Дисертації з теми "Phéophycinées – Teneur en substances radioactives"
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Zerbini, Micol. "Impact des métaux radioactifs sur les écosystèmes marins : spéciation in vivo et mécanismes moléculaires de leur accumulation par les algues brunes." Electronic Thesis or Diss., Université Côte d'Azur, 2025. http://www.theses.fr/2025COAZ5013.
Повний текст джерелаLegacy radioactive waste, primarily from the early development of the nuclear industry and weapon test, has resulted in significant environmental contamination. Oceans, covering 70% of Earth's surface, serve as the primary reservoir for pollutants, including metallic radionuclides, which pose a threat for both marine organisms and human health. Studies on the biochemical mechanisms driving the accumulation of radioelements remain limited and underexplored, particularly in ecologically relevant organisms such as brown algae, which are widely used as biomonitoring species. This thesis investigates the accumulation of radionuclides in Ascophyllum nodosum, a brown macroalga selected for its ecological relevance and its ability to bioaccumulate metal ions. The study focuses on uranium, a naturally occurring actinide, americium, an anthropogenic derived element and europium, used as a chemical surrogate for americium. This work addresses three key questions: how radionuclides are bioaccumulated, where they are localized within the alga and which biomolecules are responsible for their uptake. A multi-scale mechanistic approach at the macroscopic, cellular and molecular levels was developed, combining biokinetic studies, imaging, and speciation analyses. A biokinetic study of radionuclide accumulation and release by the alga was conducted through contamination experiments with concentrations ranging from 10-4 M for U(VI), 10-7 M for Eu (III), to 10-12 M for Am (III). For uranium, contamination studies revealed active bioaccumulation in living algae, with compartmentalization across tissues. Receptacles (reproductive organs) exhibited the highest uranium accumulation (Concentration Factor - CF ~ 49), while branches and thallus retained minimal amounts. For americium and europium, the biokinetic study revealed consistent trends, confirming that europium can be used in this context as an analogue for americium. Unlike uranium, europium showed homogeneous accumulation across algal tissues (CF ~1100). At the microscopic scale, advanced imaging tools were used to map uranium distribution within algal tissues. Superficial absorption was observed in the thallus, branches and male receptacles, while localized areas of high uranium concentration were detected in the egg cells of female conceptacles.At the molecular scale, speciation studies using X-ray Absorption Spectroscopy (XAS) revealed that uranium forms uranyl-alginate complexes in the branches and uranyl-phosphate complexes (pseudo-autunite) in the male receptacles, likely influenced by surface bacteria. In female receptacles, uranium appears to be chelated by phosphorylated proteins, highlighting distinct gender-specific sequestration mechanisms. For europium and, by extension, americium, speciation analyses identified europium-carboxylate complexes, suggesting that polysaccharides may act as potential chelating agents in algal tissues.This thesis enhances our understanding of radionuclide behavior in marine ecosystems and provides insights into the bioaccumulation mechanisms employed by brown macroalgae. The findings highlight potential applications for monitoring and remediating pollution by radioactive metals
Besson, Benoit. "Sensibilité radioécologique des zones de prairies permanentes." Besançon, 2009. http://www.theses.fr/2009BESA2048.
Повний текст джерелаThe project “SENSIB" of the Institute for Radiological Protection and Nuclear Safety (IRSN) aims at characterizing and classifying parameters with significant impact on the transfer of radioactive contaminants in the environment. This thesis is focused on permanent grassland areas. Its objectives are the analysis of the activity variations of two artificial radionuclides in the chain from soil to dairy products as well as the categorization of ecological and anthropogenic parameters, which determine the sensitivity of the studied area. For this study, in situ sampling is carried out in 15 farms in 3 different French regions (Charente, Puy-de-Dome and Jura). The sampling sites are chosen according to their natural variations (geology, attitude and climate) and the soil types. Additionally to the radiologic measurements, geographic, soil and vegetation data as well as data concerning cattle-rearing and cheese manufacturing processes are gathered. […] A nonlinear approach based on a discretization method of the transfer factor with multiple comparison tests admits a classification of the sensitivity factors from soil to grass vegetation. We can determine 20 factors interfering in the CS transfer into the vegetation, for instance, the clay rate of the soils or a marker for soil particles adhered on vegetation. Cs transfers into milk depend on the clay rate of the vegetation sample and on the cattle feed. […]
Dechery, Fabien. "Simulations optiques pour le projet S3 - Super Spectromètre Séparateur - et Première spectroscopie prompte gamma-électron en coïncidence d'un noyau transfermium : le Mendélévium-251." Paris 7, 2012. http://www.theses.fr/2012PA077265.
