Les contaminants de l'eau et leurs effets sur la santé

La transmission des maladies par la voie hydrique est sous contrôle dans la majorité des pays industrialisés. Malgré tout des maladies épidémiques ou endémiques sont encore observées. Plusieurs microorganismes sont en émergence, et Cryptosporidium a été impliqué dans des épidémies importantes dans plusieurs pays. Le conrôle de ces maladies transmissibles par la voie hydrique requiert des autorités des nouvelles approches qui allient le contrôle des risques de cancer dûs aux sous-produits de la désinfection au contrôle des micro-organismes les plus résistants . Aux Etats-Unis, l'objectif proposé est l'absence de microorganismes dans l'eau potable. Cet objectif ne peut être contrôlé par les indicateurs usuels et l'on recommande donc un niveau de traitement équivalent. Le traitement est alors contrôlé en temps réel par des moyens physico-chimiques tels la turbidité ou la mesure des particules, et un contrôle a posteriori par de nouveaux indicateurs telles les spores des bactéries sporulantes aérobies.Le vieillissement des installations, des populations immunocompromises et une urbanisation grandissante sont autant de causes de l'émergence de nouvelles maladies infectieuses dont certaines transmissibles par la voie hydrique. La proportion des maladies gastro-intestinales qui est attribuable à l'eau de consommation est encore très grande et elle contribue à maintenir ces infections en circulation dans la population. Le dilemme du contrôle des risques de cancer dus aux sous-produits de la désinfection ne doit pas conduire à une réduction de l'efficacité des traitements, car le niveau de risque à partir duquel ont été fixées les concentrations maximales admissibles de ces sous-produits dans l'eau (10-6 cas de cancer par vie entière d'exposition) est bien plus faible que celui de contracter une maladie infectieuse d'origine hydrique en absence de traitement adéquat. La situation en matière de pathologies induites par la consommation d'eau est extrêmement contrastée selon les pays. En effet la transmission de maladies infectieuses par la voie hydrique a été maîtrisée dans la plupart des pays industrialisés par la mise en place d'installations de traitement et d'un contrôle sanitaire s'appuyant sur une réglementation abondante. A l'opposé la situation des pays en voie de développement reste souvent très mauvaise dans ce domaine et l'Organisation Mondiale de Santé estime que 1,5 milliards d'habitants ne disposent pas encore d'eau potable dont cent millions en Europe et que 30 000 morts journalières sont dues à l'absence d'une eau en quantité et qualité satisfaisantes (Ford et Colwell 1996).En revanche les pays développés voient la qualité chimique des eaux distribuées de plus en plus souvent mise en cause par les associations de consommateurs. Outre le progrès très rapide des techniques analytiques qui permet de découvrir la présence de traces dont on ne soupçonnait guère la présence dans l'eau du robinet, la pollution croissante de la ressource, les traitements de désinfection et le contact avec les matériaux des réseaux de distribution apportent des molécules dont la toxicité à moyen et long terme mérite d'être évaluée.La mise en oeuvre de traitements de désinfection dont l'utilité est indiscutable et l'effet sur la morbidité et la mortalité par pathologie infectieuse chez des populations desservies parfaitement significatif, s'accompagne de la formation de sous-produits. Certains de ceux-ci étant cancérigènes et/ou mutagènes en expérimentation de laboratoire et des études épidémiologiques ayant pu montrer une légère augmentation du risque de cancer dans la population, l'impact médiatique de cette information peut conduire à une mauvaise appréciation dans la gestion des risques pour la santé. Ainsi l'arrêt de la chloration pour éviter la formation de sous produits et quelques cas de cancers aurait conduit un pays d'Amérique du Sud a enregistrer une importante épidémie de choléra et des centaines de décès.Il n'est pas facile de gérer ce paradoxe entre sophistication du traitement lié à la pollution de la ressource entraînant la présence de sous produits de désinfection et la persistance d'éléments traces et de divers microorganismes dans une eau de qualité conforme aux critères de potabilité mais que le consommateur ne veut plus consommer. Dans cet article nous tenterons de faire le point sur le risque hydrique pour la santé lié d'une part aux contaminants biologiques et d'autre part aux contaminants chimiques. Sa meilleure connaissance est la