Plastic debris in lakes and reservoirs.

Plastic debris is thought to be widespread in freshwater ecosystems globally1. However, a lack of comprehensive and comparable data makes rigorous assessment of its distribution challenging2,3. Here we present a standardized cross-national survey that assesses the abundance and type of plastic debris (>250 µm) in freshwater ecosystems. We sample surface waters of 38 lakes and reservoirs, distributed across gradients of geographical position and limnological attributes, with the aim to identify factors associated with an increased observation of plastics. We find plastic debris in all studied lakes and reservoirs, suggesting that these ecosystems play a key role in the plastic-pollution cycle. Our results indicate that two types of lakes are particularly vulnerable to plastic contamination: lakes and reservoirs in densely populated and urbanized areas and large lakes and reservoirs with elevated deposition areas, long water-retention times and high levels of anthropogenic influence. Plastic concentrations vary widely among lakes; in the most polluted, concentrations reach or even exceed those reported in the subtropical oceanic gyres, marine areas collecting large amounts of debris4. Our findings highlight the importance of including lakes and reservoirs when addressing plastic pollution, in the context of pollution management and for the continued provision of lake ecosystem services.

Polycyclic aromatic hydrocarbon dynamics in soils along proglacial chronosequences in the Alps.

Polycyclic aromatic hydrocarbons (PAHs) were studied in the soils of three proglacial areas in France (Noir and Chardon Glaciers) and Italy (Miage Glacier). PAH contents, PAH stocks and PAH contents normalized to the total organic carbon contents (PAHs/TOC ratio) were investigated along proglacial soil chronosequences to infer their evolutions with soil age (from 3 to 4200 years), where the PAH contamination was only related to long-range atmospheric transport. Evolutions of PAH and TOC contents, PAHs/TOC ratio and PAH stock were fitted with exponential and logarithmic relations. For the three proglacial areas, PAH contents increased rapidly during the first 150 years of soil development, ranged from 4 to 152 ng·g-1, and showed a strong relationship with total organic carbon (TOC) contents (r = 0.83, p < 0.05). The joint increase of PAH and TOC contents suggested that PAH accumulation in soils were not only driven by PAH inputs but also by the capacity of soils to store these contaminants. PAH contents in the oldest soils (from 1200 BCE and 2200 BCE) were similar than for soils from 1850 CE. The period 1850-2019 CE corresponded to a decrease in the PAHs/TOC ratio suggesting both a faster accumulation of TOC than PAHs and a dilution effect of PAHs already present in soils. For the oldest soils, the PAHs/TOC ratio appeared similar to those for soils from 1850 CE, with values ranging from 0.48 to 2.06 ng·mg-1, suggesting an equilibrium between both parameters for soils older than 170 years. Finally, PAH stocks ranged from 0.41 mg·m-2 to 6.80 mg·m-2 in the youngest and oldest soils, respectively. These results do not allow us to identify the same period of greatest emission as other studies (estimated ~1960), but they revealed changes in the capacity of soils to store these pollutants.

Microplastic pollution of worldwide lakes.

Studies on microplastic (MP) pollution in lakes are recent, although the problem of MP particles in the oceans was first discovered in the 1970s. The first study on lakes was published in 2011. Since then, to our knowledge, 98 lakes have been investigated worldwide. In recent years, studies on this topic have increased worldwide, particularly those focusing on urbanised lakes. Most of the plastic waste in the seas and oceans originates from the terrestrial environment and inland waters. Moreover, lakes are potential temporary or long-term MP accumulators, according to the residence time of water. They are also of high interest for biodiversity, ecology, and the economy. Lacustrine ecosystems may suffer the same fate as marine ecosystems, or even worse, owing to their greater exposure. With the significant focus on ocean and sea contamination, contamination of freshwater ecosystems and lakes is a new and rising topic. However, as a new field of research, several methodological issues have been raised. The team diversity worldwide has led to contrasting sampling techniques and materials, sample treatments, analyses, and presentation of results. Consequently, it is necessary to determine several consensuses between scientific teams in order to work together with accuracy, produce comparable results, speed up knowledge sharing and reduce the reproducibility crisis. This review focuses on (1) MP contamination in 98 worldwide lakes. We identify (2) the theoretical sources of MPs and provide (3) an estimate of MP pollution in different compartments of the lakes based on current state-of-the-art methods. In addition, we also report (4) the predominant MP size classes and polymer types. Finally, we suggest (5) several recommendations to build a consensus between all the working teams to facilitate decision-making by public authorities.

