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Public authorities, in response to the Water Framework Directive, impose to take measures to protect catchments that provide drinking water when the levels of contamination exceed (or are susceptible to exceed) drinking water standards. Companies and public research institutes involved in the transformation of conventional agricultural practices are therefore engaged in the development of methods aiming at assessing the vulnerability of territories towards diffuse pollutions. This poster presents an uncertainty and sensitivity analysis on a model able to assess the vulnerability towards hydrological transfers of pesticides. This research work helps to enhance the reliability of the information that is given to public authorities regarding priority areas for reduction of pesticide use. The research is being conducted in an agricultural study area located in the center of France (30km2). The studied model makes calculations based on cartographic data (DTM, soil properties, hydrographic network, climate, land cover) to identify vulnerable plots and subcatchments, on the basis of institutional guidelines for pesticide risk transfer assessment. Considered uncertainties for the analysis are the accuracy and resolution of the input cartographic data, as well as the parameterization of the model. The results highlight that these uncertainties can influence, in some cases significantly, the outputs of the model and therefore information given to public authorities. This research collaboration between two French public research institutes (INRAE, AgroParisTech) and a private company (Envilys) on an operational case study allows to identify levers to enhance the reliability of outputs from vulnerability models and in turn the efficiency of measures for catchment protection. It also allows the determination of the resolution of vulnerability mapping outputs according to obtained uncertainties.

International audience; A comprehensive review of quantitative structure-activity relationships (QSAR) allowing the prediction of the fate of organic compounds in the environment from their molecular properties was done. The considered processes were water dissolution, dissociation, volatilization, retention on soils and sediments (mainly adsorption and desorption), degradation (biotic and abiotic), and absorption by plants. A total of 790 equations involving 686 structural molecular descriptors are reported to estimate 90 environmental parameters related to these processes. A significant number of equations was found for dissociation process (pKa), water dissolution or hydrophobic behavior (especially through the KOW parameter), adsorption to soils and biodegradation. A lack of QSAR was observed to estimate desorption or potential of transfer to water. Among the 686 molecular descriptors, 5 were found to be dominant in the 790 collected equations and the most generic ones: four quantum-chemical descriptors, the energy of the highest occupied molecular orbital (EHOMO) and the energy of the lowest unoccupied molecular orbital (ELUMO), polarizability (α) and dipole moment (μ), and one constitutional descriptor, the molecular weight (MW). Keeping in mind that the combination of descriptors belonging to different categories (constitutional, topological, quantum-chemical…) led to improve QSAR performances, these descriptors should be considered for the development of new QSAR, for further predictions of environmental parameters. This review also allows finding of the relevant QSAR equations to predict the fate of a wide diversity of compounds in the environment.

An experimental study was conducted in a 91.4-ha Mediterranean vineyard catchment in southern France to characterize the fate and transport of oryzalin in runoff water and thus to assess the risk of contamination of surface waters. Oryzalin concentrations in soil were monitored on two fields, one no-till and one tilled from March 1998 to March 2000. Concentrations in solution and on solid phase of runoff water were measured at the outlets of both fields and the catchment. The droughts in the two summer periods reduced the dissipation of oryzalin and increased its field half-life up to 35 days. Consequently, oryzalin was detected throughout the year in runoff water, with maximum dissolved concentrations > 600 microg l(-1) at the field scale. Oryzalin transport essentially occurred in solution. At the no-till field, seasonal losses were 2.29% and 1.89% of the applied amount in 1998 and 1999, respectively. The corresponding values at the tilled field were 1.56% and 0.29%, since tillage reduced total losses by reducing surface runoff. At the catchment scale, oryzalin concentrations were smaller than those at the field scale, due to dilution effects and staggering of application. Large part of the overland flow from the fields reinfiltrated in the ditches before reaching the outlet of the catchment. As a result, seasonal oryzalin losses were

