L'asymétrie fluctuante un biomarqueur morphométrique pour évaluer la qualité de l'environnement

Un des défis pour les scientifiques en environnement est de signaler, d'analyser, de prédire et d'évaluer les effets des activités humaines sur l'environnement. L'objectif de cette thèse était de démontrer la pertinente de l'asymétrie fluctuante des organismes comme biomarqueur morphométrique pour évaluer la qualité de l'environnement. L'asymétrie fluctuante d'un organisme est une petite déviation aléatoire à partir d'une symétrie bilatérale parfaite qui résulte d'un stress génétique et/ou environnemental durant le développement. Pour atteindre cet objectif, l'impact de l'épandage sylvicole des boues d'épuration des eaux usées municipales sur la qualité de l'environnement a été évalué à l'aide de méthodes couramment utilisées (e.g. analyse chimique) pour détecter la présence de contaminante et à partir de l'estimation de l'asymétrie fluctuante de deux espèces animales (un micromammifère herbivore et un insecte prédateur). Les boues d'épuration municipale contiennent des éléments nutritifs qui peuvent améliorer la croissance des végétaux et entre autres celles des arbres. Un an après l'épandage de boues d'épuration, une première série d'expériences a montré que les teneurs en cadmium, plomb, et mercure (trois métaux considérés comme très toxiques) mesurées dans les feuilles des arbres et dans les micromammifères pouvait être considérée comme sans effet biologique négatif. De plus, dès la première année, les boues ont amélioré la croissance en hauteur des chênes blancs (Quercus alba L.). Une deuxième série d'expériences a démontré que l'épandage des boues n'augmentait pas la charge en helminthes (parasites) dans la cavité générale et le tube digestif des campagnols des champs (Microtus pennsylvanicus) et des musaraignes (Blarina brevicauda). Ces premiers résultats -- à court terme -- suggèrent que l'application des boues, respectant la réglementation établie par le gouvernement québécois, permet de garantir une certaine qualité de l'environnement, tout en favorisant la croissance de certaines espèces d'arbres. Ces résultats ont été confirrnés en estimant l'asymétrie fluctuante des campagnols et d'un insecte prédateur (Pterostichus melanarius). L'asymétrie fluctuante des animaux prélevés sur les parcelles traitées par les boues d'épuration municipale n'était pas significativement différente de celle des animaux habitant des parcelles témoins. La principale conclusion de cette étude est que l'asymétrie fluctuante représente un indicateur de stress environmental [i.e. environnemental] peu coûteux, rapidement applicable, sensible et complémentaire aux analyses chimiques ou aux biomarqueurs biochimiques pour évaluer la qualité de l'environnement. Cependant, d'autres travaux de recherches sont encore nécessaires pour s'assurer de la réelle valeur de ce biomarqueur dans diverses conditions de stress."--Résumé abrégé par UM

Alteration of leaf decomposition in copper-contaminated freshwater mesocosms

The influence of copper on leaf litter decomposition was examined in experimental streams. Controls and three levels of contamination (5, 25, and 75 microg/L) were tested in triplicate in 20-m-long mesocosms. Equal quantities of alder, maple, and oak leaves were enclosed in mesh bags and placed in the upper and lower mesocosm sections that exhibited different habitat characteristics (shallow with pebble substrate or deep with fine substrate and macrophytes, respectively). Decomposition rate in the upper section of the 75 micro.g/L mesocosms was significantly reduced to 28% of control values. No significant reductions in the decomposition rate were seen in the lower section. No differences in the leaf-associated mycelial biomass and sporulation rates were observed between treatments, but they were consistently higher in the upper sections. The aquatic hyphomycete community was not affected by the contamination. The abundances of total leaf-associated macroinvertebrates and the dominant shredder (Gammarus pulex) were considerably reduced in the upper sections at 75 microg/L. Therefore, the reduced leaf decomposition probably resulted from a reduction in the abundance of macroinvertebrate detritivores. In addition, local variations in physical and biological characteristics of the habitat along the mesocosms significantly influenced the effects of copper on leaf-associated decomposers

A long-term copper exposure on freshwater ecosystem using lotic mesocosms: Individual and population responses of three-spined sticklebacks (Gasterosteus aculeatus)

