Simulation par le modèle AgriFlux du devenir de l'atrazine et du dééthylatrazine dans un sol du Québec sous mais sucré

Les outils mathématiques sont de plus en plus utilisés pour simuler la contamination d'origine agricole des eaux souterraines. Le modèle AgriFlux permet, à l'aide du module PestiFlux, de simuler les processus responsables du devenir des pesticides dans le sol: ruissellement, volatilisation, adsorption/désorption rapide, adsorption/désorption lente, complexation par la matière organique dissoute, biodégradation en sous-produits, hydrolyse, drainage et lessivage. AgriFlux est utilisé pour simuler le devenir de l'atrazine et du dééthylatrazine sur une parcelle expérimentale de la région de Québec (Québec, Canada) cultivée en maïs sucré (Zea mays, L.) traité à l'atrazine. Des prélèvements d'eau interstitielle ont été réalisés (1986-1990) à l'aide de lysimètres avec succion (0,5 et 1,0 m de profondeur) et analysés pour leur contenu en atrazine et dééthylatrazine. De manière générale, AgriFlux reproduit bien l'évolution des concentrations mesurées, dans le temps et dans le profil de sol (r=0,76). Certains pics de concentrations observés sur le terrain ne sont toutefois pas représentés ou sont décalés dans le temps, ce qui pourrait être attribué à une sous-estimation de la variabilité spatiale des paramètres. Le rapport dééthylatrazine/atrazine est relativement bien simulé en 1988 à 0,5 m, mais est moins représentatif pour les autres données, ce qui pourrait être dû à une certaine imprécision dans la simulation de la biodégradation. Une analyse de sensibilité du modèle aux variations de différents paramètres a montré que le paramètre le plus influent dans les conditions testées est la constante de biodégradation. Les résultats obtenus montrent la pertinence d'AgriFlux (PestiFlux) dans la simulation du devenir des pesticides dans le sol et donc des risques de contamination des eaux souterraines en région agricole.Groundwater and surface water contamination by agricultural practices has become an increasingly preoccupying problem. Mathematical models are valuable tools to help prevent this type of pollution from non-point sources. AgriFlux is a mechanistic, stochastic model simulating the fate of agricultural contaminants in the unsaturated zone at the scale of the agricultural field. AgriFlux, through the PestiFlux module, now simulates pesticide transformations in the soil from their application to the field until their leaching with percolating water. The processes represented include volatilization, complexation by the soluble organic matter, instantaneous adsorption and desorption, slow adsorption and desorption to less available sites, biodegradation to by-products and hydrolysis to non-toxic compounds. The pesticide freely dissolved in solution or complexed with soluble organic matter can be mobilized with runoff, drainage and leaching waterAn application of PestiFlux to an experimental field near Quebec City (Quebec, Canada) is presented. The soil is a well-drained loamy sand cropped from 1986 to 1990 with sweet corn (Zea Mays, L.) receiving atrazine treatments (1.6 to 1.8 kg.ha-1 of active ingredient). Interstitial water was sampled using 12 suction lysimeters located at both the 0.5 and 1.0 m depths in the soil. All stations were sampled monthly in 1986 and 1987 and the collected water was analyzed for atrazine alone. In 1988, the sampling (every two weeks) was limited to the lysimeters which had previously shown the highest pesticide concentrations (two lysimeters at 0.5 m and one lysimeter at 1.0 m). The interstitial water was analyzed for atrazine and deethylatrazine. There was no sampling in 1989. In 1990, all stations were sampled on a weekly basis and a composite water sample