Arsenic rich iron plaque on macrophyte roots--an ecotoxicological risk?

Arsenic is known to accumulate with iron plaque on macrophyte roots. Three to four years after the Aznalcóllar mine spill (Spain), residual arsenic contamination left in seasonal wetland habitats has been identified in this form by scanning electron microscopy. Total digestion has determined arsenic concentrations in thoroughly washed 'root+plaque' material in excess of 1000 mg kg(-1), and further analysis using X-ray absorption spectroscopy suggests arsenic exists as both arsenate and arsenite. Certain herbivorous species feed on rhizomes and bulbs of macrophytes in a wide range of global environments, and the ecotoxicological impact of consuming arsenic rich iron plaque associated with such food items remains to be quantified. Here, greylag geese which feed on Scirpus maritimus rhizome and bulb material in areas affected by the Aznalcóllar spill are shown to have elevated levels of arsenic in their feces, which may originate from arsenic rich iron plaque.

Arsenic sequestration in iron plaque, its accumulation and speciation in mature rice plants (Oryza sativa L.)

A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order: iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain.

Direct evidence showing the effect of root surface iron plaque on arsenite and arsenate uptake into rice (Oryza sativa) roots

The present study aimed to investigate the effects of root surface iron plaque on the uptake kinetics of arsenite and arsenate by excised roots of rice (Oryza sativa) seedlings. The results demonstrated that the presence of iron plaque enhanced arsenite and decreased arsenate uptake. Arsenite and arsenate uptake kinetics were adequately fitted by the Michaelis-Menten function in the absence of plaque, but produced poor fits to this function in the presence of plaque. Phosphate in the uptake solution did not have a significant effect on arsenite uptake irrespective of the presence of iron plaque; however phosphate had a significant effect on arsenate uptake. Without iron plaque, phosphate inhibited arsenate uptake. The presence of iron plaque diminished the effect of phosphate on arsenate uptake, possibly through a combined effect of arsenate desorption from iron plaque.

Iron plaque formation, arsenic uptake and speciation in different genotypes of mature rice plants (Oryza sativa L.)

A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order:? iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain. A compartmented soil-glass bead culture system was used to investigate characteristics of iron plaque and arsenic accumulation and speciation in mature rice plants with different capacities of forming iron plaque on their roots. X-ray absorption near-edge structure spectra and extended X-ray absorption fine structure were utilized to identify the mineralogical characteristics of iron plaque and arsenic sequestration in plaque on the rice roots. Iron plaque was dominated by (oxyhydr)oxides, which were composed of ferrihydrite (81-100%), with a minor amount of goethite (19%) fitted in one of the samples. Sequential extraction and XANES data showed that arsenic in iron plaque was sequestered mainly with amorphous and crystalline iron (oxyhydr)oxides, and that arsenate was the predominant species. There was significant variation in iron plaque formation between genotypes, and the distribution of arsenic in different components of mature rice plants followed the following order:? iron plaque > root > straw > husk > grain for all genotypes. Arsenic accumulation in grain differed significantly among genotypes. Inorganic arsenic and dimethylarsinic acid (DMA) were the main arsenic species in rice grain for six genotypes, and there were large genotypic differences in levels of DMA and inorganic arsenic in grain.

Une étude du développement professionnel par l'intégration dans la pratique d'enseignement d'une approche visant le développement du potentiel mathématique des élèves

Les enseignants passent une bonne partie de leur à temps à produire, à adapter et à modifier des ressources pédagogiques, ce qui place ce travail, appelé travail documentaire, au coeur de leur développement professionnel (Gueudet et Trouche, 2008). Dans le cadre d'une recherche collaborative ayant pour but le développement professionnel d'orthopédagogues et d'enseignants, effectuée par des chercheurs de l'Université de Sherbrooke, des ressources pédagogiques visant le développement du potentiel mathématique des élèves en difficulté d'apprentissage ont été conçues, adaptées et modifiées. Nous appuyant sur l'approche documentaire du didactique de Gueudet et Trouche (2008), nous décrivons le processus d'intégration de l'approche de développement du potentiel mathématique dans la pratique d'enseignement d'une enseignante ayant participé à la recherche collaborative. L'analyse de différents types de données recueillies lors des phases préactive, interactive et postactive de l'enseignement nous a permis d'identifier cinq schèmes d'usage (schèmes d'instrumentation et d'instrumentalisation) dans la pratique d'enseignement de notre enseignante. Notre mémoire traite donc de la problématique du développement professionnel des enseignants en considérant, sous un angle didactique, leur travail sur des ressources pédagogiques.

