Discrimination des sources de contamination et des voies du mercure au moyen de ses isotopes stables chez le bar commun, Dicentrarchus labrax.

Mercury (Hg) is a persistent toxic compound whose amount in the global biosphere has at least tripled since industrialization. The biogeochemical cycle of mercury is particularly complex because elemental mercury is very volatile, has a long residence time in the atmosphere and thus can potentially reach locations that are very distant from the initial emission source. Since the 70’s, many international organisations (OECD, EU, UNEP) have implemented different policies to reduce Hg pollution. However, for these policies to be efficient, the polluters/Hg sources have to be fully assessed and identified. So, there is a crucial need to trace Hg sources and to assess the quantitative impact of local versus global Hg sources on ecosystems. Recently, the study of the seven Hg stable isotopes has emerged as a new promising technique affording to explore the Hg cycle both in situ and in laboratory. Mercury stable isotopes display both mass dependent fractionation (MDF, reported as δ202Hg) and mass independent fractionation (MIF, reported as Δ199Hg and Δ201Hg). The combination of both values should allow to trace back sources and pathways of Hg and methylmercury (MeHg). But, so far, few studies have considered Hg isotopes in marine vertebrates. Thus, the general objective of this thesis was to study a marine predator, the European seabass, Dicentrarchus labrax, to explore the possibility of using mercury stable isotopes to investigate Hg sources and pathways in European coastal waters. Our specific objectives were to characterize the Hg profile (THg, MeHg and isotopy) of wild populations of seabass, to assess whether Hg isotopes differed between populations and could give indications on Hg sources, with special attention paid to differentiate local versus global Hg sources. We also wanted to explore internal variation of Hg profiles by comparing several tissues. And, we wanted to validate our interpretations of in situ results by experimentally evaluating the potential fractionation between muscle and liver tissues of D. labrax, and between the diet and fish tissues. To fulfill our objectives, we split the thesis in 3 axes. First, juvenile seabass were collected in seven geographically distinct locations: the Agiasma lagoon in the northern Aegean Sea (AeS), the North Sea (NS) along Belgian and English coasts, the Seine estuary (SE), the Turkish coast of the Black Sea (BS), the Marano and Grado lagoons in the northern Adriatic Sea (NAS), the Portuguese lagoon, Ria de Aveiro, at two distinct sites: a very contaminated one (RAC) and a least contaminated one (RAR). v Our results showed seabass displayed extremely variable THg (Total mercury) concentrations amongst locations. Environmental contamination of the fish habitats seemed to be the main driving factor of THg concentrations in their tissues. Then, we showed that the populations also had distinct Hg isotopic niches (using SIBER on Hg stable isotopes, a premiere!), and that Hg isotopes (Δ199Hg and δ202Hg) could be used as a discriminating tool. We showed that Hg isotopes also told more about the origin of THg contaminating juvenile seabass: Δ199Hg values indicated a rather coastal MeHg source while δ202Hg could be linked with the global versus local Hg origin. Some populations like AeS were thought to be affected mainly by background, global Hg source, while other sites such as RAC (and SE and NAS) that were more heavily contaminated, would undergo a strong influence of local contamination. The previous observations were made in muscle tissue. Since different tissues often have distinct turnover times and different affinity for pollutants, the second axis of this thesis aimed at comparing liver and muscle results. So, we investigated the liver tissue of the very same individuals than in axis 1. The THg RATIO (THgliver/THgmuscle) was very variable amongst populations. We found that Hg organotropism (affinity for different organs) was influenced by the overall contamination level and maybe also by the food regime (via the %MeHg in diet). The Hg isotope composition also differed between muscle and liver of wild seabass. Hg speciation was most probably not the only cause of such a difference, and there was certainly an internal fractionating process (MDF). We even found serious indication of mercury demethylation happening in seabass, although demethylation in fish had yet to be proven. This is what our 3rd axis addressed. We exposed captive juvenile seabass to environmentally relevant THg concentrations through the diet. Observations confirmed in situ results: Hg organotropism depends on the %MeHg in diet, and THg RATIOs < 1 are to be related to the extremely small proportion of inorganic Hg in the seabass diet. Most of all, we found strong and concordant indications of demethylation process occurring in seabass that would be responsible for the systematically distinct δ202Hg values observed between muscle and liver. In conclusion, our findings constitute the first large scale Hg stable isotope study, on a single fish species, from European coastal waters. They demonstrate the interest and relevance of using Hg stable isotopes to investigate the Hg cycle and sources on both small and large scales and show the possibility to differentiate between global and local Hg sources. This takes a crucial sense in the current context where tracing Hg contamination sources is necessary to implement efficient environmental policies.Discrimination of Hg contamination sources in European seabass usin Hg stable isotope

