Silicone rubber selection for passive sampling of pesticides in water.

The authors thank G. Raffin and M. Hangouet (ISA, UMR 5280) for TGA analysis and interpretation, and C. Guillemain (Irstea) for analytical support.International audienceSilicone rubber can extract organic compounds with a broad range of polarities (logKow>2-3) from aqueous samples. Such compounds include substances of major concern in the protection of aquatic ecosystems and human health, e.g. pesticides. Silicone rubbers (SRs) with various characteristics have been successfully used in sorptive methods for water sample extraction in the laboratory (SPME, SBSE), and for passive sampling in aquatic environments. However, only few studies have evaluated variability in organic compound sorption due to the origin of SRs, particularly for pesticides. The aim of this study was to select an SR for the extraction of pesticides from water samples by passive sampling. To this end we measured the impact of seven SR formulations on sorption capacity, defined by the partition coefficient (Ksw). Kinetic experiments and sorption isotherms were performed to determine extraction recovery as a selection criterion for SRs, and pesticide partition coefficients. Very large differences in affinity for pesticides were found between two kinds of SRs: "Polymerized SR kits" and "Manufactured SRs". One SR was chosen among the "Manufactured SRs", and the Ksw values of 21 pesticides were determined, filling a gap in the literature (1.50<logKow<5.51). In light of sorption properties, literature data and additional economic and technical factors, we suggest using SR from Goodfellow in future work to reduce the variability of Ksw literature values

Rétention des produits phytosanitaires dans les fossés de connexion parcelle-cours d'eau

