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.
Since 1945, a large amount of heterogeneous data has been acquired to survey river sediment quality, especially concerning regulatory metals such as Cd, Cr, Cu, Hg, Ni, Pb, and Zn. Large-scale ...syntheses are critical to assess the effectiveness of public regulations and the resiliency of the river systems. Accordingly, this data synthesis proposes a first attempt to decipher spatio-temporal trends of metal contamination along seven major continental rivers in Western Europe (France, Belgium, Germany, and the Netherlands). A large dataset (>12,000 samples) from various sediment matrices (bed and flood deposits – BFD, suspended particulate matter – SPM, dated sediment cores – DSC) was set up based on monitoring and scientific research from the 1950s to the 2010s. This work investigates the impact of analytical protocols (matrix sampling, fractionation, extraction), location and time factors (related to geology and anthropogenic activities) on metal concentration trends. Statistical analyses highlight crossed-interactions in space and time, as well as between sediment matrices (metal concentrations in SPM ≃ DSC > BFD) and extraction procedures (also related to river lithology). Major spatio-temporal trends are found along several rivers such as (i) an increase of metal concentrations downstream of the main urban industrial areas (e.g. Paris-Rouen corridor on the Seine River, Bonn-Duisburg corridor on the Rhine River), (ii) a long-term influence of former mining areas located in crystalline zones, releasing heavily contaminated sediments for decades (Upper Loire River, Middle Meuse section), (iii) a decrease of metal concentrations since the 1970s (except for Cr and Ni, rather low and stable over time). The improvement of sediment quality in the most recent years in Europe reflects a decisive role of environment policies, such as more efficient wastewater treatments, local applications of the Water Framework Directive and urban industrial changes in the river valleys.
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•Assessment of metal contaminations in sediments along Western European Rivers•Sediment monitoring and cores covering the period from the 1960s to the 2010s.•Deciphering of spatial and temporal factors over contamination trends•Secondary influence of the matrix-types and extraction process on metal levels
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.
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 ...present study 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, and μSXRD) 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 TE such 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 studied TE. 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 phases in 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.
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•Sedimentological, metallic and organic contaminants analyses in riverbank sediments.•FingerPro unmixed model to assess geochemical fingerprinting.•Storage of legacy sediments along ...the banks since the 1950 s.•Low transport capacity of contaminant bounded particles.•Strong decrease of the contamination gradient 60 km downstream of hotspot.
As within many European rivers in mountainous areas, the Bienne River (Jura Mountains, France) has been severely impacted by the implementation of obstacles to river flow. The aim of this study is to better understand how hydro-sedimentary dysfunctions (complex alterations of sediment transport in response to river engineering) can influence contaminants storage along the river. The sediment pollution trajectory was reconstructed based (1) on a well-dated sediment core, and (2) on several sediment samples taken at different depths on six riverbank profiles. Age control was established with a well-defined 137Cs profile and time-related grain size transitions in the sediment core, and only relatively for riverbank profiles using a plasticizer and PCB contents as chemical markers of the Anthropocene. Riverbanks and the core are composed of fine-grained legacy sediments deposited during the 20th century. They covered the former active channel mostly composed of pebbles and cobbles. Historical contaminants were the highest in the most upstream station and declined in the downstream direction to reach relatively low values in the lower river section. This historical upstream signal poorly influences the geochemical composition of sediments in the lower reaches, due its attenuation by numerous human-made obstacles to river flow and to the limited sediment transport capacity of the river. According to an unmixing model, the contribution of the upper sediments only weights a small percentage of the sedimentary mixture at the river outlet. These results highlight the sedimentary storage capacity of historical contaminants in mountain coarse-bedded river. This phenomenon has been led by a riverbed narrowing and stabilization caused by deep alterations of hydro-sedimentary processes. It finally emphasizes storage of sedimentary contaminants and leads to limited source influences. Hence, this study shows the key role of sedimentary transport, which triggers spatial and temporal variability of contaminants stored 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.
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•Aquatic POC in sedimentary archives does not record 14C from the nuclear industry.•Δ14C values of terrestrial POC as a tool to determine the transit time of sediments within the watershed•Δ14C as a useful tool to document the trajectories of social and economic milestones
Platinum (Pt) is a Technology Critical Element (TCE) which, since the 1990s, has been mainly used in the industry in catalytic converters for automobile emission control. Previous studies have shown ...Pt contamination of road-side sediments and surface sediments in urban rivers and lakes but few of them have addressed temporal variations. The present work presents historical Pt concentration trends in 137Cs-dated sediment cores from floodplains or secondary channels at the outlets of three major French watersheds (Loire, Rhone, and Seine Rivers) covering the past ∼110 years, i.e., from the 1910s to 2021. Platinum baseline levels in the sediment were estimated for the Loire River (0.76 ± 0.22 μg kg−1 for the period ∼1910-∼1955) and the Rhone River (1.64 ± 0.41 μg kg−1), and historical Pt variations seem to reflect variations in hydrodynamics and grain size composition. Since the early 2000s, Pt concentrations in the Loire and the Rhone River sediments tend to increase (>2.5 μg kg−1) and were attributed to the use of car catalytic converters, an emerging technology since the 1990s using >50 % of European Pt demand. High and variable historical Pt concentrations (up to 14.6 μg kg−1) in the Seine River sediments may reflect legacy Pt sources due to former anthropogenic activities in this watershed, such as the use of Pt-based catalysts for petroleum refinery since the end of the 1940s, coal handling and precious metals refining, probably concealing the likely presence of an emerging traffic-related Pt signal. This first comparison of historical Pt concentration trends in sediments from contrasting watersheds allows to distinguish signals originating from different natural and anthropogenic sources (background level, historical sources, road traffic).
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•Few studies on Pt level in sediment for reconstructing the past geochemical quality•Ad-CSV analysis on selected sediments collected in dated cores in 3 French rivers•Temporal evolution of Pt concentrations (trajectory) between 1910 and 2021•Signals originating from different natural (baseline) and anthropogenic sources•Highest Pt concentrations in the Seine R. to past/historical and emerging sources
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.
•The mineralogy of As and Pb mainly control their mobility.•Plumbojarosite, anglesite and beudantite ensure As and Pb stability.•Carbonates and Fe/Mn oxides are the less stable As and Pb host phases.•Remobilized Pb concentrations exceed regulation limit values for wastes and water.
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 first high-resolution mapping of metal contamination in the Loire Estuary•The strongest EF values are obtained for Ag and Hg in the Loire surface sediments.•Grain size and POC contents mainly control the spatial distribution of concentrations.•Hg and Ag anomalies originated from the Loire watershed and intra-estuarine sources.•The Loire Estuary is mainly characterized by slightly toxic or non-toxic sediments.
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.
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