FR :

L'étude des interactions entre les ions chlorite, un charbon actif en grains (CAG CECA 40) et des composés phénoliques (phénol et para-nitrophénol) a été réalisée à partir d'expériences de filtration sur mini-colonnes de CAG de solutions aqueuses de chlorite et du composé organique en mélange ([C10²-] inf=50 mg.l-¹; [Composé Organique]jnf=200 µmol.l-¹ ; 3 g de CAG; Vitesse de filtration: 3,7 m.h-¹). Les résultats obtenus ont permis de montrer que la présence de chlorite conduit à une augmentation des capacités du CAG vis-à-vis de l'élimination du phénol et du para-nitrophénol. Cette augmentation résulte de réactions chimiques entre le composé organique et les sous-produits de décomposition des ions chlorite par le charbon actif. Les analyses par couplage CG/SM des extraits issus des charbons actifs à la fin des filtrations ont permis de mettre en évidence la présence de nombreux composés adsorbés sur le charbon actif. Les composés identifiés résultent de réactions d'oxydation, de deshydroxylation, de carboxylation, d'halogénation, d'hydroxylation et de dimérisation. L'action des ions chlorite sur le charbon actif peut conduire à la formation de radicaux à la surface du charbon actif ou en solution capables de réagir avec les composés organiques pour former les sous-produits observés.

EN :

The use of chlorine dioxide for the chemical preoxidation of potable water with high oxidant demand requires that the major inorganic byproduct, chlorite, in the treatment system be removed, owing to the potential toxicity of this oxychlorine species. Granular Activated Carbon (GAC) filtration, in converting chlorite ions into chloride, appears to be an interesting approach, but very few data are available concerning possible interactions in the presence of organic matter. The present research was designed to examine the influence of phenolic compounds on the efficiency of activated carbon in removing chlorite and to study the reactions between chlorite, activated carbon and organic molecules. Laboratory experiments have been carried out with relatively high substrate concentrations in order to identify the resulting byproducts.

Materials and Methods.

Filtrations of solutions containing chlorite and a phenolic compound (phenol or para nitrophenol; [Organic Compound]inf=200 µmol.L-¹;[C102-] inf=50 mg L-¹; pH=7.2); were performed using 1- cm i.d. glass columns packed with 3.0 g of GAC CECA 40 (Flow rate: 3.7 m.h-¹). Inorganic species were analysed by HPLC, with an anion column and a conductimetric detector for chloride and chlorate, and with a C-18 column and a UV detector for chlorite. Phenol and para nitrophenol were also analysed by HPLC, in the reverse mode. At the conclusion of the filtrations, the Total Organic Halogen (TOX) adsorbed on the carbon was determined after combustion of the carbon and measurement of the liberated halides with a micro coulometer (Dohrmann DX20). In order to identify organic reaction byproducts, carbon samples were Soxhlet extracted with methylene chloride and half of the extracts were methylated with diazomethane. Identification of the organic products was then carried out by gas chromatography / mass spectrometry with a DB5 capillary column and a quadrupolar hyperbolic filter system CPV/MS.

Results and Discussion.

Effects of phenol and p nitrophenol on removal of chlorite by GAC. The effluent curves from columns that received solutions containing both chlorite and an organic solute (columns A and B; fig. 1) showed that the presence of phenol or p nitrophenol in the influent decreases the capacity of GAC to remove chlorite.

Effect of chlorite on removal of phenol and p nitrophenol. An increase in the cumulative removal of the organic solute was observed for columns A and B compared with columns that received solutions of the phenolic compound only (fig. 2; table 11). p benzoquinone was found in the eff1uent of column A fed with a chlorite phenol solution (fig. 3).