obtained for each depth was analyzed for both compounds. Most of the pesticide-related parameters required to run PestiFlux were deduced from the literature, with the exception of the biodegradation rate coefficient which was estimated from field monitoring of atrazine. The parameters required to simulate water fluxes and plant uptake were the same as those used in a previous application of AgriFlux to the same experimental field for the simulation of nitrate fluxes (LAROCQUE and BANTON, 1995).Results show that PestiFlux generally represents well the measured atrazine and deethylatrazine concentrations in the interstitial water at 0.5 and 1.0 m. A linear regression using all measured and simulated concentrations indiscriminately gives a correlation coefficient of 0.76 when using the logarithm of concentrations. The temporal evolution of the pesticide concentrations is relatively well simulated, especially on the long term with an adequate representation of the increase in pesticide concentrations in the soil profile at 1.0 m. This increase is probably due to the fallow existing in 1985 which would have favored leaching of adsorbed pesticide below the soil profile, leaving only low residual pesticide concentrations. Over one growing season, the transport of atrazine and deethylatrazine is well represented by the model, although some peak concentrations are delayed or attenuated. This result could be due to an underestimation of the spatial variability of the different parameters. It is possible that the coefficient of variation of 10% adopted may not represent adequately the spatial variation of some parameters. Nevertheless, most measured concentrations of both compounds are within the mean simulated concentrations and included between two standard deviations. For 1988, most of the measured concentrations are located near the upper limit of the envelope curve which is consistent with the fact that the sampled lysimeters were those yielding the highest concentrations. The simulated concentrations show a generally good representation of the relative atrazine and deethylatrazine concentrations. The ratio of the mean deethylatrazine to atrazine concentrations provides a closer look at the adequacy between the simulated concentrations of both compounds. A comparison between the measured and the simulated ratios shows a good adequacy at 0.5 m in 1988 and both over- and under-estimation of the ratio for the other available data. This is probably due to an imprecision in the simulation of biodegradation rates during some periods. All the parameters used in the simulation have an important uncertainty, due to the significant spatial variation of the parameters in the field and to the imprecise knowledge of some pesticide characteristics. In order to identify the parameters which have the most important influence on the results, an analysis of the sensitivity of the cumulated leaching mass of both compounds at 1.0 m to variations of the different input parameters was performed. The results show that the biodegradation rate has the greatest influence on the results. This is probably due to the importance of this process in the simulated situation. This result confirms the importance of an adequate quantification of this parameter and of its spatial variation. PestiFlux offers a comprehensive representation of pesticide transformations in the soil and is easy to use. As a module of AgriFlux, it has the advantage of being integrated into a well-tested and reliable modeling environment. The presented simulation results show that, apart from some limits due to the quantification of some of the parameters, PestiFlux is a useful and comprehensive tool for estimating potential groundwater pollution by pesticides

