A physiologically based toxicokinetic model for the zebrafish Danio rerio.

Zebrafish (Danio rerio) is a widely used model for toxicological studies, in particular those related to investigations on endocrine disruption. The development and regulatory use of in vivo and in vitro tests based on this species can be enhanced by toxicokinetic modeling. For this reason, we propose a physiologically based toxicokinetic (PBTK) model for zebrafish describing the uptake and disposition of organic chemicals. The model is based on literature data on zebrafish, other cyprinidae and other fish families, new experimental physiological information (volumes, lipids and water contents) obtained from zebrafish, and chemical-specific parameters predicted by generic models. The relevance of available models predicting the latter parameters was evaluated with respect to gill uptake and partition coefficients in zebrafish. This evaluation benefited from the fact that the influence of confounding factors such as body weight and temperature on ventilation rate was included in our model. The predictions for six chemicals (65 data points) yielded by our PBTK model were compared to available toxicokinetics data for zebrafish and 88% of them were within a factor of 5 of the corresponding experimental values. Sensitivity analysis highlighted that the 1-octanol/water partition coefficient, the metabolism rate, and all the parameters that enable the prediction of assimilation efficiency and partitioning of chemicals need to be precisely determined in order to allow an effective toxicokinetic modeling.

Nonlinear SAR Modelling of Mosquito Repellents for Skin Application.

Finding new marketable mosquito repellents is a complex and time-consuming process that can be optimized via modelling. In this context, a SAR (Structure-Activity Relationship) model was designed from a set of 2171 molecules whose actual repellent activity against Aedes aegypti was available. Information-rich descriptors were used as input neurons of a three-layer perceptron (TLP) to compute the models. The most interesting classification model was a 20/6/2 TLP showing 94% and 89% accuracy on the training set and test set, respectively. A total of 57 other artificial neural network models based on the same architecture were also computed. This allowed us to consider all chemicals both as training and test set members in order to better interpret the results obtained with the selected model. Most of the wrong predictions were explainable. The 20/6/2 TLP model was then used for predicting the potential repellent activity of new molecules. Among them, two were successfully evaluated in vivo.

Integrated Plan of Insecticide Resistance Surveillance in Mosquito Vectors in France.

Mosquito-borne diseases such as malaria, dengue, or chikungunya have been re-emerging all over the world, including in Europe. Managing resistance to public health pesticides in mosquitoes is essential and requires global, integrated, and coordinated actions and strong engagement of decision-makers, scientists, and public health operators. In this context, the present work aims at proposing an integrated plan of resistance surveillance in France and in the French Overseas territories in order to provide graduated and appropriate responses according to the situation. Briefly, the plan relies on periodic monitoring of insecticide resistance at the population level in predefined sites using adequate biological, molecular, and/or biochemical approaches and a stratification of the level of resistance risk at the scale of territory to adjust surveillance and vector control actions. The plan relies on the latest methods and indicators used for resistance monitoring as recommended by the World Health Organization in order to prevent or slow down its extension in space and time. The plan has been developed for France but can be easily adapted to other countries in order to provide a coordinated response to the growing problem of mosquito resistance in Europe.

Honeybee tracking with microchips: a new methodology to measure the effects of pesticides.

Losses of foraging bees are sometimes attributed to altered flight pattern between a meliferous plant treated with an insecticide and the hive. Only a limited number of studies has investigated the impact of pesticides on homing flight due to the difficulty of measuring the flight time between the food source and the hive. Monitoring the flights of the foraging bees needs their individual identification. The number of bees monitored simultaneously and the time span during which observations can be made limit most of the monitoring techniques. However, techniques of automatic tracking and identification of individuals have the potential to revolutionize the study of the ecotoxicological effects of xenobiotics on the bee behaviors. Radio Frequency Identification (RFID) offer numerous advantages such as an unlimited number of codes, a large number of simultaneous recording, and a quick reading, especially through materials (e.g., wood). The aim of this study was to show how the RFID device can be used to study the effects of pesticides on both the behavioral traits and the lifespan of bees. In this context, we have developed a method under tunnel to automatically record the displacements of foragers individualized with RFID tags and to detect the alteration of the flight pattern between an artificial feeder and the hive. Fipronil was selected as test substance due to the lack of information on the effects of this insecticide on the foraging behavior of free-flying bees. We showed that oral treatment of 0.3 ng of fipronil per bee (LD50/20) reduced the number of foraging trips. The strengths of our approach were briefly discussed.

