Validation of a multi-residue method to determine deltamethrin and alpha-cypermethrin in mosquito nets by gas chromatography with electron capture detection (GC-µECD)

Background: Nowadays long-lasting insecticidal mosquito nets (LNs) are frequently used around the world to protect people against malaria vectors. As they contain insecticide, laboratory control is needed to check whether the content of the active ingredient follows the conditions of the manufacturer and also if the active ingredient is still present after some time of use. For this purpose, an analytical method had to be developed. The fact that LNs include a range of polymers for the yarn and use coated or incorporated technologies for the active ingredient, it is a challenge to find only one analytical method determining the active ingredient in LNs, which takes into account both impregnation technologies. Some methods are provided by international organizations but are limited by the determination of only one pesticide per method. The aim of this study was to optimize a short time extraction method for deltamethrin and alpha-cypermethrin from coated and incorporated mosquito nets and also to detect both insecticides in one analytical run, using gas chromatography with electron capture detection (GC-mu ECD). Methods: Based on the literature, the most suitable solvent and the adequate extraction process for the insecticides used for net making were identified and adapted for the new multi-residue method. Results: The validation data of the multi-residue method to determine deltamethrin and alpha-cypermethrin in mosquito nets by GC-mu ECD are given. Depending on the concentration of the active ingredient spiked on the nets, the mean recovery for alpha-cypermethrin ranged between 86% and 107% with a relative standard deviation below 3.5%. For deltamethrin it ranged between 90% and 108% with a relative standard deviation also below 3.5%. The limit of detection is 0.009 g.a.i/kg of net (0.3 mg a.i./m(2) of net) both for alpha-cypermethrin and deltamethrin. Conclusions: Data obtained are excellent. A 30 minutes reflux extraction method with xylene was developed to determine alpha-cypermethrin and deltamethrin in long-lasting insecticidal mosquito nets (LNs) by gas chromatography with electron capture detection (GC-mu ECD). The method can be easily extended to others pyrethroid used for mosquito net treatment. This paper also presents an overview of the studies dealing with pesticide determination in mosquito nets

Public-public partnerships (PUPs) in water

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Electrochemical attachment of a conjugated amino-ferrocifen complex onto carbon and metal surfaces

International audienceThe attachment of a pi-conjugated amino-ferrocifen complex was electrochemically achieved either by direct oxidation of the amino group or via the oxidation of the ferrocene moiety. In the first case, the modification consists in oxidizing, at +0.70V/SCE, the amino moiety to its radical cation, which upon deprotonation from the amino group, yields all aminyl radical that may add onto the electrode surface. Alternatively, it is demonstrated that the amine moiety can be indirectly oxidized through an intramolecular electron transfer from the amino moiety to the ferrocenyl group after oxidation of the ferrocene part at +0.40 V. This can occur thanks to the conjugated pi system of the complex. More importantly. it is demonstrated that the covalent attachment of the complex can be achieved on glassy carbon, gold, and platinum surfaces whatever the approach used. The possible mechanisms for the covalent attachment are discussed. Interestingly, it is also shown that the amino-ferrocene compound adsorbs very well likely via pi stacking between grafted and non-grafted molecules. Nevertheless, the adsorbed molecules could be easily removed after passing the electrode in an ultrasonic bath. The electrode coverage was determined under various conditions by integration of the corresponding voltammograms. (C) 2008 Elsevier B.V. All rights reserved

Comparison of the laboratory standard washing using CIPAC washing agent and the domestic washing on three recommended types of long-lasting insecticidal mosquito nets

