Comparison of species sensitivity distributions based on population or individual endpoints

International audienceSpecies sensitivity distributions (SSDs) developed from individual and population endpoints were compared based on simulations and a case study. The simulations were performed with five invertebrate species accounting for the diversity of benthic macroinvertebrate communities in large European lowland rivers and for five benthic invertebrates used as laboratory species. Population growth rate 10% effective concentration (EC10) values were, in most of the simulations, higher than the lowest of the EC10 values at the individual level. However, for the set of ecologically representative species, the fifth percentile level of this distribution (HC5) was more protective for population endpoints than for individual endpoints. This was the opposite for the set of laboratory species. Population and individual SSDs were also compared based on existing data on Cu for the five laboratory invertebrate species. In this case, the calculated population HC5 value was almost twice the individual value, and the authors showed much reduced variability between species sensitivities at population level compared with individual level. They conclude that population-based HC5 would generally be more protective than individual-based HC5. However, the change of level could reveal higher homogeneity at population level than at individual level, supporting the use of population-based HC5 to avoid overprotection. The authors thus advise the derivation of population-based HC5, as soon as it is possible, to derive such value with a relevant panel of species

Energy-based modelling to assess effects of chemicals on Caenorhabditis elegans: A case study on uranium

International audienceThe ubiquitous free-living nematode Caenorhabditis elegans is a powerful animal model for measuring the evolutionary effects of pollutants which is increasingly used in (eco)toxicological studies. Indeed, toxicity tests with this nematode can provide in a few days data on the whole life cycle. These data can be analysed with mathematical tools such as toxicokinetic-toxicodynamic modelling approaches. In this study, we assessed how a chronic exposure to a radioactive heavy metal (uranium) affects the life-cycle of C. elegans using a mechanistic model. In order to achieve this, we exposed individuals to a range of seven concentrations of uranium. Growth and reproduction were followed daily. These data were analysed with a model for nematodes based on the Dynamic Energy Budget theory, able to handle a wide range of plausible biological parameters values. Parameter estimations were performed using a Bayesian framework. Our results showed that uranium affects the assimilation of energy from food with a no-effect concentration (NEC) of 0.42 mM U which would be the threshold for effects on both growth and reproduction. The sensitivity analysis showed that the main contributors to the model output were parameters linked to the feeding processes and the actual exposure concentration. This confirms that the real exposure concentration should be measured accu-rately and that the feeding parameters should not be fixed, but need to be reestimated during the parameter estimation process

Analysis of community-level mesocosm data based on ecologically meaningful dissimilarity measures and data transformation

The principal response curve (PRC) method is a constrained ordination method developed specifically for the analysis of community data collected in mesocosm experiments, which provides easily understood summaries and graphical representations of community response to stress. It is a redundancy analysis method and is usually performed on log-transformed abundance data. The choice of a measure of dissimilarity between samples and the choice of the data transformation significantly affect the results of multivariate analysis. Dissimilarity measures that are more ecologically meaningful than the Euclidean distance can be incorporated into the PRC using distance-based redundancy analysis. The present study investigates the ordinations produced by a small selection of dissimilarity measures: the Euclidean distance using log-transformed and Hellinger-transformed data and the Bray-Curtis dissimilarity using raw and log-transformed data. It compares 2 data sets from experiments on the effect of the anti-inflammatory drug diclofenac and the insecticide chlorpyrifos on macroinvertebrate communities. The choice of dissimilarity measure can determine the outcome of a risk assessment. For the diclofenac data set, the PRCs were different depending on the dissimilarity measure: the community no-effect concentration was lowest for the Bray-Curtis on log-transformed data and Hellinger dissimilarity measures. For chlorpyrifos, however, the PRCs were similar for all dissimilarity measures

Modèle de la gestion de l’énergie sur l’ensemble du cycle de vie de l’épinoche à trois épines

