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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
141

Φυσική ραδιενέργεια των κλαστικών και ανθρακικών ιζημάτων στην περιοχή ανατολικά της Ηγουμενίτσας / Natural radioactivity of clastic and carbonate sediments located eastern of Igoumenitsas area (Western Greece)

Αναγνωστούδη, Θωμαή 09 May 2012 (has links)
Η μεταπτυχιακή διατριβή με θέμα: «Φυσική Ραδιενέργεια των κλαστικών και ανθρακικών ιζημάτων στην περιοχή ανατολικά της Ηγουμενίτσας», έχει ως αντικείμενο την αναγνώριση, μελέτη και ανάλυση της φυσικής ραδιενέργειας των φυσικών ραδιονουκλιδίων U238, Th232, Ra226 και K40 στις κλαστικές αποθέσεις ηλικίας Μειοκαίνου (Ακουιτάνιο) και στις κλαστικές αποθέσεις των υποθαλάσσιων ριπιδίων Ηωκαίνου και Ολιγοκαίνου, και στο ποσοστό συγκέντρωσής τους στις παλαιότερες ανθρακικές και σύγχρονες κλαστικές ακολουθίες της περιοχής Νεράιδας Θεσπρωτίας, καθώς επίσης και στην ερμηνεία των αποτελεσμάτων ως προς την ταυτοποίηση της πηγής προέλευσής τους. Η περιοχή μελέτης ανήκει στη λεκάνη Φιλιάτες-Παραμυθιάς Ηπείρου και αποτελεί τμήμα ενός εκ των φλυσχικών συγκλίνων, τα οποία αναπτύσσονται στη δυτική Ελλάδα μέσα στην Ιόνια ζώνη, εξαιτίας της δράσης των εσωτερικών επωθήσεων. Η υπαίθρια δειγματοληψία πραγματοποιήθηκε στην ανθρακική και κλαστική ακολουθία, με τη συλλογή 45 συνολικά δειγμάτων, εκ των οποίων 8 ήταν ασβεστολιθικά, 18 ψαμμιτικά, 18 πηλιτικά και 1 σύγχρονης ποτάμιας άμμου. Η περιγραφή των ιζηματολογικών ενοτήτων βασίστηκε σε βιβλιογραφικά δεδομένα των γύρω περιοχών, καθότι δεν πραγματοποιήθηκαν ιζηματολογικές και γεωχημικές αναλύσεις. Οι κλαστικές ακολουθίες ταξινομήθηκαν βάσει του γεωλογικού χάρτη του Ι.Γ.Μ.Ε. φύλλο Φιλιάτες 1962-63, 1:50.000, ως αποθέσεις του Ανώτερου Φλύσχη ηλικίας Ακουιτανίου και αποθέσεις του Φλύσχη των Αγ. Πάντων ηλικίας Ηωκαίνου-Ολιγοκαίνου. Στην κατεύθυνση της ραδιοχημικής έρευνας, πραγματοποιήθηκε μια σειρά από ραδιοχημικές αναλύσεις σε όλο των αριθμό των δειγμάτων, προκειμένου να εκτιμηθεί η συγκέντρωση ενεργότητας των φυσικών ραδιονουκλιδίων των ανθρακικών και κλαστικών ακολουθιών, με σκοπό να εντοπιστεί η πηγή προέλευσής τους και η δυνατότητα αποθήκευσής τους, στους συγκεκριμένους σχηματισμούς. Η μέτρηση της συγκέντρωσης ενεργότητας του 238U, 226Ra, 232Th, και 40K έγινε με τη μέθοδο της γ-φασματομετρίας, με τη χρήση υπερκάθαρου ανιχνευτή γερμανίου (HPGe) της Canberra. Ο κύριος στόχος αυτής της προσπάθειας, ήταν να διαπιστωθεί η ύπαρξη των φυσικών ραδιονουκλιδίων στην ανθρακική ακολουθία, καθώς και η συγκέντρωσή τους στην κλαστική ακολουθία, λόγω δευτερογενούς μετανάστευσής τους, από τις ήδη ταυτοποιημένες φωσφορούχες αποθέσεις των γειτονικών περιοχών. Η περιοχή μελέτης δεν εμφάνισε υπερβολικές τιμές συγκέντρωσης ενεργότητας φυσικών ραδιονουκλιδίων σε κανέναν από τους γεωλογικούς σχηματισμούς που ερευνήθηκαν. Η ανθρακική ακολουθία της περιοχής χαρακτηρίστηκε πολύ φτωχή στα υπό μελέτη φυσικά ραδιονουκλίδια, σε αντίθεση με την κλαστική ακολουθία, η οποία εμφάνισε γενικά αυξημένες τιμές συγκέντρωσης ενεργότητας φυσικών ραδιονουκλιδίων. Τέλος, βάσει των συγκεντρώσεων που εντοπίστηκαν στις σύγχρονες ποτάμιες προσχώσεις της περιοχής μελέτης, τα Τεταρτογενή ιζήματα της περιοχής χαρακτηρίστηκαν ως αρκετά εμπλουτισμένα, συμπεραίνοντας την ύπαρξη σύγχρονης τροφοδοσίας φυσικών ραδιονουκλιδίων μέσω οριζόντιων ρηγμάτων. Συμπεραίνοντας, οι κλαστικές ακολουθίες του Φλύσχη των