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

Wind Forced Variability in Eddy Formation, Eddy Shedding, and the Separation of the East Australian Current

The East Australian Current (EAC), like many other subtropical western boundary currents, is believed to be penetrating further poleward in recent decades. Previous observational and model studies have used steady state dynamics to relate changes in the westerly winds to changes in the separation behavior of the EAC. As yet, little work has been undertaken on the impact of forcing variability on the EAC and Tasman Sea circulation. Here using an eddy‐permitting regional ocean model, we present a suite of simulations forced by the same time‐mean fields, but with different atmospheric and remote ocean variability. These eddy‐permitting results demonstrate the nonlinear response of the EAC to variable, nonstationary inhomogeneous forcing. These simulations show an EAC with high intrinsic variability and stochastic eddy shedding. We show that wind stress variability on time scales shorter than 56 days leads to increases in eddy shedding rates and southward eddy propagation, producing an increased transport and southward reach of the mean EAC extension. We adopt an energetics framework that shows the EAC extension changes to be coincident with an increase in offshore, upstream eddy variance (via increased barotropic instability) and increase in subsurface mean kinetic energy along the length of the EAC. The response of EAC separation to regional variable wind stress has important implications for both past and future climate change studies

Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima

A sequence of global ocean circulation models, with horizontal mesh sizes of 0.5°, 0.25° and 0.1°, are used to estimate the long-term dispersion by ocean currents and mesoscale eddies of a slowly decaying tracer (half-life of 30 years, comparable to that of 137Cs) from the local waters off the Fukushima Dai-ichi Nuclear Power Plants. The tracer was continuously injected into the coastal waters over some weeks; its subsequent spreading and dilution in the Pacific Ocean was then simulated for 10 years. The simulations do not include any data assimilation, and thus, do not account for the actual state of the local ocean currents during the release of highly contaminated water from the damaged plants in March–April 2011. An ensemble differing in initial current distributions illustrates their importance for the tracer patterns evolving during the first months, but suggests a minor relevance for the large-scale tracer distributions after 2–3 years. By then the tracer cloud has penetrated to depths of more than 400 m, spanning the western and central North Pacific between 25°N and 55°N, leading to a rapid dilution of concentrations. The rate of dilution declines in the following years, while the main tracer patch propagates eastward across the Pacific Ocean, reaching the coastal waters of North America after about 5–6 years. Tentatively assuming a value of 10 PBq for the net 137Cs input during the first weeks after the Fukushima incident, the simulation suggests a rapid dilution of peak radioactivity values to about 10 Bq m−3 during the first two years, followed by a gradual decline to 1–2 Bq m−3 over the next 4–7 years. The total peak radioactivity levels would then still be about twice the pre-Fukushima values

The use of a multifactorial approach to reduce Salmonella shedding

An analytic epidemiological survey was carried out in france to assess the circumstances for Salmonella shedding in finishing pigs. This study gave out a combination of risk factors. The aim of our study was to evaluate that the implementation of a programme based on these risk factors reduces Salmonella carriage

Calibration of quasi-static aberrations in exoplanet direct-imaging instruments with a Zernike phase-mask sensor. II. Concept validation with ZELDA on VLT/SPHERE

Warm or massive gas giant planets, brown dwarfs, and debris disks around nearby stars are now routinely observed by dedicated high-contrast imaging instruments on large, ground-based observatories. These facilities include extreme adaptive optics (ExAO) and state-of-the-art coronagraphy to achieve unprecedented sensitivities for exoplanet detection and spectral characterization. However, differential aberrations between the ExAO sensing path and the science path represent a critical limitation for the detection of giant planets with a contrast lower than a few $10^{-6}$ at very small separations (<0.3\as) from their host star. In our previous work, we proposed a wavefront sensor based on Zernike phase contrast methods to circumvent this issue and measure these quasi-static aberrations at a nanometric level. We present the design, manufacturing and testing of ZELDA, a prototype that was installed on VLT/SPHERE during its reintegration in Chile. Using the internal light source of the instrument, we performed measurements in the presence of Zernike or Fourier modes introduced with the deformable mirror. Our experimental and simulation results are consistent, confirming the ability of our sensor to measure small aberrations (<50 nm rms) with nanometric accuracy. We then corrected the long-lived non-common path aberrations in SPHERE based on ZELDA measurements. We estimated a contrast gain of 10 in the coronagraphic image at 0.2\as, reaching the raw contrast limit set by the coronagraph in the instrument. The simplicity of the design and its phase reconstruction algorithm makes ZELDA an excellent candidate for the on-line measurements of quasi-static aberrations during the observations. The implementation of a ZELDA-based sensing path on the current and future facilities (ELTs, future space missions) could ease the observation of the cold gaseous or massive rocky planets around nearby stars.Comment: 13 pages, 12 figures, A&A accepted on June 3rd, 2016. v2 after language editin

