Evaluation des valeurs de fonds géochimiques dans l’eau de mer des 4 métaux de l’état chimique DCE. Cas des Départements d’Outre-Mer

The Water Framework Directive 2000/60/EC requires monitoring of the chemical status of waters, based on the comparison of measured concentrations of selected chemicals to environmental quality standards (EQS). However, for metal elements, background concentrations are not zero (geochemical background) and vary depending on the geological context. As these concentrations may sometimes reach high levels, the WFD permits their inclusion in the surface waters. In metropolitan France, many studies provide an extensive literature on the concentrations of trace metals in coastal marine environment, which even if they are not natural are very low compared with the concentrations of these EQS. However, there are no such data arising from the overseas departments except French Guyana. Evaluation of the geochemical background (also called the present day reference levels) in these generally volcanic regions potentially enriched in trace elements, needs therefore an exhaustive sampling, from which the acquired set of data will indicate whether the situation differs from the metropolitan situation.La Directive Cadre 2000/60/CE sur l’Eau requiert un contrôle de l’état chimique des eaux, basé sur la comparaison de niveaux mesurés de concentrations de substances chimiques sélectionnées à des normes de qualité environnementales (NQE). Or, pour les éléments métalliques, les concentrations naturelles ne sont pas nulles (« fond géochimique ») et varient en fonction de la nature géologique du milieu. Ces concentrations pouvant parfois atteindre des niveaux importants, la DCE autorise leur prise en compte dans les eaux de surface. En métropole, de nombreuses études fournissent une littérature abondante sur les concentrations des métaux traces en milieu marin côtier, qui même si elles ne sont pas des niveaux naturels sont très faibles comparées aux concentrations de ces NQE. En revanche, on ne dispose pas à part en Guyane de données sur les eaux côtières des départements d’outremer. L’évaluation des fonds géochimiques (que l’on peut appeler aussi concentrations de référence actuelle) dans ces régions généralement volcaniques, potentiellement enrichies en éléments traces, a donc pour préalable un échantillonnage exhaustif, à partir duquel les données acquises indiqueront si la situation est différente de la situation métropolitaine

Trace metal concentrations in the muscle of seven marine species: Comparison between the Gulf of Lions (North-West Mediterranean Sea) and the Bay of Biscay (North-East Atlantic Ocean)

Concentrations of 6 trace metals (Ag, Cd, Cu, Ni, Pb, Zn) in the muscle of 2 sharks (Galeus melastomus and Scyliorhinus canicula), 4 teleosts (Helicolenus dactylopterus, Lepidorhombus boscii, Micromesistius poutassou and Phycis blennoides) and 1 crustacean (Nephrops norvegicus) were compared between the Bay of Biscay (Atlantic Ocean) and the Gulf of Lions (Mediterranean Sea). Although average concentrations and the trace element pollution index were generally higher in the Gulf of Lions, significant differences between the two ecosystems were only found for Zn for Helicolenus dactylopterus, and for Ag and Cu for the crustacean N. norvegicus. Moreover, some relationships between trophic level or size and metal concentrations were found for these two species. The absence of clear pattern may result from the blurring effect of contamination and excretion that may act differentially for all species and all elements

Patterns of trace metal bioaccumulation and trophic transfer in a phytoplankton-zooplankton-small pelagic fish marine food web

International audienceTrace metal contamination in the European sardine and anchovy food web was investigated in the Gulf of Lions, NW Mediterranean Sea, including seawater and size fractions of plankton. The results highlighted: i) higher and more variable concentrations in the smaller plankton size classes for all metals except cadmium; ii) higher concentrations in anchovy versus sardine for all elements except lead; iii) different patterns of metal bioaccumulation through the food web: cobalt, nickel, copper, silver, lead and zinc displayed continuously decreasing concentrations (with the exception of increased zinc in fish only), while mercury concentrations dropped considerably in larger plankton size classes and rose significantly in fish. Lastly, cadmium concentrations were found to be highest in intermediate plankton size classes, with very low levels in fish. The need to efficiently characterize the biological composition of plankton in order to fully identify its role in the mobilization and transfer of metals was highlighted

Two-dimensional distribution of living benthic foraminifera in anoxic sediment layers of an estuarine mudflat (Loire Estuary, France)

