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In freshwater ecosystems, dynamic hydraulic events (floods or dam maintenance) lead to sediment resuspension and mixing with waters of different composition. Microbial communities living in the sediments play a major role in these leaching events, contributing to organic matter degradation and the release of trace elements. However, the dynamics of community diversity are seldom studied in the context of ecological studies. Therefore, we carried out laboratory-induced leaching experiments, using sediments from the Villerest dam reservoir (Villerest, France). To assess whole microbial community diversity, we sequenced the archaeal and bacterial 16S rRNA genes using Illumina MiSeq. Our results suggest that the degree of dissolved oxygen found in the water during these resuspension episodes influenced community dynamics, with anoxic waters leading to drastic shifts in sedimentary communities compared to oxic waters. Furthermore, the release of microbial cells from sediments to the water column were more favorable to water colonization when events were caused by oxic waters. Most of the bacteria found in the sediments were chemoorganotrophs and most of the archaea were methanogens. Methylotrophic, as well as archaeal, and bacterial chemoorganotrophs were detected in the leachate samples. These results also show that organic matter degradation occurred, likely participating in carbonate dissolution and the release of trace elements during freshwater resuspension events.

Since 60 years, a large amount of data has been acquired to survey river sediment quality, especially concerning regulatory trace metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn. Large-scale syntheses are still rare and show some limits to assess the effectiveness of public regulations and the river systems' resilience. Based on a sediment contamination database comprising more than 12,000 samples, we propose a first attempt to decipher spatio-temporal trends of metal contamination along seven major rivers in Western Europe (Garonne-Lot, Loire, Meuse Rhine, Rhone, Scheldt and Seine Rivers). Facing heterogeneous sampling and analytical methods on different sediment matrices (bed and flood deposits – BFD, suspended particulate matter – SPM, dated sediment cores – DSC), this work investigates the effect of analytical protocols, spatial and temporal factors on metal concentration trends. At a large scale, an increase in metal concentrations (especially for Cd, Pb and Zn) is reported along most of the investigated rivers. It appears closely related to major urban-industrial hotspots (Paris-Rouen corridor on the Seine River, Bonn-Duisburg corridor on the Rhine River, etc.) and to the geology of each watershed, both influencing the regional sediment quality. Former mining and metallurgical districts, generally located in crystalline areas, also caused high metal concentrations on the long term (Upper Loire River, Middle Meuse River, Lot River). A global decrease of metal concentrations is observed in all river sections since the 1960s-1970s onwards, in response to European and national regulations, and to socio-economical changes affecting urban-industrial areas. The high influence of the location of the samples along the rivers and the decade of sampling is confirmed by a Factor Analysis of Mixed Data (FAMD). Secondary factors such as the influence of the sediment matrix type (BFD, SPM and DSC) and the different digestion procedures prior to elemental analysis also explained significant differences for Cr, Cd, Cu, Pb, or Zn, although this can also be locally balanced by the substratum (i.e. for alkaline rivers). This approach points out the limitations of the available data, particularly regarding the need of regional geological backgrounds and the more systematic acquisition of ancillary data such as grain-size and TOC. It also provides critical clues to intercompare metal sediment pollution in rivers at large spatial and temporal scales worldwide.

A broad range of contaminants has been recorded in sediments of the Loire River over the last century. Among a variety of anthropogenic activities of this nuclearized watershed, extraction of uranium and associated activities during more than 50 years as well as operation of several nuclear power plants led to industrial discharges, which could persist for decades in sedimentary archives of the Loire River. Highlighting and identifying the origin of radionuclides that transited during the last decades and were recorded in the sediments is challenging due to i) the low concentrations which are often close or below the detection limits of routine environmental surveys and ii) the mixing of different sources. The determination of the sources of anthropogenic radioactivity was performed using multi-isotopic fingerprints (

International audience; Purpose The threat of trace elements (TE) stored in sediments depends on total concentrations, their chemical form, and also on the type of TE–particle association and their resultant stability. The presentstudy aimed at identifying the major TE-bearing phases in river sediments and quantifying their in situ concentrations once total concentrations of TE had been determined in order to understand potential TE mobility and ensuing environmental risk during early diagenesis mechanisms and the sediment cascade.Materials and methods Several TE-enriched layers of sediment cores were selected in a polymetallic-contaminated river basin (Loire basin, France). Selected samples were taken from up- and downstream areas far from sites of specific mining, or heavy industrial or urban activities. They thus represent non-site-dependent sediments which were not modulated or controlled by specific mineralogy or anthropogenic activities. Detailed microscale investigation techniques (SEM, EPMA, andμSXRD) were used to characterize directly the complex TE–solid phase association within river sediments. Despite Bi, Cd, and Hg representing the highest enrichment of the studied sediment layers, these elements were not detected at a microscale and only ubiquitous TEsuch as As, Cu, Pb, and Zn could be quantified on polished thin sections (EPMA quantification limit = 1000 mg kg−1,n= 111).Results and discussion Three mineralogical groups were evidenced by PCA, EPMA, and μSXRD data. (i) Fine-grained aggregates of aluminosilicates were frequently detected, appearing multiphased in organic matrices. They were mostly enriched with Zn and Pb without any As or Cu. (ii) (Mn, Ti)-rich Fe oxyhydroxides were predominantly SEM observed, either as isolated grains, silicate coatings, or included in aggregates. They represented the highest detected in situ concentrations for all the studiedTE. And finally, (iii) Mn-rich particles were not frequently observed with SEM but when present were characterized by the highest TE concentrations. Phosphates, carbonates, and S-rich particles (sulfides and/or sulfates) were also determined by PCA as a potential mineralogical group. However, due to their very low TE concentrations and frequency, they could not be considered representative of a TE-bearing mineralogical group.Conclusions This fine sorting classification, combining different techniques at the particle scale, was used to visualize and quantify complex mineralogy and particle associations of TE-bearing phasesin river bed sediments under no specific mineralogical control. It represents an interesting approach to understand TE mobility during sediment cascade and post-depositional processes in sediments.