clef d'une stratégie de gestion efficace et d'une reconquête du consommateur que la publicité a trop tendance à orienter vers les eaux embouteillées.The transmission of waterborne diseases is now controlled in most developed countries but a residual level of both epidemic and endemic diseases can still be observed. Recent observations have involved emerging pathogens such as Cryptosporidium which has been implicated in several very large outbreaks worldwide. To control these waterborne outbreaks many countries are proposing treatment goals that would achieve a significant reduction in the risk to the population without increasing the risks of cancer due to disinfection by-products. In the United States, the objective is zero pathogen in drinking water. This objective can be approached by appropriate treatment but monitoring cannot be done using the current biological indicators. Reliance on continuous measurement of physico-chemical parameters such as disinfectant residual and contact time, turbidity and particulate measurement in real-time are proposed solutions. Microbiological indicators remain an active mean of controlling afterwards water quality : spores of aerobic or anaerobic bacteria are extremely resistant to treatment and ofter means of assessing removal of pathogens over a range of several order of magnitude.Numerous pathogens have been involved in waterborne outbreaks and some are just emerging. Urbanisation, aging of water treatment plants, the increasing number of immunocompromised individuals are potential causes for increased risk of waterborne infectious diseases. The endemic level of gastrointestinal disease due to drinking water consumption is still significant and could contribute to pathogens in circulation in the populations affected. The dilemma of balancing microbial and cancer health risk remains a difficult one to resolve but it should not result in a reduction of treatment efficiency, because of the low risk-level for cancer used for the Maximum Admissible Concentration (MAC) values (10-6 fall life) as compared to the risk of waterborne infectious disease in absence of adequate water treatment.For setting these MAC values in water it is necessary to consider all sources of exposition of the considered compound and according to is mode of action two ways of evaluation may be followed. The first one, for the molecules with a deterministic effect (or non stochastic effect) the dose-effect relationships dose-effet on individuals and dose responses relationships on populations, are considered, and only no indesirable effect in the consumming population may be accepted. For the second one, for the molecules with a probabilistic (stochastic) effect, (absence of dose-effect relationship but increase of the incidence of cancer or genetic abnormalities in population according to levels of exposure), MAC values are setted by computation off all exposures and considering an accepable risk of apparition of the pathology ranging from 10-5 (WHO) to 10-6 (North America and Europe) for consumption of two liters of drinking water during 70 years.Because of the lack of information about these very conservative approaches, associations of consumers are often misinterpreating : in this situation water is not in accordance with drinking water standards but may be used during a short period without any risk increase for the population. Examples are developped in this paper with description of hazards due to nitrate, nitrite, pesticides and desinfection by-products which are actually frequently associated with debates within water specialists, politicians and consumers.If situation is now more clearly defined for nitrates and pesticides, the lack of scientific information for the effects of bromates combined with the conservative approach for the molecules with "probabilistic" effect, leads to a severe MAC value in comparison with the analytical capacities of laboratories and technical data of water desinfection both with ozone and bleaching agent.This situation may not lead to the diminution of adequate desinfection water treatment because of the consequences on the increase of the risk of waterborne infectious disease. More progresses are needed, both in terms of knowledges in toxicological and epidemiological data and technological ways of treatment, for being able to produce safe drinking water, with a taste and a price acceptable for the consumer. But the levels of risk considered for setting standards insures that drinking water is one of the safer products offer for consumption