Investigating the metal contamination of sediment transported by the 2016 Seine River flood (Paris, France).

Fine sediment transport in rivers is exacerbated during flood events. These particles may convey various contaminants (i.e. metals, pathogens, industrial chemicals, etc.), and significantly impact water quality. The exceptional June 2016 flood of the Seine River (catchment area: 65 000 km2, France), potentially mobilized and deposited contaminated materials throughout the Paris region. Flood sediment deposits (n = 29) were collected along the Seine River and its main tributaries upstream (Yonne, Loing and Marne Rivers) and downstream of Paris (Oise and Eure Rivers). Fallout radionuclides (137Cs, 7Be) were measured to characterize the sources of the material transiting the river, while trace elements (e.g. Cr, Ni, Zn, Cu, As, Cd, Sb, Pb, Tl, Ag) and stable lead isotopes (206Pb/207Pb) were analyzed to quantify the contamination of sediment transported during the flood. In upper sections of the Seine River, sediment mainly originated from the remobilization of particles with a well-balanced contribution of surface and subsurface sources. In the upstream tributaries, sediment almost exclusively originated from the remobilization of subsurface particles. In Paris and downstream of Paris, recently eroded particles and surface sources dominated, suggesting particles were mainly supplied by urban runoff and the erosion of agricultural soils. The highest metal concentrations and Enrichment Factors (EF) were found in the sediment collected in the Loing, Orge and Yvette upstream tributaries. Although these inputs were diluted in the Seine River, an increase in elemental concentrations was observed, progressing downstream through Paris. However, EFs in sediment collected along the Seine River were lower or in the same range of values sampled over the last several decades, reflecting the progressive decontamination of the urbanized Seine River basin.

Contamination of soils by metals and organic micropollutants: case study of the Parisian conurbation.

Soils are playing a central role in the transfer and accumulation of anthropogenic pollutants in urbanized regions. Hence, this study aimed at examining the contamination levels of selected soils collected within and around the Paris conurbation (France). This also evaluated factors controlling contamination. Twenty-three trace and major elements as well as 82 organic micropollutants including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), phthalates (PAEs), polybrominated diphenyl ethers (PBDEs), alkylphenols (APs), and perfluoroalkylated substances (PFASs) were analyzed. Results reinforced the concern raised by the occurrence and levels of metals such as Zn, Pb, Cu, and Hg, identified as metallic markers of anthropogenic activities, but also pointed out the ubiquitous contamination of soils by organic micropollutants in the 0.2-55,000-µg/kg dw range. For well-documented compounds like PAHs, PCBs, and to a lesser extent PBDEs, contents were in the range of background levels worldwide. The pollutant stock in tested soil was compared to the annual atmospheric input. For PAHs; Pb; and to a lesser extent Zn, Cu, Cd, Hg, Sb, PAEs, and APs, a significant stock was observed, far more important than the recent annual atmospheric fluxes. This resulted from both (i) the persistence of a fraction of pollutants in surface soils and (ii) the cumulative atmospheric inputs over several decades. Regarding PBDEs and PFASs, stronger atmospheric input contributions were observed, thereby highlighting their recent dispersal into the environment.

Mass balance and decontamination times of Polycyclic Aromatic Hydrocarbons in rural nested catchments of an early industrialized region (Seine River basin, France).