Statistique de photons d’une jonction tunnel déduite de mesures de potentiel électrique à l’aide d’un amplificateur paramétrique Josephson

On présente dans ce mémoire la mesure de la statistique de photons des fluctuations électromagnétiques micro-ondes d’une jonction tunnel placée à ultra-basse température. En particulier, on déduit cettedite statistique en mesurant les cumulants des fluctuations de courant générées par une jonction tunnel polarisée en courant continu et photoexcitée par un signal haute fréquence. On utilise un amplificateur paramétrique Josephson en tant que premier maillon de la chaîne d’amplification en raison de son bruit près de la limite quantique. On développe aussi un modèle pour tenir compte de sa saturation, celle-ci étant apparente à des puissances de signal incident très faibles. C’est, à ma connaissance, la première fois qu’un tel amplificateur est utilisé pour étudier la physique au sein du bruit émis par un conducteur mésoscopique. Les résultats mettent en évidence l’apparition d’un excès dans le quatrième cumulant lorsque la photoexcitation s’effectue au double de la fréquence de mesure. Un développement mathématique simple nous permet d’associer cet excès à la statistique de photons, sous la forme d’une augmentation – à nombre de photons fixe – de la variance du nombre moyen de photons contenue dans le signal. C’est en fait une signature de l’émission de paires de photons corrélés par la jonction tunnel photoexcitée. Ces résultats font le pont entre ceux obtenus précédemment par notre groupe de recherche quant aux cumulants d’ordre supérieur du bruit et ceux associées aux parallèles entre l’optique quantique et les fluctuations de courant des dispositifs mésoscopiques. [Gasse et al. PRL 111, 136601 (2013) ; Forgues et al. Scientific Reports 3, 2869 (2013) ; Forgues et al. PRL 113, 043602 (2014)] Ils dressent un portait intéressant du bruit photoexcité en termes normalement associés à l’optique quantique.

Évaluation du potentiel de croissance et de rendement d’une culture de tomates biologiques cultivées dans une serre climatisée à l’aide d’un système géothermique

Ce projet visait à comparer les effets agronomiques d’une serre de tomates biologiques semi-fermée utilisant un système de climatisation par géothermie comparativement à une serre ouverte. Deux serres de 228 et 230 m2 ont été équipées d’un système d’échangeur d’air avec géothermie qui refroidissait et déshumidifiait l’air (serre semi-fermée) et d’un système de ventilation naturelle (serre témoin). Ces dernières ont été comparées au cours des années 2012 et 2013 entre lesquels les traitements ont été permutés. Les variables mesurées étaient les paramètres de croissance des plants ainsi que le rendement, le calibre des fruits et les propriétés physico-chimiques des tomates. Les résultats ont démontré que le système de climatisation n’a pas eu d’effets significatifs sur la croissance des plants, la qualité des fruits ainsi que le rendement. Les deux serres avaient des cibles de concentration en CO2 comprises entre 450 µL L-1 et 1000 µL L-1 selon l’ensoleillement. Les quantités de CO2 injectées ont été de 11 kg/m2 et 15 kg/m2 respectivement en 2012 et 2013 dans la serre semi-fermée alors qu’elles ont été de 24 kg/m2 et 25 kg/m2 dans la serre témoin. Bien qu’ayant nécessité moins d’injection, la serre semi-fermée a permis de conserver des concentrations en CO2 de 638 µL L-1 en 2012 et de 593 µL L-1 en 2013. Ces concentrations sont plus élevées que celles obtenues dans la serre témoin qui étaient respectivement de 385 µL L-1 et 486 µL L-1 en 2012 et 2013. De ce fait, le coût monétaire associé à l’enrichissement carboné a été de 1,6 à 2,0 fois plus élevé dans la serre témoin que dans la serre semi-fermée.

