Multifragmentation of a very heavy nuclear system (I): Selection of single-source events

A sample of `single-source' events, compatible with the multifragmentation of very heavy fused systems, are isolated among well-measured 155Gd+natU 36AMeV reactions by examining the evolution of the kinematics of fragments with Z>=5 as a function of the dissipated energy and loss of memory of the entrance channel. Single-source events are found to be the result of very central collisions. Such central collisions may also lead to multiple fragment emission due to the decay of excited projectile- and target-like nuclei and so-called `neck' emission, and for this reason the isolation of single-source events is very difficult. Event-selection criteria based on centrality of collisions, or on the isotropy of the emitted fragments in each event, are found to be inefficient to separate the two mechanisms, unless they take into account the redistribution of fragments' kinetic energies into directions perpendicular to the beam axis. The selected events are good candidates to look for bulk effects in the multifragmentation process.Comment: 39 pages including 15 figures; submitted to Nucl. Phys.

Shadowing effects and transverse momentum dependence of particle emission in intermediate energy heavy ion collisions

Light particle emission was studied at Ganil for 36 Ar +27 Al between 55 and 95 MeV/u and for 64 Zn+58 Ni between 35 and 79 MeV/u. The correlation of these particles with the reaction plane was analyzed. In intermediate impact parameter events, the transverse momentum dependence of this correlation changes drastically with the energy for midrapidity particles. For both systems, at the upper incident energies, particles with highest transverse momenta are preferentially emitted perpendicular to the reaction plane. This can be qualitatively reproduced by simulations taking into account shadowing effects

A multibiomarker approach in juvenile turbot, Scophthalmus maximus, exposed to contaminated sediments

International audienceJuvenile turbot were exposed in laboratory conditions to a mixture of chemical contaminants associated with harbour and estuarine sediments for seven and 21 days. Several molecular biomarkers of exposure were then measured in fish liver: two biotransformation parameters [ethoxyresorufin-O-deethylase (EROD) and phase II glutathione S-transferase (GST) activities] and an antioxidant enzyme activity [catalase (CAT)]. Modifications at the histological level were analysed by the measurement of the number and size of melanomacrophage centres (MMCs) and disturbances to the immune function by the measurement of cytokine transforming growth factor-beta (TGF-β) and development of the thymus. The responses of these molecular and immunological biomarkers were correlated with metal and PAH concentrations measured in sediments and with the physiological performance of turbot analysed in a previous study on the same fish (growth rates, condition factor K, RNA:DNA ratio and lipid index). While no difference was found in thymus analysis, some molecular and immunological responses were observed in fish exposed to contaminated sediments. Weak relationships between molecular biomarkers' responses and PAH concentrations were recorded, while their responses were significantly correlated with some metals. MMC and aggregates were weakly related to chemical contaminants whereas some significant correlations were found between TGF-b1 responses and some metal concentrations. However, molecular and immunological biomarkers were weakly related to fish physiological damages since low responses were observed in the condition which led to the lowest growth and condition indices. These data suggest the complexity of cause-effect relationships between exposure to pollutants, metabolisms and health damages. Precautions should be considered in the use of molecular and immunological biomarkers alone in biomonitoring programs. Their complementary use with physiological biomarkers, such as fish growth and condition indices, could improve their utilisation

Variations in gene expression levels in four European zebra mussel, Dreissena polymorpha, populations in relation to metal bioaccumulation: A field study.

International audienceThe present study was performed to validate the suitability of using gene expression in zebra mussels, Dreissena polymorpha, for biomonitoring of freshwater environment. Mussels were collected in four French rivers (Meuse, Moselle, Oise and Vilaine) in spring and autumn. Relative gene expression of 9 candidate genes involved in cellular metabolic activities (Cytochrome-c-oxidase - cox, and ATP synthase - atp), detoxification process (Metallothionein - mt and Glutathion-S-Transferase - gst), oxidative stress (Catalase - cat, Superoxyde Dismutase - sod and Glutathion peroxidase - gpx) and digestive functions (Amylase - amy and Cellulase - ghf) were measured in digestive gland. Metal bioaccumulation in tissues and morphometric parameters were also analyzed to interpret molecular responses. All our results are consistent with different physiological reactions to environmental condition between zebra mussel populations. In spring, the levels of mt, sod, gpx, cat, atp, amy and ghf relative expression were significantly higher in mussels with the lowest metal bioaccumulation (the Meuse) compared to at least one of the other sites. In autumn, this higher expression levels in Meuse River were still observed for gpx, cat, atp and amy. This study has also pointed out different sources of variability in gene expression (individual size, season, trophic resources and origin of mussels) which are inevitable in natural fluctuant environment. This underlines the importance to take them into account in field study to propose a correct interpretation of biomarker responses

Zebra mussel as a new tool to show evidence of freshwater contamination by waterborne Toxoplasma gondii

International audienc

Abandoned uranium mine-induced effects in caged roach : a multiparametric approach for the evaluation of in situ metal toxicity