As carriers of dissolved and particulate loads that connect continental surfaces to oceans, river systems play a major role in the global carbon cycle. Indeed, riverine particulate organic carbon (POC) is a melange of various origins characterized by their own 14C labeling. In addition, civil nuclear activities have brought new 14C source that remains poorly documented. We propose to unravel the Δ14C value of POC stored in a sedimentary archive collected downstream the most nuclearized European rivers (the Loire River). We postulate that riverine POC is a mixture of aquatic POC (which could be impacted by the liquid discharge from nuclear industry), terrestrial and petrogenic POC. With a combination of radiocarbon measurements, POC analyses and the palynofacies method, we assessed the respective Δ14C value of the POC origins. The gaps between the Δ14C values of the sedimentary POC and those of the atmosphere were the result of the dilution from dead-C, the freshwater reservoir effect imprinting the Δ14C of aquatic POC and the age and transit time of terrestrial POC within the catchment. Importantly, we consider that the unravelling of radiocarbon composition of riverine POC could be useful to determine either the transit time of material from source to sink, some past industrial or natural events, the resilience of the river system and milestones of the social and economic trajectory of a catchment. For the last three decades, riverine sediments could also act as a source of radiocarbon for the atmosphere.

Spatio-temporal distribution and leachability of some trace elements (TE) were investigated in sediments of the Xiangjiang River, tributary of the Yangtze River. Based on data collected during 2015–2017, a literature review and geoaccumulation indexes, the pollution level was the highest for Cd, Sb and Hg (Igeo &gt, 3). Over the period reviewed, the TE contamination level displayed almost no temporal variation but an obvious spatial distribution. The most upstream contamination hotspot (Cd &gt, Cr &gt, As, Cu, Pb, Zn &gt, Hg, Sb) was the Songbai section. This hotspot did not spread further downstream. The second hotspot identified was the Zhuzhou–Xiangtan section, impacted by Cd &gt, Hg, Pb, Zn &gt, Cu, with the Zhuzhou area being particularly highly impacted by Pb and Zn. A 30-day leaching experimental protocol under aerobic and anaerobic conditions was carried out to access TE mobility. Low percentages of TE released were calculated, showing that the TE fate mostly depends on the stability of bearing phases under specific physicochemical and microbial conditions. In this case, the studied sediments can be an important sink for these TE. However, some environmental issues have to be considered as some leachate concentrations of contaminants (As, Cr, Cu and U) released into water exceed freshwater aquatic life criteria.

Environmental pollution by polychlorinated biphenyls (PCBs) is a key cause for concern about river quality because of their low degradation rates leading to their accumulation in sediments and living organisms. An original interdisciplinary work was conducted along the four main French rivers (Seine, Rhône, Loire and Garonne rivers), which flow into major European seas. We completed a dataset based on sediment analyses provided by monitoring agencies, port authorities and research teams on different solid matrices (sediment cores, bed and flood deposits, suspended particulate matter and dredged sediments). This dataset focused on the seven indicator PCBs and their sum (ΣPCBi) from 1945 to 2018 (nΣPCBi =1416). Special effort was put into the quality control to provide robust spatio-temporal information. Taking into account hydrological and human drivers, we outlined two main pollution trends: (1) from 1945 to 1975, a quick increase in ΣPCBi (up to 4 mg kg−1 dry weight, dw) and a sharp decrease in the 1980s on the Seine and Loire rivers and (2) increasing but moderate ΣPCBi levels (50 to 150 µg kg−1 dw) followed by a decline after the 1990s on the Rhône and Garonne rivers. In addition to these patterns, PCB emissions from urban and industrial areas or accidental events were significant in each river. Finally, when calculating specific flux, the Rhône exhibited the uppermost ΣPCBi load (up to 12 µgm-2yr-1 in 1977–1987), at least 25 % higher than those of the Seine and Loire rivers, while the Garonne showed a very low flux. In western Europe, we confirmed that the Rhône, Seine and Loire rivers contribute significantly to the PCB contamination of the seas, while French specific ΣPCBi fluxes are 2 orders of magnitude lower than those found in American or Asian rivers. The dataset is available at https://doi.org/10.1594/PANGAEA.904277 (Dendievel et al., 2019).

The reconstruction and modelling of contamination trajectories in rivers is a key concern to investigate spatio-temporal impacts of long-term anthropogenic activities. This issue is highly significant for persistent organic pollutants, such as polychlorinated biphenyls (PCBs), known for their toxicity, their low degradation rates and their hydrophobic properties leading to their accumulation in sediments and biota. Increasingly produced and released worldwide from the 1930s to the 1970-1980s, PCBs were analysed in numerous studies dealing with river sediment quality. However, data syntheses are uncommon at the scale of large hydrosystems, and source-to-estuary approaches along rivers are still needed. Accordingly, we propose an original work integrating PCBs analyses on different solid matrices (sediment cores, bed and flood deposits, suspended particulate matters, and dredged sediments) originating from both research programmes and monitoring. Based on more than 1400 validated analyses, temporal trends of the PCB contamination were reconstructed since 1945 along the four main fluvial corridors in France (Rhône, Seine, Loire and Garonne Rivers). The relationships with socio-environmental factors were also deciphered by integrating hydrological and human spatio-temporal data (cumulative river discharge, population hot spots, urban and industrial surfaces). This work highlighted that the main contaminant trends were driven by regulation, but also by sediment transport and accidental releases (especially since the 1990s). In general, urban and industrial areas were the main contributors to the PCB contamination of rivers: around and downstream of Paris and Rouen (Seine River), Lyon and its “Chemical Valley” (Rhône River), Saint-Etienne and Nantes conurbations (Loire River), and probably downstream of Toulouse and Bordeaux (Garonne River). Relatively high concentrations persisted after the end of the PCB production due to chronic diffuse inputs and accidental releases, particularly on the Rhône River. Moreover, the estimation of specific fluxes revealed that up to 12 µg/m²/yr (i.e. 0.9 t/yr on average) of PCBs were brought by French rivers, especially by the Rhône, Seine and Loire Rivers (ranked in order of importance) to Western European seas since the 1970s.