Повний текст джерелаIn analogy with the atomic closed shells giving rise to the stability and high ionisation energies of noble gases, nuclear physics also has "magic" numbers of protons and neutrons which enhance nuclear structure stability. Knowledge of the structure of doubly-magic nuclei, both proton and neutron numbers, is crucial to parameterize theoretical models. The discovery of the next and ultimate magic numbers will provide a strong constraint on the many predictions. These two numbers are like the centre coordinates of an area of enhanced stability of the nuclear chart, well known as "island of stability". These "superheavy" nuclei only exist due to pure quantum shell effects. My thesis work deals with two distinct, but complementary, aspects of fundamental physics with the common goal of studying these extreme mass nuclei structure. The first part corresponds to the development of a next generation instrument for nuclear physics to allow synthesis and spectroscopy studies of superheavy nuclei: the Super Separator Spectrometer S3. This project will be installed at SPIRAL2 (GANIL) and has been approved by the French Research National Agency (ANR) within the EQUIPEX framework. It has been designed to take advantage of the high intensity heavy ion beam from the LINAC, giving access to a wide range of physical programs. The second part corresponds to the preparation, realisation and analysis of an experiment on 251-Mendelevium in which the very first prompt gamma-electron coincidence spectroscopy was performed for a transfermium nuclei
Guérin, Guillaume. "Modélisationet simulations numériques des effets dosimétriques dans les sédiments quaternaires : application aux méthodes de datation par luminescence." Bordeaux 3, 2011. https://extranet.u-bordeaux-montaigne.fr/memoires/diffusion.php?nnt=2011BOR30051.
Повний текст джерелаWhereas research on the determination of equivalent doses has made significant progress in the field of luminescence dating during the last decade, research on dose rates has severely lagged behind. The particle-matter simulation toolkit GEANT4 was here been used to study the effects of heterogeneities in sedimentary media. A series of virtual experiments was designed to refine a field gamma spectrometry technique, improving accuracy and precision while reducing counting times. These results were used for the experimental calibration of a gamma ray probe. A technique, which is non invasive and compatible with archaeological excavations, was proposed for mapping gamma dose rate in soils. On a grain scale, numerical simulations of dosimetric effects revealed the limited validity of the widely used concept of infinite matrix in palaeodosimetric dating. A new set of factors influencing dose rates to sedimentary grains were identified, and called geometry factors. Adequate tools for quantifying the corresponding microdosimetry effects were developed. Finally, thermoluminescence and optically stimulated luminescence were applied to the chronology of the Paleolithic site of the Roc de Marsal. The results were used to provide a chronological frame for the human occupations and their climatic and environmental contexts, in regard of past global climate variations
Duchemin, Charlotte. "Étude de voies alternatives pour la production de radionucléides innovants pour les applications médicales." Nantes, 2015. https://archive.bu.univ-nantes.fr/pollux/show/show?id=235ec580-c5bc-4a65-ab94-22690cad4585.
Повний текст джерелаNuclear medicine is a specialty that uses radioactive nuclei for therapy or diagnosis of diseases such as different types of cancer. These radionuclides are coupled to carrier molecules to target sick cells. Currently, only few isotopes are used in clinical practice. However, many others may be of medical interest due to their emitted radiation and/or their half-life that can be adapted to the carrier molecule transit time and to the pathology. The aim of this PhD thesis is to study the production of innovative radionuclides for therapy and diagnosis applications in collaboration with the GIP ARRONAX, which possesses a multi-particle high energy cyclotron. A fundamental physical parameter to access the production rate of a radionuclide is the production cross section. Experimental data were measured for a selection of radionuclides: photon emitter (Tc-99m) and positron emitter (Sc-44g) for diagnosis, as well as electron emitters (Re-186, Tb-155 and Sn-117m) and α particles emitters (Th-226, Ra-223 and Bi-213) for therapeutic applications. These acquired data are obtained using alternative production routes compared to the commonly used. Data related to the contaminants produced during the irradiations were also extracted. The experimental cross section values are compared with theoretical model predictions. The large set of data obtained contributes to the theoretical physicist studies allowing to constrain their models to improve and/or validate them
Charni, Halima. "Contribution à la connaissance de la radioactivité des sols tunisiens conséquences locales en matière de radioprotection : cas particuliers des phosphates." Toulouse 3, 1992. http://www.theses.fr/1992TOU30004.
