Prévention des risques pour le consommateur liés aux résidus de phytosanitaires

International audienceLes bénéfices qu'apportent à l'humanité les produits phytosanitaires les rendent indispensables, mais de nombreuses substances présentent des dangers qui méritent d'être bien identifiés pour faire une évaluation lucide et responsable des risques encourus par les écosystèmes et la santé de l'homme. Cette démarche fondée sur la définition de dose journalière admissible (ou tolérable) permet de fixer des concentrations limites en résidus de chaque substance dans l'eau et le denrées alimentaires. Des procédés spécifiques permettent d'éliminer ces substances de l'eau. Si les procédés d'oxydation notamment radicalaire n'offrent pas la sécurité attendue, les procédés qui utilisent l'adsorption sur charbon actif et les membranes de filtration offrent des rendements qui garantissent une eau de qualité fiable

Influence des facteurs environnementaux et des pratiques agricoles sur les variations spatio-temporelles des niveaux de contamination de l'atmosphère par les pesticides

Dès les années 60, certains auteurs suggèrent d'utiliser pluies comme indicateur des niveaux de contamination de l'atmosphère par les pesticides. Mais encore faut-il comprendre les liens qui existent entre ces niveaux dans les pluies et ceux de l'atmosphère pour leur donner tout leur sens. C’est l'objectif de se travail. Il a fallut pour cela observer et comprendre le comportement des pesticides dans l'atmosphère. Dans un premier temps, les départs, depuis les zones traitées, ont été décrits pour 2 composés modèles afin de fournir les données nécessaires à la mise au point d’un modèle mécaniste de simulation des émissions. Les niveaux de contamination des pluies ont ensuite été décrits pour 5 sites, entre 2000 et 2003, dans différents contextes environnementaux afin de montrer l'influence de ces facteurs sur les concentrations observées. Cette étude a été complétée par un suivi de lévolution des concentrations en pesticides dans les pluies d'un même événement pluvieux pour comprendre les phénomènes de lessivage. Enfin un photoréacteur a été construit afin de décrire lévolution des pesticides dans l'atmosphère et compléter certaines interprétations.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Cinétiques et mécanismes de l'action oxydative de l'hypochlorite sur les acides α-aminés lors de la désinfection des eaux