Heterogeneity of atherosclerotic plaque phenotypes and composition in four different arterial beds: an intravascular ultrasound virtual histology study

Purpose: The purpose of this study was to compare the plaque morphology between coronary and peripheral arteries using intravascular ultrasound (IVUS). Methods: IVUS was performed in 68 patients with coronary and 93 with peripheral artery lesions (29 carotid, 50 renal, and 14 iliac). Plaques were classified as fibroatheroma (VH-FA) (further subclassified as thin-capped [VH-TCFA] and thick-capped [VH-ThCFA]), fibrocalcific plaque (VH-FC) and pathological intimal thickening (VH-PIT). Results: Plaque rupture (13% of coronary, 7% of carotid, 6% of renal, and 7% of iliac arteries; P=NS) and VH-TCFA (37% of coronary, 24% of carotid, 16% of renal, and 7% of iliac arteries; P=0.02) was observed in all arteries. Compared to coronary arteries, VH-FA was less frequently observed in renal (P<0.001) and iliac arteries (P<0.006), while VH-PIT and VH-FC were prevalent in both of these peripheral arteries. Lesions with positive remodeling demonstrated more characteristics of VH-FA in coronary, carotid, and renal arteries compared to those with intermediate/negative remodeling (all P<0.01). There was positive relationship between RI and percent necrotic core area in all four arteries. Conclusions: Atherosclerotic plaque phenotypes were heterogeneous among four different arteries. In contrast, the associations of remodeling mode with plaque phenotype and composition were similar among the various arterial beds.

Impact of carotid plaque screening on smoking cessation and other cardiovascular risk factors: a randomized controlled trial.

BACKGROUND: Screening of peripheral atherosclerosis is increasingly used, but few trials have examined its clinical impact. We aimed to assess whether carotid plaque screening helps smokers to improve their health behaviors and cardiovascular risk factors. METHODS: We randomly assigned 536 smokers aged 40 to 70 years to carotid plaque ultrasonographic screening (US group) vs no screening (control group) in addition to individual counseling and nicotine replacement therapy for all participants. Smokers with at least 1 plaque received pictures of their plaques with a 7-minute structured explanation. The outcomes included biochemically validated smoking cessation at 12 months (primary outcome) and changes in cardiovascular risk factor levels and Framingham risk score. RESULTS: At baseline, participants (mean age, 51.1 years; 45.0% women) smoked an average of 20 cigarettes per day with a median duration of 32 years. The US group had a high prevalence of carotid plaques (57.9%). At 12 months, smoking cessation rates were high, but did not differ between the US and control groups (24.9% vs 22.1%; P = .45). In the US group, cessation rates did not differ according to the presence or absence of plaques. Control of cardiovascular risk factors (ie, blood pressure and low-density lipoprotein cholesterol and hemoglobin A(1c) levels in diabetic patients) and mean absolute risk change in Framingham risk score did not differ between the groups. The mean absolute risk change in Framingham risk score was +0.6 in the US group vs +0.3 in the control group (P = .56). CONCLUSION: In smokers, carotid plaque screening performed in addition to thorough smoking cessation counseling is not associated with increased rates of smoking cessation or control of cardiovascular risk factors. Trial Registration  clinicaltrials.gov Identifier: NCT00548665.

Potentiel des liposomes pour l'injection intravitréenne de molécules thérapeutiques [Potential of liposomes for the intravitreal injection of therapeutic molecules].

Intravitreal administration has been widely used since 20 years and has been shown to improve the treatment of diseases of the posterior segment of the eye with infectious origin or in edematous maculopathies. This route of administration allows to achieve high concentration of drug in the vitreous and avoids the problems resulting from systemic administration. However, two basic problems limit the use of intravitreal therapy. Many drugs are rapidly cleared from the vitreous humor; therefore, to reach and to maintain effective therapy repeated injections are necessary. Repeated intravitreal injections increase the risk of endophthalmitis, damage to lens, retinal detachment. Moreover, some drugs provoke a local toxicity at their effective dose inducing side-effects and possible retinal lesions. In this context, the development and the use of new drug delivery systems for intravitreal administration are necessary to treat chronic ocular diseases. Among them, particulate systems such as liposomes have been widely studied. Liposomes are easily injectable and permit to reduce the toxicity and to increase the residence time of several drugs in the eye. They are also able to protect in vivo poorly-stable molecules from degradation such as peptides and nucleic acids. Some promising results have been obtained for the treatment of retinitis induced by cytomegalovirus in human and more recently for the treatment of uveitis in animal. Finally, the fate of liposomes in ocular tissues and fluids after their injection into the vitreous and their elimination routes begin to be more known.