Participation des radicaux carbonate à l’oxydation de l’atrazine lors de l’ozonation de solutions aqueuses contenant des ions hydrogénocarbonate

L’étude porte sur la détermination de la contribution des espèces O3, OH° et CO3°- dans la dégradation de l’atrazine lors de l’ozonation de solutions contenant différentes concentrations en ions hydrogénocarbonate et en carbone organique. Le suivi de la concentration en atrazine et en ozone dissous, et les expressions cinétiques ont permis de calculer les concentrations en radicaux hydroxyle et carbonate au cours des réactions. A partir des données expérimentales obtenues sur des eaux pures additionnées de carbone organique et inorganique, les résultats indiquent que l’élimination du micropolluant résulte de l’action de l’ozone (pour une faible part), des radicaux hydroxyle issus de la décomposition de l’ozone, mais aussi pour une part très significative, des radicaux carbonate. La participation des radicaux CO3°- diminue lorsque la concentration en carbone organique augmente. Les radicaux carbonate peuvent être responsable de plus de 40 % de la dégradation de l’atrazine lors de l’ozonation en présence de 7 mM d’ions hydrogénocarbonate et 129 µM d’ions glycolate utilisés comme molécule modèle pour l’apport de carbone organique. Les résultats obtenus sur des eaux naturelles confirment les conclusions déduites des expériences sur des eaux de composition connue.The inhibiting effect of bicarbonate ions on the oxidation of organic molecules by the hydroxyl radicals is well known. However, the carbonate radicals resulting from the consumption of the OH° radicals by these ions have only rarely been considered to participate in the reactions of organic pollutant removal. In this study, the contribution of O3, OH° and CO3°- radicals in the degradation of atrazine during ozonation of aqueous solutions containing various concentrations of bicarbonate ions and organic carbon, was determined.Experiments were performed in a bubble column fed continuously by ozone gas and an aqueous solution containing atrazine (0.05 µM) as the model molecule. Three sets of experiments were carried out at pH 8:1. pure water with different concentrations of bicarbonate ions (0.35-70 mM);2. pure water with different concentrations of bicarbonate ions (0.35 and 7 mM) and glycolate ions (0-129 µM) selected as the organic carbon source;3. surface and tap waters.For different contact times in the ozonation reactor, the concentrations of atrazine and dissolved ozone were determined. Inputting these data into kinetic equations enabled us to calculate the concentrations of hydroxyl and carbonate radicals during ozonation. In the absence of organic carbon, the concentration of hydroxyl radicals was determined by assuming steady state conditions (equation II). The concentration of carbonate radicals was deduced from the slope of the evolution of atrazine concentration ([A]0 -[A])/[A] versus the contact time, and the values of ozone and OH° radical concentration (equation IV). In the presence of organic matter, the concentration of OH° radicals was calculated from the evolution of ([A]0 -[A])/[A] versus the contact time, and by replacing the carbonate radical concentration by the expression involving the OH° radicals (equations VI-IX). From the steady state assumption, the concentration of carbonate radicals followed the hydroxyl radical evolution.In the absence of organic carbon, the results confirmed the global inhibiting effect of bicarbonate ions on the removal of atrazine molecules. However, the concentrations of the carbonate radicals were much higher than the OH° radical concentrations (above 4x10-10 M compared to 2x10-12 M, respectively). The concentration of these latter radicals decreased as the concentration of bicarbonate ions increased. Under these conditions, the carbonate radicals were mainly responsible for the removal of atrazine.From the experiments in pure water with given concentrations of bicarbonate and glycolate ions, the hydroxyl radical concentration increased with the concentration of glycolate ions, thus confirming the promoter property of this organic molecule, which favours the removal of atrazine. However, in most cases, the presence of organic carbon was found to be unfavourable to the concentration of carbonate radicals. Therefore, the participation of the carbonate radicals decreased with increasing organic carbon content. Nevertheless, their contribution to atrazine degradation can reach more than 40% during ozonation in the presence of bicarbonate ions (7 mM) and glycolate ions (129 µM) used as an organic carbon source.The results obtained from the experiments carried out in natural waters agree with the main conclusions from the above experiments. The removal of atrazine involved ozone, hydroxyl radicals as well as carbonate radicals. The contribution of carbonate radicals decreased when the ratio of inorganic carbon to organic carbon decreased. In the surface and tap waters tested, this contribution was found to be 10 to 40 % and 43 % respectively

Estimating the burden of malaria in Senegal : Bayesian zero-inflated binomial geostatistical modeling of the MIS 2008 data