A whole life-cycle bioenergetic model based on the dynamic energy budget (DEB) theory was developed for the threespined stickleback (Gasterosteus aculeatus). Experiments on growth and reproduction were performed: adult and juvenile growth, size at first reproduction and amount of eggs spawned by females were monitored under different feeding levels and water temperatures. The DEB parameters were estimated using Bayesian statistics based on the data produced during these experiments and on data found in the literature. The model fitted accurately the different datasets used for the calibration process and, in addition, predicted accurately the datasets used to assess its predictability. Our bioenergetic model of the whole life cycle of the three-spined stickleback accounting for environmental variations could contribute in many ways to improved ecological assessment: supporting change of scale from individual to populations, developing new biomarkers of exposure and effect, analysing ecotoxicity tests with biology-based models.L’épinoche à trois épines (Gasterosteus aculeatus) est un petit poisson téléostéen qui constitue un composant majeur des chaînes alimentaires des écosystèmes aquatiques peu profonds dans l’hémisphère nord. Ce poisson est aussi un des modèles expérimentaux les plus utilisés en écologie, évolution et éthologie aquatique. En particulier, l’épinoche à trois épines est une espèce sentinelle utilisée pour la surveillance des milieux aquatiques et une des espèces de poissons dont la dynamique de population peut être étudiée en mésocosmes. Les modèles mathématiques sont de plus en plus utilisés en évaluation des risques, notamment pour extrapoler les effets mesurés sur des individus lors d’expériences en laboratoire aux conséquences à long terme sur la viabilité des populations. Dans ce contexte, les modèles mécanistes de gestion de l’énergie par les organismes, qui prennent en compte des facteurs environnementaux, offrent une description réaliste du cycle de vie des individus. Ils peuvent également contribuer à réduire les données nécessaires pour développer un modèle de dynamique de population lorsqu’ils relient explicitement l’alimentation, la croissance et la reproduction et identifier les effets des composés toxiques sur les processus physiologiques des organismes

Effets du bisphénol a sur les écosystèmes aquatiques évalués en mésocosme

Bisphenol A (BPA) is commonly used by manufacturers and can be found in many aquatic ecosystems. Data relative to BPA ecotoxicity are only available for studies in laboratory conditions on macro-invertebrates and fish. There is thus a lack of information for other trophic levels such as macrophytes. Moreover, the impacts of BPA within an ecosystem context, i. e. with populations from different trophic levels studied at long term in environmental conditions, have never been assessed. We carried out a long-term lotic mesocosm study in 20 m long channels under three exposure concentrations of BPA (nominal concentrations of 0, 1, 10 and 100 μg/L) delivered continuously for 165 days. Three trophic levels were followed: macrophytes, macro-invertebrates (with a focus on Radix balthica) and fish (Gasterosteus aculeatus). Significant effects were shown at 100 μg/L BPA on the three trophic levels. BPA had a direct impact on macrophyte community structure, direct and indirect impacts on macroinvertebrates and on fish population structure. Gonad morphology of fish was affected at 1 and 10 μg/L of BPA, respectively for female and male sticklebacks. In addition to these ecotoxicity data, our results suggest that fish are good integrators of the responses of other communities (including macro-invertebrates and macrophytes) in mesocosm systems.Le bisphénol A (BPA ; 4,4’-dihydroxy-2,2-diphénylpropane) est une substance chimique de synthèse utilisée depuis plus de 50 ans. Un très grand nombre d’usages, d’articles et de préparations susceptibles de contenir du BPA ont été identifi és récemment. Ses deux principales utilisations sont la fabrication de matières plastiques de type polycarbonate et de résines époxydes. En raison de sa fréquente utilisation, le BPA est retrouvé régulièrement dans les eaux de surface à des concentrations proches du dixième de μg/L mais qui peuvent aller jusqu’à une vingtaine de μg/L. De plus, de nombreuses publications ont mis en évidence la capacité du BPA à perturber le système endocrinien chez différentes espèces animales. Par conséquent, la question d’effets possibles sur les écosystèmes aquatiques se pose. L’évaluation des substances chimiques s’appuie généralement sur la mise en oeuvre de bioessais pour évaluer l’écotoxicité des substances et établir des valeurs seuils de concentration. Ces tests standardisés présentent de nombreux avantages (reproductibilité, fi abilité, rapidité…) mais ont leurs limites : ils sont réalisés en conditions de laboratoire souvent peu représentatives des conditions écologiques (e.g., pas de prise en compte de la compétition pour la nourriture ou la prédation). Les écosystèmes artifi ciels (appelés mésocosmes) permettent d’étudier de manière plus « réaliste », du point de vue écologique, l’impact d’une substance chimique sur un système complexe de communautés d’organismes vivants. Les effets sur le système endocrinien des organismes aquatiques du BPA ont été observés en laboratoire, mais son impact environnemental dans des conditions écologiques réalistes est inconnu. Les effets à long terme du BPA ont donc été étudiés sur les organismes, populations et communautés aquatiques en mésocosmes

