HAL-BRGM, les publications scientifiques en libre accès du BRGM
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FATE OF MICROPLASTICS IN RIVER ENVIRONMENT: CHEMICAL COMPOSITION OF MOLECULAR RELEASING AFTER PHOTOLYSIS AND HYDROLYSIS
No full textInternational audienceThe persistence of microplastics (1 µm–5 mm) in the environment, combined with their large-scale production, raises major scientific and societal concerns. These particles undergo degradation through abiotic (photodegradation, hydrolysis, mechanical fragmentation) and biotic (biodegradation) processes, with photolysis playing a key role in breaking polymer chains under UV-B exposure.Besides, more than 1,000 rivers contributing significantly to marine pollution (Meijer et al., 2021), understanding microplastic degradation in freshwater environments is crucial. This study examines how abiotic processes, like photodegradation and hydrolysis contribute to (i) greenhouse gas emissions and (ii) the diversity of molecules released from microplastics in aquatic environments, by using an experimental approach.The plastics selected represent the main types in international demand: polypropylene (PP), low-density polyethylene (LDPE), high-density polyethylene (HDPE), polyethylene terephthalate (PET) and polystyrene (PS). The polymers were exposed to simulated solar radiation (321,8 W/m2) for eight weeks under dry and wet conditions using sterilized river water. Headspace was analyzed with a GC/TCD, structural degradation and organic adjuvants composition were determined by FTIR and GC/MS and aqueous phase was characterized (pH, DOC, DIC, ...).Results indicate that all plastics consume O2 and release greenhouse gases (CO₂, CO, and CH₄) for both conditions. In dry conditions, extract of these polymers show that irradiation allow the release of some adjuvants like palmitic or stearic acids, principally in PP and PS. Hydrolysis led to increased dissolved organic carbon and a pH drop.Our results show that plastics appear to be a significant source of greenhouse gases to the atmosphere. Photolysis is the main process involved in greenhouse gases and hydrolysis allows the release of small organics degradation products in the environment. However, our study is based on a closed environment. The confined environment, with its production of free radicals, can accelerate degradation reactions and increase the production of volatile and water-soluble molecules.[1] Meijer, L. J. J., Van Emmerik, T., Van Der Ent, R., Schmidt, C., & Lebreton, L. (2021). More than 1000 rivers account for 80% of global riverine plastic emissions into the ocean. Science Advances, 7(18), eaaz5803. https://doi.org/10.1126/sciadv.aaz580
Grands
No full textInternational audienceConfined aquifers, naturally protected by impermeable layers, represent a relatively unexploited groundwater resource, characterized by water that is often of good quality and protected from climatic fluctuations. The main challenge therefore lies in their sustainable and long-term exploitation. Despite large reserves, their exploitation, combined with low renewal rates, can lead to depletion of the resource and deterioration of water quality. Their strategic use for drinking water supply requires dedicated management. The DEESAC project "Groundwater sustainability in the exploitation of confined aquifers" (2023-2027) is part of the OneWater – Water as a Common Good research program and aims to explore the potential and limitations of the sustainable exploitation of groundwater from confined or covered aquifers in France. The project aims to conduct transdisciplinary research combining geology, geophysics, hydrogeology, geochemistry, sociology, and management sciences, while also involving water stakeholders. The project has multiple objectives: to better understand the hydrogeological and geochemical functioning of these aquifers, identify the conditions for their renewal, assess their vulnerability, and work with stakeholders—managers, agencies, water unions—to develop management tools. This includes developing relevant indicators, acceptable exploitation thresholds, and a methodological guide for managers and decision-makers.This work received government funding managed by the French National Research Agency under France 2030, reference number 22-PEXO-0010.Les nappes captives, naturellement protégées par des couches imperméables, représentent une ressource en eau souterraine relativement peu exploitée, caractérisée par des eaux souvent de bonne qualité et une inertie face aux fluctuations climatiques. Le principal enjeu réside donc dans leur exploitation soutenable et durable. Malgré de larges stocks, leur exploitation combinée à de faibles taux de renouvellement, peut entraîner un épuisement de la ressource, et une dégradation de la qualité de l’eau (activités industrielles et agricoles, mobilisation d’éléments chimiques géogéniques). Leur utilisation stratégique pour l’alimentation en eau potable impose une gestion dédiée. Le projet DEESAC (Durabilité et Exploitabilité des Eaux Souterraines des Aquifères Captifs ou sous Couverture ; 2023 à 