Background: One of the best ways to prevent malaria is the use of insecticide-treated bed nets. Manufacturers pursue easier, safer and more efficient nets. Hence, many studies on the efficacy and wash resistance using World Health Organization standards have been reported. The commonly used detergent is "Savon de Marseille", because it closely resembles actually used soaps. At the 54th Collaborative International Pesticides Analytical Council (CIPAC) Technical Meeting in 2010, it was suggested to replace it by a standardized "CIPAC washing agent". The aim of this study was to investigate the difference between a laboratory hand washing simulation using the CIPAC washing agent (method-1) and a domestic washing (method-2) on different bed nets, as well as the effect of the drying process on the release of active ingredient. Methods: Interceptor (R), Permanet (R) 2.0 and Netprotect (R) nets were used in three treatments, each repeated 20 times. The first treatment included method-1 washing and indoor drying. The second treatment included method-2 washing and indoor drying. The third treatment used method-2 washing and UV-drying. The residual insecticide contents were determined using gas chromatography. Results: The washing procedure and the number of washes have a significant effect on the release of active ingredient. Statistically, the two washing methods have the same effect on removing the active ingredient from the Interceptor (R) and Permanet (R) 2.0 net, but a significantly different influence on the Netprotect (R) nets. The drying process has no significant effect on the insecticide. Conclusion: Both washing procedures affected the amount of insecticide remaining on nets independently of the impregnation technology. The active ingredient decreases with the number of washing cycles following an exponential or logarithmic model for coated nets. The laboratory hand washing simulation had more impact on the decrease of active ingredient content of the Netprotect (R) nets. All net types seemed to be effectively protected against UV-light

Identification of quantifiers related to circadian rhythm variations

International audienceThe aim of this study is to propose quantifiers allowing to characterize the adaptation speed of the circadian rhythm of a living being based on temperature measurements. While the most commonly used model to represent circadian rhythm is the COSINOR model, it is not adapted to analyze changes. An extended COSINOR model is then proposed here in order to take into account temperature disturbances related to the activity of the studied living being. The quantifiers are obtained in a two step process. First, the extended COSINOR parameters are determined with a modified recursive least square algorithm, which is modified in order to compensate for the lack of persistent excitation. The estimates of these parameters are further filtered in order to provide several quantifiers which provide useful information on the adaptation speed of the studied living being. The proposed methodology is evaluated on rats temperature measurements obtained from a laboratory experiment

Plasmonic and Hydrodynamic Effects in Ultrafast Laser-Induced Periodic Surface Structures on Metals

International audienceWe report results on the development of laser-induced periodic surface structures produced by ultrashort laser pulses irradiating metallic surfaces. The surface topology features are discussed in terms of periodicity and amplitude contrast of the pattern formation, and in relation to the chrono-logical sequence of laser-induced events. Resonant excitation of Surface Plasmons in metallic grat-ings show that the surface wave excited during the femtosecond laser pulse can initiate the observed patterning. Metallic behavior under nonequilibrium conditions on the picosecond timescale is then investigated to correlate the amount of material experiencing solid-to-liquid transitions and the sub-sequent structure amplitude. With the derived observation, the calculation of the transient nonequi-librium thermodynamic characteristics of excited nickel is performed, allowing to define character-istic timescales of thermocapillary processes which may occur under multi-pulse irradiation

Les choix méthodologiques influencent-ils les résultats ? Application aux essais de lixiviation en colonne de sol