Exportation saisonnière d'herbicides vers les cours d'eau mesurée sur six champs agricoles sous quelques pratiques culturales du maïs (Basses-Terres du St-Laurent)

L'identification de pratiques agricoles qui minimisent les risques de contamination des eaux de surface nécessite d'évaluer l'importance des voies de transfert des herbicides vers les cours d'eau. Le but de cette étude est d'évaluer à l'échelle du champ agricole et pour une saison de culture l'exportation effective de l'atrazine et du métolachlore par ruissellement de surface et par drainage, ceci pour des conditions pédo-climatiques et agronomiques représentatives de la culture intensive du maïs-grain dans les Basses-Terres du St-Laurent (Québec). Pour les deux premiers événements pluviaux d'importance suivant l'application des herbicides, seulement deux des six champs étudiés ont présenté un ruissellement quittant le champ : les concentrations en herbicides ont atteint 1200 mg/L et 2400 mg/L. La charge exportée en herbicides semble inférieure dans le cas du non travail du sol (semis direct), comparativement au labour conventionnel. Les concentrations en herbicides dans l'eau de drainage sont inférieures à 6 mg/L (pour la majorité inférieures à 1-2mg/L) pour quatre champs, alors que deux champs ont présenté des concentrations atteignant 40-60 mg/L. La charge exportée par drainage apparaît être faible dans le cas de l'application d'herbicides en bandes, comparativement à l'application en surface totale. La masse en herbicides exportée par ruissellement (estimée à partir de coefficients de ruissellement probables) serait supérieure à celle par drainage. Une démarche destinée à diminuer les masses en herbicides exportées devrait ainsi viser la principale voie de cette exportation, c'est-à-dire le ruissellement de surface.The use of pesticides in agriculture may result in the degradation of surface water quality. Since agricultural practices affect the transport of pesticides, there is a need to identify practices which minimize the contribution of the different transport paths to the streams, i.e. runoff and drainage. The aim of this study was to evaluate at the field scale and for one growing season the transport of the herbicides atrazine and metolachlor to surface water under soil, climatic and agricultural conditions representative of those encountered for intensive corn cropping in the St-Lawrence Lowlands (Quebec).Six agricultural fields (Figure 1) were studied in 1995. Previous agricultural practices in 1994 and soil texture are summarized in Tables 1 and 2, respectively. Conventional practices (tillage with moldboard plow and application of herbicides over the entire area of the field) and conservation practices (no-till and banded application of herbicides over the seeded row) were studied. Each field was solely and entirely drained by one subsurface drain. The commercial formulation used in 1995 contained a mass of metolachlor two times higher than that for atrazine. Herbicide concentrations in runoff and drainage waters were monitored during the two first important rainfall events that occurred after herbicide application (Table 3). Sampled runoff corresponded to the water reaching a drainage channel or a stream. Drainage water was also collected for 3.5 - 4.5 months following the initial application. A total of 164 water samples was obtained. After sediment removal, metolachlor, atrazine and its dealkylated metabolite deethylatrazine (DEA) were extracted using a liquid-solid extraction procedure and analyzed by gas chromatography.Only two fields produced runoff and the concentrations