2027) s’inscrit dans le programme de recherche OneWater – Eau Bien Commun, vise à explorer les potentialités et les limites de l’exploitation durable des eaux souterraines issues d’aquifères captifs ou sous couverture en France. Le projet a pour objectif de conduire des recherches transdisciplinaires combinant géologie, géophysique, hydrogéologie, géochimie, mais également sociologie et sciences de gestion, tout en en mobilisant des acteurs de l’eau. Les objectifs du projet sont multiples : mieux comprendre le fonctionnement hydrogéologique et géochimique de ces nappes, identifier les conditions de leur renouvellement, évaluer leur vulnérabilité, et co-construire avec les parties prenantes — gestionnaires, agences, syndicats des eaux — afin de développer des outils de gestion. Cela comprend l’élaboration d’indicateurs pertinents, de seuils d’exploitation acceptables, et d’un guide méthodologique à destination des gestionnaires et décideurs.Ce travail a bénéficié d'une aide de l’État gérée par l'Agence Nationale de la Recherche au titre de France 2030 portant la référence 22-PEXO-0010
RGF : Le chantier du Bassin parisien
No full textInternational audienceConçu comme une continuité du chantier de la carte géologique mené depuis plus de 70 ans, le RGF, Référentiel Géologique de la France, a pour objectif d’offrir une nouvelle représentation géologique du territoire français. Lancé en mai-2018, le chantier Bassin parisien vise à produire un ensemble de cartes mises à jour dans un référentiel lithostratigraphique harmonisé avec un focus sur le coeur cénozoïque du bassin. A terme, un modèle géologique sera construit sur la base d’un ensemble de logs validés permettant la reconstruction de surfaces représentatives des différentes formations sédimentaires déposées depuis le crétacé. Un travail de caractérisation des propriétés pétrophysiques des différents faciès identifiés permettra une utilisation du modèle vers différents secteurs d’application comme l’hydrogéologie, les risques naturels ou la géothermie. Une collaboration avec la société du Grand Paris a permis de premiers échanges d’échantillons sur la zone Ile de France, le long des transects des grandes lignes de métro. Enfin, en collaboration avec la communauté scientifique académique, un programme de thèses permet de compléter les connaissances géologiques sur différents sujets comme la cartographie des alluvions, celle des formations superficielles ou des surfaces d’altérations, une meilleur compréhension des faciès de dépôts à différentes échelles, la construction des géométries des différentes formations, la datation des différents étages, ainsi qu’une meilleure connaissance du schéma structurale du bassin. Parmi les différentes perspectives du chantier sont envisagés des travaux en lien vers une BDLISA (le référentiel hydrogéologique des aquifères de France) pour une représentation 3D des aquifères de Franc
Deep Physico-Chemical Profiling in a Flooded Mine Shaft: Understanding Water Dynamics in Gardanne Lignite Mine (France)
No full textInternational audienceNeutral Mine Drainage (NMD) in the flooded Gardanne lignite mine (Southern France) remains poorly understood, with persistently high Fe (30 mg/L) and SO₄ (2000 mg/L) concentrations. In 2024, a field campaign conducted in the Gérard shaft, using in-situ profiling and water sampling, reveals a deep tratification. Comparisons with 2011 data indicate a shift from a predominantly static regime with diffusive processes in the deeper part to a more dynamic system, characterized by convective loops and forced convection driven by pumping. Persistent inflows seem to influence the water column structure, shaping its stratification and internal dynamics
Hysteresis of submarine karst springs reveals tipping points in flow reversal and saline intrusion phenomena
No full textInternational audienceSubmarine springs that drain inland karst aquifers may be subject to abrupt flow reversals in which alternatively freshwater outflows to the sea or saltwater inflows into the aquifer. Here we provide a full flow reversal long-duration data time series at the Vise spring (below Thau lagoon, south of France) during which saltwater inflows into the aquifer. We demonstrate that the driving parameter of the hydrosystem regime shifts is the hydraulic gradient between the aquifer and the lagoon, controlled by water density changes. We reveal the existence of two tipping points: (i) below a hydraulic gradient threshold, the hydrosystem suddenly degrades from a normal regime to saltwater intrusion, and (ii) a much larger hydraulic gradient is necessary for the recovery of the hydrosystem. The high hysteresis of the hydrosystem, due to the vertical karst conduit filling by saltwater, is responsible for the long duration of the degradation and saltwater intrusion. In a changing climate context, flow reversal at submarine karst springs could be more frequent and longer in the future due to sea level rise and a decrease in recharge, threatening inland or offshore freshwater resources