Three-spined stickleback (Gasterosteus aculeatus) was used as the highest trophic level predator in an outdoor mesocosm study assessing the effect of environmentally realistic copper concentration (0, 5, 25 and 75 μg L−1) over 18 months of continuous exposure. Condition factor, organosomatic indices (HIS, GSI and SSI) as well as copper bioaccumulation in the liver were measured at 15 days, 2, 4, 6, 10, 14 and 18 months after the beginning of the contamination. Population monitoring was realised after 6 and 18 months of contamination, allowing two reproduction periods to be measured. Results showed that condition factor was affected at medium and high copper concentrations and HSI was sporadically affected in all copper exposure, depending on the sex of the fish. GSI did not show any significant differences and SSI was lowered in the medium and high copper levels. Bioaccumulation was significantly different in males and females and fluctuated with season. A negative correlation was observed between copper bioaccumulation in the liver and fish size and a positive correlation with nominal copper concentration in the water was found. There was a negative correlation between condition factor, organosomatic indices and bioaccumulation in the liver. Population monitoring showed a significantly higher fish mean length after 6 months and a higher abundance after 18 months of exposure at the highest copper level. We conclude that indirect effects such as food and habitat availability or lower predation pressure on eggs and juveniles might have led to higher stickleback population abundances at the highest copper level. This highlights the need to study all the trophic levels when monitoring ecosystem health. Considering the population and the individual responses after 18 months of copper exposure, the NOEC for three-spined sticklebacks was 25 μg L−1 (or 20 μg L−1 if we consider the average effective concentration), with a LOEC of 75 μg L−1 (or 57 μg L−1, AEC)

Influence of Chironomus riparius (Diptera, Chironomidae) and Tubifex tubifex (Annelida, Oligochaeta) on oxygen uptake by sediments. Consequences of uranium contamination

The diffusive oxygen uptake (DOU) of sediments inhabited by Chironomus riparius and Tubifex tubifex was investigated using a planar oxygen optode device, and complemented by measurements of bioturbation activity. Additional experiments were performed within contaminated sediments to assess the impact of uranium on these processes. After 72 h, the two invertebrate species significantly increased the DOU of sediments (13–14%), and no temporal variation occurred afterwards. Within contaminated sediments, it was already 24% higher before the introduction of the organisms, suggesting that uranium modified the sediment biogeochemistry. Although the two species firstly reacted by avoidance of contaminated sediment, they finally colonized it. Their bioturbation activity was reduced but, for T. tubifex, it remained sufficient to induce a release of uranium to the water column and an increase of the DOU (53%). These results highlight the necessity of further investigations to take into account the interactions between bioturbation, microbial metabolism and pollutants

Assessment of exposure to ionizing radiation in Chernobyl tree frogs (Hyla orientalis)

Ionizing radiation can damage organic molecules, causing detrimental effects on human and wildlife health. The accident at the Chernobyl nuclear power plant (1986) represents the largest release of radioactive material to the environment. An accurate estimation of the current exposure to radiation in wildlife, often reduced to ambient dose rate assessments, is crucial to understand the long-term impact of radiation on living organisms. Here, we present an evaluation of the sources and variation of current exposure to radiation in breeding Eastern tree frogs (Hyla orientalis) males living in the Chernobyl Exclusion Zone. Total absorbed dose rates in H. orientalis were highly variable, although generally below widely used thresholds considered harmful for animal health. Internal exposure was the main source of absorbed dose rate (81% on average), with 90Sr being the main contributor (78% of total dose rate, on average). These results highlight the importance of assessing both internal and external exposure levels in order to perform a robust evaluation of the exposure to radiation in wildlife. Further studies incorporating life-history, ecological, and evolutionary traits are needed to fully evaluate the effects that these exposure levels can have in amphibians and other taxa inhabiting radio-contaminated environments

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

Effects of radionuclide contamination on leaf litter decomposition in the Chernobyl exclusion zone

The effects of radioactive contamination on ecosystem processes such as litter decomposition remain largely un- known. Because radionuclides accumulated in soil and plant biomass can be harmful for organisms, the function- ing of ecosystems may be altered by radioactive contamination. Here, we tested the hypothesis that decomposition is impaired by increasing levels of radioactivity in the environment by exposing uncontaminated leaf litter from silver birch and black alder at (i) eleven distant forest sites differing in ambient radiation levels (0.22–15 μGy h−1) and (ii) along a short distance gradient of radioactive contamination (1.2–29 μGy h−1) within a single forest in the Chernobyl exclusion zone. In addition to measuring ambient external dose rates, we estimat- ed the average total dose rates (ATDRs) absorbed by decomposers for an accurate estimate of dose-induced eco- logical consequences of radioactive pollution. Taking into account potential confounding factors (soil pH, moisture, texture, and organic carbon content), the results from the eleven distant forest sites, and from the single forest, showed increased litter mass loss with increasing ATDRs from 0.3 to 150 μGy h−1. This unexpected result may be due to (i) overcompensation of decomposer organisms exposed to radionuclides leading to a higher decomposer abundance (hormetic effect), and/or (ii) from preferred feeding by decomposers on the un- contaminated leaf litter used for our experiment compared to locally produced, contaminated leaf litter. Our data indicate that radio-contamination of forest ecosystems over more than two decades does not necessarily have detrimental effects on organic matter decay. However, further studies are needed to unravel the underlying mechanisms of the results reported here, in order to draw firmer conclusions on how radio-contamination affects decomposition and associated ecosystem processes

