RESPONSES AND STRUCTURAL RECOVERY OF PERIPHYTIC DIATOM COMMUNITIES AFTER SHORT-TERM ENVIRONMENTAL DISTURBANCE IN SOME RIVERS (HANOI, VIETNAM)

Joint Research on Environmental Science and Technology for the Eart

Étude des effets de la pollution métallique (Cd/Zn) sur la structure des communautés de diatomées périphytiques des cours d'eau (approches expérimentales in situ et en laboratoire)

BORDEAUX1-BU Sciences-Talence (335222101) / SudocSudocFranceF

Etude de la toxicité d’un produit virucide sur une espèce d’escargot aquatique Lymnaea stagnalis

International audienceAvec le contexte épidémique actuel, l’utilisation des biocides a connu un essor sans précédent qui risque de conduire à une augmentation de leur présence dans les écosystèmes aquatiques. Parmi eux, le chlorure de benzyldiméthyldodecylammonium (BAC 12), un biocide utilisé dans plus de la moitié des produits virucides conseillés par l'US EPA contre le SARS-CoV 2 soulève des questions. En effet, dans les rejets urbains les concentrations peuvent varier entre quelques ng/L à 170 µg/L tandis que la concentration maximale retrouvée dans l’environnement était de 6 mg /L dans les eaux usées d’un hôpital. Ce composé est connu pour être toxique pour de nombreux invertébrés aquatiques et très peu d’études se sont intéressées à son impact sur les mollusques d’eau douce. C’est pourquoi nous avons testé la toxicité aigüe et chronique du BAC 12 sur l’espèce Lymnaea stagnalis qui est un escargot aquatique ayant une distribution géographique large comprenant l’Europe, l’Amérique du Nord et l’Asie. Dans un premier temps nous nous sommes intéressés à la mortalité des escargots face au contaminant en les exposant à une gamme de concentration allant de 100 µg/L à 10 mg/L pendant une cinétique de 96h. Puis dans un second temps, nous avons prolongé l’exposition sur 21 jours pour les concentrations sublétales afin d’étudier les effets chroniques et la bioaccumulation du BAC 12 sur L. stagnalis. Les résultats de cette expérience sont en cours d’acquisition

Riverine Particulate Matter Enhances the Growth and Viability of the Marine Diatom <i>Thalassiosira weissflogii</i>

Riverine particulates dominate the transport of vital nutrients such as Si, Fe or P to the ocean margins, where they may increase primary production by acting as slow-release fertilizer. Furthermore, the supply of particulate surface area to the ocean is considered to be a major control of organic carbon burial. Taken together, these observations suggest a close link between the supply of riverine particulate material and the organic carbon cycle. To explore this link, we conducted microcosm experiments to measure the growth of the marine diatom Thalassiosira weissflogii in the presence and absence of different types and concentrations of riverine particulate material. Results demonstrate a strong positive effect of riverine particulate material on diatom growth with increased total diatom concentrations and slowed post-exponential death rates with increasing particulate concentration. Moreover, SEM and optical microscope investigations confirm that riverine particulates facilitate organic carbon burial through their role in the aggregation and sedimentation of phytoplankton. The supply of riverine particulate material has been shown to be markedly climate sensitive with their fluxes increasing dramatically with increasing global temperature and runoff. This pronounced climate sensitivity implies that riverine particulates contribute substantially in regulating atmospheric CO2 concentrations through their role in the organic carbon cycle

Detoxification and recovery capacities of Corbicula fluminea after an industrial metal contamination (Cd and Zn): A one-year depuration experiment

This study aimed to assess the recovery capacity of the freshwater bivalve Corbicula fluminea subjected to industrial metal discharges (Cd, Zn). After a 24-day exposure in a metal-contaminated river, bivalves were transferred and maintained in the laboratory for one year under metal-free conditions. Metal accumulation, metallothionein production and genetic expressions of genes involved in metal stress were studied. Results demonstrated the high persistence of Cd in tissues (only 73% eliminated after 365 days) whereas Zn was rapidly depurated. The Cd half-life was estimated around 240 days. Metallothioneins were strongly induced within the 28 first days of decontamination, then decreased by 45% after 365 days. The metal exposure of bivalves led to a significant gene induction. After 28 days, most of the genes were no longer overexpressed, suggesting that the bivalves may withstand small amounts of non-essential metals in their tissues without showing signs of detrimental effects on the tested genes

Riverine Particulate Matter Enhances the Growth and Viability of the Marine Diatom Thalassiosira weissflogii

Riverine particulates dominate the transport of vital nutrients such as Si, Fe or P to the ocean margins, where they may increase primary production by acting as slow-release fertilizer. Furthermore, the supply of particulate surface area to the ocean is considered to be a major control of organic carbon burial. Taken together, these observations suggest a close link between the supply of riverine particulate material and the organic carbon cycle. To explore this link, we conducted microcosm experiments to measure the growth of the marine diatom Thalassiosira weissflogii in the presence and absence of different types and concentrations of riverine particulate material. Results demonstrate a strong positive effect of riverine particulate material on diatom growth with increased total diatom concentrations and slowed post-exponential death rates with increasing particulate concentration. Moreover, SEM and optical microscope investigations confirm that riverine particulates facilitate organic carbon burial through their role in the aggregation and sedimentation of phytoplankton. The supply of riverine particulate material has been shown to be markedly climate sensitive with their fluxes increasing dramatically with increasing global temperature and runoff. This pronounced climate sensitivity implies that riverine particulates contribute substantially in regulating atmospheric CO2 concentrations through their role in the organic carbon cycle

Biosynthesis of gold nanoparticles by the living freshwater diatom Eolimna minima, a species developed in river biofilms.