Повний текст джерелаPatryl, Luc. "La radioactivité naturelle des sédiments de la Loire (France) : relations avec la lithologie." Tours, 2000. http://www.theses.fr/2000TOUR4038.
Повний текст джерелаMarion, Cédric. "Dynamique et bilans des transferts particulaires de radioéléments d’origine anthropique et naturelle dans le Golfe du Lion : cas particulier des apports rhodaniens." Perpignan, 2010. http://www.theses.fr/2010PERP1006.
Повний текст джерелаDue to its 30. 2 year half-life and of its great affinity with silts and clays, 137Cs was used as a Rhône River inputs tracer. Rhône prodelta sediments recorded values of 137Cs activities originated by nuclear power plants releases, global fallout and Tchernobyl accident (600 Bq. Kg-1). A sharp decrease in liquid radioactive effluents releases and the dismantlement of the Marcoule fuel reprocessing plant in 1997 induced 137Cs fluxes decrease to the Mediterranean Sea. At present time, mean concentrations are around 10 Bq. Kg-1 in the prodelta sediments. Sedimentary records of oceanographic campaigns achieved between 2001 and 2008 enabled to map a 20 km² 137Cs accumulation area close to the Rhône River mouth and to estimate a store of 3. 35 TBq, i. E. The eighth of the Gulf of Lions store. The CARMA and EXTREMA projects (2006-2008) allowed to observe prodelta sedimentation. Short-live radionuclides like 7Be and 234Th were used to estimate sedimentary pluridecimetric thicknesses deposits generated by some Rhône River floods. Altimeter data showed 8 cm thick sediment total accretion during two mean floods recorded by a current profiler. They also showed an important erosion phase linked to a south-east swell episode with a bottom shear stress reaching 5 Pa. Results showed that the sediment remobilization was very important in this area but that the exports of suspended solid matters towards the Gulf of Lions were weak, or even deposited in fine on the prodelta
Maillant, Sophie. "Conséquences d'un refroidissement climatique sur le comportement de radionucléides dans les sols du Barrois." Vandoeuvre-les-Nancy, INPL, 2005. http://docnum.univ-lorraine.fr/public/INPL/2005_MAILLANT_S.pdf.
Повний текст джерелаFor the safety assessment of underground radioactive waste disposal conducted by Andra, it is required to estimate the behaviour of radionuclides in soils for the next ten thousand years. Within this time scale, soils would probably evolve from their actual status, according to climate changes. It is then necessary to assess these changes in order to predict the behaviour of the radiochemicals that would enter the soils. We present a pedological forecast method for the assessment of a specific case (i. E. Limestone plateau), undergoing periglacial conditions. Then we study the retention of mobile radionuclides, iodine (I) and technetium (Tc) on the forecast periglacial soils. The method relies on the study of analogous soils, sampled in regions with similar geochemical (calcareous) and topographical contexts but undergoing a cold climate which mimics future periglacial conditions of the reference region (steppe-tundra or boreal forest biomes). We have added to the cold and dry climatic series a cold and humid biome (montane strata). The organic matter compartment (OM), considered as an indicator of the effects of the climate on the soils, was thoroughly characterised and taken into account. The analogous soils sampled have developed under boreal forest, cold steppe and subalpine conditions from limestone or calcareous parent materials. The observed soils were eutric Leptosols under boreal forest, and Chernozems under cold steppe. In both biomes, under hydromorphic conditions, OM accumulated in the soil and was high in aromatic molecules in the humified fraction. In the montane strata, the leaching of carbonates was strong enough to allow a diversification of soil genesis: from humic Leptosols to dystric Luvisols. The OM of these soils was different from that of the soils from dry biomes. This study has confirmed that the main differences between soils were observed between the humid and cold climate (montane) on one side and the dry and cold (cold steppe and boreal) on the other. Evolution scenarios constructed from these results indicated that the periglacial conditions would probably favour the persistence of soils still similar to the present ones in the reference region, especially during the boreal stage. However these soils would display higher OM content. In this biome, soils would be mainly rendzic Leptosols and eutric (or calcaric) Cambisols as presently, but with a higher OM content in the surface horizon because of the forest cover. In the steppe-tundra biome, a pergelisol would favour hydromorphy in most soils (stagnic Cryosols). In both biomes, hydromorphic soils, developped on marly material could display very high OM content (fen). Maps summarising these scenarios have been edited for each biome. The consequences of these pedological changes on the behaviour of mobile radionuclides were studied through the retention of Tc and I in the analogous soils at field capacity in batch experiments. The experiment showed that the dehydration of soils could favour the retention of both elements under aerobic