International audience; The transfer and storage of chemical elements in particulate matter are controlled by physical, chemical and biological processes. Their dynamics are well understood, especially in environments that show strong tectonic and/or geomorphic pressures, and are frequently reconstructed over centuries or decades to evaluate climate change effects for example. However, observations carried out at high spatial and temporal resolutions are less common, particularly in lowland areas. The present study aimed to better understand the links between earth surface processes, such as soil weathering and erosion, by combining pedology, geochemistry and hydrology at a small catchment scale. It focuses on the transfer of selected chemical elements (Ca, K, Ti, Fe, Mn, Rb and Sr) associated with particulate erosion and transport. The first (topsoil) and last (subsoil) soil horizons from different soil profiles and stream bed-load sediments of the Egoutier catchment (8 km2, Loiret, France) were studied. The objective was to investigate the relationship between the weathering and erosion processes. The soils are developed on ancient alluvium as evidenced by their physical and chemical properties, which clearly displayed a weathering profile from bedrock to topsoil layers. Ca, Fe and Rb showed migration dynamics from the topsoils to the subsoils, whereas Mn appeared immobilized within topsoils. Enrichments of all investigated elements increased in bed-load sediments. Topsoil erosion is the main source of sediment. However, Fe and Rb enrichments also highlight the remobilization of subsoils during periods of enhanced precipitation. Furthermore, Fe and Rb enrichments show a selective erosion of clay minerals. K and Sr contents evidence mineral break-up processes favoring mechanical erosion of all mineral phases. Moreover, their enrichments can be interpreted as the result of higher erosion rates and deposition during high rainfall events. The same conclusion can be drawn for Mn and Ca although their spatial variabilities depend on contributions from runoff in urban areas, as rainwaters from anthropized areas supply Ca mineral phases and diluted Mn depleted bearing phases from topsoil layers.

Environmental pollution by Polychlorinated Biphenyls (PCBs) is a key concern about river quality because of their low degradation rates leading to their accumulation in sediments or living organisms. This original interdisciplinary work was conducted at a large scale along the four main French rivers (Seine, Rhône, Loire and Garonne Rivers), which flow into major European seas. We completed a dataset based on sediment analyses provided by monitoring agencies, port authorities and research teams on different solid matrices (cores, bed and flood sediments, suspended particulate matters, dredged sediments). This dataset (n=1416) focused on the seven indicator PCBs and their sum (∑PCBi) from 1945 to 2018. Special effort was put on the quality control to provide robust spatio-temporal information. Taking into account hydrological and human drivers, we outlined two main pollution trends: (1) from 1945 to 1975, a quick increase of ∑PCBi (up to 4 mg.kg−1 dry weight, dw) and a sharp decrease in the 1980s on the Seine and Loire Rivers; (2) increasing but moderate ∑PCBi levels (50 to 150 µg.kg−1 dw) followed by a decline after the 1990s on the Rhône and Garonne Rivers. In addition to these patterns, PCBs emissions from urban and industrial areas or accidental events were significant on each river. Finally, when calculating specific fluxes, the Rhône River exhibited the biggest ∑PCBi load (up to 12 µg.m−2.year−1 in 1977–1987), at least 25 % higher than those of the Seine and Loire Rivers, while the Garonne River showed very low fluxes. French specific ∑PCBi fluxes are two orders of magnitude lower than those found in American or Asian Rivers. In Europe, we confirmed that the Rhone and Seine Rivers provide a major supply of PCBi to the Western Mediterranean and the English Channel, respectively. The dataset is available at https://doi.pangaea.de/10.1594/PANGAEA.904277.

International audience; Bed sediments and a dated sediment core were collected upstream and downstream from the city of Lyon (France) to assess the spatial and temporal trends of contamination by per- and polyfluoroalkyl substances (PFASs) in this section of the Rhône River. Upstream from Lyon, concentrations of total PFASs (ΣPFASs) in sediments are low (between 0.19 and 2.6 ng g−1 dry weight - dw), being characterized by a high proportion of perfluorooctane sulfonate (PFOS). Downstream from Lyon, and also from a fluoropolymer manufacturing plant, ΣPFASs concentrations reach 48.7 ng g−1 dw. A gradual decrease of concentrations is reported at the coring site further downstream (38 km). Based on a dated sediment core, the temporal evolution of PFASs is reconstructed from 1984 to 2013. Prior to 1987, ΣPFASs concentrations were low (≤2 ng g−1 dw), increasing to a maximum of 51 ng g−1 dw in the 1990s and then decreasing from 2002 to the present day (∼10 ng g−1 dw). In terms of the PFAS pattern, the proportion of perfluoroalkyl sulfonic acids (PFSAs) has remained stable since the 1980s (∼10%), whereas large variations are reported for carboxylic acids (PFCAs). Long chain- (C > 8) PFCAs characterized by an even number of perfluorinated carbons represent about 74% of the total PFAS load until 2005. However, from 2005 to 2013, the relative contribution of long chain- (C > 8) PFCAs with an odd number of perfluorinated carbons reaches 80%. Such changes in the PFAS pattern likely highlight a major shift in the industrial production process. This spatial and retrospective study provides valuable insights into the long-term contamination patterns of PFAS chemicals in river basins impacted by both urban and industrial activities.

Tritium of artificial origin was initially introduced to the environment from the global atmospheric fallout after nuclear weapons tests. Its level was increased in rainwaters by a factor 1000 during peak emissions in 1963 within the whole northern hemisphere. Here we demonstrate that tritium from global atmospheric fallout stored in sedimentary reservoir for decades as organically bound forms in recalcitrant organic matter while tritium released by nuclear industries in rivers escape from such storages. Additionally, we highlight that organically bound tritium concentrations in riverine sediments culminate several years after peaking emission in the atmosphere due to the transit time of organic matter from soils to river systems. These results were acquired by measuring both free and bound forms of tritium in a 70 year old sedimentary archive cored in the Loire river basin (France). Such tritium storages, assumed to be formed at the global scale, as well as the decadal time lag of tritium contamination levels between atmosphere and river systems have never been demonstrated until now. Our results bring new lights on tritium persistence and dynamics within the environment and demonstrate that sedimentary reservoir constitute both tritium sinks and potential delayed sources of mobile and bioavailable tritium for freshwaters and living organisms decades after atmospheric contamination.