Formation of organic byproducts by reactions between chlorite and phenol or p nitrophenol in the presence of GAC. TOX analyses showed that interactions between chlorite, GAC, and phenol or p nitrophenol led to the production of organohalogenated compounds. These data clearly demonstrate that halogenation reactions take place in the GAC bed and that a fraction of the total amount of phenol or p nitrophenol removed can be due to chemical reactions. GC/MS analyses of GAC extracts of columns A and B (tables IV and V) indicated that the phenol chlorite GAC reactions yield a variety of organic byproducts that are produced by hydroxylation and carboxylation of the aromatic ring by oxidation to quinones, by chlorine substitution and by dehydroxylation and dimerization reactions. Fewer products could be identified in the reaction between p nitrophenol, chlorite, and GAC. Since chlorite is unreactive with phenol and p nitrophenol in neutral aqueous solution, the formation of these organic byproducts can be attributed to reactions between phenol or p nitrophenol present in the GAC pore solution or adsorbed on GAC and the chemical species (Cl· ClO·, ClO2, HOCl (ClO-), surface free radicals ...) generated from the reaction of chlorite and carbon. Thus, aromatic acids could come from radical processes between adsorbed molecules and carbon surface functional groups oxidized by chlorite. The formation of dimers can also be explained by a freeradical mechanism. The reactions between Cl·, ClO· radicals or radicals present on the GAC surface, with organic compounds produce organic radicals via H atom abstraction or one electron transfer. Organic radicals such as phenoxy radicals or other aromatic radicals can then undergo dimerization by carbon-oxygen or carbon-carbon coupling. The formation of organochlorinated compounds can be explained by the reaction of chlorine (HOCl, ClO-) and chlorine radicals with organic molecules present in the solution. However further investigation is needed in order to evaluate if such compounds can be formed on GAC filters and then desorbed in the effluent in thc case of drinking waters pretreated with chlorine dioxide.

FR :

Les résultats de l'adsorption sur charbon actif en poudre de solutions aqueuses de différents composés organiques: phénol, aniline, nitrobenzène, acide salicylique, nitro-4 phénol, méthyl-2 dinitro-4,6 phénol, phénylalanine et tyrosine ont été traités à l'aide des équations de Langmuir, Elovich, Freundlich, Temkin, Fowler-Guggenheim, Hill et De Boer, Kiselev afin de déterminer divers paramètres d'équilibre: la capacité maximum d'adsorption, l'énergie d'adsorption, l'énergie d'interaction, les constantes d'équilibre adsorbat-adsorbant et les interactions (éventuelles) entre les molécules adsorbées.

La relation de Temkin (3=RTt~Q In KoC permet de déterminer la variation de l'énergie d'adsorption ~Q et la constante Ko de l'équilibre (~3 est le degré de re- couvrement du charbon par le soluté, et C la concentration à l'équilibre). L'équa- tion de Fowler-Guggenheim KC=~3/(1~3) Exp (2 ~ W/RT) conduit à la déter- mination de l'énergie d'interaction W entre molécules adsorbées et à une constante d'équilibre K. Par contre, dans l'équation de Hill et de De Boer KlC=~/(1~)) Exp [~/(1~) - K2~/RTI, K2 représente une constante d'énergie d'interaction entre molécules adsorbées et, dans celle de Kiselev KIC=~3/[(1+ ~) (1 + Kn~3)]~ Kn est une constante de formation de complexe éventuel entre molécules adsorbées.

On vérifie que l'application de la relation de Temkin est satisfaisante pour tous les composés étudiés et permet de les classer selon leur affinité sur le charbon mais les résultats obtenus en utilisant les équations suivantes (Fowler ...) montrent qu'il n'y aurait pas de formation de complexe ou d'interaction entre molécules adsorbées.

EN :

Analysis of the results of adsorption from aqueous liquid media onto activated carbon can be carried out by different models based on thermodynamic principles. Classically the Langmuir (eq. 1), Freundlich or Elovich (eq. 4) isotherms are used, which lead to the determination of an experimental maximum capacity, qm, and a constant K, characteristic of the adsorbate-adsorbent interactions. The following equations (Table I) have been transposed from the vapour phase to the liquid phase. With the Temkin relation: [Theta]=RT/[Delta]QlnK[inf]0C (eq. 6), it is possible to determine the variation of adsorption energy, [Delta]Q, between the adsorbed molecules and the solid phase, and the equilibrium constant K[inf]0 ([Theta] is the degree of surface covering of the solid phase [Theta]=q/qm, q is the adsorption capacity). The Fowler-Guggenheim equation: KC=[[Theta]/(1-[Theta])] Exp (2[Theta]W/RT) (eq. 7) gives the interaction energy, W, between the adsorbed molecules and an equilibrium constant, K. The Hill and De Boer relation: K[inf]1C=[Theta]/(1-[Theta])] Exp [[Theta]/(1-[Theta]) -K[inf]2[Theta]/RT] (eq. 8) yields an energetic interaction constant K[inf]2 (J.mol-¹) characteristic of the interactions between the adsorbate molecules and an equilibrium constant, K[inf]1. In the Kiselev relation: K[inf]1C=([Theta]/[(1-[Theta]) (1 + K[inf]n[Theta]] (eq. 9), K[inf]n is a complex formation constant between adsorbed molecules and K[inf]1 is a constant relative to the adsorbate-adsorbent interaction. Linearization of the equations of Langmuir, and Elovich leads to qm and K values. For the Freundlich relation, if the experiments are made at constant Co and variable concentrations of adsorbent, the Freundlich relation can be transformed as relation (5): q=qm (C/Co)[sup]1/n). The value of qm and K are reported in the Table II. When the values obtained by the Elovich equation are very different from the Langmuir relation, they are not in concordance with the experimental adsorption isotherm as shown on the Figures 4, 5 and 6.