conditions, although the latter are not usually favourable to Tc and I retention (Kd > 1 l. Kg-1 in analogous soils of boreal forest after one year of contact time). These results were used to establish maps of the retention of each element for both periglacial biomes. It is suggested that Tc would be retained in the soils in the cold steppe soils whereas I would be more retained in soils of the boreal biome. In both biomes, soils with the highest retention towards I and Tc would be peaty soils located in the bottom of marly valleys. Special attention was paid therefore to peaty soils : we studied the behaviour of I in situ in a peat bog. I had accumulated at the bog surface (Kd was multiplied by 6 within 15 years) and was found to be associated to polyphenolic substances from the humified peat. Carex sp was identified as the species that accumulated the highest contents of I amongst the vegetation of the bog. The proposed method underlain by analogy and laboratory retention studies should help to understand and forecast the behaviour of the long-lived radionuclides. It should help in the determination of the site specific parameters for the dose computation of safety assessment in a cold biosphere scenario
Nasreddine, Lara. "Nouvelles données en sécurité sanitaire des aliments au Liban : Définition du panier de la ménagère Beyrouthin : Evaluation de la contamination des aliments en radionucléides : Evaluation de l'exposition aux métaux lourds par voie alimentaire." Brest, 2005. http://www.theses.fr/2005BRES2010.
Повний текст джерелаThe present study is the first in Lebanon to evaluate, by the market basket approach, the contamination of foods by radionuclides and heavy metals and the dietary exposure of the Lebanese population to the heavy metals Pb, Cd and Hg. An individual dietary survey has been realized on 444 adult individuals living in Beirut. Food consumption data were collected using a quantitative food frequency questionnaire. The market basket was identified by selecting those foods with a mean daily intake exceeding 1g/day. The contamination levels of the selected foods with heavy metals and radionuclides were assessed. The results show that the level of radioactivity of the analyzed food does not present any concern for public health. The average dietary exposure of the average individual to Pb, Cd, and Hg corresponds to 7,17 and 6 % of the respective PTWIs. This permits to conclude that, for the average individual, there is no risk of exceeding the PTWIs
Postel, Catherine. "Contribution à l'étude des radionucléides émetteurs gamma dans les huitres du département de la Manche." Caen, 1991. http://www.theses.fr/1991CAEN3070.
Повний текст джерелаLaguionie, Philippe. "Mesures in situ et modélisation du transport des sédiments en rivière : application au bassin versant de la Vilaine." Rennes 1, 2006. http://www.theses.fr/2006REN1S160.
Повний текст джерелаGarcia, Vindas José Ralph. "Transport du radon en milieu poreux (expérimentation et modélisation) : implication pour la réalisation et l'interprétation de mesures "in situ"." Montpellier 2, 1999. http://www.theses.fr/1999MON20003.
Повний текст джерелаAbou, Moustafa Aly. "La bioremédiation : une méthode actuelle de dépollution des sols." Littoral, 2005. http://www.theses.fr/2005DUNK0117.
Повний текст джерелаThe alternative methods of soil treatment were initiated in the middle of years 80, among them the biological methods which use the plants or the living micros-organisms to clean up the soils. They are commonly known by the name of "bioremediation", and are economically interesting as their application is simple and always "in situ". Our research was oriented in two principal directions : firstly the mechanism of soil pollution by radioisotopes in order to specify the radiological status of the soil surface and the migration of the active isotope within the soil. This was completed for various soil types and with consideration to the possibility of bioremediation, in particular by wheat. To clarify the mechanism of migration of the polluting elements in the soil and the plants, we particularly concentrated on Caesium, Strontium and Iodine, because after the accident of Chernobyl, these radioactive isotopes contaminated great areas in Europe. The measurement of the radioactivity of the K-40 isotope was used to improve understanding the effect of the artificial and natural radioactivity on the plants, and to compare with the radioactive isotopes of anthropic origin such as Cs-137. Cadmium was also selected because it is among the heavy metals which accumulate in the human body. The studies of bioremediation using wheat showed that this method can effectively decontaminate soil of the radio nuclides (Cs-137) and heavy metals (Cd, Sr). The Model CTSPAC confirms the important role of the diffusion of the polluants in the soil, which depends at the same time on the nature of the soil (sandy, argillaceous, calcareous, etc. ) and the nature of the diffusing species (Cs+ or Sr2+, for example)
Marchetto, Catherine. "Modélisation et simulation numérique du transport des produits de corrosion dans le circuit primaire des réacteurs à eau pressurisée." Aix-Marseille 1, 2002. http://www.theses.fr/2002AIX11037.