L’intensification de l’agriculture avec l’utilisation importante de pesticides a eu des répercussions néfastes sur l’environnement avec des pollutions au niveau des sols, de l’air et des masses d’eau. A ce jour, l’agriculture est devenue une des pressions majeures qui pèsent sur la qualité des eaux. En effet, une grande partie des pesticides appliquée au sol n’atteint pas sa cible et est volatilisée, adsorbée, dégradée en métabolites ou lixiviée à travers le profil de sol. Pour cette raison, la recherche scientifique sur le devenir de ces composés dans l’environnement s’est grandement développée. En effet, les connaissances en terme du transfert de pesticides au sein d’un profil de sol sont encore très limitées. Or, une meilleure compréhension du devenir de ces derniers est indispensable afin d’en améliorer la gestion et d’assurer la protection de l’environnement. Afin d’étudier le devenir des pesticides au sein d’un profil de sol, plusieurs types d’expériences sont retrouvés dans la littérature. Les expériences les plus proches de la réalité sont les longues expériences de terrain avec l’application de pesticides aux sols agricoles. Cependant, ces expériences sont généralement très onéreuses et ne peuvent être réalisées partout. Il est alors utile d’acquérir des informations grâce à des expériences en laboratoire. Les expériences en laboratoire sont généralement des expériences en batch, de chromatographie en couche mince ou en colonne de sol. Afin d’obtenir des informations pertinentes sur la mobilité potentielle des pesticides dans les sols et de bien simuler les flux d’eau, les expériences en colonnes de sol sont massivement rencontrées dans la littérature (USEPA, 2008). Elles permettent de comparer la mobilité des pesticides entre eux ainsi que d’étudier leurs comportements de lixiviation dans différents sols. Les expériences en colonne servent également à analyser les mécanismes qui sous-tendent les mouvements de ces pesticides en colonne (Katagi, 2013). La courbe d’élution des pesticides ainsi que la distribution des pesticides adsorbés au sein de la colonne peuvent alors être étudiées et permettent d’obtenir les paramètres de sorption et de dégradation des pesticides. Cependant, au sein de la littérature traitant des expériences de lixiviation en colonne de sol, les modalités des colonnes utilisées sont très variables, empêchant les résultats obtenus d’être comparés ou transposés à d’autres cas. Une première modalité variant fortement dans la littérature est la structure du sol mise dans les colonnes. Les expériences de mobilité des pesticides sont généralement réalisées avec du sol remanié, à savoir préalablement séché, tamisé puis tassé uniformément dans la colonne. Ces colonnes remaniées ont l’avantage d’être plus reproductibles que des colonnes non remaniées (Isensee et al., 1992). Les colonnes de sol non perturbées, prélevées directement sur le terrain, offrent quant à elles l’avantage de se rapprocher des conditions réelles et d’investiguer les flux préférentiels, l’effet de l’amendement, du travail du sol ou encore des cultures. Une deuxième modalité très variable est la taille de la colonne. Le diamètre de la colonne ainsi que la longueur de cette dernière varient fortement d’une expérience à l’autre sans justifications. Ainsi, l’objectif de cette étude est d’analyser l’impact des choix méthodologiques sur le comportement de lixiviation au sein d’une colonne de sol. Cette recherche vise à comparer l’effet de la structure du sol, du diamètre et de la hauteur des colonnes sur le comportement de lixiviation d’un soluté au sein d’une colonne de sol. Un pulse de CaCl2 a été appliqué à 15 colonnes de sol limoneux agricole prélevé à Gembloux. Des colonnes de sol remanié et non remanié, de 8,4 et de 24 cm de diamètre ainsi que de 20 et de 35 cm de hauteur ont été réalisées. Une hauteur d’eau de 2,21 cm a été appliquée régulièrement à la surface des colonnes. Le pH, la conductivité électrique et le volume de l’eau percolée ont été mesurés. Les résultats montrent une grande influence de la structure du sol sur la lixiviation du CaCl2. La courbe d’élution des colonnes remaniées montre un pic plus haut et plus fin que la courbe d’élution des colonnes non remaniées (figure 1). Le CaCl2 est rapidement lixivié des colonnes remaniées avec 65,9% de la masse de CaCl2 qui ressort après 10 cm d’eau percolé alors qu’il est plus longtemps retenu dans les colonnes en structure conservée où seulement 47,7% ressort après 10 cm d’eau percolé. De plus, après 16 cm d’eau percolé, 100% du CalCl2 est lixivié à travers la colonne contre 80,1 % pour les colonnes non remaniées. De plus, l’avantage des colonnes remaniées mis en avant dans la littérature est la plus grande reproductivité de ces colonnes. Or, les écarts-types des colonnes non remaniées sont en moyenne plus faible que les écarts-types des colonnes remaniées (40,5 mg L-1 pour les colonnes non remaniées contre 67,8 mg L-1 pour les colonnes remaniées). Le diamètre de la colonne a une influence moindre sur la lixiviation des solutés. La courbe d’élution des colonnes de 24 cm de diamètre et des colonnes de 8,4 cm de diamètre se suivent globalement (figure 1). Cependant, un plus grand effet de dispersion est observé dans les colonnes de 24 cm de diamètre avec un pic légèrement plus aplati et plus large. Ainsi, après 12 cm d’eau percolé, 91,5% de CaCl2 est ressorti pour les colonnes de 8,4 cm de diamètre contre 84,4% pour les colonnes de 24 cm de diamètre. La variation de la hauteur de la colonne de sol n’a pas une grande influence sur la courbe d’élution du CaCl2 excepté au niveau du pic, plus important pour les colonnes de 20 cm. En effet, le CaCl2 sort plus rapidement des colonnes de 20 cm que des colonnes de 35 cm. Après 10 cm d’eau percolé, 69,2 % du CaCl2 est ressorti des colonnes de 20 cm de haut contre 63,7% pour les colonnes de 35 cm de haut. La hauteur de la colonne de sol ainsi qu’une potentielle semelle de labour dans les colonnes de 35 cm pourraient également expliquer ces résultats. Afin de déterminer la dispersion du CaCl2 au sein des colonnes et l’influence de la semelle de labour, une modélisation des colonnes sur le logiciel Hydrus sera nécessaire.AIL4WaterQualit