International audienceIn the field of water treatment, one increased concern over the quality of the environment requires an understanding of the fate of compounds generated by the addition of chemicals. One area of considerable interest is the stability of chlorine compounds produced when chlorine is added to natural water or swimming pool water. It is desirable to be able to predict the lifetimes of these harmful compounds under various conditions. In this study we examine for a range of hypochlorite α-amino acid ratios and pH, the kinetics and mechanism of the decomposition of α(N-chloro) and α(N,N-dichloro) amino acid, one of the products of chlorination.The interaction of chlorine with amino acids has been studied by several investigators Langheld (1909) was the first who discussed the decomposition of the α(N-chloro) amino acids. He noted that hypochlorous acid salts react with α-amino acids in the same manner as they do with amines to form monochlorinated or dichlorinated derivatives. Then, the decomposition of chloro-amino acids leads to the corresponding aldehydes or ketones, ammonia, carbonic acid, and sodium chloride. As an intermediate step Langheld assumed an imine formation.Wright (1936) and Pereira et al. (1973) have investigated the decomposition products of α(N,N-dichloro) amino acids. Their results indicate rapid formation of carbon dioxide, chloride ion, and the corresponding nitrile.Recently, many authors have investigated the rates of α(N-chloro) amino acids decomposition and the stability of its products (William and Wendy, 1979; Yoshiro et al., 1980; Le Cloirec-Renaud, 1984). However, they have neither differentiated between the decomposition of α(N-chloro) amino acid and α(N,N-dichloro) amino acid, nor have they demonstrated the combined effect of pH and molar ratio of hypochlorite and α-amino acid.In this study the hypochlorite oxidation of simple α-amino acids in aqueous solution has been investigated in the dark. The concentration of α(N-chloro) amino acid and α(N,N-dichloro) amino acid was monitored by DPD-fast titrimetric method and by measuring the absorbance at 255 and 293 nm respectively, this is illustrated in Figs 3 and 4. These results and the amino acids determination (O-phtalaldehyde—2 mercapto ethanol method) suggest that the intermediates α(N-chloro) and α(N,N-dichloro) amino acid are formed rapidly at an initial stage. Then, they decompose spontaneously by first order kinetics as shown in Table 1, to give a mixture of aldehyde and nitrile.When equimolar (1:1 mmol) amounts of hypochlorite and amino acid are used at pH 7, only aldehyde, carbon dioxide, chloride and ammonia are formed. However the corresponding nitrile compound appears, when operating condition allow the formation of α(N,N-dichloro) amino acid (acid pH or basic aqueous solutions with high molar ratio of hypochlorite and amino acid). This is illustrated in Table 2. The rate constant shows a dependence on pH, which is caused by the various forms that can arise from addition of protons to or removal of protons from the amino and carboxyl groups of the molecule William and Wendy, 1979). We assume an intermediate step of imine for the decomposition of both compounds: α(N-chloro) and α(N,N-dichloro) amino acid (scheme 6). The reaction should be considered as a spontaneous decarbonylation followed by a rapid hydrolysis of the imine. Scheme 7 illustrated how α(N,N-dichloro) amino acid can lead to the corresponding nitrile and aldehyde, however the α(N-chloro) amino acid gives only the corresponding aldehyde.The products of decomposition of α(N-chloro) amino acid are relatively stable in aqueous solution. Although we noted at pH = 3.5–5 that aldehyde react with chloramines and lead to the formation of corresponding nitrile, as shown in scheme 9.It appears that α(N-chloro) and α(N,N-dichloro) amino acid formed during the chlorination of natural or swimming pool water will degrade in a few hours to what are probably irritating products (like as aldehydes). The production of decomposition are a function of molar ratio of hypochlorite and amino acid and pH. However, since most natural water has a pH in the range of 5.5–9, there will be little variation of the rate of decomposition with pH. It seems that it is only temperature dependent.La formation des α(N-chloro) et des α(N,N-dichloro) acides aminés est très rapide en présence de chlore. Ces composés sont instables. Ils évoluent par décarbonylation vers une imine intermédiaire qui, par hydrolyse, donne l'aldéhyde et le nitrile correspondants. Pour des pH voisins de 7, seul l'aldéhyde se forme lorsque le rapport molaire est de l'ordre ou inférieur à 1. Le nitrile n'est produit que si les conditions opératoires permettent la formation du α(N-N-dichloro) amino acide (pH acide ou rapport molaire R élevé en milieu neutre). En présence de chloramines minérales, les aldéhydes peuvent conduire par une réaction réversible à la formation du nitrile correspondant. La réaction est catalysée par une légère acidité du milieu réactionnel (pH 3.5–5)

A comparative study of the photoinactivation of bacteria by meso -substituted cationic porphyrin, rose Bengal and methylene blue

International audienceAdvances in wastewater treatment technology have led many to predict that planned wastewater reuse in agriculture will soon become more common in some regions of the world which face acute problems of water quality and quantity. The use of ecologically friendly wastewater disinfection techniques could be one of the most exciting advances in this field. The combined action of a photosensitizer (meso-substituted cationic porphyrin, TMPyP; rose Bengal, RB; methylene blue, MB) and visible light, particularly sunlight, seem to be a promising approach to microbial inactivation, potentially applicable for disinfection of domestic effluents. In the present work, photosensitization was either performed on Gram-positive and Gram-negative bacteria in pure culture (Enterococcus hirae and Escherichia coli), or carried out with wild strains in secondary wastewater effluent (enterococci and E. coli). The results described in this paper show that TMPyP is the most effective for photoinactivation of the bacterial models studied here. The relative effectiveness of RB and MB was found to be tightly linked to bacteria Gram type. Whatever the sensitizer used, Gram-negative bacteria were more resistant to photosensitization than Gram-positive strains. The order of increasing effectiveness of the photosensitizers for photoinactivation of Gram-positive bacteria (TMPyP ≥ RB > MB) and Gram-negative bacteria (TMPyP > MB > RB) remains unchanged for either pure culture or wild strains (bacterial communities in wastewater). The effectiveness of the photochemical process depends primarily on the type of microorganisms as well as the type of photosensitizers (concentration, singlet oxygen quantum yield, ionic charge), and the reaction medium

Cinétiques de l'action bactéricide des chloroisocyanurates sur trois bactéries: pseudomonas aeruginosa, streptococcus faecalis et staphylococcus aureus