A value of qm is necessary to calculate the ([Theta](=q/qm) of the Temkin, Hill-De Boer, Fowler- Guggenheim and Kiselev equations; [Theta] is calculated with the Langmuir value of qm: the linearized relations were tested for the following compounds: phenol, aniline, nitrobenzene, salicylic acid, 4-nitro phenol, 2-methyl-4,6 dinitro phenol, phenylalanine and tyrosine, studied at micromolar concentration. The results are shown in Table II. The Temkin linearization is of good quality for all the compounds; an example is given on the Figure 1. For the others (Figs. 2, 3), the linearization is not always verified (Hill-De Boer for phenylalanine: Fig. 3a) and the results are framed two times in the Table II.

With the obtention of the two parameters [Delta][Theta], K K, W; K[inf]1, K[inf]2 and K[inf]1, K[inf]n, the isotherm can be recalculated. The results for some solutes are on Figures 4, 5, 6, 7, 8. Relatively poor results are obtained for Fowler-Guggenheim, Kiselev or Hill-De Boer models, where no association is present between the adsorbed molecules.

The evolution of the variation of the adsorption energy ([Delta][Theta]) is reported on the Figure 9 for the different compounds. The greatest values are obtained for nitrobenzene and 4-nitro-phenol (+ 80, + 40 kJ.mol-¹ probably due to the presence of the nitro group). All the values are positive (exothermic reaction ( [Delta][Theta]=-[Delta]H)) showing the affinity of molecules for the activated carbon.

FR :

Les dégradations du bromoxynil heptanoate et du bromoxynil ont été étudiées pour différents traitements chimiques (03, Cl2) et photochimiques (H202/W; W254) en milieu aqueux dilué. Les expériences ont été réalisées à pH 7 pour le bromoxynil (CO=5 10-5 mol 1-1) et à pH 4 pour le bromoxynil heptanoate (CO=10-6 mol 1-1) afin de limiter la réaction d'hydrolyse.

Les résultats obtenus montrent une bonne dégradation de ces deux pesticides aussi bien par irradiation W que par oxydation chimique au chlore ou à l'ozone. L'ajout de peroxyde d'hydrogène dans le milieu n'augmente pas de façon significative l'efficacité du traitement par rapport à l'irradiation seule. Parmi tous les traitements étudiés, l'ozonation est le procédé le plus efficace.

L'analyse par couplage GC-MS des produits de réaction au cours de l'irradiation UV a permis d'identifier quatre photoproduits correspondant à la substitution des atomes de brome soit par un atome d'hydrogène, soit par un groupement OH. Les produits identifés sont A: -3,4 dihydroxy -5 bromobenzonitrile; B: -3,4,5 trihydroxybenzonitrile; C: -3,4 dihydroxybenzonitrile; D: -4 hydroxybenzo- nitrile. Un schéma réactionnel de photodégradation du bromoxynil heptanoate a été proposé dans cette étude.

EN :

In the aquatic environment hydrolysis and phototransformation processes are the main abiotic degradation routes of chemicals. The aim of this study is to investigate the degradation pathway of 2 pesticides (bromoxynil heptanoate and its hydrolysis product bromoxynil) by UV photolysis and by chemical oxidation. The chemical oxidation processes studied are ozonation chlorination and radical oxidation with OH radicals. These radicals are produced by photolysis of hydrogen peroxide.