of parent-compounds (Figures 2 and 3) were high and varied during rainfall events between 60-500 mg/L (Field 2) or 130-2400 mg/L (Field 6). Concentrations found during the first rainfall event were higher than those encountered during the second event. The DEA/atrazine concentration ratio (DAR) was below or near 0.1, indicating runoff of recently applied atrazine (low degradation). These two fields present similar soil texture, pluviometry and sampling periods after herbicide application. Based on runoff coefficients observed for other agricultural fields (1-30%), it was estimated that the mass losses for herbicides (Table 4) would be higher under conventional tillage(Field 6) as compared to no-till (Field 2).Significant transport of herbicides by drainage was observed during the two rainfall events. The losses of herbicides that occurred after these events and during a dry growing season (little or no drainage flow) were low. The drainage losses (concentration or masses) during the two rainfall events for Field 1 (clay) were very low. This was attributed to the low drainage capacity of the soil, to the low rainfall intensities as well as to the important delay between the initial application and the subsequent rainfalls. For silty clay loam to loam soils, the drainage flow increased in the 6-12 h period following the onset of rainfall, as did the herbicide concentrations. Metolachlor concentrations were slightly higher or close to those for atrazine: this was attributed to its possible more rapid decay and to its stronger tendency to adsorb to the soil.During the rainfall events, four fields exhibited herbicide concentrations from drainage less than 6 mg/L (mostly < 1-2 mg/L). Fields 2 and 6 yielded parent-compound concentrations as high as 40-60 mg/L (Figures 4 and 5). The DAR values found for drainage water of Field 2 (0.1-0.5) were higher than those observed from runoff, indicating significant dealkylation of atrazine had occurred during its transport in the unsaturated zone. Field 6 allowed the monitoring of the DAR over the growing season and an inverse relationship was found between the DAR and atrazine concentration (Figure 6). This was attributed to the larger variation in atrazine concentration during a rainfall as compared to that of DEA. A DAR value near 1 was obtained at 1-2 months after application, indicating important degradation of atrazine.The total mass losses of parent-compounds (two rainfall events) were evaluated (Table 5) except for Fields 2 and 4 which present frequent submerged drains. Banded herbicide application (Field 5) results in consistent lower losses of herbicide masses than those obtained for application over the entire surface (e.g. Field 5 compared to Fields3 and 6). It should be noted that the higher export observed for the entire surface application may be partly attributed to a shorter delay between application and rainfalls (Fields 3 and 6) or to a higher rainfall intensity (Field 6).Although runoff reaching surface waters was limited, it was estimated that the total herbicide losses (Table 4) during the two rainfall events were higher than those from drainage (Table 5). In the perspective of reducing the herbicide loads reaching streams, it appears that remedial actions should focus on this main route of transport. Thus, complementary actions such as vegetated buffer strips to intercept crop land runoff may possibly be useful to limit herbicide transfer to streams in intensive agricultural zones

Délimitation des périmètres de protection des puits de pompage en zone agricole à l'aide de la simulation mathématique