The contamination of soil and runoff water by two herbicides, diuron [N'-(3,4-dichlorphenyl)-N,N-dimethylurea] and simazine (6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine), were monitored on two fields, one no-till and one tilled. Experiments were carried out in a 91.4-ha watershed in southern France during the 1997 growing season in order to understand the patterns of pesticide transport from field to watershed. The persistence of the herbicides in soil was prolonged due to the climatic conditions. At the field scale, annual herbicide loads were due to overland flow and amounted to 65.6 and 6.3 g ha(-1) of diuron for the no-till and tilled field, respectively, and to 29.6 and 1.83 g ha(-1) of simazine. Maximum herbicide concentrations exceeded 580 microg L(-1) during the first storm event after application and decreased thereafter but remained for 8 mo above 0.1 microg L(-1). At the watershed outlet, estimated annual loads amounted to 4.12 g ha(-1) of diuron and 0.56 g ha(-1) of simazine. Among them, 96% of the losses in diuron and 83% of those in simazine were caused by the fast transmission through the network of ditches of the overland flow exiting the fields. For diuron, which was sprayed over most of the vineyards, its in-stream concentrations during storm flow were close to those at the outlet of the fields. The herbicide loads in baseflow were smaller than 0.2 g ha(-1). The patterns of the loads at the field and watershed scales suggested that a major part of the herbicides leaving the fields reinfiltrated to the ground water by seepage through the ditches, and was there degraded or adsorbed.

Predicting the impact of land use changes on the hydrological response is crucial for water resource management. In the particular case of small catchments (1–10 km2), distributed models could provide useful answers regarding the effects of cultivation practices and man-made works on water fluxes. However, the impacts of specific land use spatial arrangements are difficult to predict because of the prohibitive number of possible cases to consider. Focusing on surface runoff, this article describes a strategy based on a water particle tracking routine to be plugged-in a distributed model that is designed to determine the spatial arrangements of land management practices that have the greatest impact on volume, peak discharge and lag time at the catchment outlet. A case study is described; the hydrological response of the Roujan catchment (Herault, France) is simulated with the MHYDAS model. The Roujan catchment contains a vineyard in a Mediterranean climate in a landscape in which weeding practices highly influence the partition between soil infiltration and runoff. Results showed that the proposed strategy is much more efficient than a random approach to design the spatial arrangements of the vineyard weeding practices with the greatest impact. Therefore, the proposed strategy may lead to innovative policies for the spatial planning of land management practices. Copyright © 2011 John Wiley & Sons, Ltd.

Communication orale, résuméCommunication orale, résumé; Le nombre et la diversité des contaminants organiques (pesticides, HAP, PCB, médicaments,…) potentiellement présents dans l’environnement est une réalité à laquelle sont confrontées les recherches portant sur le devenir et les impacts de ces substances. Selon les estimations, entre 30 000 et 100 000 substances sont concernées, il est donc impossible de les étudier au cas par cas. Cette difficulté se rencontre notamment dans le contexte de la Directive Européenne REACH (Registration, Evaluation, Authorisation and Restriction of Chemical substances) qui vise à mettre en place un système d’enregistrement de 30 000 substances chimiques pour lesquelles des informations précises sur la dispersion de ces substances dans l’environnement et leurs impacts écotoxicologiques sont exigées. Parallèlement à ces besoins en lien direct avec le travail d’évaluation des risques, notre communauté scientifique ressent fortement la nécessité de classer les contaminants organiques en fonction de leurs propriétés essentielles dans les mécanismes responsables de leur comportement dans l’environnement, de leur passage dans les organismes vivants et de leurs effets toxicologiques. Nous avons récemment développé une méthodologie permettant de classer des contaminants organiques selon des propriétés directement liées aux processus d’intérêt environnementaux, par exemple leur rétention irréversible, leur dégradation biotique ou abiotique, leur transfert vers l’air ou les eaux, leur passage dans les organismes vivants ou encore leurs effets toxicologiques. Cet outil, appelé TYPOL, est basé à la fois sur une approche «in silico» calculant des descripteurs moléculaires et sur des méthodes de classification combinant descripteurs moléculaires et paramètres comportementaux. Les classes sont construites à partir d’une analyse statistique (type PLS) des propriétés déduites de la prise en compte des caractéristiques structurales des molécules considérées et des paramètres environnementaux. Le choix des relations entre paramètres et descripteurs est en grande partie basée sur des relations de type QSAR (structure-activité). De par son mode de construction, l’outil est adaptable à différentes questions de recherche et concerne l’ensemble des contaminants organiques existants ou potentiels. Il vise à extrapoler des connaissances au sein d’une classe de composés à partir des résultats obtenus sur quelques molécules. Il est composé d'une base de données en MySQL accessible sur un serveur commun. L'ajout de nouvelles données se fait soit par transfert d'un fichier tableur (type Excel), soit par modification de la base à l'aide d'un outil web (phpMyAdmin). Les interfaces d'interrogation de la base de données et des traitements statistiques sont programmées dans le langage R qui intègre de nombreuses bibliothèques de méthodes de traitements statistiques des données. Les sorties graphiques sont aussi réalisées par le logiciel R. Des perspectives d’améliorations sont envisagées : - Ajouts de paramètres environnementaux. Un travail important sera à réaliser autour des données manquantes pour combler une partie des manques. Au sein de l’ANSES, des contacts dans les services BIOCIDE et REACH sont envisagés. Pour les pesticides, il sera possible d’insérer des données extraites de la base AGRITOX pour notamment pour des paramètres écotoxicologiques. Des possibilités non explorées existent auprès de l’INERIS. Des travaux en cours au Cemagref de Lyon pourraient potentiellement se raccrocher à ce travail. - Ajouts de descripteurs moléculaires. Pour d’autres pesticides ou des contaminants émergents, la phase d’obtention des descripteurs pourra être améliorée en réalisant l’analyse conformationnelle pour localiser le minimum global grâce à l’utilisation de méthodes comme la dynamique moléculaire ou des méthodes de type Monte Carlo. - Travailler sur les liens entre molécules parent et métabolites Il serait intéressant de les prévoir pour par exemple faire apparaître les filiations lors des changements de classes suite à des processus de biodégradation. Ce travail a démarré en 2011 dans le cadre du projet BIODECHLORD « Etudes exploratoires de la dégradation microbienne de la chlordécone » (financement AIP DEMICHLORD et coordination Fabrice Martin (INRA Dijon) où TYPOL sera utilisé pour tester des scénarios de biodégradation de la chlordécone et de cyclodiènes apparentés (approche in silico).