Αγ. Πάντων, Ηωκαίνου και Ολιγοκαίνου και τα Τεταρτογενή ιζήματα της περιοχής, δεν χαρακτηρίζονται ως άμεσα προτεινόμενοι σχηματισμοί για τη χρήση αδρανών υλικών, ενώ προτείνεται εκτενέστερη μελέτη στους Τεταρτογενείς σχηματισμούς της Εξωτερικής Ιονίου. / The subject of postgraduate thesis «Natural radioactivity of clastic and carbonate sediments located eastern of Igoumenitsas area (Western Greece)» is dealing with the recognition, study and analysis of natural radioactivity of natural radionuclides U238, Th232, Ra226 και K40 in the Miocene (Aquitanian) clastic deposits, Eocene and Oligocene clastic deposits of the submarine fans and their concentration amount in the older carbonate and contemporary clastic sequences of the study area located in the village Neraida of Thesprotia. It also deals with the interpretation of results in terms of the identification of the source. The study area is located in the basin of Filiates-Paramithia of Epirus and constitutes a part of the flysch syclins, developed in Western Greece within the Ionian zone, due to the activity of internal thrusts. The sampling was accomplished in the carbonate and clastic sequences, with the collection of 45 rock samples: 8 limestones, 18 sandstones, 18 siltstones and 1 sample of contemporary fluvial sand. The sedimentological units description was based in bibliographical data, since sedimentological and geochemical analyses were not accomplished. The clastic sequences were classified based on the geological map of I.G.M.E. Filiates sheet 1962-63, 1:50.000, as Upper Flysch depotites Aquitanian ages and Ag. Panton Flysch deposites Eocene-Oligicene ages. Towards the radiochemical research a sequence of radiochemical analyzes were accomplished, in order to evaluate the activity concentration of natural radionuclides of carbonate and clastic sequences, with the aim of locating their source and the potential of their storage in these specific formations. The activity concentration measurement of 238U, 226Ra, 232Th, and 40K was carried out with gamma-spectometry method, using the High Purity Germanium detector (HPGe) of Canberra Company. The main aim of this effort was the establishment of the existence of the natural radionuclides in the carbonate sequence, as well as their concentration in the clastic sequence, due to their secondary migration from the already identified phosphatic deposits of the adjacent areas. None of the studied geological formations of the study area presented exaggerating activity concentration of natural radionuclides values. The carbonate sequence in terms of the studied natural radionuclides was characterized as quite poor, contrasting to the clastic sequence, which generally showed increasing activity concentration of natural radionuclides values. Finally, based on the concentrations traced in the contemporary fluvial deposits of the study area, the Quaternary sediments of the area were characterized as sufficiently enriched, concluding to the existence of contemporary source of natural radionuclides through horizontal faults. Concluding, the Eocene – Oligocene clastic sequences of Ag. Panton Flysch and the Quaternary sediments of the area, are not characterized as immediately preferred formations for the usage of aggregate materials, while additionally a more extensive research in the Quaternary formations of External Ionian Zone is suggested.
142