Évaluation du risque toxique lié à la prévalence de trihalométhanes dans l'eau utilisée pour la dialyse

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.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

Thomson and Compton scattering with an intense laser pulse

Our paper concerns the scattering of intense laser radiation on free electrons and it is focused on the relation between nonlinear Compton and nonlinear Thomson scattering. The analysis is performed for a laser field modeled by an ideal pulse with a finite duration, a fixed direction of propagation and indefinitely extended in the plane perpendicular to it. We derive the classical limit of the quantum spectral and angular distribution of the emitted radiation, for an arbitrary polarization of the laser pulse. We also rederive our result directly, in the framework of classical electrodynamics, obtaining, at the same time, the distribution for the emitted radiation with a well defined polarization. The results reduce to those established by Krafft et al. [Phys. Rev. E 72, 056502 (2005)] in the particular case of linear polarization of the pulse, orthogonal to the initial electron momentum. Conditions in which the differences between classical and quantum results are visible are discussed and illustrated by graphs

Experimental observation of nonlinear Thomson scattering

A century ago, J. J. Thomson showed that the scattering of low-intensity light by electrons was a linear process (i.e., the scattered light frequency was identical to that of the incident light) and that light's magnetic field played no role. Today, with the recent invention of ultra-high-peak-power lasers it is now possible to create a sufficient photon density to study Thomson scattering in the relativistic regime. With increasing light intensity, electrons quiver during the scattering process with increasing velocity, approaching the speed of light when the laser intensity approaches 10^18 W/cm^2. In this limit, the effect of light's magnetic field on electron motion should become comparable to that of its electric field, and the electron mass should increase because of the relativistic correction. Consequently, electrons in such high fields are predicted to quiver nonlinearly, moving in figure-eight patterns, rather than in straight lines, and thus to radiate photons at harmonics of the frequency of the incident laser light, with each harmonic having its own unique angular distribution. In this letter, we report the first ever direct experimental confirmation of these predictions, a topic that has previously been referred to as nonlinear Thomson scattering. Extension of these results to coherent relativistic harmonic generation may eventually lead to novel table-top x-ray sources.Comment: including 4 figure

Does microbicide use in consumer products promote antimicrobial resistance? A critical review and recommendations for a cohesive approach to risk assessment

The increasing use of microbicides in consumer products is raising concerns related to enhanced microbicide resistance in bacteria and potential cross resistance to antibiotics. The recently published documents on this topic from the European Commission have spawned much interest to better understand the true extent of the putative links for the benefit of the manufacturers, regulators, and consumers alike. This white paper is based on a 2-day workshop (SEAC-Unilever, Bedford, United Kingdom; June 2012) in the fields of microbicide usage and resistance. It identifies gaps in our knowledge and also makes specific recommendations for harmonization of key terms and refinement/standardization of methods for testing microbicide resistance to better assess the impact and possible links with cross resistance to antibiotics. It also calls for a better cohesion in research in this field. Such information is crucial to developing any risk assessment framework on microbicide use notably in consumer products. The article also identifies key research questions where there are inadequate data, which, if addressed, could promote improved knowledge and understanding to assess any related risks for consumer and environmental safety

Effet du chlore sur la colonisation bactérienne d'un réseau expérimental de distribution d'eau