Contact: pare@supagro.inra.fr; International audience; Soil surface characteristics (SSC) influence strongly hydrological processes and are known to vary largely in space and time according to soil characteristics and soil management. Because tillage is a main source of variation, the goal of this study was to present and evaluate a prediction model of the temporal variation of the SSC after tillage at the catchment level. The study focused on bare soils prevailing in spring and summer. A logistic regression approach was used to predict the evolution along three stages, starting from the fresh tillage stage to the crusted soil stage. This method provides the probabilities of occurrence of each stage. The predictor candidates tested were a rainfall characteristic, namely cumulative rainfall depth or cumulative kinetic energy, basic soil properties and tillage features. The results showed that a model based on cumulative kinetic energy since tillage and soil stoniness accurately predicts the dynamics of SSC: the rate of well classified SSC was 91%. However, no significant difference in the prediction performance was found using as predictor either cumulative kinetic energy or cumulative rainfall amount since tillage. In the prediction model, the rainfall characteristic was the most significant predictor for the SSC evolution and the only one during the first stages of crust development since tillage. Stoniness was also shown to influence SSC evolution but only during the last stages of crust development: high stone cover speeds up soil surface evolution. The same approach using logistic regression can be applied elsewhere but will require a re-examination of the most relevant predicting variables. Finally, to be able to predict the soil surface characteristic evolution on an annual scale, weed growth characteristics must be considered in the list of predictor candidates.

Contact: silvio.gumiere@gmail.com; International audience; In this paper, we present MHYDAS-Erosion, a dynamic and distributed single-storm water erosion model developed as a module of the existing hydrological MHYDAS model. As with many catchment erosion models, MHYDAS-Erosion is able to simulate sediment transport, erosion and deposition by rill and interrill processes. Its originality stems from its capacity to integrate the impact of land management practices (LMP) as key elements controlling the sedimentological connectivity in agricultural catchments. To this end, the water-sediment pathways are first determined by a specific process-oriented procedure defined and controlled by the user, which makes the integration of LMP easier. The LMP dynamic behaviours are then integrated into the model as a time-dependent function of hydrological variables and LMP characteristics. The first version of the model was implemented for vegetative filters and tested using water and sediment discharge measurements at three nested scales of a densely instrumented catchment (Roujan, OMERE Observatory, southern France). The results of discharge and soil loss for simulated rainfall events have been found to acceptably compare with available data. The average R(2) values for water and sediment discharge are 0.82 and 0.83, respectively. The sensitivity of the model to changes in the proportion of LMP was assessed for a single rain event by considering three scenarios of the Roujan catchment management with vegetative filters: 0% (Scenario 1), 18% (Scenario 2, real case) and 100% (Scenario 3). Compared to Scenario 2 (real case), soil losses decreased for Scenario 3 by 65% on the agricultural plot scale, 62% on the sub-catchment scale and 45% at the outlet of the catchment and increased for Scenario 1 by 0% on the plot scale, 26% on the sub-catchment scale and 18% at the outlet of the catchment.