In the frame of the characterization of environmental risk assessment linked to abandoned uranium mines in the Limousin region (France) and in the context of the DEVIL program (Development and validation of fish biomarkers for the implementation of environmental legislation) led by INERIS (National institute for industry environment and risks), a study has been conducted on the effects of uranium mining releases on roach health status. The first part of the work was the search of potential sites for the study. Based on information from IRSN (National institute for radioprotection and nuclear safety) and from the owner of old mines, two private pounds were identified: one presenting uranium contamination, and one upstream the mining zone presenting no uranium in water. Roaches were therefore caged during one month on these two pounds. Biological sampling have been performed at the beginning of the experiment, and 2 and 4 weeks after, in order to measure several parameters: immune parameters followed by flow cytometry (phagocytosis, ROS production, apoptosis, lyosomes), genotoxicity (comet assay), oxidative stress (glutathione, lipoperoxidation), biotransformation (EROD, GST, ABC transporter), neurotoxicity (AChE), endocrine disruption (vitellogenin) and physiological parameters (ADN/ARN ratio, stomach contents, otoliths, condition index, sex ratio). Physico-chemical parameters of water and sediments (cations, anions, metals, radioactive elements) were also followed and bioaccumulation of metals in several organs (muscle, liver, kidney, gonad and gill) was measured. The results showed on the uranium contaminated site a water contamination of iron, aluminium, barium and manganese. Aluminium and iron were also present in the water of the uranium-free site. The sediments from the uranium contaminated site showed high levels of radioactive elements coming from the disintegration chain of uranium. Preliminary biological results indicated a stimulation of immune parameters, an increase of oxidative stress and a decrease of AChE in fish coming from the uranium contaminated site compared to the uranium-free site. The whole results, using integrated index, will allow the establishment of roach health status in the context of pluri-metallic mining release pollution. These data will strengthen the research for the improvement of methods and tools needed for the environmental risk assessment associated to radioactive substances in the environment

Dealing with confounding factor : Alterations of Dreissena polymorpha gonads exposed to a pharmaceutical pollutant (diclofenac) or to nutritive stress

The zebra mussel Dreissena polymorpha is a fresh water bivalve considered as suitable monitoring organisms because of it abundance, wide distribution and interesting responsiveness to pollutant. However it also presents a sensibility to variation of environmental parameters, particularly to modification of the nutritive capacity of the environment. So the nutritional state of mussels may constitute a confounding factor in ecotoxicological survey. The non-steroidal anti-inflammatory drug diclofenac is one of the most used drug in France (10 tons per year) and it is part of the three pharmaceuticals proposed for the Water Framework Directive's priority list of pollutant in surface waters. Few data exist on its effect on bivalves. So the goal of this study was to assess the impact of this drug on reproductive apparatus of the zebra mussel. In this aim mesocosm approach was developed with 12 artificial canals and a flux of water containing 0, 0.1, 1 or 10 µg/l of diclofenac in triplicate. The histopathological alterations eventually induced were analyzed in 10 to 20 mussels after 0, 46, 64 and 160 days. However, it appeared that the diclofenac have an impact on macrophyte and periphyton biomass and distribution. To analyze the effect of nutritive stress on gonadic structure of the bivalve, zebra mussels were placed during 150 days in aquarium and fed two time per week by controlled alga volume (Scenedesmus obliquus and chlorella) in duplicate: 100 000 cells (ad libitum diet called 100%), 10 000 cells (10 %) or to 0 alga (0%). Observed ovary histopathological alterations induced by diclofenac (follicle atresie, oocyte necrosis, perifollicular fibrosis, decrease in mature ovocyte production) revealed the gonadic toxicity of this drug. The nutritive stress (10 %) and the total food deprivation (0%) also produced important alterations of the mussel ovary development (follicle atresie, reduction of mature oocyte size). However in the mesocosm experiment the mussel diet was modified but not severally reduced. Moreover the gonadic alterations observed with diclophenac were not similar to these obtained with nutritive deprivation. So it was possible to conclude that the gonadic alterations observed depended mostly of diclofenac direct toxic impact. These results were discussed with amounts of energetic reserves, activity of digestive enzymes and foot protein expression in order to better appreciate the way that Dreissena polymorpha adapt to nutritive deprivation

Dealing with confounding factor : Alterations of Dreissena polymorpha gonads exposed to a pharmaceutical pollutant (diclofenac) or to nutritive stress

The zebra mussel Dreissena polymorpha is a fresh water bivalve considered as suitable monitoring organisms because of it abundance, wide distribution and interesting responsiveness to pollutant. However it also presents a sensibility to variation of environmental parameters, particularly to modification of the nutritive capacity of the environment. So the nutritional state of mussels may constitute a confounding factor in ecotoxicological survey. The non-steroidal anti-inflammatory drug diclofenac is one of the most used drug in France (10 tons per year) and it is part of the three pharmaceuticals proposed for the Water Framework Directive's priority list of pollutant in surface waters. Few data exist on its effect on bivalves. So the goal of this study was to assess the impact of this drug on reproductive apparatus of the zebra mussel. In this aim mesocosm approach was developed with 12 artificial canals and a flux of water containing 0, 0.1, 1 or 10 µg/l of diclofenac in triplicate. The histopathological alterations eventually induced were analyzed in 10 to 20 mussels after 0, 46, 64 and 160 days. However, it appeared that the diclofenac have an impact on macrophyte and periphyton biomass and distribution. To analyze the effect of nutritive stress on gonadic structure of the bivalve, zebra mussels were placed during 150 days in aquarium and fed two time per week by controlled alga volume (Scenedesmus obliquus and chlorella) in duplicate: 100 000 cells (ad libitum diet called 100%), 10 000 cells (10 %) or to 0 alga (0%). Observed ovary histopathological alterations induced by diclofenac (follicle atresie, oocyte necrosis, perifollicular fibrosis, decrease in mature ovocyte production) revealed the gonadic toxicity of this drug. The nutritive stress (10 %) and the total food deprivation (0%) also produced important alterations of the mussel ovary development (follicle atresie, reduction of mature oocyte size). However in the mesocosm experiment the mussel diet was modified but not severally reduced. Moreover the gonadic alterations observed with diclophenac were not similar to these obtained with nutritive deprivation. So it was possible to conclude that the gonadic alterations observed depended mostly of diclofenac direct toxic impact. These results were discussed with amounts of energetic reserves, activity of digestive enzymes and foot protein expression in order to better appreciate the way that Dreissena polymorpha adapt to nutritive deprivation