Повний текст джерелаJeambrun, Marion. "L'uranium et ses descendants dans la chaine alimentaire." Phd thesis, Université de Strasbourg, 2012. http://tel.archives-ouvertes.fr/tel-00821054.
Повний текст джерелаGallois, Nicolas. "Réponse cellulaire d'isolats environnementaux de Microbacterium à une exposition à l'uranium." Thesis, Aix-Marseille, 2018. http://www.theses.fr/2018AIXM0423.
Повний текст джерелаUranium is a radionuclide used in nuclear energy. It has radiological and chemical toxicity, causing environmental and human health problems. Soil microorganisms and uranium have complex relationships. The goal of this study is to describe bacterium-uranium interactions through the use of bacteria isolated from contaminated environments. The four strains are related to the bacterial genus Microbacterium. They present a contrasted uranium tolerance phenotype from tolerant (ViU2a and Hg3) to sensitive (ViU22) and intermediate (A9). During exposure to uranium, different mechanisms of interaction with uranium occur sequentially: a first step of rapid sequestration of uranium due to passive biosorption, followed by an active step of uranium and phosphate efflux, observed only in tolerant strains, and finally, an active intracellular accumulation of uranyl phosphate precipitates. In order to identify the molecular actors involved in cell-uranium interactions, a comparative analysis based on a proteogenomic approach was performed. Between 1 100 and 2 000 proteins were identified. Statistical analyses revealed that uranium exposure impacts phosphate and iron metabolisms. The protein with the highest positive fold-change has been further studied. The UipA protein is a very affine and specific for uranium and iron, with Kd of the nanomolar order. Biophysic analyses revealed mono- and bidental coordination for uranium and iron. Upstream of the uipA gene, two genes sharing sequence homology with the two-component czcRS system were detected. The UipRSA cluster is only present in the tolerant strains. These data suggest that the uipRSA cluster is involved in uranium tolerance
Monfort, Marguerite. "Influence du milieu aqueux récepteur sur le devenir de produits de fission dans l'environnement : cas d'aérosols susceptibles d'être émis lors d'un accident grave survenant sur un réacteur à eau pressurisée." Montpellier 2, 1989. http://www.theses.fr/1989MON20100.
Повний текст джерелаMondani, Laure. "Analyse et exploitation des populations bactériennes de sols naturellement riches en uranium : sélection d'une espèce modèle." Thesis, Aix-Marseille 2, 2010. http://www.theses.fr/2010AIX22113.
Повний текст джерелаIt is well known that soils play a key role in controlling the mobility of toxic metals and this property is greatly influenced by indigeous bacterial communities. This study has been conducted on radioactive and controls soils, collected in natural uraniferous areas (Limousin). A physico-chemical and mineralogical analysis of soils samples was carried out.The structure of bacterial communities was etimated by Denaturing Gradient Gel Electrophoresis (DGGE). The community structure is remarkably more stable in the uranium-rich soils than in the control ones, indicating that uranium exerts a high selection from the soils was constructed and screened for uranium resistance in order to study basteria-uranium interactions. Scanning electron microscopy revealed that a phylogenetically diverse set of uranium-resistant species ware able to chelate uranium at the cell surface
Cherif, Mohamed Amine. "Modélisation dynamique de la (bio)disponibilité des radionucléides dans les sols : approche comparative modèles-expériences appliquée au transfert de césium dans la rhizosphère." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0547/document.