We present a new rapid and accurate protocol to simultaneously sample benthic living foraminifera in two dimensions in a centimeter scale vertical grid and dissolved iron in high resolution (200 μm). Such an approach appears crucial to study foraminiferal ecology in heterogeneous environments. The foraminiferal faunas of the main intertidal mudflat of the Loire estuary are dominated by Ammonia tepida, which accounts for 92 % of the living assemblage (CTG-labeled). Its vertical distribution shows a first density maximum at the surface, a sharp decrease in the next two centimeter followed by a well defined second maximum between 3 and 8 cm depth. The heterogeneity of A. tepida in this 3–8 cm depth layer was calculated by the Moran's Index and reveals lateral patches with a characteristic length of 1 to 2 cm. We investigate mechanisms potentially responsible for this distribution by observation of burrow structures and two-dimensional high-resolution imaging of dissolved iron. The surface maximum corresponded to the area of maximum oxygen availability. Observable burrows have no clear relation with the distribution of A. tepida but were closely related to dissolved iron distribution. Consequently, no evident relation between A. tepida and dissolved iron was observed. Nevertheless, two one cm-wide structures, enriched in dissolved iron produced by anaerobic degradation of labile organic matter, corresponded to increased A. tepida densities. This observation suggests that within strongly oxygen-depleted sediments, A. tepida could still be favoured by labile organic carbon. The main characteristics of the vertical distribution of A. tepida are interpreted in the present study as a combination of passive downward transport by biomixing into deeper suboxic (without both oxygen and sulfide) sediment layers and a subsequent mobility driven by a sensitivity to geochemical gradients. We hypothesize that the survival of A. tepida in oxygen depleted environments is explained its ability to lower its metabolism between periods of oxygen renewal by bioirrigation

Monitoring of Pb Contamination in Loire Estuary: Trends, Distribution and Isotopic composition

The Loire River is one of the largest river systems in Western Europe and a major source of continental inputs to the marine environment in the Bay of Biscay. Its catchment area drains agricultural and industrial zones and its estuary is increasingly urbanized. Even if the Loire River is not considered as a highly polluted system, studies have shown estuarine Pb contamination due to industrial inputs and combustion of leaded gasoline until the mid 1990’s. A retrospective study, based on the analysis (Pb levels and isotopic composition) of mussel samples collected by the French mussel watch program (RNO/ROCCH) has highlighted this contamination and its trend between 1985-2005 (Couture et al., 2010). This poster furthers the work initiated by Couture et al. Here, Pb levels and isotopic signatures in samples from the environmental sample bank from RNO/ROCCH over the last 10 years will be presented and confronted to measurements of other environmental samples

Role of suspended particulate material on growth and metal bioaccumulation in oysters (Crassostrea gigas) from a French coastal semi-enclosed production area, Arcachon Bay

International audienceArcachon Bay is a prominent oyster production area on the coast of Western Europe, and is subject to chemical contamination including by trace metals. Recently, the national "mussel-watch" monitoring network - using local bivalves as semi-quantitative bioindicators of coastal chemical contamination - highlighted a significant increase in copper (Cu) concentrations in oysters from this bay. Here, we conducted a one-year multi-compartment and multi-parameter field study to investigate some aspects of the surrounding environment of oysters that could explain their metal bioaccumulation. Sediment, seawater (through punctual and passive sampling), particles (suspended particulate material of selected sizes, including trophic resources for oysters) and transplanted oysters were regularly collected at two contrasted sites of the bay (i.e. under continental versus more oceanic influence). These matrices were characterised for their total Cu, zinc (Zn), nickel (Ni), cadmium (Cd) and lead (Pb) concentrations. Several physico-chemical and biological parameters (e.g. salinity, particle loads, oyster growth rate and condition indices, carbon and nitrogen stable isotope compositions, etc.) were also analysed. Overall, sediment, particles and oysters from the outermost site had slightly lower δ13C values, confirming the more oceanic influence in this part of the bay. Among organic particles, although dinoflagellates tended to be more abundant at the outermost site while ciliates were more abundant at the innermost site of the bay, the two sites did not differ in mean total microphytoplankton and diatom densities. However, the variations observed for most of the other parameters studied show that oysters located near the continental shore are exposed to higher loads of particles in general, and to higher metal contents in the dissolved phase and "bulk" seawater (dissolved plus particulate phases) during the year. While fluvial inputs and continental/urban run-offs are suspected sources of anthropogenic metal inputs into the bay, (fine) sediment particle resuspension appears to be a likely major contributor to metal release and hence to the contamination of the bay including oysters. The decline of seagrass beds in the last two decades in the bay could also have decreased the potential of fine particle retention in the sedimentary stratum. Concomitantly, oysters presenting the highest metal concentrations were those with the lower growth rates and condition indices, which may be induced by physical constraints, high amounts of pseudo-faeces produced and/or reduced food and energy acquisition by oysters due to high particle loads in the water column. The findings of this study imply that using raw metal concentrations in bivalves to monitor marine coastal contamination can lead to misleading interpretations if potentially great spatial variations in bivalve growth rates or condition indices are not considered. Finally, peculiar trends were observed for Cu compared to other metals, highlighting the need of further studies to fully address the Cu contamination in this marine system (e.g. specific sources of contamination for this metal in the bay). This study more broadly raises the issue of potentially man-induced ecological changes (e.g. modification of natural habitats) and their consequences on metal transfer and physiological performance of marine biota

