ISOGIRE

"Insights from heavy stable isotopes to the study of Ag (and Ag-nanoparticles), Cu and Zn contaminations and biogeochemical processes in the Gironde Watershed and Estuary"

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 Obiettivo del progetto (Objective)

'The use of heavy stable isotopes for tracing the source of Metallic Trace Elements (MTE) in the environment has been well established during the last decade but focused mostly on simple cases (local point source pollutions), while Ag has remained unexploited in this respect. The ISOGIRE project aims at investigating heavy stable Cu, Zn and Ag isotope fractionation in the large scale (80000 km²) and well constrained Gironde continuum (as a model case system). The objective is to use MTE isotopes to identify and discriminate different (diffuse and point) source of pollutions and their evolution in time, accounting for biogeochemical processes (non-conservative behaviour by reactive estuarine mixing and biological uptake by oysters) that may modify their isotopic signatures. The ISOGIRE project relies on a multidisciplinary approach linking metallic trace elements isotope geochemistry, biology/ecotoxicology and mineralogical in situ analysis. The ISOGIRE project will address the recent issue of emerging Ag contamination observed in the Gironde estuary and surface waters worldwide, presumably due to the rise of Ag (and Ag nanoparticles (NP)) in consummer’s goods. A versatile analytical methodology for Ag isotopes measurements by MC-ICP-MS will be developed for various environmental matrices in order to evaluate the possibility of identifying and discriminating Ag and Ag-NP sources and follow their environmental route using their isotopic compositions. In addition of being complementary to the “nanosafetycluster” group, promoting studies on the environmental impact of NP at the European level, the ISOGIRE project is consistent with the priority objectives related to Environment from the work programme with respect to the multidisciplinary approach and development of new monitoring methodologies.'

Introduzione (Teaser)

Human activities have strongly modified the biogeochemical cycles of metallic trace elements (MTEs) increasing their fluxes towards and between surface environments. New isotope data has fostered better models of MTE sources, transfer and reactivities in dynamic and multi-sources systems, as required for targeting emission controlled strategies to combat origins and consequences of metal contamination.

Descrizione progetto (Article)

The Gironde Watershed and Estuary (France) have served as a test case for the EU-funded project ISOGIRE. The research team studied heavy stable isotopes of copper (Cu), zinc (Zn) and silver (Ag) to get a handle on their biogeochemical reactivity, sources and evolution over time in this fluvial-estuarine system affected by intensive wine production, urbanisation and resilience of contamination from former metal refining activities. Ag was of interest as isotopic studies of it are limited but could be useful in addressing rising Ag concentrations in surface waters and organisms. This phenomenon could possibly be linked to increased use of Ag nanoparticles in consumer goods, making Ag an emerging contaminant.

ISOGIRE results revealed transient Cu isotopic signals in the freshwater reach of the estuary, related to a Cu enrichment and a preferential uptake of light isotopes by the phytoplankton, with possible transposition of anthropogenic Cu signatures. The mineralisation of organic matter in the estuary leads to a continuous addition of dissolved Cu characterised by the release of heavy isotopes in solution, following a Rayleigh process. In contrast, Zn showed a strong adsorption onto particles of the estuarine turbidity maxima, featured by an enrichment of heavy Zn isotopes in the dissolved phase. Given the same trend in worldwide river data, adsorption onto particles could be the main driver of the isotopic composition of dissolved Zn globally.

Metal isotopic signatures in oysters at the estuary mouth provided new constraints for their use in biomonitoring studies. Specifically, the unchanging isotopic signatures of Cu, Zn and Ag over a more than 30-year time frame, suggest that the estuarine biogeochemical reactivity rather than the temporal evolutions of environmental sources in the Gironde Watershed is prevalent at explaining isotopic compositions of bioaccumulated metals.

Finally, the study was able to discriminate between natural and anthropogenic sources of Cu and Zn on the basis of isotopic signatures in the watershed and showed contrasting biogeochemical reactivities and isotopic fractionation mechanisms in the estuarine waters. However, they also pointed to the limited use of isotopic Ag to trace nano-Ag at this point, unless industry is encouraged to label nanoparticles with one of the heavy or light Ag isotopes.

New isotopic data on Ag, Cu and Zn have successfully led to new models for interpreting geochemical and isotopic variations in river and estuary systems and in local organisms. These models will support better coastal pollution assessments and more effective policies to reduce contamination and threats to the environment and public health.