Evaluation of PermaNet 3.0 a deltamethrin-PBO combination net against Anopheles gambiae and pyrethroid resistant Culex quinquefasciatus mosquitoes: an experimental hut trial in Tanzania

BACKGROUND: Combination mosquito nets incorporating two unrelated insecticides or insecticide plus synergist are designed to control insecticide resistant mosquitoes. PermaNet 3.0 is a long-lasting combination net incorporating deltamethrin on the side panels and a mixture of deltamethrin and synergist piperonyl butoxide (PBO) on the top panel. PBO is an inhibitor of mixed function oxidases implicated in pyrethroid resistance. METHOD: An experimental hut trial comparing PermaNet 3.0, PermaNet 2.0 and a conventional deltamethrin-treated net was conducted in NE Tanzania using standard WHOPES procedures. The PermaNet arms included unwashed nets and nets washed 20 times. PermaNet 2.0 is a long-lasting insecticidal net incorporating deltamethrin as a single active. RESULTS: Against pyrethroid susceptible Anopheles gambiae the unwashed PermaNet 3.0 showed no difference to unwashed PermaNet 2.0 in terms of mortality (95% killed), but showed differences in blood-feeding rate (3% blood-fed with PermaNet 3.0 versus 10% with PermaNet 2.0). After 20 washes the two products showed no difference in feeding rate (10% with 3.0 and 9% with 2.0) but showed small differences in mortality (95% with 3.0 and 87% with 2.0). Against pyrethroid resistant Culex quinquefasciatus, mediated by elevated oxidase and kdr mechanisms, the unwashed PermaNet 3.0 killed 48% and PermaNet 2.0 killed 32% but after 20 washes there was no significant difference in mortality between the two products (32% killed by 3.0 and 30% by 2.0). For protecting against Culex PermaNet 3.0 showed no difference to PermaNet 2.0 when either unwashed or after 20 washes; both products were highly protective against biting. Laboratory tunnel bioassays confirmed the loss of biological activity of the PBO/deltamethrin-treated panel after washing. CONCLUSION: Both PermaNet products were highly effective against susceptible Anopheles gambiae. As a long-lasting net to control or protect against pyrethroid resistant mosquitoes PermaNet 3.0 showed limited improvement over PermaNet 2.0 against Culex quinquefasciatus

Interceptor® long-lasting insecticidal net: phase III evaluation over three years of household use and calibration with Phase II experimental hut outcomes.

