Détermination en milieu naturel du dioxide de chlore, des ions chlorite et chlorate basée sur l'utilisation du carmin indigo: étude des interférences

Différentes méthodes fondées sur l'exploitation d'un même réactif à savoir le carmin indigo ont été mises en œuvre pour réaliser le suivi du dioxyde de chlore et des sous-produits de dégradation que sont les ions chlorite et chlorate.L'étude de la stabilité du carmin indigo a permis de montrer que la détermination du dioxyde de chlore doit être effectuée dans les premières heures qui suivent l'ajout de carmin indigo, une légère diminution de l'absorbance étant observée au delà de vingt heures. L'absorbance du carmin indigo en présence d'ions chlorite et chlorate reste en revanche stable plusieurs jours.La recherche d'éventuelles interférences (substances humiques, ozone, hypochlorite) a également été effectuée. Les ions chlorite et chlorate réagissent avec les substances humiques en milieu acide selon une cinétique réactionnelle beaucoup plus lente que celle des ions chlorite et chlorate sur le carmin indigo. De ce fait, les pourcentages d'erreur sur les concentrations restent faibles. L'hypochlorite ou plus précisément l'acide hypochloreux réagit avec le carmin indigo ce qui conduit à des erreurs dans la détermination du dioxyde de chlore, des ions chlorite et chlorate. Dans le cas du dosage du dioxyde de chlore, les sources d'erreur peuvent être éliminées en ajoutant de l'ammoniaque avant l'introduction du carmin indigo dans l'échantillon.Après avoir été validés dans des milieux synthétiques, les protocoles ont été appliqués à un milieu naturel : l'eau de distribution de la ville de Brest. Une analyse statistique a été effectuée dans le but de comparer les résultats avec ceux déduits d'autres méthodes basées sur des principes différents.Over the last decade, chlorine dioxide has been increasingly used for disinfecting drinking water in many countries. A guarantee for the protection of the consumer is the presence of a sufficient residual concentration of the bactericidal reagent in drinking water. Thus it is important to determine exactly and accurately the levels of chlorine dioxide at the tap. During water treatment and subsequent distribution, chlorine dioxide can undergo a variety of reduction and disproportionation reactions producing primarily chloride but also chlorite and chlorate, which have been shown to cause haemolytic anemia. Reliable analytical methods are needed to identify and determine levels of chlorine dioxide, chlorite and chlorate in drinking water. A procedure based on the use of indigo carmine for the determination of each species in natural waters is suggested in this paper.In phosphate buffer (pH 6.8), two moles of chlorine dioxide oxidize one mole of indigo carmine. The concentration of the bactericidal reagent can be determined by measuring the difference in absorbance of the dye at 610 nm before and after reaction with chlorine dioxide. This method is selective as chlorite and chlorate do not react with indigo carmine in phosphate buffer at pH 6.8. Although the spectrophotometric method can be used successfully used at levels of chlorine dioxide down to 30 µg/l, the determination of lower levels in tap water requires a more sensitive method such as an electrochemical stripping procedure. This analysis is based on the measurement of the decrease in the indigo carmine signal after addition of chlorine dioxide. The detection limit is around 1 µg/l.At pH=2, one mole of indigo carmine reduces one mole of chlorite. Thus the chlorite concentration can be determined by measuring the indigo carmine absorbance at pH=2. At pH=0, indigo carmine reacts with both chlorite and chlorate. A measurement at pH=0 allows chlorate concentrations to be determined since the decrease in absorbance due to the presence of chlorite can be calculated.The stability of indigo carmine absorbance has been studied. An indigo carmine solution prepared in phosphate buffer is stable over several days if kept in light-proof bottles. It is not surprising that the presence of chlorite and chlorate does not lead to a change in absorbance as they do not react with the dye at pH=6.8. A slight decrease in absorbance of an indigo carmine solution containing chlorine dioxide is observed after about twenty hours. This means that the chlorine dioxide concentration has to be determined in the first hours, which follow the addition of the dye to the sample in order to avoid errors.Interferences can arise from other residual oxidants, which may also be used in water treatment, or from substances present in the sample, which may react with indigo carmine, chlorite and chlorate. Accordingly, we have considered the influence of humic substances, ozone and hypochlorite. The absorbance of indigo carmine at pH=2 and at pH=0 does not change in presence of natural organic matter (1 mg/l). Chlorite and chlorate react with humic substances but the kinetics are much slower than those of the reactions with indigo carmine. Errors arising from humic substances in chlorite and chlorate measurements are thus very weak. Ozone may interfere in analyses as it reacts with indigo carmine. However its existence in the distribution network is unlikely as it also reacts with chlorine dioxide, which is in excess, and chlorite to give chlorate. Hypochlorite causes errors in chlorine dioxide, chlorite and chlorate determinations as a result of a reaction with indigo carmine. In the case of chlorine dioxide determinations, errors can be eliminated by adding ammonia to the sample before indigo carmine.Once the validity of the procedures had been proven in synthetic media, the methods were applied to a natural water, that of the water distribution network of the city of Brest, France. The results have been compared with those of other analytical techniques

Effects of the total replacement of fish-based diet with plant-based diet on the hepatic transcriptome of two European sea bass (Dicentrarchus labrax) half-sibfamilies showing different growth rates with the plant-based diet