Chelatující polymery pro léčbu Wilsonovy nemoci / Chelating polymers for the therapy of Wilson's disease

Mattová, Jana January 2017 (has links)
Wilson's disease is a hereditary disorder of copper metabolism, which causes copper accumulation in organism, especially in the liver, kidneys and brain. Current treatment is based on using low-molecular weight copper chelators and high doses of zinc salts. Unfortunately, they can induce some severe side effects due to systemic action. The aim of this thesis is to improve the treatment of Wilson's disease by using of polymeric drug delivery systems. The size of polymer particles in tens of microns should provide non-resorbability of the drug after oral administration. Synthetic microparticles of poly(glycidyl methacrylate-co- ethylene dimethacrylate), natural microcrystalline cellulose and cross-linked chitosan were used as polymer matrices. N,N-di(2-pyridylmethyl)amine, triethylenetetraamine and 8-hydroxyquinoline were selected as specific copper chelators, which can complex copper cations with high efficiency. The principle of the proposed treatment is that the polymeric carrier-bound chelator complex copper directly from the food in digestive tract of the organism. Because of non-resorbability, the entire complex should be eliminated from the body together with stools. This virtually eliminates systemic side effects. The ability of adsorption of copper and the stability of polymer complex under...
143

Pertinence de la prise en compte des réponses épigénétiques chez des organismes chroniquement exposés à de faibles niveaux de substances radioactives / Integration of epigenetic response in radioecology

Gombeau, Kewin 17 December 2015 (has links)
Ce travail s’intègre dans le cadre du programme européen COMET (7ième PCRD EURATOM) et vise à évaluer les réponses épigénétiques (particulièrement la méthylation de l’ADN), lors d’expositions chroniques à de faibles niveaux de substances radioactives.Lors d’une première expérience, les poissons zèbres (Danio rerio) ont été exposés au laboratoire à des concentrations environnementales d’uranium appauvri : 2 et 20 µg L-1. Cette expérimentation a révélé un impact sur la méthylation de l’ADN génomique, majoritairement chez les mâles exposés, croissant avec la durée et le niveau d’exposition. Lors d’une seconde expérience, nous avons observé un impact sur les profils de méthylation de la descendance issue de parents exposés, ainsi qu’une perturbation du statut transcriptomique et des dommages histologiques dans le muscle squelettique des larves issues de parents exposés.Les outils développés ont pu être appliqués à la problématique d’étude des effets biologiques induits par les radionucléides émis lors de l’accident de la centrale nucléaire de Fukushima Daiichi. Les analyses réalisées sur la grenouille arboricole Japonaise (Hyla japonica) ont révélé une corrélation positive entre la dose totale de radioactivité absorbée par ces grenouilles, l’hyperméthylation de l’ADN génomique et l’augmentation des dommages à l’ADN mitochondrial.L’ensemble de ces travaux a permis de mettre en évidence la sensibilité des réponses épigénétiques chez différents organismes soumis à de faibles doses de radionucléides, qui pourraient ainsi permettre de mieux caractériser les mécanismes d’adaptation et les potentiels effets transgénérationnels induits par les radionucléides. / This work integrates within the general framework of the European program COMET (7th Framework Programme EURATOM) and aims to assess the epigenetic responses (particularly DNA methylation), during chronic exposure to low levels of radioactive materials. During a first experiment, zebrafish (Danio rerio) were exposed in laboratory controlled conditions to environmentally relevant concentrations of depleted uranium: 2 and 20 µg L-1. This experiment allowed an impact on the genomic DNA methylation to be demonstrated, mainly in exposed males, which increased with the duration and level of exposure. In a second experiment, we observed an impact on DNA methylation patterns in the progeny of exposed parents, as well as a perturbation of transcriptomic, and histological damage in larvae skeletal muscle from exposed parents.The methods developed were applied to the second context focusing on the study of biological effects induced by radionuclides emitted following the Fukushima Daiichi nuclear power plant accident. The analyses performed on the Japanese tree frog (Hyla japonica) revealed a positive correlation between the total dose of radiation absorbed by these frogs, hypermethylation of genomic DNA as well as increasing damage to mitochondrial DNA.This work highlighted the sensitivity of epigenetic responses in different biological models exposed to low levels of radionuclides, and could be used to further characterize adaptation mechanisms and potential transgenerational effects induced by radionuclides.
144