An intensive surface sediment survey was carried out over 24 locations from the upstream to downstream sections of two large rivers (Adyar and Cooum) in Chennai (India) during the February dry season of 2015. Trace element concentrations were assessed on a &lt, 63 &micro, m fraction using the Geoaccumulation Index (Igeo) and the newly proposed Geochemical Urban Footprint Index (GUFI), which can be performed to determine the pollution status of any megacity river influenced by urban development. The sediment quality of Chennai&rsquo, s rivers was also compared to worldwide megacity pollution using sediment quality guidelines (SQGs), and a new megacity pollution ranking was determined. The Igeo results indicate that the Chennai rivers studied are strongly to extremely polluted regarding trace element content of sediment. Silver (Ag), Cadmium (Cd) and Mercury (Hg) are the most significant tracers of urban contamination. Chromium (Cr) concentrations show an industrial contamination gradient in relation to levels of other trace elements (As, Cu, Ni, Pb, and Zn) at the Chennai megacity scale. The GUFI ranges from moderate to extreme contamination, particularly in the downstream stretches of the two rivers. This spatial trend is related to various point sources and identified at specific sampling stations, with a lack of identifiable buffer zones. According to the worldwide comparison of megacity pollution, Chennai is ranked in fifth position. The present position can be attributed to a number of explanations: a population explosion associated with the unplanned growth of the city and non-controlled point sources of pollution in Chennai&rsquo, s waterways.

International audience; During the 20th century, the local economy of the Upper Loire Basin (ULB) was essentially based on industrial coal mining extraction. One of the major French coal districts with associated urban/industrial activities and numerous coking/gas plants were developed in the Ondaine-Furan subbasins, two tributaries of the upper Loire main stream. To determine the compositional assemblage, the level and the potential sources of contamination, the historical sedimentary chronicle of the 16 US EPA priority polycyclic aromatic hydrocarbons (PAHs) has been investigated. PAH concentrations were determined using gas chromatography/mass spectrometry (GC/MS) in a dated core, sampled in the Villerest flood-control reservoir located downstream of the Ondaine-Furan corridor (OFC). The most contaminated sediments were deposited prior to 1983 (Σ16PAHs ca. 4429–13,348 ng/g) and during flood events (Σ16PAHs ca. 6380 ng/g – 1996 flood; 5360 ng/g – 2003 flood; 6075 ng/g – 2008 flood), especially in medium and high molecular weight PAHs. Among them, typical pyrogenic PAHs such as FLT, PYR, BbF and BaP were prevalent in most of the core samples. In addition, some PAHs last decade data is available from the Loire Bretagne Water Agency and were analyzed using high-performance liquid chromatography with postcolumn fluorescence derivatization (HPLC/FLD). These results confirm that the most highly contaminated sediments were found downstream of OFC (Σ16PAHs ca. 2264–7460 ng/g). According to the observed molecular distribution, PAHs are originated largely from high-temperature pyrolytic processes. Major sources of pyrogenic PAHs have been emphasized by calculation of specific ratios and by comparison to reported data. Atmospheric deposition of urban and industrial areas, wood combustion and degraded coal tar derived from former factories of coking/gas plants seem to be the major pyrogenic sources. Specifically, particular solid transport conditions that can occur during major flood events lead us to emphasize weathering of former contamination sources, such as more preserved coal tar.

International audience; Les carottes sédimentaires font l'objet d'un intérêt grandissant de la part des paléo-environnementalistes mais également d’écologues qui s'intéressent à la trajectoire des écosystèmes (Pansu et al., 2015; Perga et al., 2015). Les carottes marines ou continentales prélevées dans le cadre de consortiums internationaux (IODP, ICDP) donnent l’exemple depuis des décennies en terme de partage d’échantillons pour ce type d’étude ; plus récemment l’augmentation de ré-études massives de données publiées (Bolliet et al., 2016; Cartapan is et al., 2016) démontrent la valeur de ces échantillons et des données associées. De leur côté depuis quelques années, les législateurs et financeurs poussent à l’ouverture, au partage et à la traçabilité des données : on peut citer l’OCDE, l’UE, l’ERC... Comment notre communauté peut-elle s’inscrire au quotidien dans ces processus qui demandent de profonds changements culturels dans nos pratiques de recherche ? C’est pour tenter d’apporter une réponse à cette question que nous avons cherché à développer un système intégré de captation et de gestion des métadonnées des échantillons issus de forages scientifiques, qui puisse être implémenté au niveau national et connecté à des initiatives internationales, sur lequel pourront venir s’appuyer les futurs Plans de Gestion de Données. Par une approche bottom-up, pragmatique et au plus près des pratiques des équipes de recherche, nombreuses, dispersées, aux moyens inégaux, et en s’appuyant sur des initiatives existantes, nous tentons de répondre petit à petit à différents niveaux - de la mission de prélèvement jusqu'à leur stockage, en passant par la mise à disposition, le suivi et la valorisation des échantillons et des métadonnées qui leur sont associées. Des avancées rapides ont pu être obtenues par la rencontre entre une communauté de paléoécologues et des équipes techniques novatrices dans le domaine du partage et de l’interopérabilité mêlant des informaticiens, géomaticiens, curateurs d’échantillons et de données. Cette dynamique s’appuie sur 3 projets nationaux (Cyber-Carothèque nationale s/c Equipex CLIMCOR ANR-11-EQPX-0009 ; QR-Code LTSER- France ; ROZA LTSER-France) et s’inscrit dans le cadre du Centre de Carottage et de Forage National (C2FN), une cellule de la division technique de l’INSU. Nous présenterons dans cette intervention 4 outils qui seront à court terme interconnectés : i)CoreBOOK, une application mobile de terrain dédiée à la captation des métadonnées de forage ; ii) le portail de la cyber-carothèque national, un hub accueillant les données nouvellement acquises et les inventaires de carothèques ; iii) Collec-Science, outil générique de gestion de collections d’échantillons naturels adapté à nos besoins (s/c projet QrCODE); enfin iv) ROZA (Rétro-Observatoire des Zones Ateliers), un prototype de découvreur et visualiseur de données destiné à favoriser la réutilisation des échantillons et des données paléoenvironnementales en mettant à disposition les données essentielles à la capitalisation des connaissances d’études successives sur un même site. Les perspectives aujourd'hui sont grandes, le système modulaire qui commence à se dessiner doit permettre à chacun de trouver son compte, à son rythme, où opérationnel peut enfin rimer avec standardisation, traçabilité et interopérabilité tout en conservant une utilisabilité au plus proche des activités et besoins quotidiens des chercheurs et personnels d’accompagnement, afin d’opérer un virage en douceur vers des pratiques de la science dite « ouverte "