Testing biotransformation capacities of living aquatic microalgae diatoms to naturally synthetize gold nanoparticles (AuNP) from gold salts and assessing aftereffects on their viability by microscope observations is a great challenge. In this work, a laboratory experiment was conducted, which aimed to observe (i) directly by transmission electronic and light microscopy and (ii) through indirect measurements (UV-visible spectroscopy) the periphytic freshwater diatom Eolimna minima exposed to gold salts. This work revealed the capacity of E. minima to intracellularly biosynthetize AuNP and to tolerate it. AuNP synthesis appears as a mechanism of detoxification to protect diatom from gold salt contamination. We also pointed out the risks associated with the spread of diatoms full of AuNP, through the trophic web of freshwater ecosystems. The preponderant part of the diatoms in natural biofilms associated with their position at the basis of the trophic webs in rivers could then make them responsible for the contamination of their consumers (grazer animals) and consequently for the potential release of AuNP through the entire food web.Approches à différentes échelles pour caractériser les interactions cellulaires, le transfert trophique et les impacts toxiques de nanoparticules métalliques chez les organismes aquatique

Herbicide toxicity on river biofilms assessed by pulse amplitude modulated (PAM) fluorometry

The use of Rapid light curves (RLCs) as a toxicity endpoint for river biofilms was examined in this study and compared to “classical fluorescence parameters” i.e. minimal fluorescence (F0), optimal and effective quantum yields of photosystem II (Fv/Fm and ФPSII). Measurements were performed after exposure to five concentrations of diuron (from 0.3 to 33.4 gL−1), its main degradation product (DCPMU) (from 1.0 to 1014 gL−1) and norflurazon (from 0.6 to 585 gL−1) with the lowest exposure concentrations corresponding to levels regularly encountered in chronically contaminated sites. Biofilm responses were evaluated after 1, 5, 7 and 14 days of exposure to the different toxicants. Overall, the responses of both “classical fluorescence parameters” and RLC endpoints were highly time dependent and related to the mode of action of the different compounds. Interestingly, parameters calculated from RLCs (˛, ETRmax and Ik) were useful early markers of pesticide exposure since they revealed significant effects of all the tested toxicants from the first day of exposure. In comparison, classical fluorescence endpoints (F0 and Fv/Fm) measured at day 1 were only affected in the DCPMU treatment. Our results demonstrated the interest of RLCs as early markers of toxicant exposure particularly when working with toxicants with less specific mode of action than PSII inhibitors

Interaction of freshwater diatom with gold nanoparticles: adsorption, assimilation, and stabilization by cell exometabolites

The rising concern about the potential toxicity of synthetic gold nanoparticles (AuNPs) in aquatic environments requires a rigorous estimation of physico-chemical parameters of reactions between AuNPs and major freshwater microorganisms. This study addresses the interaction of 10-nm size, positively charged AuNPs with periphytic freshwater diatoms (Eolimna minima). The adsorption experiments on viable cells were performed in 10 mM NaCl and 5 mM NaCl + 5 mM NaHCO3 solution at a variable pH (3–10), at an AuNPs concentration from 1 µg/L to 10,000 µg/L, and an exposure time from a few minutes to 55 days. Three types of experiments, adsorption as a function of time (kinetics), pH-dependent adsorption edge, and constant-pH “Langmuirian” type isotherms, were conducted. In addition, long-term interactions (days to weeks) of live diatoms (under light and in the darkness) were performed. The adsorption was maximal at a pH from 3 to 6 and sizably decreased at a pH of 6 to 10. Results of adsorption experiments were modeled using a second order kinetic model, a Linear Programming Model, Freundlich isotherm, and a ligand binding equation for one site competition. The adsorption of AuNPs(+) most likely occurred on negatively-charged surface sites of diatom cell walls such as carboxylates or phosphorylates, similar to previously studied metal cations. Under light exposure, the AuNPs were stabilized in aqueous solution in the presence of live cells, probably due to the production of exometabolites by diatoms. The adsorbed amount of AuNPs decreased after several days of reaction, suggesting some AuNPs desorption. In the darkness, the adsorption and assimilation were stronger than under light. Overall, the behavior of positively charged AuNPs at the diatom–aqueous solution interface is similar to that of metal cations, but the affinity of aqueous AuNPs to cell exometabolites is higher, which leads to the stabilization of nanoparticles in solution in the presence of diatoms and their exudates. During photosynthetic activity and the pH rising above 9 in the vicinity of diatom cells, the adsorption of AuNPs strongly decreases, which indicates a decreasing potential toxicity of AuNPs for photosynthesizing cells. The present study demonstrates the efficiency of a thermodynamic and kinetic approach for understanding gold nanoparticles interaction with aquatic freshwater peryphytic microorganisms.Approches à différentes échelles pour caractériser les interactions cellulaires, le transfert trophique et les impacts toxiques de nanoparticules métalliques chez les organismes aquatique

La perception des risques et des comportements spécifiques des pêcheurs à la ligne concernant la contamination au mercure des poissons

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