THEREDA-Journal

20 April 2022 (has links)
Das THEREDA-Journal ist die Zeitschrift zur „Thermodynamischen Referenz-Datenbasis“ (THEREDA). Die Datenbasis erlaubt in Verbindung mit geeigneten Programmen die Berechnung von Löslichkeiten und Mineralumwandlungen in wässrigen Elektrolytlösungen bis zu hohen Konzentrationen. Im Mittelpunkt der Arbeit stehen geochemische Randbedingungen, wie sie für die Bewertung von Nah- und Fernfeldprozessen in verschiedenen Gesteinsformationen, welche als potenzielle Endlager für radioaktive Abfälle in der Diskussion stehen, relevant sind. THEREDA stellt derzeit für das Wirtsgestein Salz die weltweit einzige polytherme Datenbasis dar. Sie wird mit dem Stand von Wissenschaft und Technik kontinuierlich von etablierten Forschungsinstitutionen, welche auf dem Gebiet der Endlagerung von radioaktiven Abfällen bzw. den potenziellen Wirtsgesteinen arbeiten, weiterentwickelt. Das THEREDA-Journal beinhaltet Beiträge zu Datensituation und Datenbestand, Neuanpassungen, Weiterentwicklungen sowie auch Bewertungen zur Anwendbarkeit. Alle Beiträge durchlaufen einen Review-Prozess innerhalb des THEREDA-Verbundes. Auch Gastbeiträge externer THEREDA-Nutzer sind willkommen. Die Datenbasis ist frei zugänglich unter www.thereda.de.
145

Novel approaches in determining baseline information on annual disposal rates and trace element content of U.S. coal combustion residues : a response to EPA’s June 2010 proposed disposal rule

Chwialkowski, Natalia Ewa 14 February 2011 (has links)
Although products of coal combustion (PCCs) such as coal ash are currently exempted from classification as a hazardous waste in the United States under the 1976 Resource Conservation and Recovery Act (RCRA), the U.S. Environmental Protection Agency (EPA) is now revising a proposed rule to modify disposal practices for these materials in order to prevent contamination of ground- and surface water sources by leached trace elements. This paper analyzes several aspects of EPA’s scientific reasoning for instating the rule, with the intent of answering the following questions: 1) Are EPA’s cited values for PCC production and disposal accurate estimates of annual totals?; 2) In what ways can EPA’s leaching risk modeling assessment be improved?; 3) What is the total quantity of trace elements contained within all PCCs disposed annually?; and 4) What would be the potential costs and feasibility of reclassifying PCCs not under RCRA, but under existing NRC regulations as low-level radioactive waste (LLRW)? Among the results of my calculations, I found that although EPA estimates for annual PCC disposal are 20% larger than industry statistics, these latter values appear to be closer to reality. Second, EPA appears to have significantly underestimated historical PCC disposal: my projections indicate that EPA’s maximum estimate for the quantity of fly ash landfilled within the past 90 years was likely met by production in the last 30 years alone, if not less. Finally, my analysis indicates that while PCCs may potentially meet the criteria for reclassification as low-level radioactive waste by NRC, the cost of such regulation would be many times that of the EPA June proposed disposal rule ($220-302 billion for PCCs disposed in 2008 alone, versus $1.47 billion per year for the Subtitle C option and $236-587 million for Subtitle D regulatory options). / text
146

