Cécile Bossy

Assessment of metal contamination in a small mining- and smelting-affected watershed: high resolution monitoring coupled with spatial analysis by GIS.

The Riou Mort River watershed (SW France), representative of a heavily polluted, small, heterogeneous watershed, represents a major source for the polymetallic pollution of the Lot-Garonne-Gironde fluvial-estuarine system due to former mining and ore-treatment activities. In order to assess spatial distribution of the metal/metalloid contamination in the watershed, a high resolution hydrological and geochemical monitoring were performed during one year at four permanent observation stations. Additionally, thirty-five stream sediment samples were collected at representative key sites and analyzed for metal/metalloid (Cd, Zn, Cu, Pb, As, Sb, Mo, V, Cr, Co, Ni, Th, U and Hg) concentrations. The particulate concentrations in water and stream sediments show high spatial differences for most of the studied elements suggesting strong anthropogenic and/or lithogenic influences; for stream sediments, the sequence of the highest variability, ranging from 100% to 300%, is the following: Mo < Cu < Hg < As < Sb < Cd < Zn < Pb. Multidimensional statistical analyses combined with metal/metalloid maps generated by GIS tool were used to establish relationships between elements, to identify metal/metalloid sources and localize geochemical anomalies attributed to local geochemical background, urban and industrial activities. Finally, this study presents an approach to assess anthropogenic trace metal inputs within this watershed by combining lithology-dependent geochemical background values, metal/metalloid concentrations in stream sediments and mass balances of element fluxes at four key sites. The strongest anthropogenic contributions to particulate element fluxes are 90-95% for Cd, Zn and Hg in downstream sub-catchments. The localisation of anthropogenic metal/metalloid sources in restricted areas offers a great opportunity to further significantly reduce metal emissions and restore the Lot-Garonne-Gironde fluvial-estuarine ecosystem.

Tracing platinum accumulation kinetics in oyster Crassostrea gigas, a sentinel species in coastal marine environments

Platinum Group Elements (PGEs) are extremely scarce in the Earths Crust and of strong interest for high-end technologies due to their specific properties. They belong to the Technology Critical Elements (TCEs) for which use is forecast to increase, implying growing emissions into the environment in the following years. In particular, with the intensive use of platinum (Pt) in car catalytic converters, the anthropogenic geochemical cycle of this element has surpassed the natural cycle. Yet, environmental Pt levels are still in the sub picomolar range, making its analytical detection a challenge. Few studies cover the behavior of Pt in marine waters in terms of speciation, reactivity and possible transfer to the biota. In this study, oysters (Crassostrea gigas) from an unpolluted estuary were exposed to the stable isotope 194Pt in seawater at a range of concentrations during 35days. Seawater was renewed daily and spiked to three nominal Pt concentrations (50, 100, and 10,000ng·L-1) for two replicate series. In addition, control conditions were monitored. Five oysters from each tank were dissected after 3, 7, 14, 21, 28, 35days of Pt exposure, and analyzed by ICP-MS. Accuracy of this analytical method applied to biological matrix was checked by an inter-method comparison with a voltammetrical technique. A concentration-dependent accumulation of Pt in oysters increasing with exposure time occurred. After 28days, oyster Pt accumulation from low and intermediate exposure conditions reached a plateau. This was not the case of the highest exposure condition for which oyster tissues showed increasing concentrations until the last day of the experiment. A linear correlation exists between seawater concentrations and Pt content in oysters for low and intermediate exposure concentrations i.e. closer to environmental concentrations. By showing high Pt accumulation potential, oysters may serve as sentinels, ensuring biomonitoring of Pt concentrations in marine coastal waters.

Antimony in the Lot–Garonne river system: a 14-year record of solid–liquid partitioning and fluxes

Environmental context Antimony is a trace element ubiquitously present in the environment, but data are lacking on its spatio-temporal distribution in aquatic environments. Long-term records serve as essential tools to decipher temporal patterns, historical sources and sinks and background concentrations in an area. We characterise the temporal concentrations, transport and behaviour of antimony in the Garonne River watershed, the main tributary to the Gironde Estuary, the largest estuary in south-west Europe. Abstract Knowledge of the environmental chemistry of antimony (Sb) in aquatic systems is limited, and a better understanding of its geochemical behaviour is needed. Based on a fourteen-year survey (2003–2016) with monthly measurements of dissolved and particulate Sb at five sites in the Lot–Garonne river system, combined with daily measurements of water discharge and suspended particulate matter, this work characterises Sb behaviour in the upstream major river watershed of the Gironde Estuary. The survey provides a first regional geochemical Sb background in the Garonne River watershed for dissolved (~0.2 µg L−1) and Th-normalised particulate Sb (Sbp/Thp ~0.25) concentrations. Observed decreasing temporal trends (<1 ng L−1 in dissolved and <0.02 mg kg−1 in particulate concentrations per month) at sites representing natural concentrations probably reflect global atmospheric Sb dynamics at the watershed scale. Regular seasonal cycles of solid/liquid partitioning, with higher solubility in summer (matching high dissolved and low particulate concentrations), reflect water-discharge and suspended particulate matter transport dynamics and possibly seasonal (bio)geochemical processes. Furthermore, this coefficient decreases from the river to the estuarine reaches (from average log10Kd 4.3 to minimum 3.7 L kg−1), suggesting an increased solubility of Sb in estuarine systems. Flux estimates indicate the relevance of the dissolved fraction in Sb transport (with negligible influence of the colloidal fraction) and a total flux (dissolved + particulate) entering the Gironde Estuary of 5.66 ± 2.96 t year−1 (~50 % particulate). These results highlight the importance of timescales and environmental parameters for understanding and prediction of future Sb biogeochemistry.