Chemical contaminants (trace metals, persistent organic pollutants) in albacore tuna from western Indian and south-eastern Atlantic Oceans: Trophic influence and potential as tracers of populations

Albacore tuna (Thunnus alalunga) is a highly commercial fish species harvested in the world's Oceans. Identifying the potential links between populations is one of the key tools that can improve the current management across fisheries areas. In addition to characterising populations' contamination state, chemical compounds can help refine foraging areas, individual flows and populations' structure, especially when combined with other intrinsic biogeochemical (trophic) markers such as carbon and nitrogen stable isotopes. This study investigated the bioaccumulation of seven selected trace metals – chromium, nickel, copper (Cu), zinc (Zn), cadmium (Cd), mercury (Hg) and lead – in the muscle of 443 albacore tunas, collected over two seasons and/or years in the western Indian Ocean (WIO: Reunion Island and Seychelles) and in the south-eastern Atlantic Ocean (SEAO: South Africa). The main factor that explained metal concentration variability was the geographic origin of fish, rather than the size and the sex of individuals, or the season/year of sampling. The elements Cu, Zn, Cd and Hg indicated a segregation of the geographic groups most clearly. For similar sized-individuals, tunas from SEAO had significantly higher concentrations in Cu, Zn and Cd, but lower Hg concentrations than those from WIO. Information inferred from the analysis of trophic markers (δ13C, δ15N) and selected persistent organic pollutants, as well as information on stomach contents, corroborated the geographical differences obtained by trace metals. It also highlighted the influence of trophic ecology on metal bioaccumulation. Finally, this study evidenced the potential of metals and chemical contaminants in general as tracers, by segregating groups of individuals using different food webs or habitats, to better understand spatial connectivity at the population scale. Limited flows of individuals between the SEAO and the WIO are suggested. Albacore as predatory fish also provided some information on environmental and food web chemical contamination in the different study areas

Substances prioritaires DCE : Etude de détermination de facteurs de bioaccumulation (BAF) sur les mollusques en milieu marin

Pour permettre d’évaluer la qualité chimique des masses d’eau en utilisant les résultats de la surveillance opérée sur les bivalves via le ROCCH ou le RINBIO, il est nécessaire de transposer les seuils existants applicables dans les eaux marines en seuils « mollusques » et ainsi d’adapter les NQE eau marine (Normes de Qualité Environnementale) en VGE mollusques (Valeur Guide Environnementale). Cette adaptation nécessite d’utiliser des facteurs de conversion eau-biote : les facteurs de bioconcentration (BCF) ou les facteurs de bioaccumulation (BAF) spécifiques de couples substance-espèce. Les BAF sont les facteurs à privilégier autant que possible car plus représentatifs de ce qui se passe dans le milieu avec notamment la prise en compte des différentes voies d’exposition des organismes aquatiques aux contaminants, i.e. la voie directe (eau) et la voie trophique (ingestion de proies contaminées). Cette démarche de détermination de VGE mollusques est engagée par Ifremer - OFB depuis 2015, et plusieurs étapes ont été réalisées : proposition de VGE mollusques (1) sur la base de données existantes, élaboration d’une méthodologie de détermination de BAF pour les mollusques en milieu marin afin d’acquérir des données BAF terrain. Cette étude de détermination des BAF sur les mollusques en milieu marin a été conduite entre 2016 et 2019, elle concerne 27 substances prioritaires : 3 composés métalliques et 24 substances organiques. Sept sites ont été échantillonnés en parallèle sur les matrices eau marine et mollusques. Suivant les points, les mollusques échantillonnés étaient des moules sauvages (ou d’élevage) et / ou des moules encagés, et deux sites disposaient en plus d’huîtres encagées. Les concentrations dans l’eau marine ont été mesurées sur eau brute et / ou eau filtrée. En dépit des nombreuses difficultés logistiques rencontrées, cette étude souligne d’un point de vue technique, l’intérêt de la SBSE (Stir Bar Sorptive Extraction), pour la recherche de certaines substances organiques dans l’eau marine, la pertinence de rechercher ces substances sur eau brute mais également sur eau filtrée. Cette étude permet de disposer de résultats acquis en parallèle à la fois sur moules encagées, sur moules sauvages ou d’élevage et de mesurer des BAF pour 10 substances : Cd, Ni, Pb, anthracène, PBDE, DDT total, HCH, naphtalène, octylphénol, TBT, permettant d’affiner les VGE mollusques