Measurement of 222Rn Exhalation Rates and 210Pb Deposition Rates in a Tropical Environment

Lawrence, Cameron Eoin January 2006 (has links)
This thesis provides the measurements of 222Rn exhalation rates, 210Pb deposition rates and excess 210Pb inventories for locations in and around Ranger Uranium Mine and Jabiru located within Kakadu National Park, Australia. Radon-222 is part of the natural 238U series decay chain and the only gas to be found in the series under normal conditions. Part of the natural redistribution of 222Rn in the environment is a portion exhales from the ground and disperses into the atmosphere. Here it decays via a series of short-lived progeny, that attach themselves to aerosol particles, to the long lived isotope 210Pb (T1/2 = 22.3 y). Attached and unattached 210Pb is removed from the atmosphere through wet and dry deposition and deposited on the surface of the earth, the fraction deposited on soils is gradually transported through the soil and can create a depth profile of 210Pb. Here it decays to the stable isotope 206Pb completing the 238U series. Measurements of 222Rn exhalation rates and 210Pb deposition rates were performed over complete seasonal cycles, August 2002 - July 2003 and May 2003 - May 2004 respectively. The area is categorised as wet and dry tropics and it experiences two distinct seasonal patterns, a dry season (May-October) with little or no precipitation events and a wet season (December-March) with almost daily precipitation and monsoonal troughs. November and April are regarded as transitional months. As the natural processes of 222Rn exhalation and 210Pb deposition are heavily influenced by soil moisture and precipitation respectively, seasonal variations in the exhalation and deposition rates were expected. It was observed that 222Rn exhalation rates decreased throughout the wet season when the increase in soil moisture retarded exhalation. Lead-210 deposition peaked throughout the wet season as precipitation is the major scavenging process of this isotope from the atmosphere. Radon-222 is influenced by other parameters such as 226Ra activity concentration and distribution, soil porosity and grain size. With the removal of the influence of soil moisture during the dry season it was possible to examine the effect of these other variables in a more comprehensive manner. This resulted in categorisation of geomorphic landscapes from which the 222Rn exhalation rate to 226Ra activity concentration ratios were similar during the dry season. These results can be extended to estimate dry season 222Rn exhalation rates from tropical locations from a measurement of 226Ra activity concentration. Through modelling the 210Pb budget on local and regional scales it was observed that there is a net loss of 210Pb from the region, the majority of which occurs during the dry season. This has been attributed to the fact that 210Pb attached to aerosols is transported great distance with the prevailing trade winds created by a Hadley Circulation cell predominant during the dry season (winter) months. By including the influence of factors such as water inundation and natural 210Pb redistribution in the soil wet season budgeting of 210Pb on local and regional scales gave very good results.
147

Nuclear structure studies with neutron-induced reactions : fission fragments in the N=50-60 region, a fission tagger for FIPPS, and production of the isomer Pt-195m / Études de la structure nucléaire avec des réaction induites par des neutron : Fragments de fission dans la région N=50-60, un marqueur d'événement de fission pour FIPPS et production de l'isomère Pt-195m