Ecotoxicity of neonicotinoid insecticides to bees.

This chapter reviews the available data on the toxicity of neonicotinoid insecticides to bees that are the prominent and the most economically important group of pollinators worldwide. Classical and new methods developed to take into account the characteristics and different types of effects of the neonicotinoid insecticides to bees are described. The available toxicity results are critically analyzed. Thus, the nitro-substituted compounds (clothianidin, dinotefuran, imidacloprid and its metabolites, thiamethoxam, nitenpyram) appear the most toxic to bees. The cyano-substituted neonicotinoids seem to exhibit a much lower toxicity (acetamiprid and thiacloprid). The chapter ends with suggestions for additional studies aiming at better assess the hazard of this important insecticide family to bees.

Fate and ecotoxicological effects of pyriproxyfen in aquatic ecosystems.

Pyriproxyfen is an insect growth regulator acting as larvicide against a large spectrum of public health insect pests, especially dipterans. It is also widely used in agriculture and horticulture for the control of many insect species. Disrupting the endocrine system by mimicking the activity of the juvenile hormone, pyriproxyfen interferes with metamorphosis in insects and prevents them from reaching maturity and reproducing. Because the aquatic ecosystems can be directly or indirectly contaminated by pyriproxyfen, the goal of this study was to establish the aquatic ecotoxicological profile of pyriproxyfen and to identify the gaps that need to be filled. Pyriproxyfen is photodegraded quickly in water. In the absence of organic matter, its persistence in aerobic water media is also limited especially with high temperature and sunlight. Analysis of the laboratory and in situ results for more than 60 aquatic algae, plants, invertebrates, and vertebrates shows that the toxicity of pyriproxyfen is highly variable including within a same taxonomical group. Abiotic and biotic factors can highly influence the toxicity of the molecule. Pyriproxyfen disrupts the development of numerous species and adversely impacts various physiological events. It can also disturb the behavior of the organisms such as their predatory and swimming performances. Although some experimental studies focus on the environmental fate of pyriproxyfen metabolites, those dealing with their aquatic ecotoxicity assessment are scarce. In the same way, the limited number of studies dealing with the search of pyriproxyfen residues in lake, river, and other natural aquatic media does not include the identification of the metabolites.

Fate of Pyriproxyfen in Soils and Plants.

Since the 1990s, the insect growth regulator pyriproxyfen has been widely used worldwide as a larvicide in vector control and in agriculture to fight a very large number of pests. Due to its widespread use it is of first importance to know how pyriproxyfen behaves in the terrestrial ecosystems. This was the goal of this work to establish the fate profile of pyriproxyfen in soils and plants. Thus, in soil, pyriproxyfen photodegrades slowly but its aerobic degradation is fast. The insecticide presents a high tendency to adsorb onto soils and it is not subject to leaching into groundwater. On the contrary its two main metabolites (4'-OH-Pyr and PYPAC) show a different fate in soil. When sprayed to plants, pyriproxyfen behaves as a translaminar insecticide. Its half-life in plants ranges from less than one week to about three weeks. The review ends by showing how the fate profile of pyriproxyfen in soils and plants influences the adverse effects of the molecule on non-target organisms.

Lethal and Sublethal Effects of Pyriproxyfen on Apis and Non-Apis Bees.

Pyriproxyfen is a juvenile hormone mimic used extensively worldwide to fight pests in agriculture and horticulture. It also has numerous applications as larvicide in vector control. The molecule disrupts metamorphosis and adult emergence in the target insects. The same types of adverse effects are expected on non-target insects. In this context, the objective of this study was to evaluate the existing information on the toxicity of pyriproxyfen on the honey bee (Apis mellifera) and non-Apis bees (bumble bees, solitary bees, and stingless bees). The goal was also to identify the gaps necessary to fill. Thus, whereas the acute and sublethal toxicity of pyriproxyfen against A. mellifera is well-documented, the information is almost lacking for the non-Apis bees. The direct and indirect routes of exposure of the non-Apis bees to pyriproxyfen also need to be identified and quantified. More generally, the impacts of pyriproxyfen on the reproductive success of the different bee species have to be evaluated as well as the potential adverse effects of its metabolites.

