Christelle Adam

Bioaccumulation, oxidative stress, and neurotoxicity in Danio rerio exposed to different isotopic compositions of uranium.

Experiments were carried out on adult male zebrafish (Danio rerio) to assess early changes induced by waterborne exposure to different isotopic compositions of uranium (depleted uranium associated or not with 233U). Oxidative stress and neurotoxicity were selected as effect endpoints to characterize uranium chemo- and radiotoxicity. Catalase, glutathione peroxidase, and superoxide dismutase activities and total glutathione content of hepatic extracts, as well as brain acetylcholinesterase activity and uranium bioaccumulation, were measured. Oxidative stress induced by uranium exposure led to decreases in superoxide dismutase and catalase activity levels as well as total glutathione content in liver extracts. These perturbations were significantly more marked in 233U-exposed fish. Furthermore, significant increase in acetylcholinesterase activity was observed in brain extracts at the same level, whatever the isotopic composition of uranium.

Comparative analysis of gene expression in brain, liver, skeletal muscles, and gills of zebrafish (Danio rerio) exposed to environmentally relevant waterborne uranium concentrations

The effects of waterborne uranium (U) exposure on gene expression were examined in four organs (brain, liver, skeletal muscles, and gills) of the zebrafish (Danio rerio). Adult male fish were exposed to three treatments: No added uranium (control), 23 +/- 6 microg U/L, and 130 +/- 34 microg U/L. After 3, 10, 21, and 28 d of exposure and an 8-d depuration period, gene expression and uranium bioaccumulation were analyzed. Bioaccumulation decreased significantly in liver during the depuration phase, and genes involved in detoxification, apoptotic mechanism, and immune response were strongly induced. Among these genes, abcb311, which belongs to the adenosine triphosphate (ATP)-binding cassette transporter family, was induced 4- and 24-fold in organisms previously exposed to 23 +/- 6 and 130 +/- 34 microg U/L, respectively. These results highlight the role of liver in detoxification mechanisms. In gills, at the highest uranium concentration, gpx1a, cat1, sod1, and sod2 genes were up-regulated at day 21, indicating the onset of an oxidative stress. Mitochondrial metabolism and DNA integrity also were affected, because coxI, atp5f1, and rad51 genes were up-regulated at day 21 and during the depuration phase. In skeletal muscles, coxI, atp5f1, and cat were induced at day 3, suggesting an impact on the mitochondrial metabolism and production of reactive oxygen species. In brain, glsI also was induced at day 3, suggesting a need in the glutamate synthesis involved with neuron transmission. No changes in gene expression were observed in brain and skeletal muscles at days 21 and 28, although bioaccumulation increased. During the depuration phase, uranium excretion was inefficient in brain and skeletal muscles, and expression of most of the tissue-specific genes was repressed or unchanged.

Selenite transport and its inhibition in the unicellular green alga Chlamydomonas reinhardtii

The influence of time, ambient concentration, and medium composition on selenite (Se(IV)) uptake by the unicellular green alga Chlamydomonas reinhardtii has been investigated. The aims of the performed experiments were to describe the kinetics of accumulation, to characterize transport capacities, to identify key nutrients influencing absorption, and to establish links between speciation and bioavailability. Our results suggested that the adsorbed fraction was negligible compared to the absorbed one. Over the short time scale considered, the absorption was linear with time, with an estimated conductance of approximately 0.2 nmol/m2/h/nM. Uptake was proportional to ambient levels in a broad range of intermediate concentrations (from nM to microM). However, conductances were higher at low concentrations (< nM) and then decreased with increasing concentrations (> microM). These results suggested that a specific but rapidly saturated transport system was involved at low concentrations, coupled with a nonspecific one that was only saturated at high ambient concentrations (approximately mM). The latter could involve transporters used by anionic macronutrients, which is supported by the fact that increasing sulfate and nitrate concentrations induced significant inhibition of Se(IV) uptake. Finally, Se(IV) speciation changes caused by varying pH did not significantly affect bioavailability.

Internal distribution of uranium and associated genotoxic damages in the chronically exposed bivalve Corbicula fluminea

Uranium (U) internal distribution and involved effects in the bivalve Corbicula fluminea have been studied after direct chronic exposure (90 d, 10 μg.L-1). U distribution was assessed at the subcellular level (Metal Rich Granules -MRG-, pellets and cytosol fractions) in two main organs of the bivalve (gills and visceral mass). Micro-localisation was investigated by TEM-EDX analysis in the gills epithelium. DNA damage in gill and hemolymph samples was measured by the Comet assay. The 90-d exposure period led to a significant increase of U concentration in gills over time (× 5) and a large U quantity in subcellular granules in gills. Finally, a significant increase (× 2) in DNA damage was noted in exposed gills and haemocytes. This study shows that the accumulation levels and consequently the potential toxicity cannot be successfully predicted only on the basis of concentration in water or in tissues and subcellular fractions after chronic exposure.