Un périmètre de protection de puits de pompage est la surface entourant le puits, dans laquelle des mesures sont prises pour empêcher des contaminants de migrer et de contaminer l'eau de ce puits. Dans l'établissement des périmètres de protection, de nombreux facteurs doivent être considérés, et une approche analytique systématique doit être adoptée. Les modèles mathématiques de simulation peuvent être employés en ce sens et sont souvent les seules méthodes capables de déterminer les périmètres de protection quand des critères quantitatifs sont utilisés. Une telle approche a été appliquée, en couplant un modèle de transport de contaminant en zone non saturée avec un modèle de transport en zone saturée. Le modèle en zone non saturée VULPEST évalue les concentrations de pesticide atteignant la nappe. Ces concentrations sont ensuite utilisées comme données d'entrée du modèle en zone saturée. Ce dernier considère les vitesses d'écoulement et l'influence de chaque puits. Les résultats quantitatifs permettent alors la détermination de périmètres de protection spécifiques à chaque contaminant potentiel. Cette application, réalisée sur un important site de culture de la pomme de terre du Québec, e permis de comparer favorablement les concentrations prédites à celles mesurées dans l'eau d'un puits, et de déterminer le périmètre de protection spécifique au pesticide utilisé. Le cas présenté est un exemple des applications possibles et futures d'une telle méthode pour la détermination des périmètres de protection des puits de pompage.A wellhead protection area is the surface and subsurface area surrounding a waterwell through which contaminants are reasonably likely to move toward and reach. In the past, various approaches have been taken to delineate wellhead protection areas : fixed circles or rings around the well; simplified variable shapes based on geo-hydrologic mapping and classification ; zones with prescribed minimum travel times. However, in establishing wellhead protection areas, many factors need to be considered : zone of influence around the well; well recharge area; flow paths; transport velocities; travel times; sources and types of contamination. To determine a site-specific wellhead protection area, a systematic analytic approach must be taken. Mathematical simulation models may be employed and are often the only method capable to determine the wellhead protection area when quantitative criteria are used.Such an approach can be used in agricultural zones, where pesticides are applied, by coupling a solute transport modal for the unsaturated zone with a saturated zone transport model. The (unsaturated zone) VULPEST model is an evaluation tool for the groundwater contamination by pesticides based on the transport modeling. Developed as a management tool, it permits the evaluation of the groundwater vulnerability to pesticides in terme of risk of contamination. It evaluates the concentrations of pesticide that reach the water table, taking into account the spatial variability of hydrodynamic, physical and physicochemical parameters of the soil. The variability of parameters is taken into account in the Monte Carlo approach. This approach consists of carrying out a sufficient number of simulations so that the distribution of values assigned to each parameter, these values being randomly selected from a chosen probability distribution, approximates the given distribution.The concentrations obtained from the VULPEST model are used as input data in the model which simulates the transport and the fate of the contaminant in the saturated zone. This model uses the finite difference technique to simulate flow and solute transport. It considers the flow velocities and the influence of each well. In steady state conditions, the linked transport models in unsaturated and saturated zones may be considered independent. The quantitative results obtained by these means determine the vulnerability level of the well. Finally, they permit the delineation of the wellhead protection area for a specific contaminant, that is a given pesticide.An application was performed to an important potato crop area in Quebec. Few years ago, this site has shown a contamination of the well water by the pesticide aldicarb. The cultivated soil consists of marine and fluvial sand with medium to coarse grain sizes, deposited on a sea clay with a thickness of about 20 m in some places. Potatoes are intensively grown in this region. In the eighties, a contamination by the pesticide aldicarb was noticed in some wells of this region. The granular form of aldicarb is applied during the sowing period (mid-May) at the recommended rate of 2.24 kg/ha. It has a high solubility (6 000 mg/l) and is leached by soil humidity. The aldicarb is transformed by oxidation to sulfoxide then to sulfone during its transit in the unsaturated zone. After a characterization of the soil physical parameters, calculations were run for both the unsaturated and the saturated zones. The depths of the well and the aquifer are 5 m and 3 m respectively. The thickness of the aquifer affected by pumping is about 2 m. The application of the pesticide aldicarb was done during 1982 and 1983.The predictive results obtained by modelling for the pesticide concentrations in the well water were favorably comparerd to the concentrations measured at the site. The concentrations of pesticide in the water reach their peaks 7 weeks after every application. The maximum concentrations reaching the water table were found to be about 0,5 mg/l. This level exceeds largely the water quality criterion of 9 µg/l set by Health and Welfare Canada, and the one of 10 µg/l of the US-EPA. The well concentrations are calculated by taking into account transport in the saturated zone and decay processes. The maximum concentrations obtained are near 24 µg/l for a decay rate of the pesticide in the aquifer of 0,003 d-1. This decay rate is the one corresponding of the hall-lite of 8 months found by other researchers for Florida soils. The analysis of the water well during this period shows concentrations of about 10 µg/l. Moreover, the leaching of the contaminant into the well, and its persistence in the soil and groundwater is still present over 3 years after the last application. Using the water quality criterion of 9 µg/l set by Health and Welfare Canada, calculations have provided the delineation of the wellhead protection area specific to the pesticide aldicarb. The boundary delineation of water well protection area is determined by the numerical technique of reverse path line. The maximum extension of the well protection area obtained by this mean is 110 meters. It corresponds to a peak arrival with a decay of 1.5 years after the application.The case study shows an example of the possible and future applications for such a method for the delineation of the wellhead protection areas. Such an approach permits to council the best use of pesticides with an appropriate groundwater protection scheme, indeed, agricultural managers can safely decide on the pesticide application rate and date, as on the choice between various pesticides, with regard to the groundwater quality protection. Through this way, regulators and scientists can base their decisions for the registration of new pesticides by testing, before their use, their possible impacts on groundwater. Comparisons can be easily doge between water quality criteria and predicted quantifies, and regulatory decisions can be taken in light of these results