La contamination bactérienne de la phase eau d'un réseau de distribution résulte d'une multiplication des bactéries sur les parois des canalisations d'eau (biofilms) suivie de leur arrachage et de leur transport dans le flux circulant. Ce travail met en évidence l'effet du chlore, d'une part, sur la formation des biofilms et, d'autre part, sur des biofilms déjà constitués. Des éprouvettes de matériaux neufs introduites dans des eaux présentant des concentrations en chlore total variant de 2,4 à 0,02 mg/l et véhiculant entre 0,5 x 106 et 5 x 105 cellules bactériennes/mi (dont 1 à 10 % de bactéries cultivables) sont rapidement colonisées (106 à 108 cellules/cm2). L'effet du chlore est sensible sur les cellules totales pour des concentrations de l'ordre de 1 à 2,4 mg/l. Sur les bactéries cultivables, un ralentissement de la croissance du biofilm est observé dès 0,3 mg/1 de chlore total. Par contre, des résiduels de 0,02 ou 0,05 mg/l sont sans effet sur la cinétique de formation des biofilms. Des résiduels moyens de chlore total compris entre 2,3 et 3,4 mg/l appliqués en continu pendant 14 jours sur un biofilm constitué d'environ 8,7 x 106 cellules par cm2 (1,7 % de bactéries cultivables), entraînent l'élimination d'environ 90 % des bactéries fixées (abattement d'1 logarithme) durant les premiers jours d'exposition. L'altération du biofilm exposé à un résiduel de chlore total de l'ordre de 1,3 mg/l est identique, mais toutefois plus étalée dans le temps. Ces essais réalisés sur des éprouvettes de PVC, PE et mortier de ciment n'ont pas permis la mise en évidence de comportements différents de ces 3 supports..Bacterial accumulation in drinking water systems results both of cell deposition on the pipe walls and attached bacteria growth. The presence of a complex biofilm (cells embedded in a matrix of exopolymers) leads to a continuous contamination of the water phase resulting from the erosion of the attached growing biomass. Then, many tentatives to lmit the formation of such a biofilm have been suggested as the removal of biodegradable organic matter fram water or as the application of disinfectant. However, the efficiency of chlorination of the distribution system is debatable. Indeed, adhesion is often described as a factor of protection of attached bacteria which counterbalances the expected effect of disinfectant. Then, the aim of this experimental work is using a model distribution system to evaluate (i) the kinetics of biofilm accumulation on coupons of new materials (Polyvinyl chlorure : PVC, polyethylene : PE, cement) disposed in a constantly chlorinated system (residual total chlorine from 0.021o 2.4 mg. l-1), (ii) the effect of chlorination on previously accumulated biofilms.The industrial pilot plant used in this study is comprised of five loops serially disposed (fig. 1). From previous study of simulation, one may assume that each loop works like a perfectly mixed reactor when the whole pilot plant is equivalent to an infinite tubular reactor with high axial dispersion coefficient. During the experiment, the pilot was continuously fed with finished drinking water front the surface water treatment plant of city of Nancy (i.e. natural finished water with its own chlorine demand, organic nutrients and heterotrophic bacteria).Total number of cells (epifluorescence counts) and heterotrophic plate count bacteria (15 days of incubation at 20 °C) were enumerated both in the water and, after sonication, on the surface of the coupons of tested materials.The first experimentations show that chlorine slows clown the kinetic of deposition of bacteria onto the pipe wall but never prohibits biofilm formation. When the drinking waters carried from 2.4 to 0.02 mg.1-1 of chlorine and from 0.5 to 5 x 105 ml-1 bacterial cells, biofilm is observed after 24 hours of immersion of the coupons with at least 101 to 106 bacteria/cm2. Respectively, the deposition or/and growth rates of total cells are drastically affected only for chlorine residual as high as 1 to 2.4 mg. 1-1. The number of heterotrophic plate count of the biofilm is affected with lower chlorine residual (around 0.3 mg.1-1) but residual concentration as low as 0.05 mg.1-1 are ineffective.The tentatives carried out in the second experience on preformed biofilms (2 months old biofilms, 8.7 x 106 cells/cm2) show that the continuous application of 2.3 to 3.4 mg. 1-1 of residual chlorine for 14 days, leads to the removal of only 90 % of attached total cells without modifications of the proportion of attached alive bacteria (around 1.7 %) into the biofitm. In other wards, a highly chlorinated networks shows at minima 106 attached cells/cm2. Its generally takes several days to reply to the chlorine demand of the system and to have a quasi steady state reactor in terms of residual chlorine.These assays carried out with three types of coupons (PVC, PE, cement lined cast iron) did not show any difference between the tested materials.The limited efficiency of chlorine against the biofilm can be explained by transfert limitations within the visquous layer, high consumption of chlorine by the biopolymers of the attached matrix (proteins...) or low sensitivity to the disinfectant of the slow growing attached bacteria. Then chlorination is really not a panacea in biofilm war but has to be applied in combination with other methods as biodegradable organic matter removal, hydraulic regime improvement..