Coupled Paleomagnetism and 40 Ar/ 39 Ar Dating of Latera Ignimbrites (Vulsini Volcanic District, Italy) Unravel Processes Associated to Piston‐Collapse Calderas
No full textInternational audienceAbstract Correlation of ignimbrite units at polygenic calderas is mandatory for the reconstruction of caldera‐forming events and proper identification of their eruption dynamics. However, ignimbrites erupted at different times from the same caldera can display similarities in composition and lithology that can hamper proper correlation of outcrops across the caldera structure. Here, high‐resolution paleomagnetic and 40 Ar/ 39 Ar data are used along with stratigraphic evidence to address and resolve the relationships between two ignimbrites associated with the Latera caldera (Grotte di Castro and Onano Formations, Vulsini Volcanic District, Central Italy). These were characterized at 32 paleomagnetic sites and eleven 40 Ar/ 39 Ar sampling sites encompassing proximal and distal facies. Overall, the paleomagnetic directions of the two ignimbrites are statistically indistinguishable whereas single‐grain 40 Ar/ 39 Ar ages of sanidine and leucite crystals show systematic preservation of pre‐eruptive ages with sectorial variations closely controlled by eruption dynamics, yet with a neatly defined common juvenile (syn‐eruptive) age at 205 ka. The data show that the two ignimbrites are the product of a single event, here renamed the “Grotte di Castro‐Onano” eruption, representing the largest and latest caldera‐forming stage of the Latera system. The sectorial preservation of pre‐eruptive 40 Ar/ 39 Ar ages across the depositional sequence is interpreted to reflect the extraction processes with selective (re)mobilization of magma batches associated to piston collapse dynamics. Coupling paleomagnetism with 40 Ar/ 39 Ar dating is shown to be a key step in such cases for successful resolution of individual caldera‐forming events at the millennial scale
Post-exploitation fate of alluvial goldmines in the Amazon: soil erosion, metal(loid) remobilisation and evolution of ecological functions during restoration
No full textInternational audienceArtisanal and small-scale gold mining is responsible for deforestation and habitat degradation in Amazonian ecosystems due to soil reworking and increased turbidity in surrounding rivers. In French Guiana, legal mines are required to perform rehabilitation after gold extraction. To assess the successfulness of this rehabilitation, the temporal evolution of particles and metal(loid)s (mercury, lead, arsenic) export was measured, as well as several parameters linked to soil functions (soil carbon and nitrogen, microbial diversity, enzymatic activities). Results show a rapid decrease in particle export (i.e., 3-fold reduction within the first 8 months, and up to 2000-fold reduction after 4 years), linked to an increase in spontaneous colonisation by herbaceous plants. This decrease in particle export induced an efficient decrease in metal(loid)s (Hg, Pb, As) export predominantly associated to the particulate fraction. The parameters associated with ecological functions did not show any significant increase within 5 years after rehabilitation, possibly due to depletion of nitrogen stocks by the herbaceous growth inducing a competition for resources with soil microbial communities. Microbial communities on the mining site displayed significant evolutions during the 5 years after restoration, with no visible convergence with forest-soil communities, but underlining the adaptability to climatic conditions and a changing environment. These results highlight that current rehabilitation practices are efficient in limiting particle and major contaminants export while more attention needs to be addressed to the recovery of soil functions and biological activitie
Leviers et contraintes à l’entrepreneuriat rural oasien dans la région de Kébili en Tunisie
No full textInternational audienceEntrepreneurship is often seen as a solution for the sustainable development of rural areas in the Maghreb. In Tunisia, a wide range of entrepreneurial support services are offered by associations, the State and international cooperation organisations. However, entrepreneurs, women in particular, still face many difficulties in setting up and implementing their entrepreneurial projects. This article analyses the disconnection between the entrepreneurial intentions of entrepreneurs, especially women, and the actual entrepreneurial support offered. The article takes the point of view of entrepreneurs in the oasis’s region of Kebili in Tunisia. It is based on interviews conducted in 2022 with 84 young entrepreneurs in the study area. The results show that projects and support programmes have benefited many entrepreneurs and are levers for the creation of projects. But the entrepreneurial ecosystem is perceived by entrepreneurs as unclear and complex. Entrepreneurs also face numerous difficulties in accessing finance, and face personal and social constraints, particularly women. Entrepreneurs use diverse strategies to supersede these difficulties: calling in experts, taking dedicated training courses, collecting money from friends and