Wilmsen, Dennis 21 December 2017 (has links)
Ce travail s'inscrit dans le cadre d'études de structures nucléaires réalisées en utilisant des réactions de fission induites par neutrons froids. Il décrit successivement les résultats d'une étude sur des noyaux ayant un nombre de neutrons N=50-60, sur le développement d'un marqueur d'événements de fission et enfin sur la production de l'isomère Pt-195m. Chacun des différents sous-thèmes trouve son origine dans la campagne EXILL qui s'est déroulée en 2012-2013 et durant laquelle un spectromètre de grande efficacité pour la détection des rayonnements γ (EXOGAM) a été utilisé auprès du réacteur à haut flux de neutrons de l'Institut Laue-Langevin (ILL). Dans la première partie de cette thèse, les noyaux d'intérêt ont été produits par fission induites par des neutrons sur les cibles fissiles U-235 et Pu-241. Des méthodes de spectroscopie γ ont été appliquées pour l'identification des fragments de fission, l'attribution des transitions γ à un noyau et l'analyse des durées de vie moyenne des états excités. L'analyse des durées de vie moyenne des états excités dans la plage de quelques picosecondes à quelques nanosecondes a été réalisée en utilisant deux méthodes complémentaires. Dans les deux cas, il s'agit de réaliser un spectre en temps construit à partir de la coincidence entre une transition qui alimente le niveau mesuré et une transition qui le désexcite. Les durées de vie moyenne pour les noyaux Kr-92, Kr-93 et Zr-101 sont présentées. Dans la seconde partie, les premiers résultats du développement d'un nouveau détecteur pour la discrimination des fragments de fission sont présentés. Ce marqueur d'événements de fission est destiné à être utilisé sur le spectromètre FIssion Prompt Product γ-ray Spectrometer (FIPPS) de l'ILL. Dans le cadre de cette étude, deux conceptions de détecteurs différentes, basées sur un scintillateur en plastique solide et un scintillateur liquide organique, ont été testées. Dans la troisième partie, la possibilité de la population spécifique de l'isomère de spin dans Pt-195 est examinée au regard particulièrement de son utilisation en tant que radio-isotope en médecine nucléaire. Une telle activation spécifique pourrait être réalisée grâce à l'existence d'états excités dont la structure permettrait une population ciblée dans le cas de l'utilisation de réactions de photo-excitation. La recherche de tels états a été initiée lors d'une expérience de capture de neutrons à EXILL dans laquelle des états potentiels ont été identifiés. L'activation de l'isomère par ces états a ensuite été testée avec des réactions photonucléaires à l'aide du faisceau haute intensité disponible auprès de l'installation γ HIGS de TUNL (Triangle Universities Nuclear Laboratory, Duke, USA). / Within the scope of atomic nuclear structure studies with neutron-induced reactions, this work presents the results of a fission fragment study in the N=50-60 region, the development of a fission event tagger, and the production of the isomer Pt-195m. Each of the different sub-topics has its origin in the 2012/13 EXILL campaign, where nuclear structure studies were carried out with neutron-induced reactions, and explored with a γ-efficient detector array. In the first part of this thesis, the neutron-rich region around neutron number N=50-60 was investigated with neutron-induced fission reactions on the fissile targets U-235 and Pu-241. Gamma spectroscopy methods were applied for the identification of the respective fission fragments, the assignment of γ transitions, and the analysis of lifetimes of excited states. The slope fit method as well as the recently developed generalized centroid difference method were used for the analysis of lifetimes in the low picoseconds to sub-nanoseconds range. Lifetimes for the nuclei Kr-92, Kr-93 and Zr-101 are presented. In the second part, first results of the development of a new detector for the discrimination of fission fragments are presented. This fission event tagger is intended to be used at the FIssion Product Prompt γ-ray Spectrometer (FIPPS) at the Institut Laue-Langevin. Within the scope of this study, two different detector designs, based on a solid plastic scintillator and an organic liquid scintillator, respectively, were tested. In the third part the possibility of the specific population of the spin-isomer in Pt-195 is discussed with special regard to its use as radioisotope in nuclear medicine. Such a specific activation could be realized via certain “doorway states” in photo-excitation reactions. The search for these doorway states was initiated within a neutron capture experiment at EXILL where potential states were found. The activation of the isomer via these states was tested afterwards with photonuclear reactions using the high intense γ-beam HIGS of the TUNL facility.
148

Application of biological sample oxidiser and low-level liquid scintillation counter for the determination of ¹⁴C and ³H content in water from the Hartbeespoort Dam in North-West Province

