterative algorithm is applied using the spatial and temporal image derivatives and a spatiotemporal smoothing step. Afterwards, the calculated velocity field is used to generate an interpolated image at the desired time by averaging intensities between corresponding points. Three quantitative measures are defined to evaluate the performance of the interpolation method. RESULTS: The behavior and capability of the algorithm is demonstrated by synthetic images. A population of 17 temporal and spatial image sequences are utilized to compare the optical flow-based interpolation method to linear and shape-based interpolation. The quantitative results show that the optical flow-based method outperforms the linear and shape-based interpolation statistically significantly. CONCLUSIONS: The interpolation method presented is able to generate image sequences with appropriate spatial or temporal resolution needed for image comparison, analysis or visualization tasks. Quantitative and qualitative measures extracted from synthetic phantoms and medical image data show that the new method definitely has advantages over linear and shape-based interpolation.

Adsorption studies of recalcitrant compounds of molasses spentwash on activated carbons.

Due to high levels of residual chemical oxygen demand (COD) in the effluent of molasses spentwash (MSW) after anaerobic treatment, acceptable COD levels for discharge cannot be achieved without some form of post-treatment. In this study, the particulate composition of molasses spentwash after anaerobic digestion (MSWD), is characterised as to its particle size distribution, using micro- and ultrafiltration and three activated carbons are characterised as to their ability to reduce significantly the COD of MSWD effluent. The activated carbons tested as adsorbent, were characterised by XPS spectroscopy, elemental analysis, surface area, pore size distribution, and acid-base titration using the Boehm's method. Adsorption of phenol, used here as a reference compound, and of some organic compounds contained in MSWD (gallic acid, tannic acid, and melanoidin, respectively), was studied. It was clearly demonstrated that an activated carbon with a significant distribution of both micropores and mesopores and a significant amount of macropores that are assumed to act as conduits providing access to micro- and mesopores, have a good adsorption efficiency for compounds such as tannic acid and melanoidins. It is a good adsorbent for melanoidin and coloured compounds of MSWD, which represents a large source of the aqueous pollution in sugar cane industries.

Computer-assisted analysis of 4D cardiac MR image sequences after myocardial infarction.

OBJECTIVES: Spatial-temporal MR image sequences of the heart contain information about shape and motion changes and pathological structures after myocardial infarction. In this paper a Heart Analysis Tool (HeAT) for the quantitative analysis of 4D MR image sequences of infarct patients is presented. METHODS: HeAT supports interactive segmentation of anatomical and pathological structures. Registration of Cine- and DE-MR image data is applied to enable their combined evaluation during the analysis process. Partitioning of the myocardium in segments enables the analysis with high local resolution. Corresponding segments are generated and used for inter/intrapatient comparison. Quantitative parameters were extracted and visualized. RESULTS: Parameters like endocard movement in the infarcted area of six infarct patients were computed in HeAT. Parameters in the infarct area show the expected dysfunctional characteristics. Based on theses parameters passive endocardial movement and myocardial areas with decreased contraction could be identified. CONCLUSION: In contrast to other software tools HeAT supports the combination of contour information of Cine-MR and DE-MR, local analysis with high resolution and inter/intra patient comparison. HeAT enables an observer-independent evaluation of the complex cardiac image data. Using HeAT in further studies can increase the understanding of left ventricle (LV) remodeling.

Surface composition of dairy powders observed by X-ray photoelectron spectroscopy and effects on their rehydration properties.

The surface composition of three dairy powders was investigated by X-ray photoelectron spectroscopy. These spray-dried casein powders were more or less enriched in hygroscopic material (lactose and/or minerals). The principal limitation of these high protein content powders is their poor rehydration ability. Consequently, information about surface composition is required in order to get a better understanding of rehydration behaviour (i.e. wetting time and time of rehydration). The obtained results indicate that the surface of the three powders was dominated by proteins. Lactose and minerals are marginal compounds at the surface whereas the surface coverage of fat was over represented. A correlation between the lactose surface content and the wetting time of the powders was found, but no relationship with the surface fat. Moreover, as the surface is partly depleted in minerals and lactose, it is concluded that these compounds are principally located in the bulk of the particle. Therefore this observation could be related with a wetting time of the powders only slightly affected by the addition of hygroscopic material whereas the time of rehydration was strongly improved; powder wetting being more affected by the surface composition whereas powder dispersion being more influenced by the powder bulk composition.