Background: Efforts towards utilisation of diets without fish meal (FM) or fish oil (FO) in finfish aquaculture have been being made for more than two decades. Metabolic responses to substitution of fishery products have been shown to impact growth performance and immune system of fish as well as their subsequent nutritional value, particularly in marine fish species, which exhibit low capacity for biosynthesis of long-chain poly-unsaturated fatty acids (LC-PUFA). The main objective of the present study was to analyse the effects of a plant-based diet on the hepatic transcriptome of European sea bass (Dicentrarchus labrax). Results: We report the first results obtained using a transcriptomic approach on the liver of two half-sibfamilies of the European sea bass that exhibit similar growth rates when fed a fish-based diet (FD), but significantly different growth rates when fed an all-plant diet (VD). Overall gene expression was analysed using oligo DNA microarrays (GPL9663). Statistical analysis identified 582 unique annotated genes differentially expressed between groups of fish fed the two diets, 199 genes regulated by genetic factors, and 72 genes that exhibited diet-family interactions. The expression of several genes involved in the LC-PUFA and cholesterol biosynthetic pathways was found to be up-regulated in fish fed VD, suggesting a stimulation of the lipogenic pathways. No significant diet-family interaction for the regulation of LC-PUFA biosynthesis pathways could be detected by microarray analysis. This result was in agreement with LC-PUFA profiles, which were found to be similar in the flesh of the two half-sibfamilies. In addition, the combination of our transcriptomic data with an analysis of plasmatic immune parameters revealed a stimulation of complement activity associated with an immunodeficiency in the fish fed VD, and different inflammatory status between the two half-sibfamilies. Biological processes related to protein catabolism, amino acid transaminations, RNA splicing and blood coagulation were also found to be regulated by diet, while the expression of genes involved in protein and ATP synthesis differed between the half-sibfamilies. Conclusions: Overall, the combined gene expression, compositional and biochemical studies demonstrated a large panel of metabolic and physiological effects induced by total substitution of both FM and FO in the diets of European sea bass and revealed physiological characteristics associated with the two half-sibfamilies

Rétrospective bibliographique et critique de l’acquisition du langage chez l’enfant

International audienceLa littérature sur la question de l'acquisition du langage chez l'enfant est énorme et nécessite une grille d'analyse, qui ordonne la rétrospective des travaux et opère un regroupement en fonction des problèmes dominants. 1) Historiquement, si l'on fait abstraction des quelques propos de philosophes en la matière, les premières études sur le sujet datent des années 1850, soit de l'époque des premiers balbutiements de cette discipline qui s'épanouira surtout au XXè siècle, la psychologie de l'enfant. Et c'est aux psychologues qu'on doit la majorité des études sur la question : ils se sont, jusqu'à une époque récente, en quelque sorte emparés du sujet. Par contre, dès lors qu'il s'agissait de pathologie -et donc ici de troubles de l'acquisition du langage -, ce sont les praticiens les plus concernés, en l'occurrence les neuropsychiatres et ultérieurement les orthophonistes, qui gardèrent le monopole des écrits sur la question

Assisted Ion Transfer at Organic Film-Modified Electrodes

International audienceAn experimental and theoretical study of a complex electrochemical mechanism at three-phase and thin organic film-modified electrodes, where the coupled electron–ion transfer reaction is complicated by complexation reaction of the transferring ion, is reported. The transfer of monovalent and divalent cations across water|nitrobenzene interface, coupled with the complexation reactions with the ionophore valinomycin, is studied. Both types of electrodes are assembled of an edge plane pyrolytic graphite electrode modified with a nitrobenzene solution of lutetium bis(tetra-tert-butylphthalocyaninato) as a redox mediator and valinomycin as an ionophore. The reversible redox transformations of the redox mediator to either a monovalent hydrophobic anion or cation serve to drive the ion transfer across the liquid|liquid interface. In contact of the modified electrode with an aqueous electrolyte containing alkali or earth alkaline metal cations, significant partition of the aqueous electrolyte is taking place, due to the interfacial complexation of the cation with valinomycin. Thus, the thermodynamics and kinetics of the interfacial complexation–partition reaction at the liquid|liquid interface affect markedly the overall electron–ion transfer reaction at the modified electrodes under voltammetric conditions. Experiments are qualitatively compared with theoretical data collected by simulation of two different electrochemical mechanisms coupled with chemical reactions under conditions of square-wave voltammetry. It has been concluded that the overall electrochemical mechanism at three-phase electrodes can be described as a specific CrE reaction scheme, where Cr represents the reversible interfacial complexation–partition reaction of the transferring ion with valinomycin at the liquid|liquid interface

Kinetic studies on Sb(III) oxidation by hydrogen peroxide in aqueous solution

cited By 39International audienceKnowledge of antimony redox kinetics is crucial in understanding the impact and fate of Sb in the environment and optimizing Sb removal from drinking water. The rate of oxidation of Sb(III) with H2O 2 was measured in 0.5 mol L-1 NaCl solutions as a function of [Sb(III)], [H2O2], pH, temperature, and ionic strength. The rate of oxidation of Sb(III) with H2O2 can be described by the general expression: -d[Sb(III)]/dt = k[Sb(III)][H 2O2][H+]-1 with log k= -6.88 (±0.17) [k: min-1]. The undissociated Sb(OH)3 does not react with H2O2: the formation of Sb(OH) 4 - is needed for the reaction to take place. In a mildly acidic hydrochloric acid medium, the rate of oxidation of Sb(III) is zeroth order with respect to Sb(III) and can be described by the expression -d[Sb(III)]/dt = k[H2O2][H+][Cl-] with log k = 4.44 (±0.05) [k: L2 mol-2 min -1]. The application of the calculated rate laws to environmental conditions suggests that Sb(III) oxidation by H2O2 may be relevant either in surface waters with elevated H2O2 concentrations and alkaline pH values or in treatment systems for contaminated solutions with millimolar H2O2 concentrations