Khumalo, Lamlile Hlakaniphile Ntando 02 1900 (has links)
The aim of the research study was to evaluate the levels of 14C and 3H radionuclides in Hartbeespoort Dam water and to determine if these radionuclides are within regulatory concerns. Water samples from Hartbeespoort Dam were prepared using the Sample Oxidiser Method and measurements of selected radionuclides were done using Liquid Scintillation Counter Quantulus 1220. The results evaluated suggest that water from Hartbeespoort Dam contains levels of 14C and 3H radionuclides that are within regulatory limits. The highest average concentration for 14C measured was 3.77E+01 (+/-2.47E-01) Bq/L, whereas the highest average concentration measured for 3H was 2.74E+01 (+/- 2.30E-01) Bq/L. The observations made regarding the impacts of climate on the 14C radionuclide were that, the concentration levels were higher during winter season when there was a rain than during rainy seasons. Tritium results showed that the climate conditions did not have any significant impacts on the concentration levels. When the concentrations of these radionuclides are above regulatory levels (14C is 100 Bq/L and 3H is10000 Bq/L), their impacts may cause harm to public`s health and the environment. Therefore, Necsa as a nuclear facility owner and National Nuclear Regulator (NNR) as a regulator are responsible for ensuring the public protection from radioactive effluents that contain not just 3H and 14C, but any radionuclide which may cause harm to public`s health. / Environmental Sciences / M. Sc. (Environmental Science)
149

Festlegung von Radionukliden und Arsen in Feuchtgebieten an Bergbaualtstandorten – Ein Beitrag zur Passiven Wasserreinigung

Dienemann, Holger 28 February 2008 (has links)
Im Abstrom von Uranbergbauobjekten (Sachsen, Deutschland) wurden Uran, Radium-226 und Arsen in unterschiedlichen Feuchtgebieten untersucht. Dabei wurden Wasser (vor¬wiegend neutrale bis leicht basische pH-Werte), Sedimente und im Wasser befindlicher Bestandesabfall (CPOM) beprobt. Zur Klärung der Genese der Urangehalte im Sediment erfolgten Untersuchungen an Pb-Isotopen. Sie zeigen u. a., dass das Uran in den obersten Zentimetern des Sediments (organische Auflage) aus der wässrigen Phase und nicht von ca. 300 Millionen Jahre alten Erzteilchen stammt. Für die Verlagerung von Radionukliden und Arsen aus dem Wasserkörper in das Sediment wird ein neuer Weg aufgezeigt. Eine Fixierung dieser Stoffe an Bestandesabfällen (plant litter) ist möglich. Allochthoner Bestandesabfall (Blätter, Früchte, Zweige von Alnus spec. und Quercus spec.) weist nach Kontakt mit kontaminiertem Wasser (ca. 100 - 300 µgU L-1) Urangehalte von 50 - 2.000 µgU g-1 auf. Im Vergleich zu Uran sind Ra-226 und Arsen labiler am Bestandesabfall gebunden. Für die Genese der Gehalte in den subhydrischen Auflagen sind die Herkunft des (autochthonen bzw. allochthonen) Bestandesabfalls und der Abbau eine entscheidende Rolle. Sedimente aus leicht abbaubaren Bestandesabfällen (z.B. Lemna spec., Algen) weisen im Vergleich mit allochthonen Bestandesabfällen (von Bäumen) deutlich geringere Urangehalte auf. Exemplarisch wurde für einen aus allochthonen Bestandesabfällen bestehenden Sedimentkern mittels Cs-137-Bestimmung eine maximale Uranfestlegung von 1 – 2 g m-² a-1 ermittelt. Neben allochthonem Bestandesabfall führen Eisen- und Manganhydroxide, die unmittelbar an den Sickerwasseraustrittstellen ausfallen, bei relativ geringen Arsen- und Radiumkon¬zentrationen im Wasser zu hohen Arsen- bzw. Radiumgehalten im Sediment (As ≤ 5 mg g-1; Ra-226 ≤ 25 Bq g-1). Unter reduktiven Bedingungen werden Ra-226 und Arsen jedoch leicht freigesetzt. Ausgehend von den Untersuchungsergebnissen wird eine mögliche Anordnung für eine naturnahe passive Sickerwasserbehandlung vorgeschlagen.

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