The Public Resource Management Game

Use of public resources for private economic gain is a longstanding, contested political issue. Public resources generate benefits beyond commodity uses, including recreation, environmental and ecological conservation and preservation, and existence and aesthetic values. We analyze this problem using a dynamic resource use game. Low use fees let commodity users capture more of the marginal benefit from private use. This increases the incentive to comply with government regulations. Optimal contracts therefore include public use fees that are lower than private rates. The optimal policy also includes random monitoring to prevent strategic learning and cheating on the use agreements and to avoid wasteful efforts to disguise noncompliant behavior. An optimal policy also includes a penalty for cheating beyond terminating the use contract. This penalty must be large enough that the commodity user who would gain the most from noncompliance experiences a negative expected net return.Renewable resources, public resources policy, optimal contracts

Analyse de sensibilité paramétrique d'un modèle simulant le transport de pesticide dans le sol

Afin de protéger l'eau souterraine des pesticides épandus à la surface des sols agricoles, on doit être capable de prédire et d'évaluer a priori les risques de contamination. La modélisation mathématique, qui est basée sur la représentation des processus, s'avère être un outil à privilégier pour une telle prédiction. Cependant, la fiabilité des résultats de ces modèles est fonction de la précision et de la représentativité des différents paramètres d'entrée. A l'aide d'une analyse de sensibilité, il est possible d'évaluer l'impact de la variabilité de ces paramètres sur les résultats de la modélisation. Une étude de sensibilité menée avec le modèle Pesticide Rosit Zone Model (PRZM) a permis d'identifier les paramètres physiques d'entrée dont la variation apporte le plus de changements au niveau des principaux résultats, c'est-à-dire les paramètres d'entrée auxquels le modèle est le plus sensible. L'utilisation du coefficient de sensibilité relatif s'avère être à cet égard un outil de comparaison fort efficace dans le cadre d'une telle étude. Les paramètres d'apport en eau (précipitations) et en pesticide (taux d'application) sont ceux dont les variations provoquent le plus d'impact au niveau des résultais de la simulation. Egalement, les résultats des simulations sont aussi sensibles aux variations de la capacité au champ et de la densité du sol. La température, le point de flétrissement, ta profondeur d'évaporation et la dispersion sont des paramètres auxquels la modélisation est peu sensible.The ever increasing number of cases of groundwater contamination by pesticides has recently given rise to numerous experimental studies on the tale of these compounds within the soil-water system. In parallel with these experimental studies, the quick and intensive development of numerous simulation models bas emphasized the importance of the various factors and processes controlling the transport of pesticides in the unsaturated zone. The calibration and the validation of such deterministic models, which are especially used in groundwater management, requires the evaluation of several parameters related to the nature of the pesticide as well as to the pedologic and hydrogeological conditions of a given site. The reliability of results predicted by those models is mainly a function of the precision and the representativeness in the evaluation of those parameters at a specific site.The aim of this study was to evaluate the sensitivity of a simulation modes of pesticide movement in the unsaturated zone with regards to the variation in soil physical properties. More particularly, a sensitivity analysis was performed in order to determine the importance of the variation in these parameters with respect to simulation results obtained from the Pesticide Root Zone Model (PRZM). The spatial variability of the composition and structure of the soil, which comes from the site pedogenesis, is the main cause of the variability of the soil water distribution and of the soil transient properties. The sensitivity analysis of a model with respect to the variation in these parameters allows the evaluation of the impact of their representativeness on the model output results. Such an analysis thus allows the determination of an acceptable level of precision (or error) for which an increase of precision in the evaluation of a parameter does not anymore correspond to a significant gain in the representativeness of the model results. It also permits the estimation of the impact of a potential variation of a parameter on the prediction of pesticide transport in the unsaturated zone.The deterministic PRZM modal used in this study has been developed by the US-EPA and devoted to pesticide application on agricultural sites. This modal evaluates the pesticide leaching towards groundwater with respect to the type of culture and pesticide used, the climatic conditions, the soil characteristics and some agricultural practices. Output results from the model can he expressed in concentrations or masses of pesticide, in fluxes or cumulated quantities. Simulations were performed using characteristics and data of the Portneuf region (Quebec). This area of potato farming was until recently one of the Quebec most important sites for aldicarb application before the recommendation of its non use. Cultivated surfaces, which are rather homogeneous, consist of medium-size sand. Simulations were performed river a ten year period (1974 to 1984), implying one application of pesticide a1 the seed-time, and a trop for each year.The parameters of water and pesticide inputs (rain and application rates) are those that induce the higher impact on the simulation results. The simulation results were also influenced by the variation of the field capacity and of the soil bulk density. Temperature, wilting point, maximum evaporation depth and dispersion are the input parameters for which the PRZM model is the less sensitive. The simulation results of pesticide transport, which ultimately consist in predicting the groundwater contamination, are very sensitive to the variations of some physical parameters for which the precision and the representativeness in the measured values are thus very important for the reliability of the results. Considering the spatial variability of a site characteristics, the representativeness of these results is very uncertain if a limited number of data is used in order to determine the mean value. A particular attention has to be focused on the parameters that induce the higher sensitivity of the model. Finally, such a sensitivity analysis shows that a stochastic approach in modelling the solute transport through soil can be a good alternative to take into account the variability of parameters encountered in field situations

Adsorption du pentachlorophenol sur divers matériaux : Influence de co-adsorbats organiques (Substances humiques et lindane)