International audience; Assessing the extent of metal contamination in estuarine surface sediments is hampered by the high heterogeneity of sediment characteristics, the spatial variability of trace element sources, sedimentary dynamics and geochemical processes in addition to the need of accurate reference values for deciphering natural to anthropogenic contribution. Based on 285 surface sediment samples from the Loire Estuary, the first high-resolution spatial distributions are presented for grain-size, particulate organic carbon (POC) and the eight metals/metalloids identified as priority contaminants (Cd, Zn, Pb, Cu, As, Cr, Ni, Hg) plus Ag (an urban tracer). Grain-size and/or POC are major factors controlling the spatial distribution of trace element concentrations. The V-normalized trace metal concentrations divided by the V-normalized concentrations in the basin geochemical background showed the highest Enrichment Factors for Ag and Hg (EF; up to 34 and 140, respectively). These results suggest a severe contamination in the Loire Estuary for both elements. Intra-estuarine Ag and Hg anomalies were identified by comparison between respective normalized concentrations in the Loire Estuary surface sediments and those measured in the surface sediments at the outlet of the Loire River System (watershed-derived). Anthropogenic intra-estuarine Ag and Hg stocks in the uppermost centimetre of the sediment compared with rough annual fluvial flux estimates suggest that the overall strong Enrichment Factors for Ag (EFAg) and and Hg (EFHg) in the Loire Estuary sediments are mainly due to watershed-derived inputs, highlighting the need of high temporal hydro-geochemical monitoring to establish reliable incoming fluxes. Significant correlations obtained between EFCd and EFAg, EFCu and POC and EFHg and POC revealed common behavior and/or sources. Comparison of trace element concentrations with ecotoxicological indices (Sediment Quality Guidelines) provides first standardized information on the sediment quality in the Loire Estuary. The overall mean Effect Range Median quotients (m-ERM-q) results suggested that the Loire Estuary is mainly characterized by slightly toxic sediments even if ecotoxicological impacts have been previously reported on biota.

The Red River (China/Vietnam, A = 155 000 km2) is a typical humid tropics river originating from the mountainous area of Yunan Province in China. Based on two sampling campaigns covering the whole Vietnamese watershed in 40 sites at low and high water levels during 2009, the seasonal and spatial variations of As concentrations in dissolved and particulate phases were determined. The dissolved As concentrations in rainy season were relatively lower than in dry season, suggesting the dilution effect of less arsenic-contaminated water. In contract, the particulate As concentrations during low water level were clearly lower than that during high water level, demonstrating a change phenomenon in As source(s) with hydrology. In addition, in order to assess spatial distribution of the As contamination in the Red River watershed and localize geochemical anomalies, multidimensional statistical analyses combined with As maps generated by GIS tool were used. The results showed that the highest As concentrations are originated from the upstream catchment and strongly decrease from upstream to downstream. Finally, the comparison between dissolved As concentrations from the Red River watershed and the national technical regulation on surface water (QCVN 08:2008/BTNMT) indicated that the quality of water in the Vietnamese Red River watershed can be classified as poor quality in the upstream part and as mediocre quality in the downstream part.

International audience; On the basis of particle size distributions, bulk chemical and mineralogical compositions and firing properties, this paper outlines an assessment of the industrial suitability of Mayouom kaolin deposit for sustainable development. The characteristics of the studied samples compared to some standards indicate that these kaolins are high quality industrial clays. Firing yielded good results for white firing ceramics and for refractory ceramics. For other industrial uses, a treatment by purification and titanium removal is necessary to improve their suitability.

International audience; This study concerns the mineralogy of the tailings of a former Ag–Pb mine (Auzelles district, France) and the contribution of the waste materials to the heavy metal dissemination in the environment. Accumulation of metals in fish flesh was reported and this pollution is attributed to past mining activities. Tailings were studied to establish the major transfer schemes of As and Pb in order to understand their mobility that leads to contamination of a whole ecosystem. Mineralogical investigation, solubility and compliance tests were performed to assess the stability of the metal-bearing phases. Among the various metallic elements measured, As and Pb show the highest bulk concentrations (up to 0.7% and 6.3% respectively) especially for samples presenting near neutral pH values. According to X-ray diffraction (XRD), Scanning Electron Microscopy (SEM-EDX), Electron Probe Micro-Analysis (EPMA) and micro-Raman spectrometry (μRS), tailings mineralogy still contain primary minerals such as sulfides (e.g., galena, pyrite), phosphates (monazite, apatite) and/or carbonates (e.g., (hydro-)cerussite, dolomite, siderite). Sulfates (e.g., anglesite, lanarkite, plumbojarosite and beudantite) are the main secondary metal-bearing phases with other interesting phases accounting for metals mobility such as Fe and/or Pb and/or Mn oxides (e.g., lepidocrocite, goethite -up to 15 wt% of Pb was measured-, plumboferrite-type phase, mimetite). The lowest Pb solubilities were obtained at pH 8–9 and at a larger range than for As for which the lowest solubilities are reached around pH 6–7. At this minimum solubility pH value, Pb concentrations released still over exceed the National Environmental Quality Standards (NEQS), whatever the samples. The highest solubility is reached at pH 2 for both elements whatever the considered sample. This represents up to 51% of total Pb and up to 46% of total As remobilized and concentrations exceeding the NEQS. As and Pb released mainly depends on the Fe/Mn oxides (e.g., goethite, lepidocrocite) and carbonates (cerussite) which are the less stable phases. Compliance tests also show that Pb concentrations released are higher than the upper limit for hazardous waste landfills. Determination of the mineralogy allows understanding both the solubility and leaching test experiments results, as well as to forecast the impact of the residues on the water quality at a mid-term scale.

International audience; From the 19th century, the Loire basin (France) presents potentially pollutant activities such as mining and heavy industries. This paper shows spatio-temporal distribution of trace elements in sediments at a basin-scale, based on a comparison of archived temporal signals recorded in four sedimentary cores. Anthropogenic sources contributing to sediment contamination are also characterized, using geochemical signatures recorded in river bank sediments of the most industrialized tributaries. This study highlights upstream-downstream differences concerning recorded contamination phases in terms of spatial influence and temporality of archiving processes. Such differences were related to (i) various spatial influences of contamination sources and (ii) polluted sediments dispersion controlled by transport capacity of metal-carrier phases and hydrosedimentary dynamics.