The COVID-19 pandemic should not jeopardize dengue control.

The concurrent circulation of dengue and coronavirus disease 2019 (COVID-19) may produce many unfavourable outcomes-such as co-infections; delays in diagnosis, treatment, and mitigation measures; overwhelming of the healthcare system; underreporting of cases; deterioration in surveillance and control interventions; and exacerbation of social inequalities. Indeed, lockdown is greatly compromising the effectiveness of vector control, especially social mobilization campaigns and preventive insecticide spraying in private spaces (indoor and peridomestic spraying). Thus, failure to appropriately implement the full range of vector control interventions can lead to a reduction in their overall effectiveness and an increasing risk of vector-borne diseases circulating. Consequently, the health community and policy makers should develop proactive policies and allocate adequate resources to prevent and manage the resurgence of dengue and other vector-borne diseases in the new era of COVID-19.

Artificial neural network modeling in environmental toxicology.

Artificial neural networks are increasingly used in environmental toxicology to find complex relationships between the ecotoxicity of xenobiotics and their structure and/or physicochemical properties. The raison d'etre of these nonlinear tools is their ability to derive powerful QSARs for molecules presenting different mechanisms of action. In this chapter, the main QSAR models derived for aquatic and terrestrial species are reviewed. Their characteristics and modeling performances are deeply analyzed.

Selecting a battery of bioassays for ecotoxicological characterization of wastes.

This study was conducted in France within the context of waste classification (Hazardous Waste Council Directive 91/689/EEC), and focused on "ecotoxic" property (H14). In 1998, an experimental test strategy was developed to assess ecotoxicological properties of wastes using a battery of six standardized bioassays. This combined direct and indirect approaches integrating two solid-phase tests: emergence and growth inhibition of Lactuca sativa (14 days), mortality of Eisenia fetida (14 days) and four standardized tests performed on water extracts from wastes: growth inhibition of Pseudokirchneriella subcapitata (3 days), inhibition of mobility of Daphnia magna (48 h), inhibition of reproduction of Ceriodaphnia dubia (7 days), inhibition of light emission of Vibrio fischeri (30 min). This study aimed to set up preliminary conclusions on relevancy of this experimental test strategy, based on data obtained since 1998. Results were analyzed from the combined use of Hierarchical Cluster Analysis, Principal Component Analysis and Nonlinear Mapping. These multivariate analyses clearly showed that it was possible to reduce this number of tests without changing the typology of the wastes. A battery of bioassays including one solid phase test and two tests performed on water extracts (L. sativa, V. fischeri and C. dubia) was found as an optimal solution for characterizing the toxicity of the studied wastes. This optimal battery represents a good basis for determining the H14 property.

Residues of plant protection products in grey partridge eggs in French cereal ecosystems.

The contamination of the eggs of farmland birds by currently used plant protection products (PPPs) is poorly documented despite a potential to adversely impact their breeding performance. In this context, 139 eggs of 52 grey partridge Perdix perdix clutches, collected on 12 intensively cultivated farmlands in France in 2010-2011, were analysed. Given the great diversity of PPPs applied on agricultural fields, we used exploratory GC/MS-MS and LC/MS-MS screenings measuring ca. 500 compounds. The limit of quantification was 0.01 mg/kg, a statutory reference. A total of 15 different compounds were detected in 24 clutches. Nine of them have been used by farmers to protect crops against fungi (difenoconazole, tebuconazole, cyproconazole, fenpropidin and prochloraz), insects (lambda-cyhalothrin and thiamethoxam/clothianidin) and weeds (bromoxynil and diflufenican). Some old PPPs were also detected (fipronil(+sulfone), HCH(α,ß,δ isomers), diphenylamine, heptachlor(+epoxyde), DDT(Σisomers)), as well as PCBs(153, 180). Concentrations ranged between <0.01 and 0.05 mg/kg but reached 0.067 (thiamethoxam/clothianidin), 0.11 (heptachlor + epoxyde) and 0.34 (fenpropidin) mg/kg in some cases. These results testify an actual exposure of females and/or their eggs to PPPs in operational conditions, as well as to organochlorine pollutants or their residues, banned in France since several years if not several decades, that persistently contaminate the environment.Routes of exposure, probability to detect a contamination in the eggs, and effects on egg/embryo characteristics are discussed with regard to the scientific literature.