Pour lutter contre les pollutions diffuses en milieu rural, de nombreux programmes d'action se mettent en place. Le développement de recherches sur les connexions parcelle - cours d'eau devrait permettre de mieux comprendre le transfert et la dissipation des polluants dans ce milieu. En particulier, les fossés, structures relativement fréquentes dans les territoires cultivés, peuvent, a priori, avoir une fonction de court-circuit et donc faciliter le transfert des produits phytosanitaires, ou au contraire constituer des éléments de pondération de la pollution. Afin d'éclaircir ce point, une première série d'expérimentations a été menée par le Cemagref (Institut français de recherche pour l'ingénierie de l'agriculture et de l'environnement) dans des fossés de drainage agricole. Une solution aqueuse contenant trois herbicides aux caractéristiques physico-chimiques différentes (isoproturon, diuron et diflufénicanil), et un traceur (chlorures) a été injectée pendant quelques minutes dans quatre fossés. Des échantillons d'eau ont été prélevés à pas de temps fins à deux emplacements en aval du point d'injection. Après dosage par chromatographie au laboratoire, les résultats indiquent une diminution du flux et de la concentration maximale du pic de polluants comparativement à un traceur. En outre, la variation observée est corrélée aux propriétés physico-chimiques des produits, en particulier au coefficient de partage Koc. L'étude présentée montre que la surface de contact (liée à la nature du substrat) et le temps de contact (dépendant essentiellement des conditions d'écoulement) entre les polluants et le substrat sont les paramètres qui influent majoritairement sur la dissipation des produits phytosanitaires.The use of pesticide may lead to the contamination of surface and groundwaters. Agricultural nonpoint source pollution originates from land areas which intermittently contribute to the compound transfer to water. Several studies report on the occurrence of pesticides in surface water resources, with concentrations over the limit set by the 80/778 EEC directive for drinking water (0.1 µg/L for each substance and 0.5 µg/L for all pesticides). Numerous herbicides of different chemical families are detected in surface waters, especially triazines and ureas. Their concentrations vary with time and space partly in relation with application patterns and pluviometry. Maximum concentrations are linked to runoff, originating from agricultural fields and primarily occur right after the application periods.Many methods and levels of actions can be used to reduce water pollution. First, better agricultural practices can be set up, such as choosing the best dose and application period, controlling toxic substance impacts, combining with non-chemical practices. However, pesticide losses from fields can't be totally cancelled because of the complexity of the involved parameters (agricultural practices, climatic conditions, soil physical, chemical and biological properties …). In fact drift during application, runoff or drainage systems may still occur and have an effect on water quality. It may be then pertinent to evaluate to which extent the non treated areas between the fields and the surface water bodies can dissipate pesticide concentrations before they reach them. Pesticides leaving a plot in surface runoff may pass through various landscape components before reaching rivers ; including another field, a ditch, a small brook, a vegetative buffer zone. Besides, pesticide leaving the plot through drainage straightly moves agricultural ditches or streams. However, the contribution of each of these elements in pesticide dissipation is not well known, except for buffer zones (grassed or forest strips) (PATTY (1997). Cemagref (a French research institute), CEH Wallingford and ITCF (Institut Technique des Cereales et des Fourrages) attempt to extend their study to the other elements as agricultural ditches.This paper deals with the role of farm ditches and small streams in the transport and retention of pesticides from fields to the main river network. Their presence seems to play a significant role in the transfer of nonpoint source pollution (especially in the West of France). Indeed they can either accelerate pesticide transport or reduce it, according to their characteristics (length, flow, bottom sediment or soil characteristics, plants and organic matter contents, etc.). Since 1998, Cemagref has been investigating the retention of pesticides by several natural ditches with varied flows and substratum. A water solution containing three herbicides with different physico chemical properties (diflufenican, diuron and isoproturon) and potassium chloride, a tracer, is introduced with a pump in each ditch for about five minutes with a constant concentration. Water samples are collected in the ditches every two or five minutes at two distances from the injection point. The samples are stored in amber polyethylene terephtalate bottles and frozen. Laboratory analysis is performed by liquid-liquid extraction with dichloromethane and then liquid or gas chromatography depending on the compounds.The analysis of the water samples highlights a reduction of the maximum concentration and of the accumulative mass of each pesticide with distance compared to the tracer. Indeed, even if all the chloride ions used as tracers are not recovered at each sampling point (due to infiltration or lateral losses), we notice more significant losses for all the studied herbicides. The reduction can reach 70 % of the applied mass for diflufenican compared to the tracer. The retention of pesticides is also linked to their own physical and chemical properties. Thus, diflufenican, which has the highest sorption coefficient value, Koc, is also the most retained pesticide, whereas the total injected mass of isoproturon is recovered in most cases. Diuron has an intermediate behaviour.In brief, this field experiment proves that the surface and time of contact between pollutants and substratum are likely to play a major role in pesticide retention. An estimated adsorption capacity of each ditch has been assessed, which is based on laboratory sorption experiments on different natural substratum. Despite the few data, a relationship between diflufenican retention in ditches and the estimated adsorption capacity of each ditch has been underscored.This study also highlighted major limits of field experiments. For example, accurate flow measurements are really difficult to carry out with simple methods for low values. The conventional techniques can't be used with small water height or in ditch where the bottom is filled with plants or grass. Chloride ion was chosen in this study because it is easy to analyze, but the results showed an initial presence of chloride ion in the natural ditch water which incites to replace it by another tracer such as bromide with is not found in the environment in future field experiments.For all these reasons, some pilot experiments with a physical model (an artificial ditch of 8 m long and 0.4 m wide) are now designed. This equipment allows to adjust and control hydrodynamic parameters such as water flow, water height, and the nature and structure of the substratum. Then, it is possible to quantify both the role played by the substratum, mainly the organic matter content, and the role of the contact time. These parameters could be then taken into account in order to optimize further experiments on adsorption. The primary tests without substratum already give references for hydrodynamic measurements, as the stability of the water flow and the homogeneity of the initial solution concentration

Assessing pesticide concentrations and fluxes in the stream of a small vineyard catchment. Effect of sampling frequency

This study reports on the occurrence and behaviour of six pesticides and one metabolite in a small stream draining a vineyard catchment. Base flow and flood events were monitored in order to assess the variability of pesticide concentrations according to the season and to evaluate the role of sampling frequency on the evaluation of fluxes estimates. Results showed that dissolved pesticide concentrations displayed a strong temporal and spatial variability. A large mobilisation of pesticides was observed during floods, with total dissolved pesticide fluxes per event ranging from 5.7*10-3 g/Ha to 0.34 g/Ha. These results highlight the major role of floods in the transport of pesticides in this small stream which contributed to more than 89% of the total load of diuron during August 2007. The evaluation of pesticide loads using different sampling strategies and method calculation, showed that grab sampling largely underestimated pesticide concentrations and fluxes transiting through the stream