BACKGROUND: Long-lasting insecticidal nets (LN) are an effective tool for malaria prevention. The World Health Organization Pesticide Evaluation Scheme has established evaluation criteria to facilitate registration for public use. A household randomised trial was conducted in Tanzania according to WHOPES Phase III procedures to evaluate the alpha-cypermethrin coated Interceptor® LN (BASF) over three years' use. Outcomes were calibrated against results of Phase II experimental hut trials. METHODS: Interceptor LN (200 mg/m(2) alpha-cypermethrin) and conventionally treated nets CTN (40 mg/m(2) alpha-cypermethrin) were randomly distributed to 934 households. At 6-monthly intervals, household surveys recorded net use, durability, adverse effects, user acceptance and washing practices. Concurrently, 30 nets of each type were collected and tested for knock-down and kill of Anopheles gambiae mosquitoes in cone and tunnel bioassays. Alpha-cypermethrin content of nets was assessed annually. RESULTS: At 12 months 97% of Interceptor LN met the efficacy criteria by cone or tunnel test; this pass rate declined to 90% at 24 months and 87% at 36 months. In contrast only 63% of CTN met the efficacy criteria at 12 months, 14 % at 24 months and 0% at 36 months. The alpha-cypermethrin content at 36 months on Interceptor LN was 20% (42 ± 13 mg/m(2)) of the initial content but on CTNs only 4% (1.3 ± 1.6 mg/m(2)) remained. Interceptor LN was reported to be used year-round and washed 4.3 times/year. A few recalled facial tingling during the first days of use but this did not deter usage. The average number of holes at 36 months was 18, hole area per net was 229 cm(2) and hole index was 332. Insecticide content and cone bioefficacy of LN and CTN after 36 months' use were similar to that of LN and CTN used in earlier Phase II hut trials, but while the 20 times washed LN tested in experimental huts gave adequate personal protection the 20 times washed CTN did not. CONCLUSIONS: More than 80% Interceptor LN fulfilled the WHOPES Phase III criteria at 36 months and thus the LLIN was granted full WHO recommendation. Phase III outcomes at 36 months were anticipated by Phase II outcomes after 20 standardized washes

Median knock-down time as a new method for evaluating insecticide-treated textiles for mosquito control

<p>Abstract</p> <p>Background</p> <p>Insecticide treated bed nets are major tools for the Roll Back Malaria campaign. There are two types of Long-Lasting Insecticide-treated Nets (LNs) on the market: coated nets and insecticide-incorporated nets. Nets provided to this market need a recommendation from the World Health Organization to be purchased by donors and NGOs. During laboratory study (phase I), the first step consists in evaluating the wash resistance of a new LN product. When insecticide-incorporated nets are washed, it takes time to regenerate the insecticidal activity, i.e. insecticide must migrate to the net surface to be accessible to mosquitoes. The interval of time required for regeneration must be carefully determined to ensure the accuracy of further results. WHOPES procedures currently recommend the determination of the regeneration time by using mortality data. However, as mortality cannot exceed 100%, a LN that regenerates a surface concentration exceeding the dosage for 100% mortality, will have its regeneration time underestimated.</p> <p>Methods</p> <p>The Median Knock Down Time (MKDT) was determined as function of insecticide dosage on an inert surface, glass, and on polyester nettings using an acetone solution or a simple emulsion. Dosage response was also established for mortality data. The same method was then applied to a commercially polyethylene netting, currently under WHOPES evaluation, to determine the dynamics of regeneration as function of repeated washings. The deltamethrin content of these nets was estimated by Capillary Gas Chromatography (GC-ECD).</p> <p>Results</p> <p>MKDT was a linear function of log insecticide dosage on glass as on nettings. Mortality data were either 0 or 100% for most concentrations except for a narrow range. MKDT was log linear function of total deltamethrin content in a commercial polyethylene net exposed to washings. The regeneration time of this net increased with the number of washes and MKDT became higher. A new, easy and rapid method to determine MKDT is suggested.</p> <p>Discussion</p> <p>The MKDT is linearly correlated to log dosage on a given substrate and shows no saturation as mortality data do. It is suited to determine regeneration time of a product that is exposed to a stress, like washing or heating, where the process impacts on the bio-availability of the insecticide. Mortality data are useful for measuring product efficacy, whereas MKDT are better to measure dynamics of surface concentration like regeneration after a stressing process. Change in MKDT can be used to illustrate the loss of insecticide due to washing, but the slope of the curve is product and surface-dependent.</p