Повний текст джерелаThe overall objective of this work is to develop a generic model able to better account and predict the transfer of radionuclides in the soil / soil solution / plant. The first part of the work was devoted to the critical analysis of the models available in the literature to describe the cesium adsorption on clay minerals (the process that mainly controls its availability in the soils). This analysis enabled us to propose a new mechanistic model combining two approaches: surface complexation and cation exchange. Our approach has been tested in order to model the adsorption of Cs on several natural clay substrates, in a wide range of Cs concentrations and physicochemical conditions. This work allowed to validate the proposed mechanistic model and to demonstrate that it constitutes a major advantage over the various existing models. The second part was devoted, to the performing of a series of experiments, carried out in controlled environments on dynamic systems and modeling the (bio)availability of Cs in these systems. Following these tests, the observed interactions between solid and solution could be correctly reproduced with the proposed model taking into account only the clay fraction of the soil. These simulations were also compared with simulations obtained using a empiric (Kd) kinetic models (E-K approach). Finally, the development of a numerical tool for coupling the description of geochemical interactions with transfer to the plant (Michaelis-Menten approach) allowed to reproduce adequately the trials carried out in Rhizotests coupling soil, solution and plant, and to better characterize of the Cs fraction available for plants
Venchiarutti, Célia. "Approche de la dynamique des particules dans le sillage des Kerguelen, à l'aide des traceurs géochimiques : 230Th et 231Pa." Phd thesis, Université Paul Sabatier - Toulouse III, 2007. http://tel.archives-ouvertes.fr/tel-00204680.
Повний текст джерелаNotre étude utilise deux radionucléides le 230Th et le 231Pa - tous deux produits de désintégration de l'uranium et très réactifs vis-à-vis des particules - comme traceurs de la dynamique des particules.
L'étude des vitesses de chute des particules, estimées à partir des distributions de 230Th a montré que, paradoxalement à son fort export de C, le plateau avait des vitesses de chute des particules plus faibles (S= 500 m.an-1) que les stations du large dans les eaux HNLC (S=800 m.an-1). Ce résultat, assez surprenant, soulève une question quant à la limitation du modèle de scavenging 1D dans le cadre de l'étude de la dynamique des particules des systèmes côte-large et suggère l'utilisation d'un modèle 2D pour reproduire le scavenging de ces régions.
Sur le plateau, les fortes concentrations de 231Pa dissous suggèrent que du 231Pa a été relâché lors de la dégradation bactérienne d'agrégats, riches en opale (phase pour laquelle le Pa a une forte affinité).
Sur l'escarpement à l'Est du plateau, la diminution des concentrations de 230Th et de 231Pa dissous, concomitante à l'augmentation de leur concentration dans les particules, a montré un intense boundary scavenging le long de la pente du plateau, sous l'effet de couches néphéloïdes ou de re-suspension depuis les sédiments, riches en opale.
Margerit, Adrien. "Etude des effets combinés de l'uranium et du cadmium chez le nématode Caenorhabditis elegans." Thesis, Montpellier, 2015. http://www.theses.fr/2015MONT3509/document.
Повний текст джерелаUranium is a natural radioactive trace element for which elevated concentrations can be found in the vicinity of some nuclear fuel cycle facilities or of intensive farming areas. Due its co-occurrence with different trace metals, such as cadmium, in geological ores, U is generally found associated with other contaminants in the environment. The study of their combined effects on ecosystems is of interest to better characterize such multi-metallic polluted sites. The mixture toxicity assessment and the identification of synergistic or antagonistic interaction are generally performed on the basis of additive reference models integrated to descriptive and purely statistical approaches with no real biological basis. Recently, mechanistic models were proposed to better account for the dynamics of biological and toxicological processes. However, such models have only been put into practice in a few number of mixture toxicity case studies. The aim of this PhD project was to assess the chronic U/Cd combined toxicity on the life history traits of the nematode Caenorhabditis elegans using both a descriptive (MixTox) and a mechanistic (DEBtox) approach. To do so, nematodes were exposed during eleven days to different U and Cd concentrations, alone or in mixture. A strong antagonistic interaction between U and Cd was identified for length increase and brood size endpoints on the basis of both approaches. From the study of the U and Cd media-to-food transfer and of the U and Cd bioaccumulation by C. elegans, we showed that the co-presence of U reduced the available Cd fraction for nematodes. To identify a possible interaction at organism level, occurring during the toxicokinetic or toxicodynamic steps, data were re-analyzed on the basis of U/Cd concentrations in food, assumed to be more closely related to available concentrations for C. elegans. Overall additive effects, without interaction, were identified between U and Cd, even if slightly contrasted conclusions were obtained on the basis of the descriptive and mechanistic approaches. The present study underlines the complexity of studying mixture toxicity and identifying chemical interactions. Despite some application problems, the mechanistic approach DEBtox is particularly promising to describe the toxicity of chemical mixtures over time and to test hypothetical interaction mechanisms. In the future, the improvement of tools to analyze the combined toxicity of contaminants would allow to better address the issue of mixtures in ecotoxicological risk assessment processes