Contribution à l`étude du devenir des produits phytosanitaires lors d`écoulements dans les fossés : caractérisation physico-chimique et hydrodynamique

The object of this research is to assess the role of drainage ditches in the transport of pesticides from agricultural fields to the main river network. Experiments have been made in natural ditches in order to get a better comprehension of the hydrochemical processes. By the means of laboratory standardised measurements, we evaluated the influence of compound properties, substratum nature or environmental conditions on pesticide sorption. An experimental channel has been build, and the results confirmed the behaviour of pesticides observed at field and laboratory scales. Finally, we managed to determine some hydrological and physicochemical factors that are implied in the retention of agrochemicals as they move through ditch systems. We have also developed an indicator, based on field investigations and laboratory measures, so as to approximate to the theoretical retention capacity of ditches.L`étude présentée porte sur le rôle des fossés d`assainissement agricole dans la rétention de produits phytosanitaires aux propriétés distinctes, lors d`écoulements dans ce milieu. Trois niveaux d`investigations complémentaires ont été déployés pour étudier conjointement l`influence de caractéristiques physico-chimiques et hydrodynamiques sur le comportement des composés : des simulations d`écoulements en milieu naturel, la caractérisation au laboratoire de l`adsorption sur des substrats de référence présents dans les fonds de fossés (sédiments, feuilles mortes) et la réalisation d`expérimentations mieux contrôlées dans un canal expérimental. Les simulations d`écoulements in situ ont permis d`acquérir des références sur le fonctionnement hydraulique et physico-chimique des systèmes naturels étudiés, et d`aboutir à des ordres de grandeur des taux de rétention des produits. Grâce aux études en conditions standardisées de laboratoire, nous avons mis en évidence l`influence de certains paramètres liés aux produits, aux substrats ou aux conditions environnantes sur les différentes composantes de l`adsorption (cinétiques et isothermes) des produits phytosanitaires étudiés. Suite à ces deux types d`expérimentations, l`emploi d`un maillon intermédiaire est apparu indispensable pour lier et contrôler les aspects physico-chimiques et hydrodynamiques des processus impliqués. L`injection en continu de solution de produits phytosanitaires a confirmé les comportements des matières actives observés sur le terrain et au laboratoire. La synthèse des travaux présentée dans la dernière partie du travail, a permis de mettre en relation les résultats acquis aux différentes échelles d`études, de dégager des facteurs (hydrodynamiques et physico-chimiques) impliqués dans la rétention des composés lors de leur transfert dans les fossés, et d`élaborer en parallèle un indicateur de rétention pour approcher les capacités de rétention théorique d`un fossé, en s`appuyant sur des observations de terrain et sur des mesures d`adsorption obtenues au laboratoire

Comment avoir confiance dans les données obtenues par les analyses suspectées et non-ciblées par LC-HRMS ?

International audienceIdentifying new or unexpected organic contaminants present in aquatic environments is of major concern for water quality monitoring. During the last 15 years, applications of suspect and non-target analyses to assess the presence of emerging contaminants and their transformation products in aquatic environments have increased to meet this challenge. To our knowledge, the data quality verification for suspect and non-target analyses in the environment field is mainly based on target analysis strategies (e.g. use of extraction and injection surrogate standards and analytical or extraction blanks). Unfortunately, these strategies are not adapted for the high number of signals obtained in full-scan HRMS analysis. Indeed, surrogate standards' addition provides an assessment of sample analyses for a targeted number of chromatographic peaks and parameters (retention time stability, peak shape, detector sensibility and mass accuracy evaluation). The non-target screening approach allows to analyze hundreds to thousands analytes covering a wide range of concentration levels and physicochemical properties. It is not conceivable to have surrogate standards for all the components, even more for the unknown. Then, for the validation of the data we propose the use of quality control (QC) based on approach already applied in metabolomics