The objective of this study is to identify parameters influencing trace elements (TE) vertical distributions in an Andosol–Andic Cambisol climosequence. In order to understand processes involved in the current distribution of trace elements from basaltic rocks to associated soils, six pedons developed on Tertiary massive basaltic formations, located at similar position in the hill-slopes, submitted to the same wet mountainous climate but under various microclimatic conditions (altitude and annual rainfall), were considered. The six studied soils are andic and rich in organo–metallic complexes. Two different and quantitative methods were used to compare the geochemical distributions of major and trace elements, both being calculated with Ti as invariant element: isovolumetric mass balance and enrichment factors. Anthropogenic, pedogenetic, microclimatic, inherited factors were discriminated. Anthropogenic influences are pointed out for K in two pedons and for Pb in all studied sites. Distributions of other TE are affected by discontinuities between underlying rocks and soil horizons. Zinc and Cu distributions are controlled by organic matter whereas Cr and Ni distributions are influenced by pedogenetic processes. Results emphasize the relative trace element immobilization in andic soils under temperate climate.

The Villerest flood-control reservoir was built in the Upper Loire River (France) during the early 1980s, downstream from the most important industrial and coal-mining area of the basin. This reservoir has constituted an important trap for sediments and associated pollutants since its operation in 1984. A 154-cm-long core was recovered in 2010 in the deepest area of the reservoir and shows the influence of sedimentary infill processes on aggradation rates and selected chemical patterns. During dam operations, the lacustrine aggradation rate is not linear because of three turbiditic-like layers resulting from sediment-laden underflows during major flood events in 1996, 2003 and 2008. These three events contribute to 43% of the 151 kg·m − 2 of accumulated sediments over the 1984–2010 period. Trace element solid sources are activated during these floods as selected metals present the highest enrichment factors, levels never reached during interflood periods. In addition, sedimentological and detrital geochemical signals during these events influence anthropogenic trace element signals by a variable dilution effect (maximum during the increasing discharge stage). Hence, coupling sedimentological and geochemical approaches allows us to understand the sedimentary infill dynamics and, more specifically, to take into account the influence of floods on the temporal trajectories of pollutants.

Natural ferrihydrite (Fh), a poorly crystalline iron oxy-hydroxide with high concentrations of As, was investigated with respect to its crystallinity in a remediated mining environment. The Fh crystallinity increases from proto-Fh to a better crystallized 2-line Fh (called better 2-line Fh), while the associated As contents decrease from 7.8 to 1.9 wt %, respectively. This evolution of crystallinity correlated with decreasing As suggests that As is more likely coprecipitated in the Fh structure than adsorbed onto the surface. The evolution of Fh crystallinity is related to (i) aqueous transformations for samples continuously submerged and controlled by water composition (pH, ionic strength and redox potential) and (ii) dry thermal transformations for samples in a seasonally humid area with variations of temperature, humidity, agglomeration and compaction. The evolution of Fh crystallinity is more pronounced during dry thermal transformation than during aqueous transformations. Although Fh evolution is observed on the field, no stable form (goethite, hematite) is detected as usually noted during dry thermal transformation. This may be explained by incorporated cations such as Si and Al that can inhibit the transformation of Fh to a more stable form. To understand this transformation in a natural environment, the discussion in this study focuses on two main points: (i) the relationship between spatial mineralogical distribution and As content and (ii) the importance of Fh evolution as a function of transformation processes observed in the field.

Geological, mineralogical and geochemical studies were carried out on Mayouom kaolin deposit located within a mylonitic shear zone about 30 km north of Foumban town (western Cameroon), in order to define the ore genesis and its economic interest. Two facies (sandy kaolin and sand-poor kaolin) were characterised by different techniques: description of outcrops and pits, X-ray diffraction, differential scanning calorimetric and thermogravimetric analyses, scanning electron microscopy, Fourier transform infrared spectrometry and bulk chemical analyses. Sand-poor kaolin (76–85% kaolinite and 2–9% quartz) forms 1 to 2 m thick veins which crosscut sandy kaolin (48–59% kaolinite and 36–47% quartz). All the samples have the following mineral phases in common, close to an advanced argillic alteration system: kaolinite + quartz + illite/muscovite + anatase ± hematite ± Ba, Sr-hydroxyapatite ± zircon ± pyrite ± florencite. Both sandy and sand-poor kaolins present kaolinite mineral with a homogeneous shape and a good crystallinity. Results from the different analytical techniques point out a hydrothermal alteration of feldspar- and mica-rich rocks as petrogenetic origin of kaolins. Sandy kaolin comes from mylonite basement while sand-poor kaolin is related to the alteration of magmatic intrusive shape veins. Due to its high kaolinite content (up to 85%) and the low iron mineral content (

Fresh floodplain deposits (FD), from 11 key stations, covering the Seine mainstem and its major tributaries (Yonne, Marne and Oise Rivers), were sampled from 1994 to 2000. Background levels for Cd, Cu, Hg, Pb, and Zn were established using prehistoric FD and actual bed sediments collected in small forested sub-basins in the most upstream part of the basin. Throughout the Seine River Basin, FD contain elevated concentrations of Cd, Cu, Hg, Pb and Zn compared to local background values (by factors>twofold). In the Seine River Basin, trace element concentrations display substantial downstream increases as a result of increasing population densities, particularly from Greater Paris (10 million inhabitants), and reach their maxima at the river mouth (Poses). These elevated levels make the Seine one of the most heavily impacted rivers in the world. On the other hand, floodplain-associated trace element levels have declined over the past 7 years. This mirrors results from contemporaneous suspended sediment surveys at the river mouth for the 1984-1999 period. Most of these temporal declines appear to reflect reductions in industrial and domestic solid wastes discharged from the main Parisian sewage plant (Seine Aval).

Potential contamination of rivers by trace elements can be controlled, among others, by the precipitation of oxyhydroxides. The streambed of the studied area, located in “La Châtaigneraie” district (Lot River Basin, France), is characterised by iron-rich ochreous deposits, acidic pH (2.7–4.8) and SO 4 –Mg waters. Beyond the acid mine drainage, the presence of As both in the dissolved fraction and in the deposits is also a problem. Upstream, at the gallery outlet, As concentrations are high (As max = 2.6 μmol/l and up to 5 wt% locally, respectively, in the dissolved and in the solid fractions). Downstream, As concentrations decrease below 0.1 μmol/l in the dissolved fraction and to 1327 mg/kg in the solid fraction. This natural attenuation is related to the As retention within ochreous precipitates (amorphous to poorly crystalline Fe oxyhydroxides, schwertmannite and goethite), which have great affinities for this metalloid. Upstream, schwertmannite is dominant while downstream, goethite becomes the main mineral. The transformation of schwertmannite into goethite is observed in the upstream deposits as schwertmannite is unstable relative to goethite. Furthermore, thermodynamic calculations indicate that the downstream goethite is not able to precipitate in situ according to the water chemistry. Goethite mainly results from the transformation of schwertmannite and its solid transport downstream. Moreover, as highlighted by leaching experiments carried out on the ochreous precipitates, this transformation does not seem to affect the As-retention in solids as no release of As was observed in the solution. Arsenic may either be strongly trapped by co-precipitation in the present minerals or it may be quickly released and re-adsorbed on the precipitate surface.