Human muscle precursor cell regeneration in the mouse host is enhanced by growth factors.

The aim of this study was to optimize human muscle formation in vivo from implanted human muscle precursor cells. We transplanted donor muscle precursor cells (MPCs) prepared from postnatal or fetal human muscle into immunodeficient host mice and showed that irradiation of host muscle significantly enhanced muscle formation by donor cells. The amount of donor muscle formed in cryodamaged host muscle was increased by exposure of donor cells to growth factors before their implantation into injured host muscle. Insulin-like growth factor type I (IGF-I) significantly increased the amount of muscle formed by postnatal human muscle cells, but not by fetal human MPCs. However, treatment of fetal muscle cells with IGF-I, in combination with basic fibroblast growth factor and plasmin, significantly increased the amount of donor muscle formed. In vivo, human MPCs formed mosaic human-mouse muscle fibers, in which each human myonucleus was associated with a zone of human sarcolemmal protein spectrin.

Atlas-based recognition of anatomical structures and landmarks and the automatic computation of orthopedic parameters.

OBJECTIVE: This paper describes methods for the automatic atlas-based segmentation of bone structures of the hip, the automatic detection of anatomical point landmarks and the computation of orthopedic parameters to avoid the interactive, time-consuming pre-processing steps for the virtual planning of hip operations. METHODS: Based on the CT data of the Visible Human Data Sets, two three-dimensional atlases of the human pelvis have been built. The atlases consist of labeled CT data sets, 3D surface models of the separated structures and associated anatomical point landmarks. The atlas information is transferred to the patient data by a non-linear gray value-based registration algorithm. A surface-based registration algorithm was developed to detect the anatomical landmarks on the patient's bone structures. Furthermore, a software tool for the automatic computation of orthopedic parameters is presented. Finally, methods for an evaluation of the atlas-based segmentation and the atlas-based landmark detection are explained. RESULTS: A first evaluation of the presented atlas-based segmentation method shows the correct labeling of 98.5% of the bony voxels. The presented landmark detection algorithm enables the precise and reliable localization of orthopedic landmarks. The accuracy of the landmark detection is below 2.5 mm. CONCLUSION: The atlas-based segmentation of bone structures, the atlas-based landmark detection and the automatic computation of orthopedic measures are suitable to essentially reduce the time-consuming user interaction during the pre-processing of the CT data for the virtual three-dimensional planning of hip operations.

Use of spectroscopic techniques for uranium(VI)/montmorillonite interaction modeling.

To experimentally identify both clay sorption sites and sorption equilibria and to understand the retention mechanisms at a molecular level, we have characterized the structure of hexavalent uranium surface complexes resulting from the interaction between the uranyl ions and the surface retention groups of a montmorillonite clay. We have performed laser-induced fluorescence spectroscopy (LIFS) and X-ray photoelectron spectroscopy (XPS) on uranyl ion loaded montmorillonite. These structural results were then compared to those obtained from the study of uranyl ions sorbed onto an alumina and also from U(VI) sorbed on an amorphous silica. This experimental approach allowed for a clear determination of the reactive surface sites of montmorillonite for U(VI) sorption. The lifetime values and the U4f XPS spectra of uranium(VI) sorbed on montmorillonite have shown that this ion is sorbed on both exchange and edge sites. The comparison of U(VI)/clay and U(VI)/oxide systems has determined that the interaction between uranyl ions and montmorillonite edge sites occurs via both [triple bond]AlOH and [triple bond]SiOH surface groups and involves three distinct surface complexes. The surface complexation modeling of the U(VI)/montmorillonite sorption edges was determined using the constant capacitance model and the above experimental constraints. The following equilibria were found to account for the uranyl sorption mechanisms onto montmorillonite for metal concentrations ranged from 10(-6) to 10(-3) M and two ionic strengths (0.1 and 0.5 M): 2[triple bond]XNa + UO2(2+) <==> ([triple bond]X)2UO2 + 2Na+, log K0(exch) = 3.0; [triple bond]Al(OH)2 + UO2(2+) <==> [triple bond]Al(OH)2UO2(2+), log K0(Al) = 14.9; [triple bond]Si(OH)2 + UO2(2+) <==> [triple bond]SiO2UO2 + 2H+, log K0(Si1) = -3.8; and [triple bond]Si(OH)2 + 3UO2(2+) + 5H2O <==> [triple bond]SiO2(UO2)3(OH)5- + 7H+, log K0(Si2) = -20.0.