Zinc is one of the most widespread trace metals (TMs) in Earth surface environments and is the most concentrated TM in the downstream section of the Seine River (France) due to significant anthropogenic input from the Paris conurbation. In order to better identify the sources and cycling processes of Zn in this River basin, we investigated seasonal and spatial variations of Zn speciation in suspended particulate matter (SPM) in the oxic water column of the Seine River from upstream to downstream of Paris using synchrotron-based extend X-ray absorption fine structure (EXAFS) spectroscopy at the Zn K-edge. First-neighbor contributions to the EXAFS were analyzed in SPM samples, dried and stored under a dry nitrogen atmosphere or under an ambient oxygenated atmosphere. We found a sulfur first coordination environment around Zn (in the form of amorphous zinc sulfide) in the raw SPM samples stored under dry nitrogen vs an oxygen first coordination environment around Zn in the samples stored in an oxygenated atmosphere. These findings are supported by scanning electron microscopy and energy dispersive X-ray spectrometry observations. Linear combination fitting of the EXAFS data for SPM samples, using a large set of EXAFS spectra of Zn model compounds, indicates dramatic changes in the Zn speciation from upstream to downstream of Paris, with amorphous ZnS particles becoming dominant dowstream. In contrast, Zn species associated with calcite (either adsorbed or incorporated in the structure) are dominant upstream. Other Zn species representing about half of the Zn pool in the SPM consist of Zn-sorbed on iron oxyhydroxides (ferrihydrite and goethite) and, to a lesser extent, Zn-Al layered double hydroxides, Zn incorporated in dioctahedral layers of clay minerals and Zn sorbed to amorphous silica. Our results highlight the importance of preserving the oxidation state in TM speciation studies when sampling suspended matter, even in an oxic water column.

Four sediment cores collected in the Seine River basin and dated between 1916 and 2003 were analyzed for lead concentrations and isotopic composition. In all four cores, the measured Pb concentration (up to 460 mg kg(-1)) lies significantly above the natural background (27-40 mg kg(-1)), although a significant decrease (down to 75 mg kg(-1)) was observed during the second half of the 20th century which can be explained by the reduction of lead emissions. The (206)Pb/(207)Pb ratio measured in these samples indicates that the main source of Pb used in the Paris conurbation is characterized by a "Rio Tinto" signature (defined as (206)Pb/(207)Pb=1.1634 ± 0.0001). A high contribution, up to 25%, from the leaded gasoline (characterized by (206)Pb/(207)Pb=1.08 ± 0.02) is revealed in the Seine River downstream Paris, indicating that lead from the leaded gasoline is preferentially released to the river. The dominating Pb signature in the Paris conurbation that is currently sampled through incinerators fumes ((206)Pb/(207)Pb=1.1550 ± 0.0005) and waste water treatment plant ((206)Pb/(207)Pb=1.154 ± 0.002), represents a mixture of highly recycled lead from the Rio Tinto mine and lead from leaded gasoline (imprinted by the low (206)Pb/(207)Pb of the Broken Hill mine). This signature is called "urban" rather than "industrial", because it is clearly distinct from the Pb that is found in areas contaminated by heavy industry, i.e. the heavy industries located on the Oise River which used lead from European ores characterized by high (206)Pb/(207)Pb ratios (~1.18-1.19) and possibly a minor amount of North American lead ((206)Pb/(207)Pb ratios>1.20). The "urban" signature is also found in a rural area upstream of Paris in the 1970's. At the Seine River mouth in 2003, Pb with an urban signature represents 70% of the total Pb sediment content, with the 30% remaining corresponding to natural Pb.

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Records on pollution by metals of minor economic importance (e.g. silver and thallium) but which prove to be toxic are rarely documented in river sediment. This study used two sediment cores collected downstream of the Seine River to describe the temporal evolution of Ag and Tl concentrations in an urban catchment. Radionuclide analysis (i.e. Cs-137 and Pb-210) allowed dating sediment deposition within the cores (1933-2003). Ag concentration reached maximum values of 14.3-24.6 mg kg(-1) in the 1960s and 1970s, before gradually decreasing up to values which approximated 4 mg kg(-1) in 2003. In contrast, Tl concentrations remained roughly constant throughout the core (median value of 0.86 mg kg(-1)). Suspended solids was collected at upstream locations in the catchment to derive the background concentrations in Ag and Tl. Very high Ag concentrations were measured in the upstream Seine River sites (0.33-0.59 mg kg(-1)), compared to the values reported in the literature (0.055 mg kg(-1)). This suggests the presence of a widespread and ancient Ag pollution in the Seine River basin, as demonstrated by the very high Ag enrichment ratios recorded in the cores. Annual flux of particulate Ag in the Seine River was estimated at 1.7 t yr(-1) in 2003. In contrast, Tl concentrations remained in the same order of magnitude as the natural background signal (0.3-0.5 mg kg(-1)). This study suggests that the Seine River basin is free of Tl contamination. Future concerns should hence mostly rely on Ag contamination, in a context of increasing Ag uses and possible releases to the environment.