Smart Focal Plane Technologies for VLT Instruments

As we move towards the era of ELTs, it is timely to think about the future role of the 8-m class telescopes. Under the OPTICON programme, novel technologies have been developed that are intended for use in multi-object and integral-field spectrographs. To date, these have been targeted at instrument concepts for the European ELT, but there are also significant possibilities for their inclusion in new VLT instruments, ensuring the continued success and productivity of these unique telescopes.Comment: 5 pages, to appear in the proceedings of the ESO Workshop "Science with the VLT in the ELT era

Looking for a reliable method to follow the salmonella status of finishing pigs

A study was undertaken to answer questions about the epidemiology of Salmonella in pig production. Does the Salmonella excretion from a group of pigs (on the same farm) remain constant during time or is there variations ? Where, and how many samples do we have to take to follow these variations, if they exist? Are the techniques to analyse samples (bacteriological and serological) practicable ? How is the relationship between serological and bacteriological methods

Arctic sea-ice-free season projected to extend into autumn

The recent Arctic sea ice reduction comes with an increase in the ice-free season duration, with comparable contributions of earlier ice retreat and later advance. CMIP5 models all project that the trend towards later advance should progressively exceed and ultimately double the trend towards earlier retreat, causing the ice-free season to shift into autumn. We show that such a shift is a basic feature of the thermodynamic response of seasonal ice to warming. The detailed analysis of an idealised thermodynamic ice–ocean model stresses the role of two seasonal amplifying feedbacks. The summer feedback generates a 1.6-day-later advance in response to a 1-day-earlier retreat. The underlying physics are the property of the upper ocean to absorb solar radiation more efficiently than it can release heat right before ice advance. The winter feedback is comparatively weak, prompting a 0.3-day-earlier retreat in response to a 1-day shift towards later advance. This is because a shorter growth season implies thinner ice, which subsequently melts away faster. However, the winter feedback is dampened by the relatively long ice growth period and by the inverse relationship between ice growth rate and thickness. At inter-annual timescales, the thermodynamic response of ice seasonality to warming is obscured by inter-annual variability. Nevertheless, in the long term, because all feedback mechanisms relate to basic and stable elements of the Arctic climate system, there is little inter-model uncertainty on the projected long-term shift into autumn of the ice-free season.</p

Estimation of the risk of Salmonella shedding by finishing pigs using a logistic model obtained from a survey

An analytic epidemiological survey was carried out in 105 French farms to identify factors associated with Salmonella shedding by finishing pigs. This study gave out a list of 7 risk factors using a logistic model. The aim of the present survey was to validate this model on a second sample of batches of pigs in order to estimate their Salmonella status. The validation study was carried out from April 2003 to August 2005 on 64 finishing pig batches distinct from those used originally to generate the logistic model. In each farm, Salmonella shedding of a batch of pigs at the end of the finishing phase was assessed using swabs as described in the analytical study. Questionnaires were filled in with the farmer to collect data related to management routines. Blood samples from10 growing and 10 finishing pigs were taken to assess sanitary risk factors: status vs Lawsonia intracellularis and Porcine Respiratory Coronavirus. Salmonella contamination status of a finishing room before loading, a further identified risk factor, was tested by environmental swabbing procedure. The estimated risk with the standard error, of Salmonella shedding was calculated using the logistic model and compared to the bacteriological Salmonella status of each batch. Several thresholds are proposed and sensitivity, specificity, positive and negative predictive values related to each cut-off value were calculated. A cut-off value of 0.34 maximised both sensitivity (76.9%) and specificity (68.6%) of the model. Whatever the threshold, the accuracy of the Salmonella non-shedding predicted status is better than the Salmonella shedding predicted status. In a bacteriological sampling programme, this model could be a useful tool to identify batches with low risk of Salmonella shedding and to focus attention on those getting a high probability for being positive