Rôle de la matière colloïdale dans le transfert des éléments chimiques en milieu boréal (Russie Européenne)

Cette thèse vise à étudier la spéciation des éléments et leur migration dans le milieu boréal (Karélie et Russie Centrale). Les objectifs principaux de ce travail sont : i) de caractériser la distribution de taille moléculaire des éléments traces et de la matière organique, ii) révéler la régularité de distribution des formes colloïdales des éléments traces dans les eaux naturelles le long du continuum sols - marécages- cours d'eau - lacs intermédiaires et terminaux des bassins versants boréaux, et iii) révéler la dépendance de la composition isotopique en fonction de la taille moléculaire, de la spéciation des éléments et des conditions physico-chimiques des eaux. L'originalité de cette thèse est d'appliquer la méthode de la filtration en cascade pour étudier la distribution de taille moléculaire des éléments traces dans les eaux naturelles et de combiner les techniques géochimiques et isotopiques pour la première fois sur les mêmes objets naturels afin de mieux comprendre les facteurs qui contrôlent les cycles biogéochimiques des éléments dans les régions boréales. La première partie de la thèse consiste en une introduction générale de la problématique. Le deuxième chapitre est consacré à l'étude de la distribution de la matière organique naturelle dans les différentes fractions granulométriques des eaux naturelles présentant des conditions redox et hydrodynamiques variables au sein des micro-systèmes (solution de sols - marécage - cours d'eau - lacs intermédiaires et terminaux) de petits bassins versants à substratum homogène. En particulier, nous avons étudié les concentrations du carbone organique dissous, son poids moléculaire, ses caractéristiques optiques et ses rapports carbone/nitrogène pour obtenir des informations précieuses sur l'origine (allochtone versus autochtones), l'aromaticité, l'hydrophilie / l'hydrophobie de la matière organique. La troisième partie de la thèse est consacrée à l'étude de la distribution de taille moléculaire des éléments traces et à la caractérisation quantitative des formes colloïdales des éléments dans les rivières et les eaux de surface de ces milieux qui sont très riches en matière organique et pas soumis à l'impact humain. Dans cette partie il est notamment montré l'existence de corrélations des éléments traces avec le fer et la matière organique dans les filtrâts ; également un intérêt particulier est porté à la distribution des colloïdes et aux coefficients de partition des éléments dans les différents micro-systèmes (solution des sols - marais de source - cours d'eau - lacs intermédiaires et terminaux). Le quatrième chapitre rapporte les résultats des compositions isotopiques en strontium (Sr), néodyme (Nd), cuivre (Cu) et magnésium (Mg) au sein des différentes fractions colloïdales des eaux naturelles du sud et du nord de la zone boréale de la Russie Européenne. Ces derniers travaux conduits sur des isotopes stables (Cu, Mg) et radiogéniques (Sr, Nd) nous permettent de définir les facteurs qui influencent le changement de la composition isotopique. Le cinquième chapitre est consacré à l'étude du fractionnement isotopique du fer dans les types différents d'eaux naturelles sur les fractions granulométriques. En particulier, nous avons étudié la composition isotopique dans les filtrats et ultrafiltrats en fonction des concentrations en fer et en matière organique, du pH et des autres paramètres physico-chimiques. Dans le sixième chapitre il est formulé les conclusions principales et les perspectives de la thèse. L'étude menée dans cette thèse vise à contribuer à la prévision de l'évolution de la spéciation et des flux des éléments traces et de la matière organique dans les régions Arctiques en réponse au réchauffement climatique global.The objective of this thesis was to study element speciation and migration in the boreal environments (Karelia and Central Russia). Specific goals were to i) characterize the molecular weight distribution of trace elements and organic matter (OM) in various types of natural waters, ii) reveal the TE colloidal forms dependence in the continuum soil solution - bog - stream - feeding and terminal lakes in the surface waters of boreal watersheds, and iii) quantify the dependence of stable and radiogenic element isotopic composition on the size fraction, element speciation and physico-chemical conditions of surface waters. The main originality of the work is to apply the method of cascade filtration to study the molecular weight distribution of trace elements in surface waters and to combine the geochemical and isotope techniques, for the first time on the same natural objects, and particularly within the watershed continuum soil solution - bog - stream - feeding and terminal lakes, in order to better understand the factors that control biogeochemical cycling of elements in the subarctic region. The first part is devoted to general introduction and the insight into the problems. The second chapter is aimed at studying natural organic matter size distribution in the natural waters with different redox and hydrodynamic conditions in the continuum soil solution - bog - stream - feeding and terminal lakes for a small watershed with homogeneous bedrock composition. In particular, we investigate organic matter concentrations, weight-average molecular weights, optical properties and carbon/nitrogen ratios to get the information about the origin of DOM (autochthonous / allochthonous), its aromaticity, and its hydrophility / hydrophobicity. The third chapter describes the study the molecular weight distribution of trace elements and it provides quantitative characterization of TE colloidal speciation in pristine, organic-rich rivers and surface waters. We demonstrate that, using TE correlations with iron and OM in the filtrates, one can characterize colloids distribution and compare partition coefficients in the continuum soil solution - bog - stream - feeding and terminal lakes, and also compare natural and modeling data. The fourth chapter describes the results of variations of stable (Cu, Mg) and radiogenic (Sr, Nd) isotopic composition in filtrates and ultrafiltrates of various size fraction in the different types of natural waters of south and north of European Russia boreal zone allowing to identify the factors influencing the isotopic composition variation along the landscape continuum in different size fractions. Finally, the fifth part is devoted to study the variations of iron isotopic composition of different water types and colloidal size fractions. In particular, we investigate the dependence of isotopic composition of filtrates and ultrafiltrate son iron and OM concentrations, pH and other physico-chemical factors. The sixth chapter presents the main conclusions and perspectives. Investigations carried out in this study should contribute to the prediction of TE and OM behavior in the Arctic and boreal regions due to climate warming mostly pronounced in these latitudes

