Impact of an urban multi-metal contamination gradient: metal bioaccumulation and tolerance of river biofilms collected in different seasons

[Departement_IRSTEA]Eaux [TR1_IRSTEA]BELCAInternational audienceThe aim of this study was to investigate the repeatability and seasonal variability of the biological response of river biofilms chronically exposed to a multi-metal pressure in an urban contamination gradient. Biofilms were grown on immersed plastic membranes at three sites on the Seine river upstream (site) and downstream (sites 2 and 3) from Paris (France). They were collected in four different seasons (autumn, spring, summer and winter). Biofilm tolerance to Cu, Ni, Pb and Zn was measured using a PICT (Pollution-Induced Community Tolerance) approach with a previously developed short-term toxicity test based on beta-glucosidase (heterotrophic) activity. Metal concentrations in the river and also in the biofilm samples (total and non-exchangeable bio accumulated metals) were also monitored. Biofilm-accumulated metal concentrations reflected the increase of the multi-metal exposure along the urban gradient. These concentrations were strongly correlated with dissolved and particulate organic carbon and with the total metal fraction in the river water, which recalls the significant influence of the environmental parameters on metal uptake processes in river biofilms. Overall, natural biofilms allow monitoring water quality by integrating the variations of a diffuse metal contamination overtime. Tolerance levels globally increased from site 1 to site 3 reflecting the metal pollution gradient measured in the river water collected at the three sites. Cu tolerance tended to increase during warm seasons but no clear seasonal tendency could be found for Ni, Pb and Zn. Furthermore, principal component analysis clearly discriminated samples collected upstream (site 1) from samples collected downstream (sites 2 and 3) along the first principal component which was correlated to the metal gradient. Samples collected in winter were also separated from the others along the second principal component correlated to parameters like water temperature and Total Suspended Solids concentration. This study shows that chronic in situ exposure to environmental metal concentrations has a significant impact on natural biofilms. Biofilm tolerance to metals and biofilm metal bioaccumulation both reflect metal exposure levels although they remain low when compared to Environmental Quality Standards from the European Water Framework Directive. Yet temperature appears as an important environmental variable shaping community structure and response to toxic exposure which shows that the sampling date is an important parameter to consider when using natural river biofilms to assess the impacts of urban pressure

To what extend the dam dredging can influence the background level of metals in the Rhine River: using chemical and biological long-term monitoring to answer

Dredging generates remobilisation of sediments contaminated by non-degradable compounds such as metals, to which aquatic organisms can be exposed. This study aims at assessing the environmental impact of sediments remobilised in the Rhine River (France) during the dredging of Marckolsheim dam by pumping/dilution in 2013 on metal speciation and organisms' exposure. The monitoring coupling chemical and biological tools was performed 2 years before dredging operation on 2 sampling sites, upstream and downstream from the discharge of pumping/dilution, to acquire data on the natural variability of labile (DGT as passive samplers), dissolved and particulate concentrations of Cd, Co, Cr, Cu, Ni, Mn, Pb and Zn in Rhine during full hydrological cycles. In parallel, size-calibrated zebra mussels were transplanted at both sites to monitor continuously metal bioavailability from particulate and dissolved fractions. This long-term monitoring allowed the establishment of reference baselines of Rhine water and mussels' contamination levels and subsequently, the detection of averred environmental changes due to the dredging. Indeed, Co and Mn accumulations in mussels exposed to the discharge were consistent with increasing labile species in Rhine whereas ones of Cr and Pb were likely due to an enhanced particulate bioavailability. Whatever the exposure route, the mussels recovered their basal metal contents 2 weeks after the end of dredging, suggesting a transient impact of sediment remobilisation on bioaccumulation. This long-term monitoring highlights the interest of coupling chemical and biological time-integrated tools for a better assessment of environmental risks because metallic exchanges between organisms and their media are complex and metal-specific

To what extend the dam dredging can influence the background level of metals in the Rhine River: using chemical and biological long-term monitoring to answer

Dredging generates remobilisation of sediments contaminated by non-degradable compounds such as metals, to which aquatic organisms can be exposed. This study aims at assessing the environmental impact of sediments remobilised in the Rhine River (France) during the dredging of Marckolsheim dam by pumping/dilution in 2013 on metal speciation and organisms' exposure. The monitoring coupling chemical and biological tools was performed 2 years before dredging operation on 2 sampling sites, upstream and downstream from the discharge of pumping/dilution, to acquire data on the natural variability of labile (DGT as passive samplers), dissolved and particulate concentrations of Cd, Co, Cr, Cu, Ni, Mn, Pb and Zn in Rhine during full hydrological cycles. In parallel, size-calibrated zebra mussels were transplanted at both sites to monitor continuously metal bioavailability from particulate and dissolved fractions. This long-term monitoring allowed the establishment of reference baselines of Rhine water and mussels' contamination levels and subsequently, the detection of averred environmental changes due to the dredging. Indeed, Co and Mn accumulations in mussels exposed to the discharge were consistent with increasing labile species in Rhine whereas ones of Cr and Pb were likely due to an enhanced particulate bioavailability. Whatever the exposure route, the mussels recovered their basal metal contents 2 weeks after the end of dredging, suggesting a transient impact of sediment remobilisation on bioaccumulation. This long-term monitoring highlights the interest of coupling chemical and biological time-integrated tools for a better assessment of environmental risks because metallic exchanges between organisms and their media are complex and metal-specific

Programme PIREN-Seine - Phase 6 Axe 4 : « Ecologie & Ecotoxicologie » Les déterminants de la qualité écologique du milieu aquatique

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASARELes organismes vivants dans le milieu aquatique sont soumis à de multiples pressions combinées : chimique, hydro- morphologique, thermique, trophique (matière organique, eutrophisation...), qui impactent, et éventuellement perturbent leur fonctionnement. La santé des individus qui composent la biocénose peut aussi être altérée par ces différentes pressions. S'il est possible de faire des relations causales entre une pression et une réponse biologique, l'enjeu aujourd'hui est de pouvoir prédire les conséquences sur les différentes composantes de la biocénose de l'ensemble des pressions qui interagissent. L'observation des organismes vivants, à différents niveaux d'organisation (la cellule, l'organe, l'organisme, la population, ou la communauté) est proposée depuis plusieurs années pour renseigner sur l'état de santé des organismes, des communautés (bio- indication de type DCE), sur l'état écologique global du milieu, ou sur l'impact des contaminants chimiques (biomarqueurs en écotoxicologie). Au cours de la phase 6 PIREN -Seine, nous avons étudié à la fois comment les observations faites sur la biocénose peuvent nous renseigner sur les impacts des différentes pressions, y compris la pression chimique (domaine de l'écotoxicologie), mais aussi comment la multiplicité de ces pressions (caractéristique d'un bassin versant très anthropisé comme l'est celui de la Seine), ou les modifications de ces pressions, impactent le vivant