In the 1980's, based on the concentrations of particulate-associated Hg, Cd, Pb, Cu and Zn relative to very low natural background levels, the Seine River Basin was one of the most impacted in the world. Over the past 20 years, there has been a general decline in these elevated concentrations that parallels declines in Paris sewage sludge trace element levels. Within the basin, marked differences in spatial and temporal geochemical patterns have been observed: (1) between major tributaries, (2) between trace elements, and (3) with stream order and population density, all of which illustrate the complexity of the geochemical processes ongoing in the basin.

Surface sediments in the Spokane River Basin are enriched in Pb, Zn, As, Cd, Sb, and Hg relative to local background levels. Maximum enrichment occurs in the Upper Spokane River in close proximity to Lake Coeur d9Alene. On average, enrichment decreases downstream. Subsurface sediments also are enriched in Pb, Zn, As, Cd, Sb, and Hg relative to background levels. Enrichment began between 1900 and 1920 in the middle of the basin; this is contemporaneous with similar findings in Lake Coeur d9Alene (the upstream source of the Spokane River), as well as the completion of Long Lake Dam (1913). In the most downstream part of the basin, enrichment began between 1930 and 1940. This temporal shift may reflect the latter9s greater distance from the Coeur d9Alene River Basin, the presumptive source of the enriched trace elements, but is more likely the result of the completion of Grand Coulee Dam (1934–1941) which backed up the Spokane River, and elevated water levels by about 30 m in the most downstream part of the basin.

The spatial and temporal distributions of major elements were investigated in the sur- face waters and in associated suspended matter at two sites of the upper Loire basin (Orleans and Brehemont) between 1995 and 1998. According to geochemical and isotopic patterns, the dissolved load appears to result from a process of mixing rainwater inputs, weathering processes of carbonate and silicate bedrock, and agricultural and urban inputs. Natural inputs influence 60% of water chemical composition at both sites. Annual dissolved fluxes were estimated to be 1300 10 3 t/y at Orleans and 1620 10 3 t/y at Brehemont. Major elements are transported mainly in the dissolved fraction. After correcting for atmospheric and anthropogenic inputs, the silicate specific export rate was calculated to be 11 t/y/km 2 throughout the basin and the carbonate specific export rate to be from 47 t/y/km 2 at Orleans to 23 t/y/km 2 at Brehemont. The suspended load appears to result from at least two particle reservoirs: a silicate reservoir and a carbonate reservoir. The silicate reservoir has a detrital origin, mainly during periods of high flow, while the carbonate reservoir has a detrital origin during periods of high flow and an authigenic origin during periods of low flow. Of the total annual flow of suspended matter, this authigenic material represents 16% at Orleans, 25% at Brehemont and 37% in the fluvial part of the estuary. After correcting authigenic inputs, the specific export rate due to mechanical weathering was estimated to be 8 t/y/km 2 throughout the Loire basin.

During 1998/1999, surface and subsurface sediment samples were collected along the entire length of the Spokane River from its outlet at the northern end of Lake Coeur d'Alene (CDA), Idaho, to Lake Roosevelt on the Columbia River, Washington. The study was conducted to determine if the trace element enrichments observed in Lake CDA and on the floodplain and in the CDA River extend through the Spokane River Basin (SRB). As in Lake CDA, surface sediments in the SRB are enriched in Pb, Zn, As, Cd, Sb and Hg relative to local background levels. Pb, Cd and Zn are the most elevated, with maximum enrichment occurring in the upper Spokane River in close proximity to Lake CDA. On average, enrichment decreases downstream, apparently reflecting both increased distance from the inferred source (the CDA River Basin), as well as increased dilution by locally derived but unenriched materials. Only Cd and Zn display marked enrichment throughout the SRB. Pb, Zn and Cd seem to be associated mainly with an operationally defined iron oxide phase, whereas the majority of the As and Sb seem to be matrix-held. Subsurface sediments also are enriched in Pb, Zn, As, Cd, Sb and Hg relative to background levels. Based on 137Cs and excess 210Pb dating, trace element enrichment began in the middle part of the SRB (Long Lake) between 1900 and 1920. This is contemporaneous with similar enrichments observed in Lake CDA, as well as the completion of Long Lake Dam (1913). In the most downstream part of the basin (Spokane River Arm of Lake Roosevelt), enrichment began substantially later, between 1930 and 1940. The temporal difference in enrichment between Long Lake and the River Arm may reflect the latter's greater distance from the presumed source of the enrichment (the CDA River Basin); however, the difference is more likely the result of the completion of Grand Coulee Dam (1934–1941), which formed Lake Roosevelt, backed up the Spokane River, and increased water levels in the River Arm by about 30 m.

The Loire River, with one of the largest watersheds in France, has been monitored just outside the city of Orleans since 1994. Physico-chemical parameters and major and trace elements were measured between 2-day and 1-week intervals according to the river flow. The sampling site represents 34% of the total Loire watershed with 76% silicate rocks and 24% carbonate rocks. Elements are transported mainly in the dissolved phase with the ratio of total dissolved salts (TDS) to suspended matter (SM) ranging between 1.6 and 17.4. Chemical weathering of rocks and soils are thus the dominant mechanisms in the Loire waters composition. The highest TDS/SM ratios are due to dissolved anthropogenic inputs. The database shows no link between NO3− content and river flow. The Na+, K+, Mg2+, SO42−, and Cl− concentrations are seen to decrease with increasing discharge, in agreement with a mixing process involving at least two components: the first component (during low flow) is concentrated and may be related with input from the groundwater and sewage station water, the second component (during high flow) is more dilute and is in agreement with bedrock weathering and rainwater inputs. A geochemical behaviour pattern is also observed for HCO3− and Ca2+ species, their concentrations increase with increasing discharge up to 300 m3/s, after which, they decrease with increasing discharge. The Sr isotopic composition of the dissolved load is controlled by at least five components — a series of natural components represented by (a) waters draining the silicate and carbonate bedrock, (b) groundwater, and (c) rainwaters, and two kinds of anthropogenic components. The aim of this study is to describe the mixing model in order to estimate the contribution of each component. Finally, specific export rates in the upper Loire watershed were evaluated close to 12 t year−1 km−2 for the silicate rate and 47 t year−1 km−2 for the carbonate rate.