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Correspondance: saison@supagro.inra.fr; International audience; The availability of pesticides in the soil is one of the factors that determine their mobilization and transport in runoff and groundwaters. In this paper, we aim to better understand the change in pesticide availability with increasing residence time in the soil. The relative contributions of degradation and sorption to the overall fate of molecules were examined, as was the remobilization of residues from the topsoil in water. The experiment was undertaken in undisturbed soil micro-lysimeters under natural climatic conditions for 1 year. We applied 14C-diuron to the soil surface to trace its residues in water-extractable (W), methanol-only-extractable (MO) and non-extractable (N) fractions and in runoff waters. Mass-balance calculations were fitted to the observed data to determine the quantities degraded or transferred within and between each of the compartments studied. Losses of diuron residues in runoff declined exponentially from 473 to 4 µg l−1 in 1 year. After 80 days, sorption of diuron residues in the soil was significant, as was degradation in the W and MO pools. Losses in runoff were small because of sparse rainfall. The following 140 days corresponded to a humid period with increased degradation in both W and MO pools. A redistribution from the MO towards the W pool occurred, probably because of intense rainfall at that time, leading to an apparent desorption of diuron residues. This was the most important result, suggesting that ageing processes should not be considered irreversible over time. The last phase of change, which occurred during winter, was slow. Leaching processes appeared to be of minor importance for diuron, with the surface layer containing more than 84% of diuron residues

Correspondance auteur: Raclot D. raclot@supagro.inra.fr; International audience; Soil erosion surveys and modeling approaches often rely on datasets collected from small experimental plots or fields. Therefore, one important issue is to assess to what extent reference data collected on small areas can be affected by soil tillage practices and extrapolated to larger areas. The objectives of this paper are to discuss: (i) the impact of superficial tillage on the erosion rates at field scale and (ii) the impact of the scale on the erosion rates for areas ranging from small fields to 1 km(2) catchments. We analyzed a dataset of 18 rainfall events including runoff and erosion data from fields of approximately 1200 m(2) and 3200 m(2) consisting of vineyards with two contrasting weeding practices - either superficial tillage or notillage with chemical weeding - and from the outlet of a 0.91 km(2) catchment that was 70% vineyard. Results showed that superficial tillage significantly reduced (4.5 times) soil losses as compared to notillage, with a large event-to-event variability. Considering the natural conditions studied by the authors, no-tillage with chemical weeding is not recommended for the study area. Erosion rates observed at catchment scale were significantly lower than those observed at the scale of individual fields. This trend, which has already been observed by many researchers, confirms that catchment soil loss cannot be estimated by the sum of individual field soil losses. In this context, the scaling transition between the field and the 1 km(2) catchment can be analyzed in terms of the spatial variability of soil management and connectivity between the sediment-producing and deposition areas

International audience; Water balance variables were monitored in a farmed Mediterranean catchment characterized by a dense ditch network to allow for the separate estimation of the diffuse and concentrated recharge terms during flood events. The 27 ha central part of the catchment was equipped with (i) rain gauges, (ii) ditch gauge stations, (iii) piezometers, (iv) neutron probes, and (v) an eddy covariance mast including a 3D sonic anemometer and a fast hygrometer. The water balance was calculated for two autumnal rain and flood events. We also estimated the uncertainty of this approach with Monte Carlo simulations. Results show, that although ditch area represents only 6% of the total study area, concentrated recharge appeared to be the main source of groundwater recharge. Indeed, it was 40-50% of the total groundwater recharge for autumnal events, which are the major annual recharge events. This indicate that both, concentrated and diffuse recharge should be taken into account in any hydrological modeling approach for Mediterranean catchments. This also means that, since they collect overland flow that is often largely contaminated by chemicals, ditches may be a place where groundwater contamination is likely to occur. The uncertainty analysis indicates that recharge estimates based on water balance exhibit large uncertainty ranges. Nevertheless, Monte Carlo simulations showed that concentrated recharge was higher than expected based on their area