Multi-generational effect of an heavy metal pollution on Caenorhabditis elegans

Assessing the evolutionary responses of long-term exposed populations requires multigeneration ecotoxicity tests. However, the analysis of the data from these tests is not straightforward. Mechanistic models allow the in-depth analysis of the variation of physiological traits over many generations, by quantifying the trend of the physiological and toxicological parameters of the model. In this study we assessed the multi-generational effect of a heavy metal, namely uranium, on the life-history traits of an ubiquitous nematode, Caenorhabditis elegans..

Modelling BPA effects on the three-spined stickleback population dynamics in mesocosms to better understand the populational effects

Bisphenol A, a well-known endocrine-disrupting chemical, is ubiquitously present in an aquatic environment. Its impacts at populational level on three-spined sticklebacks have been studied in a long-term mesocosm experiment at low-dose BPA, however the causes explaining the observed effects have remained unclear. Here, we used an individual-based model coupled to a Dynamic Energy Budget model for (i) assessing the potential of modelling to predict impacts on population viability from organism ecotoxicological endpoints and (ii) provide insights on the mechanisms of BPA toxicity in the artificial streams. To do that, both direct and indirect effects of BPA on three-spined sticklebacks were incorporated in the model. BPA impacts on the physiological processes of fish have been identified based on literature data and effects on stickleback preys have been t into account using sampling data from exposed mesocosms. Simulations were made with the model integrating dose-responses only calibrated on literature data to assess the predictive capacity of the model. Then, simulations were made with a re-calibration of the toxic parameters on the populational data to better understand the observed BPA impacts found in mesocosms. Results showed that direct BPA effects on fish (impacts on gonad formation, growth, male reproductive behavior, eggs and larvae survival) mostly explained the three-spined stickleback population structure in mesocosms, but indirect effects were not negligible. Hence, this study showed the potential of modelling in risk assessment to predict the impacts on the fish population viability from behavioural and physiological effects measured on organism in controlled conditions

Modélisation intégrée de la perturbation endocrinienne à différents niveaux d'organisation biologique chez le poisson zèbre

The translation of subtle functional deficits within individuals into population-level effects is identified as a main challenge for the hazard and risk assessment of endocrine disruptor compounds (EDCs). Thus, the aim of MOZAIC project was to propose an integrated modelling framework for zebrafish (Danio reiro) to assess impacts of EDCs at different biological levels from the organism to the population. The first phase of the project was focused on the generation of new experimental data to fulfill the lack of knowledge concerning the zebrafish endocrinology and physiology. These original datasets were used to develop a physiologically-based pharmacokinetic (PBPK) for the zebrafish using validated and/or new QSAR/QSPR models to predict some toxicokinetic parameters. The impacts of EDCs on populations was predicted using a population dynamics model for zebrafish developed by coupling a model of individual bioenergetics with an individual-based model. The model was tested to predict the impacts of the ethinylestradiol at the population level conformed to these observed experimentally. The models which remain to be developed are those relating these different biological levels, in particular between hormonal disturbances and individual performances.Certains composés chimiques dénommés perturbateurs endocriniens (PE) possèdent la capacité de perturber le système endocrinien entraînant des dysfonctionnements de la reproduction et du développement des individus, entre autres. Un enjeu majeur pour l'évaluation des risques écologiques des PE est la traduction des déficits fonctionnels des individus en effets quantifiables au niveau des populations, i.e. un ensemble d'individus d'une même espèce se perpétuant dans un territoire donné et qui est l’unité biologique à protéger. Dans ce contexte, le projet MOZAIC, coordonné par l’INERIS, visait à proposer un ensemble de modèles mathématiques mécanistiques permettant d'évaluer les modifications hormonales dues aux PE et leurs incidences sur les performances des individus et sur la dynamique des populations. L’INERIS s’est intéressé à une espèce modèle le poisson zèbre (Danio rerio) très utilisée en écotoxicologie