De l'observation à l'expérimentation : la démarche scientifique

National audienceCe poster décrit de manière pédagogique comment la démarche scientifique est appliquées tant dans les sciences de la vie et de la terre que dans les sciences humaines

Prédiction des temps de rétention chromatographique dans le cadre de l'analyse non-ciblée

Les analyses non-ciblées, effectuées par chromatographie couplée à un spectromètre de masse haute résolution, visent ladétection et l'identification de composés non recherchés initialement. L'identification d'une substance non-connue est généralement effectuée selon les informations qui peuvent être générées lors de l'analyse par spectrométrie de masse en comparaisonavec des bases de données spectrométriques. Un des éléments qui peut être pris en compte pour l'identification d'une substance est le temps de rétention chromatographique.En effet, c'est un paramètrerépétable et qui reflète les interactions et donc les propriétés physico-chimiques entre une substance d'intérêt et le système chromatographique. De nombreuses approches, des plus simples (prenant uniquement en compte le log D des composés), à de plus complexes (réseau de neurones, modèle LSER-Linear Solvatation Energy Relationships-,...) ont été explorées afin de pouvoir améliorer la précision des prédictions de la rétention chromatographique. Deux approches de prédiction de temps de rétention ont été évaluées lors de cette étude. Dans le cadre du réseau NORMAN, un modèle a été mis au point par l'Université d'Athènes pour la chromatographie liquide. Ce modèle peut être adapté à différentes conditions chromatographiques par l'injection d'un mélange qui sert à établir une courbe d'étalonnage spécifique au système utilisé. L'injection de composés modèles, dont le temps de rétention et la structure étaient connus, a permis de montrer que le modèle permettait d'obtenir en majorité des prédictions relativement correctes (±2 min) mais que dans 20% des cas, les prédictions n'étaient pas suffisamment précises. La relative imprécision obtenue pour certains composés dans ces essais doit être reliée aux conditions chromatographiques relativement différentes de celles ayant été utilisées pour développer le modèle et ce malgré l'utilisation de composés servant à l'étalonnage du modèle.Un modèle pour chromatographie liquide a été développé par Irstea sur la base d'une sélection des descripteurs les plus utilisés selon la littérature et facilement accessibles pour tout composé organique. Le modèle a été développé et validé en phase inverse et permet d'estimer la rétention d'un contaminant avec un intervalle de confiance de ±13,7% de phase mobile organique à l'élution quelle que soit la chaine analytique utilisée (soit ±1,9min en temps de rétention avec l'appareillage utilisé dans cette étude). L'applicabilité du modèle à différents lots de colonnes ainsi qu'à des échantillons en matrice réelle (injection directe d'eau de surface ou extrait SPE) a été démontrée

Utilisation du PICT avec des biofilms phototrophes de rivières pour évaluer la récupération écologique suite à l'interdiction de l'herbicide diuron

International audienceChanges in agricultural practices related to environmental policies such as the European Water Framework Directive should lead to a decrease in pesticide contamination levels in rivers draining agricultural areas. However, there is still a need for biological tools to evaluate resulting ecological recovery following the improvement of surface water chemical quality. Accordingly, the main purpose of this study was to assess the relevance of a pollution induced community tolerance (PICT) approach in natural phototrophic biofilms to estimate microbial community recovery following a decrease in diuron contamination due to the ban of the use of this herbicide on vineyards. To this end, we performed a 3-year field study (2009–2011) in the Morcille River (France), located in the French Beaujolais wine region. This river was frequently contaminated by diuron (among other organic and inorganic pesticides), with increasing concentrations downstream. Following the ban on diuron, imposed in December 2008, a progressive decrease in diuron concentrations was observed in the Morcille River. While the mean annual tolerance levels measured at the low contaminated station remained relatively constant over years, a clear and significant decreasing trend was observed at the medium and high contaminated stations during the survey. This temporal evolution revealed a direct link between a change in agricultural practice due to the ban of diuron and an increase in the sensitivity of phototrophic biofilms to this herbicide. This finding brings further new evidence that PICT has great potential to detect microbial community recovery following chemical restoration due to changes in the agricultural use of pesticides