E-mail Addresses: dages@supagro.inra.fr; International audience; Farmed catchments in the Mediterranean area often exhibit dense networks of ditches which are also preferential zones of water table recharge, and thereby of groundwater contamination. This study presents an experimental analysis of seepage losses and related groundwater recharge patterns during a typical Mediterranean runoff event at the scale of a ditch located above a shallow water table. The objectives were (i) to evaluate the patterns of water table recharge by seepage in a ditch, (ii) to study the main flow processes occurring during recharge, and (iii) to estimate solute propagation in case of contaminated flow in the ditch. The field observation indicated three major points. Firstly, they showed that seepage losses during a runoff event in a ditch can rapidly lead to a significant recharge of a shallow water table. Secondly, the recharge induces a groundwater mound much larger than the event plume. The infiltrated water and the accompanying solutes remained in the vicinity of the ditch. The patterns of groundwater recharge and contamination appeared very different. Lastly, both unsaturated and saturated-piston flow processes were observed which suggests that a variably-saturated flow modelling approach ought to be used to simulate the ditch-water shallow table interaction. Finally, the study indicates that the patterns of water table recharge and contamination in Mediterranean catchments with dense ditches network vary largely in space and time, and will require dense monitoring networks to estimate the evolution of the average contamination levels..

Publication Inra prise en compte dans l'analyse bibliométrique des publications scientifiques mondiales sur les Fruits, les Légumes et la Pomme de terre. Période 2000-2012. http://prodinra.inra.fr/record/256699; International audience; Abstract: In tropical humid environments under intensive banana production, pesticide transfer in waters can be of particular concern due to heavy rainfall, steep slopes, and soils with high infiltration capacities. The transfer in percolation and runoff waters of the nematicide cadusafos was investigated during a three month field experiment. The spatial heterogeneity of the banana plantation was taken into account by measuring percolation fluxes both under the banana plants and in the interrows with a specially designed lysimeter device installed at 60 cm depth. At the field scale, 0.34% of the pesticide applied was transferred in percolation, 0.13% in runoff. Forty-nine percent of cadusafos losses occurred by percolation under the banana plants, 23% by interrow percolation, and 28% by runoff. Losses were highest during the three weeks following cadusafos application, and this is also when dissipation in the soil was highest (calculated half-life in the soil: 7d). After this period, losses of cadusafos were low, both in soil and waters. Under the banana plant, saturated fluxes carried most of the pesticide, despite total percolation fluxes being at least five-times higher than saturated ones. Although overall pesticide transfer in water was low (0.5% of applied), it was not negligible due to the frequency of pesticide application in these areas

E-mail addresses: louchart@supagro.inra.fr; International audience; Realistic estimation of sorption parameters is essential to predict long-term herbicide availability in soils and their contamination of surface water and groundwater. This study examined the temporal change of an effective partition coefficient K-d(eff) for the herbicides simazine, diuron, and oryzalin from a 0.12 ha field experiment during 7 vineyard growing seasons. K-d(eff) is the ratio of solvent extractable herbicide concentrations in the top soil (0-2 cm) to the average concentrations in runoff water and is considered to assess the effective availability of herbicides to runoff transfer. K-d(eff) increased largely with aging time since application, from values similar to those of the literature (determined in 24 h batch conditions, K-d(ref)), up to 88, 164, and 30 times these initial values for simazine, diuron, and oryzalin respectively. The seasonal variation of K-d(eff) values between years and compounds could be adequately described by a unique model, taking into account the cumulative rainfall since application and K-d(ref) of each compound. This simple model was able to represent the influence of the soil moisture content and its changes in the different biological and physicochemical processes that may contribute to the (bio)available, sorbed, or entrapped state of any of the studied herbicides with aging time under Mediterranean climate.

Corresponding author. fax: +49 381 498 2159. E-mail address: bernd.lennartz@uni-rostock.de (B. Lennartz).; International audience; This work was initiated to study the effects of climate induced soil water status variations which can reach extreme values under natural conditions on the sorption process of hydrophobic organic compounds. Based on the classical slurry batch methodology an approach is developed that allows the fast and careful complete drying of soil suspensions (microwave technique). Classical adsorption experiments were followed by three desorption steps with and without drying cycles. Drying and re-wetting enhanced the sorption-desorption hysteresis and Freundlich adsorption coefficients increased from 5.9 to 16 and 5.2 to 21 over three drying cycles for diuron and terbuthylazine respectively. Assuming the validity of a dual stage adsorption process, model evaluation suggests that drying is as a shrinking-like process leading to conformational changes of the dominant sorbent (soil organic matter) which restrict the intra-micro-particle diffusion. Rewetting only leads to a partial recovery of the diffusional pore space.