Techniques de regularisation et de lissage en analyse discriminante

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 81762 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Using features of mercury and methylmercury to discriminate contamination profiles between sea bass, Dicentrarchus labrax, populations

Despite many efforts consented in the last decades, Mercury (Hg) emissions have kept rising worldwide. Currently, anthropogenic inputs dominate Hg emissions to the atmosphere by far, natural releases accounting only for a 4th of the total. Because Hg has a stable gaseous form (Hg0) with a long residence time in the atmosphere (~1year), both natural and industrially produced Hg can be transported far from point sources. Therefore, many uncertainties remain in our knowledge about Hg biogeochemistry. Our study aims at identifying the different Hg forms found in marine predators in order to discriminate different polluted areas and potential pollution sources. More specifically, we seek to discriminate contaminations of local origins versus contamination of global origins. To achieve this, we are currently studying different sea bass, Dicentrarchus labrax, populations from the Atlantic Ocean and Mediterranean. In muscle, liver, kidney and brain tissues, we analyze total Mercury (THg) and methylmercury (MeHg). We are also testing the discrimination power of Hg's stable isotopes (199Hg, 201Hg and 202Hg). Indeed, recent findings show that Hg isotopes can exhibit both mass-dependent (MDF) and mass-independent fractionation (MIF). This means that Hg isotopes provide two different types of information at once, both on biological cycling of Hg, including bioaccumulation (MDF), and on chemical pathways such as photochemical transformations (MIF). Eventually, we are planning to extend our results with compound specific isotope analysis (CSIA) on the carbon of methylmercury. Preliminary analysis performed on 14 juvenile specimens from the North Sea and the Aegean Sea indicate that THg concentrations are higher in individuals from the North Sea than from Greece. The lack of correlation with size and weight indicate that it is likely linked to a difference in contamination levels between the two areas. MeHg is the predominant form of Hg in muscle, while the same cannot be asserted for liver. Mass dependent isotopic values (δ202Hg), were always higher in muscle than in liver and, for each tissue, values were similar between the two areas. This is probably related to the species distribution and to some internal Hg metabolism. For mass independent isotopic signature (MIF), sea bass from the Aegean Sea had a systematically higher Δ201Hg value than individuals from the North Sea. Thus, mass independent values seem definitely site dependent and might be in agreement with differences in both mercury sources and cycling in the North and Aegean Seas. These preliminary results consequently indicate that Hg isotopes may help to discriminate fish from different areas. This promising outcome must be further confirmed by extending our sampling and will be coupled to other results obtained through CSIA.Discrimination des sources de contamination en mercure chez Dicentrarchus labra

Mercury stable isotopes discriminate different populations of common Seabass around Europe and provide insight on mercury cycle

In a context where worldwide emission of mercury, a global pollutant, are increasing, research for new tools and data enabling a deeper understanding of mercury fluxes and sources are crucial. Over the past few years, the analysis of stable isotopes of mercury has emerged as a new promising technique affording to explore the Hg cycle, somewhat like what is being done for the carbon and nitrogen cycles. Hg can exhibit both mass-dependent (MDF, δ202Hg) and mass-independent fractionation (MIF, Δ199Hg). While MDF may occur during biological cycling inter alia and could be used to understand bioaccumulation processes, MIF provides a unique fingerprint of specific chemical pathways, such as photochemical transformations. In this context, information provided by Hg isotopes would help to improve environmental management strategies. However, so far, few studies considered Hg isotopes in marine vertebrates. Our study reports the first data on Hg isotopic composition in marine European fish, for seven distinct populations of the common seabass, Dicentrarchus labrax. The combination of δ202Hg and Δ199Hg values enabled us to successfully discriminate several populations and recursive partitioning analyses demonstrated their relevance as discriminating tools. Moreover, mercury isotopic values provided insight on Hg contamination sources for biota and on MeHg cycling. We showed that δ202Hg in seabass muscle is probably a good integration of the δ202Hg of MeHg in their diet, except when concentrations are low, in which case in vivo processes would significantly influence the δ202Hg in fish muscle. The δ202Hg was also linked with known Hg point sources in several sites and the overall range of δ202Hg around Europe was suggested to be related to global atmospheric contamination. Δ199Hg in seabass was shown to reflect the level of contamination of fish and their habitat but not only. MIF was also clearly influenced by ecological characteristics of fish and their habitats, and therefore could be used to identify and investigate peculiar Hg environments such as in the Black Sea. Throughout this study, results from the Black Sea population stood out, underlying the particularities of Black Sea Hg which seemed to display a Hg cycling similar to what is observed in fresh water lakes. Data on Hg sources and levels in Europe are scarce and Hg cycling is still poorly understood. Our findings constitute the first large scale isotopic analyses of Hg in the area. They bring out the possibility to use mercury isotopes in order to discriminate distinct populations, to explore the global Hg cycle on a large scale (Europe) and to identify particularities in the Hg cycle of several sites. The interest of using mercury isotopes to investigate the whole European Hg cycle is clearly highlighted by our results.Discrimination of Hg contamination sources in European seabass usin Hg stable isotope