Bromoxynil heptanoate (-4 cyano -2,6 dibromophenyl heptanoate) is an ester which is quite unstable in aqueous medium. Preliminary experiments, carried out in diluted solution (C[inf]o=10-[sup]6 mol l-¹) and in phosphate buffer (µ=10-² mol l-¹), showed that 20 to 25% of bromoxynil heptanoate is hydroIyzed after 24 hours at pH 7. The hydrolysis decreases strongly with pH; it is only 3 % at pH 4 after one day.

In order to limit the hydrolysis reaction, the following experiments were carried out at pH 7 for bromoxynil (C[inf]o=5 10-[sup]5 mol l-¹) and at pH 4 for bromoxynil heptanoate (Co=10-[sup]6 mol l-¹). The pH was adjusted with a phosphate buffer.

Absorption spectra of bromoxynil heptanoate and bromoxynil do not show any absorption band up to 320 nm (bromoxynil heptanoate l max=218, 290 nm; bromoxynil I max=222, 280 nm; fig. 1). Therefore, the removal of these two pesticides by direct photolysis with the sun light will be very small. The measurement of the quantum yield (number of molecules undergoing photodegradation transformation per number of photons absorbed by these molecules) in the UV region in both monochromatic and polychromatic lights (HPK, Philips; I[inf]0=1.48 10-[sup]8 Einstein sec-¹, indicates that these 2 compounds are easily eliminated by a UV irradiation treatment (10-² < F < 10-¹ at I=254 nm and 290 nm).

The irradiation of these two pesticides at 254 nm (low pressure vapor mercury lamp, l[inf]0=5.8 10-[inf]8 Einstein sec-¹) in the presence of hydrogen peroxide does not seem to significantly improve the efficiency of the treatment by UV irradiation alone. For example, the half life time of bromoxynil is 11 minutes by UV compared to 8 minutes when hydrogen peroxide is present. This small difference of reactivity of H2O2/UV system is due to the small quantity of H202 photolyzed during this irradiation time; at t=8 min only 1 % of H202 is decomposed.

The oxidation of bromoxynil heptanoate and bromoxynil by ozonation was performed in a semi-batch reactor (Q=5 mg O3 min-¹). Results show that these two compounds are very reactive with ozone. 50 % of elimination was obtained after 5 and 2 minutes of ozonation for bromoxynil heptanoate and bromoxynil respectively. In both cases the transfer of ozone was the limiting factor.

Finally chlorination of bromoxynil at a rate of 35.5 mg Cl2-l-¹ indicates that this pesticide is also oxidized by chlorine but the degradation rate is quite slow; a total degradation is observed after 90 min of reaction.

Comparison of the different treatments studied shows that ozonation is certainly the most effective process. Only a few minutes with reasonable ozone doses are necessary to eliminate these pesticides from aqueous medium. The other treatment (UV, H2O2/UV, Cl2) can also be a good alternative for the removal of these compounds from water.

For the different oxidation treatments, the HPLC analysis of the bromoxynil reaction mixture shows the formation of by-products. Only UV and H2O2/UV byproducts were identified in this work; but comparison of the retention times from the HPLC analysis indicates that certain by-products from ozonation are similar to the ones observed by UV and H202/UV oxidation. On the other hand, the products formed during chlorination, probably chlorinated products, have different retention times.

The reaction intermediates werc identified by GC-MS analysis after 10 min of irradiation (with and without H2O2). This time corresponds to the maximum concentration of one of the photoproduct. Two kinds of compounds wers identified from the GC-MS analysis: hydroxylated compounds (-3,4 dihydroxy -5 bromobenzonitrile; -3,4,5 trihydroxybenzonitrile) and hydrogenated compounds (-3,4 dihydroxybenzonitrile; -4 hydroxybenzonitrile). In both cases the bromine atoms were substituted either by an H atom or by an OH group. A reaction mechanism of photodegradation of bromoxynil heptanoate is proposed in this study (Fig. 6).