family, networking. We conclude by suggesting ways of developing entrepreneurial ecosystems that are better adapted to the specific characteristics of each entrepreneurial environment, along the lines of the work on ‘entrepreneurship in place’. This involves focusing entrepreneurial support on the opportunities specific to each place, taking greater account of sustainable development and supporting local relational ecosystems. We emphasise the need to personalize and contextualize research on rural entrepreneurship, in order to better understand the perceptions of the various stakeholders and to carry out more in-depth and sensitive analyses of the contexts in which they operate.L’entrepreneuriat est souvent considéré comme une solution pour développer durablement les zones rurales au Maghreb. En Tunisie, il existe de multiples offres d’accompagnement à l’entrepreneuriat proposées par des associations, l’Etat ou des organismes de coopération internationale. Néanmoins les entrepreneurs et entrepreneuses font encore face à de nombreuses difficultés dans la concrétisation de leurs projets. Cet article analyse la déconnexion entre les intentions entrepreneuriales des entrepreneurs et entrepreneuses et l’accompagnement entrepreneurial proposé. L’article se place du point de vue d’entrepreneurs et entrepreneuses dans la région oasienne de Kébili en Tunisie. Il se base sur des entretiens menés en 2022 auprès de 84 entrepreneuses et entrepreneurs dans la zone d’étude. Les résultats montrent que les projets et programmes d’accompagnement ont pu bénéficier à de nombreux entrepreneurs et entrepreneuses et sont des leviers de création de projets. Mais l’écosystème entrepreneurial est perçu comme flou et complexe du point de vue des entrepreneurs et entrepreneuses. Ces derniers rencontrent également des difficultés d’accès au financement ainsi que des contraintes personnelles et sociales, notamment les femmes. Plusieurs stratégies sont mises en place par les entrepreneurs et entrepreneuses pour contourner ces difficultés : sollicitation d’experts, recours à des formations dédiées, collecte d’argent auprès de leur entourage, réseautage. Nous concluons en suggérant des pistes permettant de développer des écosystèmes entrepreneuriaux davantage adaptés aux spécificités de chaque milieu entrepreneurial, dans la lignée des travaux sur l’« entrepreneurship in place ». Il s’agit d’orienter l’accompagnement des entrepreneurs et entrepreneuses sur les opportunités spécifiques à chaque lieu, de prendre davantage en considération le développement durable et d’appuyer les écosystèmes relationnels locaux. Nous mettons en avant la nécessité de personnifier et de contextualiser les recherches sur l’entrepreneuriat rural, afin de mieux comprendre les perceptions des différents acteurs et de réaliser des analyses plus approfondies et sensibles des contextes dans lesquels ils évoluent
Opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES) on the risks to human health associated with the proliferation of Ostreopsis spp. on the Basque coast
No full textN/AInternational audienceIn France, the presence of marine microalgae of the genus Ostreopsis has been identified repeatedly on the Mediterranean coast for several years, whereas on the French Basque coasts its presence is much more recent. In the summers of 2021 and 2022, major Ostreopsis flowering episodes were reported on the Basque coast, resulting in several hundred cases of intoxication among holidaymakers and residents. The main route of human exposure is inhalation of aerosols, although it is not yet known whether the agents responsible for poisoning are Ostreopsis cells, cell debris, known toxins produced by Ostreopsis, or other as yet unidentified compounds. Other routes of exposure (dermal contact, eye contact, ingestion of contaminated water or seafood) are also possible. Poisoning is manifested through various signs and symptoms, occurring within 48 hours of exposure (Neurosensory and neurological, respiratory, dermal and digestive). This document presents the opinion of the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), established from the work of its WATER and ERCA Expert Committees. ANSES received a request from the Directorate General for Health (DGS) and the Directorate General for Food (DGAL) to update knowledge about Ostreopsis that had been reported in the Agency's opinions from 2007 and 2008 (ANSES, 2007 and 2008), and draw up specific recommendations for managing Ostreopsis proliferation on the Basque coast. The literature review conducted as part of this expert appraisal revealed that knowledge about the genus Ostreopsis (diversity, biology, ecology, toxins produced) is still too fragmentary to characterise the hazard and risk to human health. Nevertheless to help local authorities affected by Ostreopsis blooms, Agency proposes a surveillance and quality monitoring strategy based on collaboration between site managers and the regional health agencies (ARSs), applicable to sites currently subject to bathing water quality monitoring and water sports sites that meet the conditions below