SELENIUM BIOACCUMULATION IN CHLAMYDOMONAS REINHARDTII AND SUBSEQUENT TRANSFER TO CORBICULA FLUMINEA: ROLE OF SELENIUM SPECIATION AND BIVALVE VENTILATION

The uptake of Se by the freshwater alga Chlamydomonas reinhardtii and the subsequent transfer to the Asiatic clam Corbicula fluminea was investigated. The objective was to investigate the bioavailability of algal-bound Se for C. fluminea while taking into account Se speciation and bivalve ventilation. First, uptake rates of waterborne Se (selenite, selenate, and selenomethionine) in the algae during a 1-h exposure period were determined for a range of concentrations up to 2,000 microg/L. Fluxes for selenite uptake were constant in the range of concentrations tested, whereas fluxes for selenate and selenomethionine uptake decreased with increasing concentrations, suggesting a saturated transport system at high concentrations (approximately 1,000 microg/L for selenate and 100 microg/L for selenomethionine). These data were used to set the algal contamination for the study of trophic transfer to the clam. Three parameters were studied: The Se form, the algal density, and the Se burden in the algae. The results show that for a fixed algal density, an Se-contaminated algal diet does not modify ventilation. In this case, the driving factor for ventilation is the algal density, with ventilation being enhanced for low algal densities. On the basis of ventilatory flow rate measurements and Se burdens in algae, it was found that bioaccumulation of Se in C. fluminea was proportional to the total quantity of Se passing through the whole organism, but with a lesser extraction coefficient for selenomethionine than for the inorganic forms. These results underline the importance of both physiological factors and speciation in understanding the trophic transfer of Se.

A unified Ecological Risk Assessment on freshwaters for chemical and radiological ecotoxicity: The uranium case

The classic ERA method is today recognised as relevant for both chemicals and radionuclides. As uranium presents the double ecotoxicity, a unique method may then now be applied to evaluate in tandem the associated ecological risks, following the classic four steps methodology (problem formulation, effect and exposure analysis, risk characterisation [1]). The approach is developed for freshwater ecosystems receiving ore mining releases, exposed to uranium as a chemical element and as the radioactive families of its isotopes 234, 235 and 238. The structure and the function of the ecosystem are described by a conceptual model on which both the exposure and the effect analysis are based. Species Sensitivity Distributions are applied (1) to the chemotoxicity data, to estimate a Predicted-No-Effect-Concentration for uranium in water (in µg/L); (2) to radiotoxicity effect data, to estimate a Predicted No-Effect-Dose-Rate (in µGy/h). The risk is assessed at first through the risk quotient approach, a screening method involving for the radiological aspect back calculation of the water limiting concentration from the PNEDR for each isotope taken into account. When significant, the assessment is refined applying probabilistic techniques. The whole approach applicability was tested on a real case-study related to a former uranium mining site.

Uranium Chemical and Radiological Risk Assessment for Freshwater Ecosystems Receiving Ore Mining Releases: Principles, Equations and Parameters

Uranium is an element that has the solely characteristic to behave as significant hazard both from a chemical and radiological point of view. Exclusively of natural occurrence, its distribution into the environment may be influenced by human activities, such as nuclear fuel cycle, military use of depleted uranium, or coal and phosphate fertilizer use, which finally may impact freshwater ecosystems. Until now, the associated environmental impact and risk assessments were conducted separately. We propose here to apply the same methodology to evaluate the ecological risk due to potential chemotoxicity and radiotoxicity of uranium. This methodology is articulated into the classical four steps (EC, 2003: problem formulation, effect and exposure analysis, risk characterisation). The problem formulation dealt both with uranium viewed as a chemical element and as the three isotopes 234, 235 and 238 of uranium and their main daughters. Then, the exposure analysis of non‐human species was led on the basis of a common conceptual model of the fluxes occurring in freshwater ecosystems. No‐effect values for the ecosystem were derived using the same effect data treatment in parallel. A Species Sensitivity Distribution was fitted : (1) to the ecotoxicity data sets illustrating uranium chemotoxicity and allowing the estimation of a Predicted‐No‐Effect‐Concentration for uranium in water expressed in μg/L; (2) to radiotoxicity effect data as it was done within the ERICA project, allowing the estimation of a Predicted No‐Effect‐Dose‐Rate (in μGy⋅h−1). Two methods were then applied to characterize the risk to the ecosystem: a screening method using the risk quotient approach, involving for the radiological aspect back calculation of the water limiting concentration from the PNEDR for each isotope taken into account and a probabilistic risk assessment. A former uranium ore mining case‐study will help in demonstrating the application of the whole methodology.Uranium is an element that has the solely characteristic to behave as significant hazard both from a chemical and radiological point of view. Exclusively of natural occurrence, its distribution into the environment may be influenced by human activities, such as nuclear fuel cycle, military use of depleted uranium, or coal and phosphate fertilizer use, which finally may impact freshwater ecosystems. Until now, the associated environmental impact and risk assessments were conducted separately. We propose here to apply the same methodology to evaluate the ecological risk due to potential chemotoxicity and radiotoxicity of uranium. This methodology is articulated into the classical four steps (EC, 2003: problem formulation, effect and exposure analysis, risk characterisation). The problem formulation dealt both with uranium viewed as a chemical element and as the three isotopes 234, 235 and 238 of uranium and their main daughters. Then, the exposure analysis of non‐human species was led on the basis of a comm...