FR :

Les lixiviats de décharge constituent une source de nuisance qui vient s'ajouter aux nombreux problèmes de contamination du milieu environnant s'ils ne sont pas traités avant leur rejet. La matière organique, principale composante de ces effluents, doit retenir une grande attention dans la mesure où il est difficile d'éviter la propagation et la diffusion de cette pollution dans les sols et vers les nappes phréatiques. Cette étude vise à fractionner et à caractériser la matière organique présente dans des lixiviats de décharges d'ordures ménagères afin de prévoir et d'orienter le choix des traitements les plus adaptés compte tenu de leur biodégradabilité.

La méthode de fractionnement utilisée comprend une adsorption spécifique sur résines macroporeuses Amberlite XAD (combinaison de XAD-7 et XAD-4) pour séparer les composés hydrophobes et hydrophiles qui sont ensuite extraits à la soude (composés acides) et au dichlorométhane (composés neutres). Le fractionnement de la matière organique par filtration sur résines XAD-7 et XAD-4, après une première étape de précipitation en milieu acide (pH=1), a permis de répartir l'ensemble des composés organiques du lixiviat dans six fractions de spécificités différentes fonction de la taille et/ou du caractère hydrophile ou hydrophobe des molécules.

Les résultats montrent que ce protocole expérimental permet d'extraire au moins 98 % de la matière organique totale (pourcentage relatif aux teneurs de la demande chimique en oxygène ou DCO), dont la plus grande proportion est constituée des substances humiques (76 % à 90 % en DCO). Diverses méthodes analytiques ont été proposées en vue de caractériser les fractions isolées telles que l'analyse élémentaire, la spectrophotométrie infrarouge, la résonanoe magnétique nucléaire C13 (RMN Cl3) et la chromatographie CG/FID et CG/SM.

EN :

Landfill leachates represent an obvious source of pollution for the environment and many studies have attempted to analyze organic pollutants found in leachates. A number of methods have been described in the literature for the isolation and concentration of dissolved organic matter from landfill leachate samples. Membrane ultrafiltration, gel permeation and high performance liquid chromatography are commonly used because these techniques can be easily adapted to separate soluble organic substances from large volumes of leachate. The objective of this study was to fractionate and characterize dissolved organic matter found in leachates collected from sanitary landfills.

The discharges are defined with regard to the geological context from which they are situated and the nature of the waste. The discharges are classified in three categories, based upon the value of the permeability coefficient K, the substratum and its continuity.

- class 1; impermeable site (K < 10-[sup]9 ms-¹ minimal thickness of 5 m).

- class 2; semi permeable site (10-[sup]9 ms-¹ < K < 10-[sup]6 ms-¹).

- class 3; permeable site ( K > 10-[sup]6 ms-¹).

The studied leachates come from landfill of class 2:

- Crézin (Haute-Vienne) of compacted type: it was used for household rubbish and assimilated ordinary wastes.

- Foussais-Payre (Vendée): leachate coming from the fermentation area of a composting plant and from the compost refuse.

Fractionation of dissolved organic matter was applied on three leachates samples. The first sample was the raw leachate collected from the Crézin landfill and the two others came from Foussais-Payre (a raw sample and a sample treated in an aerated lagoon for 52 days). Because of the wide variety of organic compounds that can be found in such leachates, we classified and isolated the different groups of organic constituents using an XAD resin adsorption procedure. The experimental method consisted of acidifying samples to pH 1 to isolate the first fraction (fig. 1) and then treating the remaining supernatant with XAD-7 and XAD-4 resins. The adsorption on XAD resins allowed the isolation of the other organic fractions (figs. 2 to 6). Various analytical techniques were applied to characterize the isolated fractions such as elementary analysis infrared spectroscopy, ¹³C nuclear magnetic resonance (¹³C CP/MAS NMR), gas chromatography (GC/FID), and gas chromatography coupled to mass spectrometry (GC/MS). Results showed that more then 90% of the total organic carbon (TOC) in leachates can he recovered by the isolation procedure. Most of the isolated compounds corresponded to humic substances (76% to 90% of the chemical oxygen demand). Hydrophobic and hydrophilic neutral compounds were found only in small concentrations.

FR :

Une estimation précise de la recharge des nappes est indispensable pour une gestion optimale des ressources en eaux souterraines. Plusieurs méthodes ont été mises au point en région soudano-sahélienne pour son évaluation, méthodes conduisant à des résultats très disparates compte tenu de la variabilité des propriétés du milieux et de la conception même des outils d'évaluation utilisés. Le travail présenté est une contribution à l'amélioration de la compréhension de la dyna- mique hydrique à l'échelle d'une parcelle.