Nous avons réalisé, pour de faibles concentrations, l'étude de l'adsoprtion d'un pesticide le pentachlorophénol, sur plusieurs matériaux adsorbants : le charbon actif, la kaolinite et la bentone. Les résultats montrent que l'adsorption du pentachlorophénol sur la kaolinite reste négligeable tandis que la bentone SD-3 (argile traitée) permet d'obtenir des résultats intéressants avec toutefois une capacité maximale d'adsorption 10 à 100 fois plus faible que celle du charbon actif. Le charbon actif reste le meilleur matériau adsorbant pour le pentachlorophénol. La solubilité de ce composé étant très variable en fonction du pH du milieu on constate que l'adsorption du pentachlorophénol-pentachlorophénate (5 mg.l-1) diminue pour des valeurs de pH supérieures au pKa du couple acide-base que nous avons déterminé expérimentalement, égal à 5,9 ± 0,1. L'adsorption du pentachlorophénol n'est pas affectée par la présence d'acides humiques (obtenus à partir de substances commerciales) utilisés comme coadsorbats (10 mg.l-1) alors que les acides fulviques (20 mg.l-1) extraits de sols semblent provoquer une promotion de l'adsorption. On observe d'autre part que le pentachlorophénol n'affecte pas l'adsorption des acides humiques mais augmente légèrement celle des acides fulviques. Ces remarques suggèrent la possible formation d'un complexe acides fulviques-pentachlorophénol. Lorsqu'on utilise le lindane, pesticide hydrophobe comme coadsorbat (165 mg.l-1), on observe encore d'une façon systématique pour tous les nombreux essais une légère promotion de l'adsorption.Adsorption studies for the removal of the pesticide pentachlorophenol found in a number of water supplies (BELAMIE and GIROUD, 1986) were carried out using various materials including kaolinite, bentone SD-3 and powdered activated carbon (WEBER and GOULD, 1966; WEBER and JODELHAH, 1985). It was found that adsorption on kaolinite was negligible, whereas bentone SD-3 presented and adsorption efficiency from 10 to 100-fold less than equivalent quantities of powdered activated carbon (LOTSE et al., 1968; SHAROM et al., 1980). The effect of the pH on the removal of pentachlorophenol by activated carbon was studied. The removal efficiency of pentachlorophenol by activated carbon is better in acidic media. A clear dependence of adsorption on the pH appeared to be the result of a marked variation of the pesticide solubility as a function of the pH (fig. 3). Adsorption of pentachlorophenol/phenate (5mg.l-1) diminishes markedly at pH values above the pKa of this weak acid (that we found equal to 5,9 ± 0,1) when the pentachlorophenol exists almost entirely in ionic form in aqueous solution, and is enhanced at low pH when the percentage of molecular species (whose concentration can be determined from pKa value) becomes significant (WARD and GETZEN, 1970). These remarks and the adsorptive capacities (163 mg.g-1= 0,6 mmol.g-1 at pH = 5,2 and 79 mg.g-1 0,3 mmol.g-1 at pH =12,7), suggest a П-П interaction between pentachlorophenol and activated carbon which seems to be confirmed by the results with bentone SD-3 (tables 1 to 4), and the values of the electrokinetic potential of these materials. This study emphasizes the effect of organic coadsorbates (e.g., dissolved humic substances and the pesticide lindane) on the adsorption capacity of activated carbon for pentachlorophenol. Two different natural organic matters were studied as coadsorbates : purified humic acids from a commercial source (at 10 mg.l-1) and fulvic acids extracted from a top soil horizon (et 20 mg.l-1) (SCHNITZER and SKINNER, 1963; THURMAN and MALCOLM, 1981). Pentachlorophenol adsorption was not affected by humic acids, whereas an increase of adsorption seemed to be observed in the presence of fulvic acids (fig. 6). Pentachlorophenol does not affect the adsorption of humic acids, but improves slightly the removal of fulvic acids. This suggests an association between the two kinds of organic compounds (WERSNAW et al., 1969; KHAN, 1972; OGNER and SCHNITZER, 1970), the resulting « complex », fulvic acids/pentachlorophenol, being more adsorbed than the compounds themselves. The coadsorbate lindane (0,65 mg.l-1) which is easily adsorbed by activated carton (GOMELLA and BELLE, 1975...) seemed also to Improve slightly the removal efficiency of pentachlorophenol by activated carton (fig. 7)

Fractionnement et caractérisation de la matière organique des lixiviats de décharges d'ordures ménagères

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.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]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

Face the Music and Glance: How Nonverbal Behaviour Aids Human Robot Relationships Based in Music

It is our hypothesis that improvised musical interaction will be able to provide the extended engagement often failing others during long term Human Robot Interaction (HRI) trials. Our previous work found that simply framing sessions with their drumming robot Mortimer as social interactions increased both social presence and engagement, two factors we feel are crucial to developing and maintaining a positive and meaningful relationship between human and robot. For this study we investigate the inclusion of the additional social modalities, namely head pose and facial expression, as nonverbal behaviour has been shown to be an important conveyor of information in both social and musical contexts. Following a 6 week experimental study using automatic behavioural metrics, results demonstrate those subjected to nonverbal behaviours not only spent more time voluntarily with the robot, but actually increased the time they spent as the trial progressed. Further, that they interrupted the robot less during social interactions and played for longer uninterrupted. Conversely, they also looked at the robot less in both musical and social contexts. We take these results as support for open ended musical activity providing a solid grounding for human robot relationships and the improvement of this by the inclusion of appropriate nonverbal behaviours