Mercury speciation and stable isotopic composition in marine vertebrates: new insights and perspectives

Mercury (Hg) is a persistent toxic compound whose amount in the global biosphere has at least tripled since industrialization. Recently, the study of the seven Hg stable isotopes has emerged as a new promising technique affording to explore the Hg cycle both in situ and in laboratory. Mercury stable isotopes display both mass dependent fractionation (MDF, reported as δ202Hg) and mass independent fractionation (MIF, reported as Δ199Hg and Δ201Hg). The combination of both values should allow to trace back sources and pathways of Hg and methylmercury (MeHg). But, so far, few studies have considered Hg isotopes in marine vertebrates. Thus, our general objective is to study Hg accumulation in marine predator species including, the European seabass, Dicentrarchus labrax, and the hooded seal, Cystophora cristata. By combining both in situ and experimental investigations, we aim to characterize the Hg profile (THg, MeHg and isotopy) of wild populations, to assess whether Hg isotopes differ between populations and could give indications on Hg sources, with special attention paid to differentiate local versus global Hg sources

Habitat use of a population of bottlenose dolphins, Tursiops truncatus gephyreus, analyzed by means of Kernel Density Estimation (KDE) method

The San Antonio Bay (SAB), in Patagonia, Argentina, harbors a resident population of bottlenose dolphins (Tursiops truncatus gephyreus). It seems a privileged area to give birth and nurse calves. In the context of declining populations worldwide and more particularly in South America, preserving the SAB population takes a considerable significance. Yet the SAB is facing human population growth and touristic development, which represent potential threats for the dolphin population, especially dolphin-watching activities. In this context, the aim of this study was to understand the bottlenose dolphin’s habitat use within the bay, and to consider how this information could be used in prospective management strategies. Particularly, we aimed at using the Kernel Density Estimation (KDE) method to map the intensity of space use for essential behavioural patterns. To this end, we collected behavioural information on dolphins during 25 boat-based surveys in the bay in 2011. The habitat use of the bay was heterogeneous: some areas were more intensely used than others. Dolphins spent most of their time traveling and diving. Variables associated to resting behaviours, e.g. school size and depth, indicated that the SAB would be a safer place compared to other known residency areas, confirming its suitability for conservation purposes. KDE analyses showed that behaviours are not evenly distributed inside the bay. Bottlenose dolphins being more sensitive to anthropogenic disturbances while engaged in resting or socializing behaviours, it is crucial to locate these behaviours. In SAB, the KDE shows that resting and socializing areas are located in the Northern part of the bay, indicating that it should constitute a priority protected area in potential future management strategies. Furthermore, our results show that the KDE method is an appropriate and advantageous tool when determining critical habitats, worth being more widely used

ELABORATION PROCESS OF REFRACTORY MATERIALS BY REACTIVE PROJECTION OF OXIDE, PEROXIDE AND METALS

Un montage a été élaboré pour pulvériser avec précision des composés d'oxydes réfractaires, péroxydes ou métaux, avec une granulométrie contrôlée. Le produit réfractaire est obtenu par fusion et recrystalisation sur un substrat préchauffé. Des compositions des systèmes Ca-Al2O3 et CaO-Al2O3-ZrO2 ont été synthétisées. Elles ont été analysées par diffraction des rayons X et MEB. Des matériaux denses et bien crystallisés ont été déposés. Ce procédé peut être utilisé avec succès pour réparer des fours en fonctionnement à 1500°C.A device has been set up for spraying with accuracy a compound having a controlled grain size of refractory oxide, peroxide and metals. The refractory material is obtained by melting and recristallisation on a preheated substrate. Composition in the CaO.Al2O3 system and in the CaO-Al2O3-ZrO2 system have been synthesized. They have been analysed by X-ray diffraction and SEM. Dense and well cristallized materials have been deposited. This process can be successfully applied for the repair of a furnace in operation at 1500°C