Accumulation of Polycyclic Aromatic Hydrocarbons (PAHs) in soils and their subsequent release in rivers constitute a major environmental and public health problem in industrialized countries. In the Seine River basin (France), some PAHs exceed the target concentrations, and the objectives of good chemical status required by the European Water Framework Directive might not be achieved. This investigation was conducted in an upstream subcatchment where atmospheric fallout (n=42), soil (n=33), river water (n=26) and sediment (n=101) samples were collected during one entire hydrological year. PAH concentrations in atmospheric fallout appeared to vary seasonally and to depend on the distance to urban areas. They varied between 60 ng·L(-1) (in a remote site during autumn) and 2,380 ng·L(-1) (in a built-up area during winter). PAH stocks in soils of the catchment were estimated based on land use, as mean PAH concentrations varied between 110 ng·g(-1) under woodland and 2,120 ng·g(-1) in built-up areas. They ranged from 12 to 220 kg·km(-2). PAH contamination in the aqueous phase of rivers remained homogeneous across the catchment (72 ± 38 ng·L(-1)). In contrast, contamination of suspended solid was heterogeneous depending on hydrological conditions and population density in the drainage area. Moreover, PAH concentrations appeared to be higher in sediment (230-9,210 ng·g(-1)) than in the nearby soils. Annual mass balance calculation conducted at the catchment scale showed that current PAH losses were mainly due to dissipation (biodegradation, photo-oxidation and volatilization) within the catchments (about 80%) whereas exports due to soil erosion and riverine transport appeared to be of minor importance. Based on the calculated fluxes, PAHs appeared to have long decontamination times in soils (40 to 1,850 years) thereby compromising the achievement of legislative targets. Overall, the study highlighted the major role of legacy contamination that supplied the bulk of PAHs that are still found nowadays in the environment.

Combining measurements and modelling to quantify the contribution of atmospheric fallout, local industry and road traffic to PAH stocks in contrasting catchments.

Various sources supply PAHs that accumulate in soils. The methodology we developed provided an evaluation of the contribution of local sources (road traffic, local industries) versus remote sources (long range atmospheric transport, fallout and gaseous exchanges) to PAH stocks in two contrasting subcatchments (46-614 km²) of the Seine River basin (France). Soil samples (n = 336) were analysed to investigate the spatial pattern of soil contamination across the catchments and an original combination with radionuclide measurements provided new insights into the evolution of the contamination with depth. Relationships between PAH concentrations and the distance to the potential sources were modelled. Despite both subcatchments are mainly rural, roadside areas appeared to concentrate 20% of the contamination inside the catchment while a local industry was found to be responsible for up to 30% of the stocks. Those results have important implications for understanding and controlling PAH contamination in rural areas of early-industrialized regions.

Evidence of the radioactive fallout in France due to the Fukushima nuclear accident.

Radioactive fallout due to the Fukushima reactor explosion in Japan was detected in environmental samples collected in France. The presence of (131)I in aerosols (200±6 µBq m(-3)) collected at the Pic du Midi observatory, located at 2877 m altitude in the French Pyrénées, indicated that the Japanese radioactive cloud reached France between 22 and 29 March, i.e. less than two weeks after the initial emissions, as suggested by a (137)Cs/(134)Cs ratio of 1.4. Cesium radioisotopes ((134)Cs and (137)Cs) were not detected in this sample but they were present in the aerosol sample collected the next week, i.e. between 29 March and 05 April (about 10 µBq m(-3)). We also report (131)I activities measured in grass (1.1-11 Bq kg(-1); fresh weight) and soil samples (0.4 Bq kg(-1)) collected in the Seine River basin between 30 March and 10 April. The (134)Cs from the damaged Fukushima power plant was also detected in grass collected in the Seine River basin between 31 March and 10 April (0.2-1.6 Bq kg(-1) fresh weight, with a (137)Cs/(134)Cs ratio close to 1, which is consistent with Fukushima radioactive release). Despite the installation of a network of nested stations to collect suspended matter in the upstream part of the Seine River basin, (131)I was only detected in suspended matter (4.5-60 Bq kg(-1)) collected at the most upstream stations between 30 March and 12 April. Neither (131)I nor (134)Cs has been detected in environmental samples since the end of April 2011, because of the rapid decay of (131)I and the very low activities of (134)Cs (about 400 times lower than after Chernobyl accident).