Teacher Education in Higher Education Systems during Pandemic and the Synergy of Digital Technology

In the modern world of education, the level of digital technology development plays a decisive role in the competitiveness of educational institutions. The transition to digital education is considered a key driving force for the development of any university. In recent years, pedagogical universities have made tangible progress in many areas of digital development. However, the introduction of digital technologies (DT) in the educational process reached its peak during the pandemic. This study aims to identify the distinctive features in the work of a teacher at a pedagogical university during the pandemic. The study revealed the following: the doubts of the teachers with no e-learning experience; didactically effective digital technologies in the educational process, the combined use of which ensures the synergistic effectiveness of e-learning; students’ attitude towards the quality of the e-learning process during the pandemic. Given the identified problems and positive aspects, the results of the study can be used to further develop a strategy for the digitalization of teacher education. The study proved that effective digitalization of the educational process is possible under the condition of cooperative and systematic work of all participants

Distance Pedagogical Education in the Conditions of the Coronavirus

The relevance of the study is due to the problem of finding optimal solutions for organizing training sessions, the need to form the personality of a teacher in a difficult social and pedagogical situation. The leading research method is a pedagogical experiment on the organization of distance learning for students, the method of theoretical substantiation of the formation of the "Digital Educational Ecosystem" project, the method of practical implementation of the digital environment in work with educational organizations and schoolchildren. This article presents practical solutions for organizing training sessions, pedagogical practices, conducting state final certification through the use of interactive educational platforms, social networks, and instant messengers. An equally significant result of the study is the educational component of the formation of a future teacher in a difficult social situation

Complex 99mTc-PDA-DTPA for myocardial imaging

The 123I-labeled fatty acids such as 123I-Iodophenylpentadecanoic acid and 123I-Beta-methyliodophenylpentadecanoic acid are the agents used clinically for myocardial imaging. Fatty acids are the major source of energy for the normal myocardium. However, under ischemic conditions the myocardial cells switch to glucose metabolism for their energy needs. Fatty acids undergo prolonged metabolic stunning in patients with reversible ischemia, thereby helping in early diagnosis of coronary artery disease in highrisk patients. High cost andlimited availability of cyclotron-produced 123I, makes 99mTc-labeled fatty acids more desirable for the purpose. In diagnosis the dominant radionuclide is 99mTc. It is estimated that it is involved in about 85% of all imaging procedures in nuclear medicine. The method for preparation of new 99mTc-fatty chemical systems based on modified diethylene triamine pentaacetic acid (DTPA) molecule has been elaborated in this work . The main advantage using DTPA as chelate agent for radioactive label, is the molecule or it's derivative ability to form sufficiently stable complexes with different radioactive metals including technetium-99. Moiety of pentadecanoic acid addition gave the ability to prepare modified complex of DTPA. In a labeling procedure, freshly eluted Na99mTcO4 (20mCi) was added to a mixture of cysteine, stannous chloride, PDK-DTPA and ethanol in a vial. On keeping the reaction mixture at 90 0C for 30 min, [99mTc-PDK-DTPA] radiopharmaceutical was formed. Thereafter, the reaction mixture was cooled over ice and characterized by HPLC. The result of dynamic scintigraphic research showed, that after being injected, the substance is actively acumulated into myocardium. Eventually one can say that modified DTPA-moleculs are functionally suitable for myocardial imaging

Fate of TiO2 nanoparticles in the aquatic environment in the presence of anthropogenic compounds

International audienceThe increasing production and use of nanoparticles (NP) in consumer products inevitably lead to ENP emissions into the environment. The physicochemical properties of NP depend on various parameters (e.g. pH, cations, IS). In natural waters, the stability of NP can vary as a function of a sum of these parameters and occurs by one of the numerous scenarios. In particular, the presence of anthropogenic organic molecules (AOM) can change the NP fate. Also, the presence of NP may affect the organic pollutants (fate and toxicity). The main objective of the work was to study the aggregation of TiO2 NP (pure hydrophilic 100 % rutile and pure hydrophilic 100 % anatase, 5−30 nm) in the presence of the most frequently occur and representative pesticides (glyphosate, AMPA, 2.4D) in natural waters considering lab experiments under relevant aqueous conditions (pH, ionic strength, presence and concentrations of mono- and bivalent cations). The presence of pesticides affected TiO2 NP homoaggregation in solutions (IS=10-3M - 10-2M) with pH values below the NP point of zero charge (PZC) for the anatase NPs (pH=6.5) and with pH values above the NP PZC for the rutile NP (pH=4.5). No changes in NP aggregation were observed in very low (IS=10-4M) or very high (IS= 10-1M) ionic strength solutions. The presence of the pesticides caused a significant modification of the NP surface charge (zeta potential) over a large range of salt concentrations (IS=10-4M - 10-1M). Compared to mono-valent cations (Na+), bi-valent cations (Ca2+) favor an increase in zeta potential of NP (anatase and rutile) at pH 8. There is no significant difference between at pH 5. Finally, these results demonstrated that, among the studied AOMs, glyphosate (with 4 pKa-s from 0.8 to 11) affects NP aggregation/stabilization in a wider range of physicochemical conditions. Overall, these results will aid in the evaluation of potential environmental risks posed by engineered NP in the aquatic environments exposed to pesticide load