International audienceThe efficiency of chloroisocyanurates in swimming pool disinfection has been demonstrated by a number of authors (Andersen, 1965; Kolwalski and Hilton, 1966; Robinton and Mood, 1967; Fitzgerald and der Vartanian, 1969). The disinfection rate was seen to slow down during studies on different bacteria; this was attributed to the existence of a weak concentration of free chlorine (HOCl + ClO-). However, since these studies were carried out when the aqueous chemistry of chloroisocyanurates was not completely elucidated, the specific action of chloroisocyanurates was difficult to determine. This, in part, was due to the large number and variety of experimental procedures and analytical methods for chlorine measurements, and to the lack of specificity of the methods employed. We studied the action of chloroisocyanurates on three environmental strains: S. faecalis, S. aureus, Ps. aeruginosa and on one collection strain: Ps. aeruginosa-CIP. Disinfection tests were carried out in the laboratory, in pH and temperature conditions typically found in swimming pools (pH 7.5, 25°C). The initial concentration of total chlorine varies from 0.5 to 2.5 mg I-1, for concentrations of isocyanuric acid, H3Cy, from 25 to 360 mg 1-1. With these concentrations, free chlorine (HOCl + ClO-) does not exceed 3% of total chlorine (that is, less than 0.08 mg 1-1). We used an easy and rapid method of dosage which distinguishes between "available chlorine" [(HOCl + ClO-) + (chlorine from isocyanurates, HnClmCyp-)] and "total chlorine": absorption spectrophotometry after reaction with the N-diethylparaphenylenediamine (DPD). We adopted a common method for monitoring simultaneously, chlorine concentration and bacterial count. In this way, we studied the kinetics of selected bacteria inactivation, relative to H3Cy concentration and for different levels of available chlorin

Cinétiques et mécanismes de la dégradation de la créatinine sous l'action de l'hypochlorite

International audienceAn area of substantial interest in current research on chlorination is the formation, stability and nature of chloramines formed by the interaction of chlorine with nitrogen organic compounds of biological origin in natural water or swimming pool water. It is desirable to be able to predict the lifetime of these harmful compounds under various conditions. The research described here constitutes an effort to gather important baseline data regarding the rate of formation of creatinine chloramines, the stabilities of these products and their identities. Some researchers have studied the effect of the presence of chlorinated creatinine compounds in swimming pool water. Lomas (1967), showed that the presence of urine in water allowed the formation of compounds which reacted with DPD like dichloramine. He reported that the presence of this apparent dichloramine could be due to a chlorine derivative of creatine and creatinine derived from urine. Hamence (1980) confirmed this work and found that urine and particularly creatinine were responsible for the apparent nitrogen trichloride. As a result of this work it was concluded that the DPD-fast titrimetric method of analysis did not determine nitrogen trichloride but other chlorine compounds, particularly those of chlorinated creatinine and creatine. We found it interesting to examine in this study, for a range of hypochlorite creatinine ratios and pHs, the kinetics and mechanisms of formation and decomposition of N-chlorocreatinines. The hypochlorite oxidation of creatinine in aqueous solution has been investigated in the dark. The following of creatinine and chloramines concentrations by the DPD-fast titrimetric method and by their u.v. spectra confirmed Lomas' and Hamence's works. However we observed dichloramine formation (Fig. 4) when the molar ratio of hypochlorite and creatinine was sufficient to decompose all chlorinated creatinine forms. The creatinine determination (HPLC method) suggested that N-chlorocreatinines were formed rapidly at an initial stage. Then they were decomposed by an apparent first order reaction at pH 8. With equimolar (1:1 mmol) amounts of hypochlorite and creatinine at pH 8, it appeared that N-chlorocreatinines were decomposed by hydrolysis to regenerate creatinine. We observed then the formation of creatine, 1-methylhydantoin, chlorocreatinines and NH2Cl (Fig. 3). When the molar ratio was greater, the N-chlorocreatinines decomposed completely to form carbon dioxide, chlorite ion and mineral chloramines (see Table 1). The reaction in the initial stage should be considered as an electrophile substitution followed slowly by hydrolysis when pH remained around 8 (Scheme 2). If the addition of hypochlorite affects the amine group of the molecule, 1-methylhydantoin is produced (Scheme 3) with NH2Cl. Reaction yield was about 10% of initial creatinine. In acid aqueous solution, with a molar ratio of 3, we also obtained trichlorocreatinine. This reaction is due to the various form of creatinine after addition of proton on amino of N-H groups of the molecule. In these conditions N-chlororcreatinines remained stable in aqueous solution for many days. However in the presence of free chlorine, we observed the production of carbon dioxide and mineral chloramines. After 4 days the residual concentration of N-chlorocreatinines was half the initial value. It appears that N-chlorocreatinines formed during the chlorination of natural or swimming pool water were relatively stable, leading to the increase of the combined chlorine level. This stability was a function of the molar ratio of hypochlorite and creatinine, and pH. However, since most of the difference types of water had a pH in the range of 6-9, there would be little effect of pH at ambient temperature.Le chlore réagit en quelques minutes avec la créatinine pour donner, en fonction du rapport molaire, la mono et la dichlorocréatinine en milieu neutre ou légèrement alcalin (pH = 8). Si le pH est inférieur à 6, la trichlorocréatinine est également obtenue pour R > 2. Ces dérivés sont stables en milieu faiblement acide, mais ils se dégradent lentement (50% après 4 jours) sous l'effet d'un excès de chlore. En milieu neutre, ou à des pH plus élevés, les chlorocréatinines subissent des réactions d'hydrolyse qui conduisent, lorsque R = 1, à la régénération de créatinine et, par ouverture du cycle, à la formation de monochlorocréatine. Celle-ci s'hydrolyse à son tour pour former de la créatine. L'augmentation du rapport molaire R favorise la production des chlorocréatines qui se dégradent lentement en donnant du dioxyde de carbone et des chloramines minérales. L'addition de chlore sur la double liaison carbone azote est également observée, mais, en raison de sa vitesse plus lente que celle des réactions de substitution, la formation de chloro-1-méthylhydantoine reste un fait marginal.Nous avons par ailleurs constaté que les atomes de chlore des chlorocréatinines oxydent l'iodure et sont pris en compte lors de la mesure du chlore résiduel total par la méthode au DPD. L'ensemble de ces résultats montrent que la présence de créatinine dans une eau induira une formation spécifique de chlore combiné relativement stable, même en présence d'un léger excès de chlore libre