A partir d'un dispositif de mesure tensio-neutronique installé aussi bien dans le sol non remanié que dans des lysimètres constitués de sols reconstruits sur une profondeur de 7 m, une étude qualitative et quantitative de ces mécanismes d'infiltration et d'évaporation dans les niveaux d'altération des roches cristallines constituant la zone non-saturée, a été menée sur un site expérimental de l'École Inter-États d'Ingénieurs de l'Équipement Rural (EIER) à Ouagadougou (Burkina Faso).

Elle a permis de:

- localiser et décrire la dynamique de l'eau dans les différentes tranches de sol concernées par les processus d'humectation et d'assèchement;

- estimer la profondeur de reprise de l'eau par évaporation et les quantités d'eau mises en jeu à différentes profondeurs;

- réévaluer la réserve en eau du sol, c'est-à-dire la lame d'eau qu'il faut restituer au sol avant qu'il y ait recharge, en tenant compte de la profondeur d'échange entre le sol et l'atmosphère. Les résultats montrent que cette réserve, généralement calculée sur des bases agro-pédologiques, est très sous-estimée pour des applications hydrogéologique

EN :

A reliable estimation of the recharge rate of an aquifer is a prerequisite for the efficient management of the groundwater resources. A variety of methods for recharge estimation in Sudano-Sahelian areas are available, but most of them do not take into account all mechanisms of water transfer in the unsaturated zone; as a result, the estimated recharge values for a given region are often dissimilar.

Field equipment was used to measure water content and capillary tension at various depths in the unsaturated zone at an experimental site at Ouagadougou, Burkina Faso, in order to study infiltration and evaporation processes. Several water content profiles and water tension profiles were used to determine mass balances and water fluxes. The calculation of the head gradients allows the determination of flow direction.

This study, carried out both in deep lysimeters (7 m) and on undisturbed soil over two years, has allowed:

- A description of water dynamics at different soil depths.

      The soil can be divided into three parts. The water movement (infiltration and evaporation) takes place in the upper part of the soil. Its extension reaches 2.5 m depth. Drainage at this depth could not be measured and can be neglected. Below this zone, the water movements are very slow. The water content is constant over time and is equal to about 22%. The third zone, which lies between 5.5 m and groundwater table (7 m depth) is influenced by the groundwater table fluctuations.

- An estimation of the depth at which water can be taken up by evapotranspiration and of the amount of this water at different depths.

      This depth is equal to 2.5 to 3 m under our experimental conditions (soil and climatic conditions). At the end of the dry period, about 180 mm water has been extracted from the soil by evaporation: 50 mm from the first meter, 100 mm between 1 m and 2 m depth and 20 mm for the last 50 cm.

- A reevaluation of the effective minimum soil capacity by taking into account the soil-plant- atmosphere exchange depth.

      The results show that this effective minimum soil capacity, usually calculated on an agricultural basis, is under-estimated for hydrogeologic purposes.

The hydrodynamic behavior of the lysimeters and the undisturbed soil are similar. Under the studied climate conditions and soil hydrodynamic properties, groundwater recharge by direct infiltration can be neglected.

FR :

L'hémodialyse est une thérapeutique réservée aux sujets insuffisants rénaux en attente d'une greffe. Elle permet de recueillir dans un soluté aqueux les déchets que l'organisme ne peut plus évacuer par voie rénale. L'eau nécessaire à la préparation de ce dialysat représente un volume de 90 à 200 litres par séance et par sujet. Elle est obtenue en faisant subir à l'eau du réseau de distribution un traitement complémentaire. Celui-ci comporte en milieu spécialisé une chloration, un adoucissement par résines cationiques, une filtration sur colonne de charbon actif en grains et une osmose inverse.

Les trihalométhanes sont probablement les sous-produits de chloration les plus répandus dans les eaux distribuées. Certains parmi eux sont cancérigènes chez l'animal et mutagènes in vitro. Chez l'homme, leurs effets à faibles doses et à long terme restent discutés. Compte tenu des importants volumes d'eau nécessaires à la pratique de l'hémodialyse, il nous a paru intéressant d'observer l'efflcacité du circuit de pré-traitement sur ces composés et d'évaluer les doses auxquelles sont exposés les patients qui bénéficient de cette thérapeutique.