Toxicity of CeO2 nanoparticles on a freshwater experimental trophic chain: A study in environmentally relevant conditions through the use of mesocosms

The toxicity of CeO2 NPs on an experimental freshwater ecosystem was studied in mesocosm, with a focus being placed on the higher trophic level, i.e. the carnivorous amphibian species Pleurodeles waltl. The system comprised species at three trophic levels: (i) bacteria, fungi and diatoms, (ii) Chironomus riparius larvae as primary consumers and (iii) Pleurodeles larvae as secondary consumers. NP contamination consisted of repeated additions of CeO2 NPs over 4 weeks, to obtain a final concentration of 1 mg/L. NPs were found to settle and accumulate in the sediment. No effects were observed on litter decomposition or associated fungal biomass. Changes in bacterial communities were observed from the third week of NP contamination. Morphological changes in CeO2 NPs were observed at the end of the experiment. No toxicity was recorded in chironomids, despite substantial NP accumulation (265.8±14.1mg Ce/kg). Mortality (35.3±6.8%) and a mean Ce concentration of 13.5±3.9mg/kg were reported for Pleurodeles. Parallel experiments were performed on Pleurodeles to determine toxicity pathways: no toxicity was observed by direct or dietary exposures, although Ce concentrations almost reached 100 mg/kg. In view of these results, various toxicity mechanisms are proposed and discussed. The toxicity observed on Pleurodeles in mesocosm may be indirect, due to microorganism’s interaction with CeO2 NPs, or NP dissolution could have occurred in mesocosm due to the structural complexity of the biological environment, resulting in toxicity to Pleurodeles. This study strongly supports the importance of ecotoxicological assessment of NPs under environmentally relevant conditions, using complex biological systems

RETRATO SIN IDENTIFICAR [Material gráfico]

Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201

L'asymétrie fluctuante un biomarqueur morphométrique pour évaluer la qualité de l'environnement

Un des défis pour les scientifiques en environnement est de signaler, d'analyser, de prédire et d'évaluer les effets des activités humaines sur l'environnement. L'objectif de cette thèse était de démontrer la pertinente de l'asymétrie fluctuante des organismes comme biomarqueur morphométrique pour évaluer la qualité de l'environnement. L'asymétrie fluctuante d'un organisme est une petite déviation aléatoire à partir d'une symétrie bilatérale parfaite qui résulte d'un stress génétique et/ou environnemental durant le développement. Pour atteindre cet objectif, l'impact de l'épandage sylvicole des boues d'épuration des eaux usées municipales sur la qualité de l'environnement a été évalué à l'aide de méthodes couramment utilisées (e.g. analyse chimique) pour détecter la présence de contaminante et à partir de l'estimation de l'asymétrie fluctuante de deux espèces animales (un micromammifère herbivore et un insecte prédateur). Les boues d'épuration municipale contiennent des éléments nutritifs qui peuvent améliorer la croissance des végétaux et entre autres celles des arbres. Un an après l'épandage de boues d'épuration, une première série d'expériences a montré que les teneurs en cadmium, plomb, et mercure (trois métaux considérés comme très toxiques) mesurées dans les feuilles des arbres et dans les micromammifères pouvait être considérée comme sans effet biologique négatif. De plus, dès la première année, les boues ont amélioré la croissance en hauteur des chênes blancs (Quercus alba L.). Une deuxième série d'expériences a démontré que l'épandage des boues n'augmentait pas la charge en helminthes (parasites) dans la cavité générale et le tube digestif des campagnols des champs (Microtus pennsylvanicus) et des musaraignes (Blarina brevicauda). Ces premiers résultats -- à court terme -- suggèrent que l'application des boues, respectant la réglementation établie par le gouvernement québécois, permet de garantir une certaine qualité de l'environnement, tout en favorisant la croissance de certaines espèces d'arbres. Ces résultats ont été confirrnés en estimant l'asymétrie fluctuante des campagnols et d'un insecte prédateur (Pterostichus melanarius). L'asymétrie fluctuante des animaux prélevés sur les parcelles traitées par les boues d'épuration municipale n'était pas significativement différente de celle des animaux habitant des parcelles témoins. La principale conclusion de cette étude est que l'asymétrie fluctuante représente un indicateur de stress environmental [i.e. environnemental] peu coûteux, rapidement applicable, sensible et complémentaire aux analyses chimiques ou aux biomarqueurs biochimiques pour évaluer la qualité de l'environnement. Cependant, d'autres travaux de recherches sont encore nécessaires pour s'assurer de la réelle valeur de ce biomarqueur dans diverses conditions de stress."--Résumé abrégé par UM