Photoinactivation de bactéries d intérêt sanitaire en condition de simulation solaire en présence de photosensibilisants synthétiques et/ou naturels

La photosensibilisation utilise une substance promotrice de l activité désinfectante de la lumière solaire faisant intervenir les espèces réactives de l oxygène. Dans ce travail nous avons retenu une porphyrine cationique (TMPyP). Pour cerner les facteurs de l efficacité de la désinfection des eaux usées, nous avons étudié les mécanismes de photoinactivation des bactéries. Les bactéries Gram-négatif (Escherichia coli) apparaissent plus résistantes à la photoinactivation que les bactéries Gram-positif (Enterococcus hirae). La même observation est réalisée sur des bactéries sauvages dans un effluent d eau usée. Les essais en résonance paramagnétique électronique (RPE) montrent que la TMPyP est susceptible d agir sur des substrats via les réactions de type I (espèces radicalaires) ou de Type II (oxygène singulet). La comparaison de l action de photosensibilisants synthétiques ou naturels à celle de la TMPyP montre que ce dernier est plus efficace pour la photoinactivation des bactéries. L efficacité du processus est lié au type de microorganismes, à la concentration et la charge électronique du photosensibilisant et à la charge organique du milieu.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Étude de l évolution du trichlorure d azote et des trihalométhanes dans l eau et l air des piscines chlorées (exploration des voies de réduction de cette contamination)

Dans l eau des piscines, le chlore utilisé comme désinfectant réagit avec la pollution apportée par les baigneurs (sueur, urine, ), pour former des sous-produits. Certains de ces composés, tels que la trichloramine et les trihalométhanes sont très volatils et se transfèrent dans l air des piscines couvertes. Ce travail renseigne d une part les niveaux et les facteurs déterminants de la contamination de l eau et de l air des piscines par les trihalométhanes, jusqu ici mal connus. D autre part, en raison des préoccupations sanitaires liées à la présence des sous-produits de désinfection dans les piscines, ce travail explore deux stratégies de réduction de cette contamination. Nous avons ainsi amélioré les connaissances relatives au traitement de l eau des bassins par les UV et à leur impact sur la formation des trihalométhanes. Nous avons également développé au laboratoire un dispositif innovant permettant de réduire significativement les teneurs en trichloramine dans les bassins.Chlorination of swimming pool water generates various disinfection by-products like trihalomethanes and nitrogen trichloride, arising from the reaction between organic compounds released by the swimmers and chlorine. These compounds are of great volatility and also contaminate indoor air of swimming pools. This work brings on the one hand useful information on trihalomethane levels in pool water and indoor air, which are poorly documented, and highlights the important contributors to this contamination. Given the great concern for public health authorities caused by exposure of the population to disinfection by-products, this work explores on the other hand two ways of reduction of this contamination. UV treatment of pool water was first studied and particularly its impact on trihalomethane levels. We also developed a promising lab-scale to remove nitrogen trichloride from water.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Etude des facteurs déterminant la fuite en aluminium dans des eaux d'alimentation préparées à partir d'eaux clarifiées par des sels de ce métal

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