Des prélèvements ont été réalisés aux différentes étapes du pré-traitement, de façon hebdomadaire dans deux installations identiques, à la recherche de trihalométhanes. Ils permettent de constater que du chloroforme à une concentration moyenne de 10,5 llgA est encore présent en bout de chaîne. En tenant compte des volumes d'eau utilisés pour chaque séance, ceci signifie que les patients dialysés sont exposés, selon leur âge, à des doses pouvant atteindre jusqu'à dix fois la valeur préconisée dans l'eau potable par l'OMS. La moitié de ce chloroforme est susceptible de passer dans la circulation sanguine et d'exercer un effet toxique. Cette situation peut être corrigée par le choix d'une ressource en eau à charge organique faible, par un renouvellement fréquent du charbon actif et par l'utilisation de membranes en polyamides dans les modules d'osmose inverse. Ces résultats doivent amener à une réflexion plus générale sur la présenoe de sous-produits de la chloration et de micropolluants dans l'eau utilisée en dialyse. Ils doivent également inciter les cliniciens à rechercher, chez les dialysés les plus exposés, d'éventuels effets délétères liés à ces produits.

EN :

Hemodialysis is an indispensable therapy for patients with chronic renal failure. Two or three times a week and over several years, their blood is dialyzed in an artificial kidney against a dialysis fluid called dialysate.

Each time, 90 to 200 liters of this fluid will flow through the apparatus. Before being mixed with the dialysis concentrate, the water will be treated in order to eliminate harmful substances such as aluminum or endotoxins.

Trihalomethanes (THM) are probably the most widespread chlorination byproducts of tap water. Most of them are known as carcinogens for animals and mutagens in vitro. Although their hepatotoxicity and nephrotoxicity are obvious after acute intoxication, their effects at low doses on human health have still not been clearly demonstrated.

Considering the great amount of water required by hemodialysis patients, we found interested in determining wether the control of these substances by the hospital water treatment plant was efficient. We decided then to analyze weekly and during two months, the tap water of two hemodialysis departments for THM, before and after various forms of treatment. The treatment in both departments was the same and made up of four important stages: chlorination, softening, charcoal filtering and reverse osmosis.

THM determinations were conducted using the headspace technique with a gas chromatograph equipped with a split injector and an [sup]63Ni electron capture detector.

Our results show that chloroform and dichlorobromomethane were present in tap water. Their respective mean concentration in both department came to 56 µg/l and 5 µg/l. After chlorination and water softening, these figures had moderately but significantly increased. In the first department, thanks to new granular activated carbon, a large part of THM (especially dichlorobromomethane) had been removed. However after seven weeks, this treatment was no longer efficient and only 7% of the influent chloroform and 50% of the dichlorobromomethane could be removed. In the second department, the charcoal filter had already been working for more than one year at the beginning of our study. No decrease of the chloroform concentration had been observed and dichlorobromomethane had significantly increased. 80 to 90% of influent THM were removed after the double stage of reverse osmosis using polyamide membranes.

With new granular activated carbon, the dialysis fluid only contains 1 µg/l of chloroform. But after seven weeks or more, it will reach an average of 10.5 g/l of chloroform and 1 µg/l of dichlorobromomethane. These figures are probably underestimated as our study was performed in winter and THM concentrations are less important during that season.

These results mean that during a single session, 0.9 to 2.1 mg of chloroform will reach the artificial kidney. Depending on the weight of the patients, this exposure will be equivalent up to 10 times the value recommended by the World Health Organization (WHO) for drinking water.

The last part of our study monitored the chloroform concentration in dialysate coming out the artificial kidney during an hemodialysis period. A significant decrease, reaching up to 45% of the influent amount, was observed. This result suggests that some of the chloroform must have crossed the dialysis membrane.

According to all these results, we think that it would be of great interest to explore the metabolism of chloroform on hemodialysis patients and to search for eventual toxic effects. Practical advices to people in charge of water treatment plants in hemodialysis department would be to use raw water with low concentrations of humic materials, in order to restrict THM formation. The charcoal filter should be changed more often (probably after 6 or 7 weeks). Alternatively, ways could be found for rapid regeneration of charcoal for THM removal. Finally and according to previous studies, a polyamide membrane should be systematically used for reverse osmosis.