In order to obtain representative dissolved and solid samples from the aquatic environment, a spectrum of sampling methods are available, each one with different advantages and drawbacks. This article evaluates the use of discrete sampling and time-integrated sampling in illustrating medium-term spatial and temporal variation. Discrete concentration index (CI) calculated as the ratio between dissolved and solid metal concentrations in grab samples are compared with time-integrated concentration index (CI) calculated from suspended particulate matter (SPM) collected in sediment traps and labile metals measured by the diffusive gel in thin films (DGT) method, collected once a month during one year at the Seine River, upstream and downstream of the Greater Paris Region. Discrete CI at Bougival was found to be significantly higher than at Triel for Co, Cu, Mn, Ni and Zn, while discrete metal partitioning at Marnay was found to be similar to Bougival and Triel. However, when using time-integrated CI, not only was Bougival CI significantly higher than Triel CI, CI at Marnay was also found to be significantly higher than CI at Triel which was not observed for discrete CI values. Since values are time-averaged, dramatic fluctuations were smoothed out and significant medium-term trends were enhanced. As a result, time-integrated concentration index (CI) was able to better illustrate urbanization impact between sites when compared to discrete CI. The impact of significant seasonal phenomenon such as winter flood, low flow and redox cycles was also, to a certain extent, visible in time-integrated CI values at the upstream site. The use of time-integrated concentration index may be useful for medium- to long-term metal studies in the aquatic environment.

This study investigates the ability of the biodynamic model to predict the trophic bioaccumulation of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni) and zinc (Zn) in a freshwater bivalve. Zebra mussels were transplanted to three sites along the Seine River (France) and collected monthly for 11 months. Measurements of the metal body burdens in mussels were compared with the predictions from the biodynamic model. The exchangeable fraction of metal particles did not account for the bioavailability of particulate metals, since it did not capture the differences between sites. The assimilation efficiency (AE) parameter is necessary to take into account biotic factors influencing particulate metal bioavailability. The biodynamic model, applied with AEs from the literature, overestimated the measured concentrations in zebra mussels, the extent of overestimation being site-specific. Therefore, an original methodology was proposed for in situ AE measurements for each site and metal.

Total lead (Pb) concentration and Pb isotopic ratio ((206)Pb/(20)7Pb) were determined in 140 samples from the Seine River basin (France), covering a period of time from 1945 to 2011 and including bed sediments (bulk and size fractionated samples), suspended particulate matter (SPM), sediment cores, and combined sewer overflow (CSO) particulate matter to constrain the spatial and temporal variability of the lead sources at the scale of the contaminated Seine River basin. A focus on the Orge River subcatchment, which exhibits a contrasted land-use pattern, allows documenting the relation between hydrodynamics, urbanization, and contamination sources. The study reveals that the Pb contamination due to leaded gasoline that peaked in the 1980s has a very limited impact in the river nowadays. In the upstream Seine River, the isotopic ratio analysis suggests a pervasive contamination which origin (coal combustion and/or gasoline lead) should be clarified. The current SPM contamination trend follows the urbanization/industrialization spatial trend. Downstream of Paris, the lead from historical use originating from the Rio Tinto mine, Spain ((206)Pb/(207)Pb=1.1634 ± 0.0001) is the major Pb source. The analysis of the bed sediments (bulk and grain size fractionated) highlights the diversity of the anthropogenic lead sources in relation with the diversity of the human activities that occurred in this basin over the years. The "urban" source, defined by waste waters including the CSO samples ((206)Pb/(207)Pb=1.157 ± 0.003), results of a thorough mixing of leaded gasoline with "historical" lead over the years. Finally, a contamination mixing scheme related to hydrodynamics is proposed.

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