International audience; The assessment of field-like sorption behaviour is critical to predict the fate and transport of organic compounds, especially when long time periods are considered. We compared field-derived sorption isotherms for diuron from a 4-year database collected in a Mediterranean catchment with adsorption and desorption isotherms from classical batch studies. In addition, a new technique of drying the slurry samples in-between various desorption steps was applied in order to reflect the recurrent drying of the topsoil under Mediterranean climate conditions. Our results show first that the field-derived isotherms indicated a larger sorption capacity of the soil at small diuron concentrations (larger Kf and smaller exponent for the Freundlich parameters) than those derived from standard batch experiments. Second, when the soil was dried before desorption, chemical release was reduced by up to 29% as compared with normal desorption, resulting in isotherms that were in line with results from the field experiment. These results suggest that the drying-wetting cycles are a key factor in the long-term adsorption and desorption processes under field conditions. Third, the new approach of batch desorption experiments that allow the fast and careful complete drying of soil suspensions appears to be an appropriate method to assess sorption behaviour of herbicides over a long time period.

Regulation of herbicide pollution in vineyard: a simulation in a mediterranean area - We investigate in a hydrologic-economic integrated model framework, how different incentive instruments aiming at regulating the emission of no-point source pollutants (herbicides) do heva an impact on cultural practices. Based on multiparametric programming techniques, two combined tools are considered by the decision model: (i) positive and negative quality-based differentiation of the price of the products and (ii) positive differentiation and tax on the polluting inputs. Non-linear responses are observed, with a favorable environmental effect at the farm level when positive différenciation of the price is noticeable. However, this favorable response at the farm level results into poor performances at the watershed level, because the described incentive design does not include location-based devices., Cet article expose une approche des possibilités de gestion des pollutions par herbicides en milieu viticole méditerranéen à l'aide des outils de la programmation multiparamétrique. Deux hypothèses de politique de limitation de la pollution sont proposées, par bonification et pénalisation des produits et en associant une taxation des intrants et une bonification des produits. Les résultats montrent que, séparément, bonification et taxation ont un effet environnemental favorable. Leur combinaison entraîne des réponses profondément nonlinéaires pouvant conduire, localement, à des résultats environnementaux contreproductifs. De plus, l'effet positif au niveau de l'exploitation correspond à de médiocres performances sur le Bassin versant proprement dit, les mesures envisagées par les scénarios n'étant pas localisées., Rio Patrick, Causeret François, Andrieux Patrick, Dejean Cyril, Frot Elisabeth, Louchart Xavier. Gérer la pollution par les herbicides: une simulation en milieu viticole méditerranéen. L'émission de polluants vue comme problème de décision. In: Économie rurale. N°259, 2000. pp. 33-49.

The variation in the availability of diuron to transport by overland flow was studied in a vineyard field under a Mediterranean climate during three years. The availability of diuron decreased with time due to the dissipation of diuron in the topsoil and the decrease of its accessibility by runoff water, which is not represented in pesticide transfer modelling. Thus, calculated concentrations of diuron with simple and actual relations are always greater than those measured in the overland flow.

The Mediterranean climate is characterized by a hot and dry summer where occasional storm events induce erosion and runoff. The high leaching potential of pesticides to surface waters under such climate conditions are not in relation to the main body of data that originated from summer-rain row-crop scenarios. In this 2-yr study we monitored runoff discharge and concentrations of the two soil applied herbicides diuron [3-(3,4-dichlorphenyl)-1,1-dimethylureal and simazine [6-chloro-N 2 ,N 4 -diethyl-1,3,5-triazine-2,4-diamine] from two field sites-one tilled and one no-till-cropped with grapevine (Vitis vinifera L.; Cinsault and Aramon, respectively). Despite a time lag of 140 d in 1994 between chemical application and first runoff event, diuron concentrations in overland flow exceeded 200 μg L -1 at the no-till site. In 1995 the first strong rainfall-runoff event following application carried >87 and 60% of the respective seasonal simazine and diuron loss at both sites, although it accounted for