Suspended particulate matter transported by the Loire River (France) comprises mainly quartz and K-feldspar during periods of high river flow, with an increase in calcite contents during periods of low flow. We studied the labile fraction (leached by HCl 0.2 N) associated with the suspended matter transported by the upper Loire River. The acid extractable matter (AEM) concentrations in the Loire exhibit a wide range from 8% during high-flow conditions in the river to 47% during the low-flow conditions. The dispersion of AEM data differentiates two fields; one related to a domain where CaCO3 precipitation is possible, and the other related to a domain where erosion is dominant. The concentrations of trace elements and REE fluctuate widely and generally decrease with increasing AEM concentrations. A middle REE (MREE) enrichment over the LREE and HREE is observed which can be related to Fe–Mn oxide coatings developed on the clastic particles. The 87Sr/86Sr ratio varies from 0.710582 to 0.711472 and displays two different trends when plotted against AEM abundance, again reflecting varying contributions from two main end-members. The hydrous Fe–Mn oxides have the lowest 87Sr/86Sr ratio (≈0.7105) and the carbonates have the highest 87Sr/86Sr ratio (≈0.7115). The highest 87Sr/86Sr ratios of AEM, obtained during the period of authigenic calcite precipitation, agree with values measured for the dissolved Sr over the same period. During the period where erosion dominates, the 87Sr/86Sr ratio of the hydrous Fe–Mn oxide end-member diverges from the mean value of the dissolved load of the Loire River. This implies that the oxides were formed in water with a lower 87Sr/86Sr ratio, suggesting that (i) the location of oxide precipitation is upland, and (ii) the oxides conserve their Sr isotope signature during transport by the river and do not re-equilibrate with local waters during transport. Stable carbon and oxygen isotope compositions of the carbonate fraction of the AEM during low-flow conditions are consistent with authigenic calcite formation in isotopic equilibrium with Loire River water. At high-flow conditions we observe an isotopic enrichment that may reflect a higher proportion of atmospheric CO2 within the river waters at this time, or a contribution of detrital carbonate material from marine sediments exposed in the watershed, or secondary calcite derived from eroded soils.

The mineralogy of the suspended particulate matter (SPM) transported by the upper Loire river consists mainly of quartz and K-feldspar during periods of high river flow, with an increase in calcite concentration during periods of low flow. Concurrently, large fluctuations are observed in the levels of CaO and Fe2O3, the main oxides present in the SPM along with SiO2. The analysed trace elements also fluctuate significantly. The bed sediments (BS) have a similar oxide content to the SPM, but lower Zn and Pb levels and higher Zr levels. Fluctuations in the chemical-element concentrations with river discharge are related to fluctuation in the mineral assemblages present in the SPM. Thus K, Ti and Rb levels increase with increasing in K-feldspar abundance during high flow, and Ca and Sr levels decrease with increasing discharge due to a decrease in calcite abundance. These mineralogical and chemical variations relate to different sources of sediments under different flow conditions—sources that can be distinguished by Sr isotopic study. The Sr isotopic composition fluctuates according to the rate of river discharge; i.e., the 87 Sr / 86 Sr ratio increases with increasing discharge and reaches a maximum with peak flow, and vice versa. The 87 Sr / 86 Sr ratio also increases with the combined increase in K-feldspar abundance and decrease in calcite abundance. These similarities suggest the existence of at least two particulate-matter reservoirs, one with detrital silicates and the other with carbonates. Finally, the relationship between the 87 Sr / 86 Sr ratios in the suspended and dissolved loads suggests the coexistence of authigenic calcite in the carbonate reservoir. The SPM flow is related to a specific mechanical erosion rate over the whole Loire watershed ranging from 9 to 23 t km−2 yr−1. During the survey at Orleans, the SPM flow of the Loire river was 37·104 t yr−1, providing an estimate of the specific erosion rate of around 9.8 t km−2 yr−1. From the shift in the SPM flux between the sampling point and the mouth of the Loire river and the divergence in the mean annual discharge, a calculation was made of the input of solid matter by the tributaries and by supplementary erosion processes along the river.

Background: While the use of plastic materials has generated huge societal benefits, the "plastic age" comes with downsides: One issue of emerging concern is the accumulation of plastics in the aquatic environment. Here, so-called microplastics (MP), fragments smaller than 5 mm, are of special concern because they can be ingested throughout the food web more readily than larger particles. Focusing on freshwater MP, we briefly review the state of the science to identify gaps of knowledge and deduce research needs. State of the science: Environmental scientists started investigating marine (micro)plastics in the early 2000s. Today, a wealth of studies demonstrates that MP have ubiquitously permeated the marine ecosystem, including the polar regions and the deep sea. MP ingestion has been documented for an increasing number of marine species. However, to date, only few studies investigate their biological effects. The majority of marine plastics are considered to originate from land-based sources, including surface waters. Although they may be important transport pathways of MP, data from freshwater ecosystems is scarce. So far, only few studies provide evidence for the presence of MP in rivers and lakes. Data on MP uptake by freshwater invertebrates and fish is very limited. Knowledge gaps: While the research on marine MP is more advanced, there are immense gaps of knowledge regarding freshwater MP. Data on their abundance is fragmentary for large and absent for small surface waters. Likewise, relevant sources and the environmental fate remain to be investigated. Data on the biological effects of MP in freshwater species is completely lacking. The accumulation of other freshwater contaminants on MP is of special interest because ingestion might increase the chemical exposure. Again, data is unavailable on this important issue. Conclusions: MP represent freshwater contaminants of emerging concern. However, to assess the environmental risk associated with MP, comprehensive data on their abundance, fate, sources, and biological effects in freshwater ecosystems are needed. Establishing such data critically depends on a collaborative effort by environmental scientists from diverse disciplines (chemistry, hydrology, ecotoxicology, etc.) and, unsurprisingly, on the allocation of sufficient public funding.