Our study could eventually be completed by searching in the dialysis fluid any other chlorination by-products which are responsible to a large extent for tap water mutagenicity.

FR :

La disponibilité depuis 1992 d'un premier vaccin contre l'hépatite virale A a soulevé la question de son indication chez le personnel exposé aux eaux usées. Nous avons évalué ce risque professionnel grâce à une étude transversale comparant les taux de prévalence des anticorps totaux (ou des IgG) anti-VHA chez 110 sujets exposés aux eaux usées appariés sur l'âge et le niveau de diplôme à 110 sujets non-exposés de la même entreprise. Chaque personne était interrogée sur ses antécédents d'ictère, la notion de voyages en zone d'endémie et la durée de l'exposition professionnelle. La prévalence des anticorps anti-VHA était globalement de 52,7 %, significativement plus élevée chez les exposés (60,9 %) que chez les non-exposés (44,S %) (p < 0,02). Cette séroprévalence augmentait avec l'âge, et apparaissait liée au niveau de diplôme dans les deux groupes. Ces résultats suggèrent fortement l'existence d'un risque professionnel d'infection par le VHA chez les travailleurs exposés aux eaux usées (risque relatif: 2,4; IC 95 % [1,6 - 3,1]). La vaccination du personnel exposé semble justifiée. La stratégie vaccinale à adopter est liée au coût élevé du vaccin et à la situation épidémiologique du VHA dans le pays.

EN :

The availability of a first hepatitis A vaccine in 1992 raised the possibility of its use for workers exposed to sewage or sludge. This occupational risk was suspected because of the excretion of hepatitis A virus (HAV) in stools and its resulting presence in sewage, because of the resistance of HAV to environmental stresses, and because of the documented wastewater-mediated transmission of HAV in the general population. On the other hand, the decreased diffusion of HAV in industrialized countries probably results in less contamination of sewage. The aim of this study was to evaluate the possible risk of HAV infection from sewage exposure, which could lead to recommendations of vaccination for exposed workers.

Methods

In a large private company involved in water supply, anti HAV IgG were sought in sera from workers in contact with sewage and from workers not exposed to sewage. Subjects were individually matched for age and education level. Cases included workers involved with the wastewater collection network, workers who monitor drinking water distribution networks in Paris (located in sewer mains in Paris), personnel of a large research laboratory involved with wastewater and sludge, as well as a few workers involved with drinking water production who may be frequently exposed to raw Seine river, Marne river or Oise river water (that could be contaminated with sewage). Histories of jaundice, travels to areas of endemic incidence of hepatitis A, and the duration of occupational exposure were noted. Anti-HAV IgG was measured in serum by an enzyme-linked immunosorbent assay (ELISA) method.

Results

At this time, 110 exposed workers and 110 non-exposed workers have been studied. Ages ranged from 20 to 58 years, with a mean value of 36.5 year. Cases and controls did not differ with respect to social class or travels in areas of endemic exposure. Duration of exposure ranged from 1 year to 36 years, with a mean value of 10.3, and was correlated to age in this company where workers are usually hired when young. The seroprevalence of anti HAV was globally 52.7 %, significantly higher in exposed workers ( 60.9 %) than in controls ( 44.5 % , p < 0.02 ). This seroprevalence varied widely according to age: for workers in their twenties it was 30.0 % vs. 27.5 %, in their thirties 68.0 % vs. 33.3%, in their forties 80.0 % vs. 54.8% and in their fifties 93.3 % vs. 86.7 %, respectively in exposed and non-exposed workers. The seroprevalence was related to education level in each group, but not to social class. History of jaundice was not correlated with anti HAV status, nor with sewage exposure. The relative risk of HAV infection in this matched range was 2.4, CI 95 % (1.6 - 3.1).

These results emphasize the role of occupational exposure to sewage in HAV infection. Exposed workers should be vaccinated because of the frequency of the symptomatic form of hepatitis A in adults with severe and relapsing cases. The strategy of vaccination should take into account the high cost of the vaccine and the epidemiological situation of HAV in the country.