National audience

Le nombre et la diversité des composés organiques (pesticides, hydrocarbures aromatiques polycycliques HAP, polychlorobiphényles PCB, médicaments...) susceptibles d’être pré-sents dans l’environnement étant très élevés, il est impossible de réaliser des expériences pour117caractériser pour chacun d’entre eux leur devenir et leurs impacts. Ainsi, des méthodes de pré-diction se développent depuis de nombreuses années et, parmi elles, des méthodes basées surl’hypothèse que la structure des molécules conditionne leurs propriétés physico-chimiques, etpar voie de conséquence leurs effets biologiques et leur comportement dans l’environnement.Dans le cadre du réseau d’animation scientifique «Ecodynamique des Micropolluants»du département AgroEnv et du réseau d’écotoxicologie d’INRAE, nous avons développé uneméthodologie basée sur une approche in silico avec le calcul des descripteurs moléculaires decomposés organiques, suivi de leur classification selon leurs comportements dans l’environnement. Ces classes sont construites à partir d’une analyse statistique des propriétés intrinsèquesdéduites des caractéristiques structurales des molécules et des propriétés comportementales.L’outil TyPolA développé pour ce classement permet comprendre et de prédire le comportementdes composés composés organiques dans l’environnement et leurs impacts écotoxicologiques.Soulignant l’intérêt d’utiliser des descripteurs moléculaires, propriétés intrinsèques des substances, et des relations de type QSAR pour ce genre d’approches, notre objectif est de classerles composés organiques non pas par familles chimiques, mais selon des propriétés directementliées aux processus d’intérêt environnemental : rétention irréversible, transformation biotiqueou abiotique, transfert vers l’air ou les eaux, bioaccumulation dans les organismes vivants ouencore impacts écotoxicologiques.Les domaines d’application de cet outil sont très divers. Ainsi par exemple, des développements de TyPol ont été réalisés pour suivre la filiation entre composé parent et produitsde transformation. Cette approche a été récemment utilisée pour explorer différentes voies dedégradation prédictive du chlordécone.C L’utilisation de ces descripteurs dans la classificationTyPol a permis de classer les produits de transformation potentiels du chlordécone dans desgroupes de comportements différents : selon leur dégradabilité et aussi leur aptitude à la rétention, mobilité et bioconcentration.Un autre développement concerne le calcul des descripteurs moléculaires quantiques(moment dipolaire, polarisabilité...) qui permettent d’approcher la réactivité des composés organiques. La méthode AM1 avait été choisie au démarrage du projet pour son coût en temps decalcul particulièrement bas. Aujourd'hui, la méthode doit allier précision et efficience calculatoire. Pour explorer de la façon la plus exhaustive possible la surface d’énergie potentielle, larecherche conformationnelle a été améliorée pour déterminer la conformation de plus basseénergie grâce à un calcul de dynamique moléculaire. Pour le calcul des propriétés, la comparaison de différentes méthodes (AM1, DFTB, DFT) est en cours sur 107 molécules.TyPol a aussi été utilisé pour sélectionner des pesticides représentant des comportementstype, dans le cadre d’un projet de recherche en chimie théorique en essayant d'identifier pourles processus environnementaux « Dissolution » et « Adsorption » un pesticide par groupes decomposés. Nous avons ainsi travaillé avec l'atrazine, la métamitrone et le fenhexamide en interaction avec la fraction minérale d’un sol modélisée par une argile.La démarche adoptée pour cette étude de l'interaction pesticide/argile est une démarcheprogressive. La complexité des systèmes étudiés va croissant. Pour commencer, le pesticideseul en phase gazeuse est étudié par une analyse conformationnelle détaillée. L'étude se poursuitpar l’exploration de la complexation de ce pesticide par un puis deux cations du type Na+ ouCa2+. Lorsque l'interaction pesticide/cation est mieux comprise, le pesticide est déposé sur uneCa-montmorillonite modèle. Le solvant eau est ajouté pour étudier la désorption du pesticidede la montmorillonite hydratée. A chaque étape, nous évaluons les changements ou constantesobservés après ajouts au modèle utilisé pour ces calculs théoriques : pesticide + cation + argile+ eau. Cette démarche permettra de mieux comprendre le rôle de chaque composante et desinteractions correspondantes dans le processus d’adsorption.