Nonlinear Radiation Pressure and Stochasticity in Ultraintense Laser Fields

The radiation force on a single electron in an ultraintense plane wave ($a = eE/mc\omega \sim 1$) is calculated and shown to be proportional to $a^4$ in the high-$a$ limit for arbitrary waveform and polarization. The cyclotron motion of an electron in a constant magnetic field and an ultraintense plane wave is numerically found to be quasiperiodic even in the high-$a$ limit if the magnetic field is not too strong, as suggested by previous analytical work. A strong magnetic field causes highly chaotic electron motion and the boundary of the highly chaotic region of parameter space is determined numerically. Applications to experiments and astrophysics are briefly discussed.Comment: 5 pages, 4 figures; uses RevTex, epsf macros. Corrected, expanded versio

Temporary Acceleration of Electrons While Inside an Intense Electromagnetic Pulse

A free electron can temporarily gain a very significant amount of energy if it is overrun by an intense electromagnetic wave. In principle, this process would permit large enhancements in the center-of-mass energy of electron-electron, electron-positron and electron-photon interactions if these take place in the presence of an intense laser beam. Practical considerations severely limit the utility of this concept for contemporary lasers incident on relativistic electrons. A more accessible laboratory phenomenon is electron-positron production via an intense laser beam incident on a gas. Intense electromagnetic pulses of astrophysical origin can lead to very energetic photons via bremsstrahlung of temporarily accelerated electrons

Asymptotic conditions of motion for radiating charged particles

Approximate asymptotic conditions on the motion of compact, electrically charged particles are derived within the framework of general relativity using the Einstein- Infeld-Hoffmann (EIH) surface integral method. While superficially similar to the Abraham-Lorentz and Lorentz-Dirac (ALD) equations of motion, these conditions differ from them in several fundamental ways. They are not equations of motion in the usual sense but rather a set of conditions which these motions must obey in the asymptotic future of an initial value surface. In addition to being asymptotic, these conditions of motion are approximate and apply, as do the original EIH equations, only to slowly moving systems. Also, they do not admit the run- away solutions of these other equations. As in the original EIH work, they are integrability conditions gotten from integrating the empty-space (i.e., source free) Einstein-Maxwell equations of general relativity over closed two-surfaces surrounding the sources of the fields governed by these equations. No additional ad hoc assumptions, such as the form of a force law or the introduction of inertial reaction terms, needed to derive the ALD equations are required for this purpose. Nor is there a need for any of the infinite mass renormalizations that are required in deriving these other equations.Comment: 15 page

Properties of electrons scattered on a strong plane electromagnetic wave with a linear polarization: classical treatment

The relations among the components of the exit momenta of ultrarelativistic electrons scattered on a strong electromagnetic wave of a low (optical) frequency and linear polarization are established using the exact solutions to the equations of motion with radiation reaction included (the Landau-Lifshitz equation). It is found that the momentum components of the electrons traversed the electromagnetic wave depend weakly on the initial values of the momenta. These electrons are mostly scattered at the small angles to the direction of propagation of the electromagnetic wave. The maximum Lorentz factor of the electrons crossed the electromagnetic wave is proportional to the work done by the electromagnetic field and is independent of the initial momenta. The momentum component parallel to the electric field strength vector of the electromagnetic wave is determined only by the diameter of the laser beam measured in the units of the classical electron radius. As for the reflected electrons, they for the most part lose the energy, but remain relativistic. There is a reflection law for these electrons that relates the incident and the reflection angles and is independent of any parameters.Comment: 12 pp, 3 fig