Quantification of potential exposure of gray partridge (Perdix perdix) to pesticide active substances in farmlands.

Estimating exposure of wild birds to plant protection products is of key importance in the risk assessment process evaluating their harmful potential. In this paper, we propose an ecologically-relevant methodology to estimate potential exposure to active substances (ASs) of a farmland focal bird, the gray partridge Perdix perdix. It is based on bird habitat use of fields at the time of pesticide applications. It accounts for spatio-temporal heterogeneity at population and landscape scales. We identify and quantify the potential exposure to 179 ASs of 140 clutches during pre-laying, laying, and incubation phases, and of 75 coveys. The data come from a large scale field study combining radiotelemetry and a farmer survey. They were collected in 12 different representative sites. The proportion of clutches potentially exposed to a given chemical was ≥5% for 32 ASs; prothioconazole and epoxiconazole ranking first. 71% of clutches were potentially exposed to ≥1 AS and 67% to ≥2 ASs. Mixtures involved 2 to 22 ASs. They emerged from commercial formulations, tank mixtures, bird habitat use, and combinations. ASs were fungicides (53%), herbicides (25%), and insecticides (16%) used on a variety of crops in April-June, when ground-nesting birds are breeding. The European Food Safety Authority conclusions report a long-term first-tier toxicity-to-exposure ratio (TERlt) <5 for 11 out of 19 documented ASs, and higher-tier TERlt <5 for 5 out of 10 ASs. This suggests a potential risk for bird reproduction in farmlands. Globally 13% of coveys were potentially exposed to 18 ASs during the first month (1-4 coveys per AS). The use of our field data in future research and risk assessment is discussed.

An individual-based model of zebrafish population dynamics accounting for energy dynamics.

Developing population dynamics models for zebrafish is crucial in order to extrapolate from toxicity data measured at the organism level to biological levels relevant to support and enhance ecological risk assessment. To achieve this, a dynamic energy budget for individual zebrafish (DEB model) was coupled to an individual based model of zebrafish population dynamics (IBM model). Next, we fitted the DEB model to new experimental data on zebrafish growth and reproduction thus improving existing models. We further analysed the DEB-model and DEB-IBM using a sensitivity analysis. Finally, the predictions of the DEB-IBM were compared to existing observations on natural zebrafish populations and the predicted population dynamics are realistic. While our zebrafish DEB-IBM model can still be improved by acquiring new experimental data on the most uncertain processes (e.g. survival or feeding), it can already serve to predict the impact of compounds at the population level.

Larval Exposure to the Juvenile Hormone Analog Pyriproxyfen Disrupts Acceptance of and Social Behavior Performance in Adult Honeybees.

BACKGROUND: Juvenile hormone (JH) plays an important role in honeybee development and the regulation of age-related division of labor. However, honeybees can be exposed to insect growth regulators (IGRs), such as JH analogs developed for insect pest and vector control. Although their side effects as endocrine disruptors on honeybee larval or adult stages have been studied, little is known about the subsequent effects on adults of a sublethal larval exposure. We therefore studied the impact of the JH analog pyriproxyfen on larvae and resulting adults within a colony under semi-field conditions by combining recent laboratory larval tests with chemical analysis and behavioral observations. Oral and chronic larval exposure at cumulative doses of 23 or 57 ng per larva were tested. RESULTS: Pyriproxyfen-treated bees emerged earlier than control bees and the highest dose led to a significant rate of malformed adults (atrophied wings). Young pyriproxyfen-treated bees were more frequently rejected by nestmates from the colony, inducing a shorter life span. This could be linked to differences in cuticular hydrocarbon (CHC) profiles between control and pyriproxyfen-treated bees. Finally, pyriproxyfen-treated bees exhibited fewer social behaviors (ventilation, brood care, contacts with nestmates or food stocks) than control bees. CONCLUSION: Larval exposure to sublethal doses of pyriproxyfen affected several life history traits of the honeybees. Our results especially showed changes in social integration (acceptance by nestmates and social behaviors performance) that could potentially affect population growth and balance of the colony.