The Research Center for Human Development in Dakar (CRDH) with the technical assistance of ICF Macro and the National Malaria Control Programme (NMCP) conducted in 2008/2009 the Senegal Malaria Indicator Survey (SMIS), the first nationally representative household survey collecting parasitological data and malaria-related indicators. In this paper, we present spatially explicit parasitaemia risk estimates and number of infected children below 5 years. Geostatistical Zero-Inflated Binomial models (ZIB) were developed to take into account the large number of zero-prevalence survey locations (70%) in the data. Bayesian variable selection methods were incorporated within a geostatistical framework in order to choose the best set of environmental and climatic covariates associated with the parasitaemia risk. Model validation confirmed that the ZIB model had a better predictive ability than the standard Binomial analogue. Markov chain Monte Carlo (MCMC) methods were used for inference. Several insecticide treated nets (ITN) coverage indicators were calculated to assess the effectiveness of interventions. After adjusting for climatic and socio-economic factors, the presence of at least one ITN per every two household members and living in urban areas reduced the odds of parasitaemia by 86% and 81% respectively. Posterior estimates of the ORs related to the wealth index show a decreasing trend with the quintiles. Infection odds appear to be increasing with age. The population-adjusted prevalence ranges from 0.12% in Thille-Boubacar to 13.1% in Dabo. Tambacounda has the highest population-adjusted predicted prevalence (8.08%) whereas the region with the highest estimated number of infected children under the age of 5 years is Kolda (13940). The contemporary map and estimates of malaria burden identify the priority areas for future control interventions and provide baseline information for monitoring and evaluation. Zero-Inflated formulations are more appropriate in modeling sparse geostatistical survey data, expected to arise more frequently as malaria research is focused on eliminatio

On-line identification of temperature-dependent thermal conductivity

du 24 au 27 juinInternational audienc

A methodological framework for assessing agreement between cost-effectiveness outcomes estimated using alternative sources of data on treatment costs and effects for trial-based economic evaluations

A new methodological framework for assessing agreement between cost-effectiveness endpoints generated using alternative sources of data on treatment costs and effects for trial-based economic evaluations is proposed. The framework can be used to validate cost-effectiveness endpoints generated from routine data sources when comparable data is available directly from trial case report forms or from another source. We illustrate application of the framework using data from a recent trial-based economic evaluation of the probiotic Bifidobacterium breve strain BBG administered to babies less than 31 weeks of gestation. Cost-effectiveness endpoints are compared using two sources of information; trial case report forms and data extracted from the National Neonatal Research Database (NNRD), a clinical database created through collaborative efforts of UK neonatal services. Focusing on mean incremental net benefits at £30,000 per episode of sepsis averted, the study revealed no evidence of discrepancy between the data sources (two-sided p values >0.4), low probability estimates of miscoverage (ranging from 0.039 to 0.060) and concordance correlation coefficients greater than 0.86. We conclude that the NNRD could potentially serve as a reliable source of data for future trial-based economic evaluations of neonatal interventions. We also discuss the potential implications of increasing opportunity to utilize routinely available data for the conduct of trial-based economic evaluations

Scaling up prevention programmes to reduce the sexual transmission of HIV in China

Background Since 2007, sex has been the major mode of HIV transmission in China, accounting for 75% of new infections in 2009. Reducing sexual transmission is a major challenge for China in controling the HIV epidemic

Effective scale-up: avoiding the same old traps

Despite progress in developing more effective training methodologies, training initiatives for health workers continue to experience common pitfalls that have beset the overall success and cost-effectiveness of these programs for decades. These include lack of country-level coordination of health training, inequitable access to training, interrupted services, and failure to reinforce skills and knowledge training by addressing other performance factors. These pitfalls are now seen as aggravating the current crisis in human resources for health and impeding the effective scale-up of training and the potential impact of promising strategies such as task shifting to address health worker shortages. Drawing on IntraHealth International's lessons learned in designing reproductive health and HIV/AIDS training and performance improvement programmes, this commentary discusses promising practices for strengthening human resources for health through more efficient and effective training and learning programmes that avoid the same old traps. These promising practices include the following

Investigation of Factors Affecting Medication Adherence Among People Living with HIV/AIDS under Non - Governmental Organizations in Senegal

Abstract A ims:This prospective cross-sectional study was carried out to determine factors such as clinical and demographic variab les that may affect medication adherence among people living with HIV/AIDS (PLWHA) receiving treatment at the Institute of health and hygiene of Dakar, but are affiliated to Non-Govern mental Organizations which are HIV/AIDS support group based in Dakar..All consenting subjects from these two support groups were enrolled into study but 305 PLWHA volunteered to participate throughout the three months period of the study. Methods: The study was conducted with the aid of structured interview assisted questionnaires to obtain informat ion on demographic characteristics such as age, sex, occupation, marital status, educational backgrounds, and source of support. Information on availability and side effects of antiretroviral drugs were also obtained. Results:This study indicated that majority of people liv ing with HIV/AIDS interviewed were females (80.3%) while (19.7%) were males. Male respondents show better adherence (91.7%) to ARV med ications than female counterparts (83.7%). Subjects in age the age groups 24-35 years wh ich is the most sexually active groups are mo re vulnerab le (59.1%) when co mpared to other age groups. A large nu mber, (67.2%) were married and there was a significant difference between marital status of PHWHA (P<0.05) and level of adherence to antiretroviral med ications. Descriptive and Chi-square statistical tests were used respectively to evaluate the distribution of respondent's opinion and investigate the level of association between the variables being consideredand respondent'sadherence to antiretroviral med ications. Conclusion: We conclude that there is need to carry out further study in order to fully exp lore the extent to which marital status and other factors can affect medication adherence of people living with HIV/AIDS