Ecotoxicity of ethylene glycol monomethyl ether and its acetate.

Ethylene glycol monomethyl ether (EGME) and ethylene glycol monomethyl ether acetate (EGMEA) have been tested for their acute and chronic toxicity to various organisms occupying different trophic levels in the aquatic ecosystems. The results obtained in this study and those collected from the literature clearly reveal that EGME does not present short- or long-term ecotoxic effects in the ranges of concentrations likely to be found in aquatic environments. Indeed, in general, concentrations of 1000 to 10,000 mg/L of EGME are necessary before significant adverse effects can be observed in aquatic species. Conversely, acute toxicity occurs in fish at about 50 mg/L of EGMEA, and reproduction of Ceriodaphnia dubia is affected by 0.06 mg/L of this chemical. A teratogenic effect-with a specific malformation of the eyes-occurs in Xenopus laevis in the presence of 75 mg/L of EGMEA. This study was partially supported by the French Ministry of the Environment as part of the PNETOX program (1998).

Ecotoxicity of ethylene glycol monobutyl ether and its acetate.

Ethylene glycol monobutyl ether (EGBE) and ethylene glycol monobutyl ether acetate (EGBEA) were tested for their acute and chronic toxicity to various organisms occupying different trophic levels in the aquatic ecosystems. The obtained results and those collected from the literature clearly show that EGBE affects the survival, growth, and reproduction of aquatic organisms only at concentrations of approximately 100 mg/L or more. EGBEA appears to be slightly more ecotoxic to aquatic species. At 1000 and 10,000 mg/L, both chemicals strongly affect the early stages of development of the Japanese oyster, but such concentrations are too high to be found in aquatic environments. Micronucleus tests on Xenopus laevis show that EGBE and EGBEA are not genotoxic in the range of concentrations tested. Consequently, neither chemical presents a risk to the aquatic environment. EGBE does affect the gonadosomatic index of adult male zebra fish (Danio rerio); however, these are preliminary results and must be confirmed by additional experiments. This study was partially supported by the French Ministry of the Environment as part of the PNETOX program (1998).

Methods for building QSARs.

Structure-activity relationship (SAR) and quantitative structure-activity relationship (QSAR) models are increasingly used in toxicology, ecotoxicology, and pharmacology for predicting the activity of the molecules from their physicochemical properties and/or their structural characteristics. However, the design of such models has many traps for unwary practitioners. Consequently, the purpose of this chapter is to give a practical guide for the computation of SAR and QSAR models, point out problems that may be encountered, and suggest ways of solving them. Attempts are also made to see how these models can be validated and interpreted.

Effects of imidacloprid and deltamethrin on associative learning in honeybees under semi-field and laboratory conditions.

We have compared the sublethal effects of two insecticides in the honeybee (imidacloprid and deltamethrin) in both semi-field and laboratory conditions. A sugar solution containing 24 microg kg(-1) of imidacloprid or 500 microg kg(-1) of deltamethrin was offered to a colony set in an outdoor flight cage. In contrast to imidacloprid, deltamethrin had lethal effect on workers bees. The contamination of syrup with imidacloprid or deltamethrin induced a decrease in both the foraging activity on the food source and activity at the hive entrance. Negative effects of imidacloprid were also observed in an olfactory learnt discrimination task. Free-flying foragers were taken from the contaminated feeder and subjected to a conditioned proboscis extension response (PER) assay under laboratory conditions. As with free-flying bees, no impact of deltamethrin was found on the learning performances of restrained individuals in the PER procedure, whilst significant effects were found with imidacloprid in both semi-field and laboratory conditions.