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.

Differentiation of sympatric zebra and quagga mussels in ecotoxicological studies: A comparison of morphometric data, gene expression, and body metal concentrations

International audienc

Metal concentrations, growth and condition indices in European juvenile flounder (Platichthys flesus) relative to sediment contamination levels in four Eastern English Channel estuaries

International audienceThe aim of the present study was to evaluate the effects of metal contamination on the biological responses of 0-group juvenile European flounder and to assess and compare the quality of four estuarine habitats located in the Eastern English Channel. Fish otolith growth and condition indices (RNA : DNA ratio, Fulton's K condition index) were measured and found to be significantly lower in individuals from the Seine estuary compared to those of the Canche, Authie and Somme estuaries. No obvious effects of hydrological condition or food availability on the flounder biological responses were observed. Sediments from the Seine showed the highest metal concentrations, bioavailable proportion and enrichment factors. Higher metal concentrations were observed in fish from the Seine compared to the other ones caught in less polluted estuaries. These results suggest that contaminants may have a negative impact on the early life history stage of flounder

Growth and condition indices of juvenile turbot, Scophthalmus maximus, exposed to contaminated sediments: Effects of metallic and organic compounds.

International audienceSince sediments have the potential to form associations with several classes of pollutants, they have been recognized as a possible and significant source of contamination for the benthic environment. Flatfish maintain a close association with sediments for food and cover, and are therefore more likely to be exposed to contaminated sediments, especially in coastal areas (e.g. nursery grounds). The assessment of these potential biological effects involves the use of adapted biomonitoring tools. The main objective of this study was to assess and compare the response of several physiological biomarkers measured on juvenile turbot (Scophthalmus maximus) exposed to contaminated sediments. Sediments were collected from three stations in a harbour in northern France (Boulogne-sur-Mer), in an anthropogenic French estuary (the Seine), and in a reference site (exposed sandy beach of Wimereux). Unexposed lab-reared juvenile turbots were exposed to sediments for 7 and 21 days in laboratory conditions. Sediments were analysed for metals, PAH and PCB contamination. Several fish growth and condition indices were individually analysed in fish according to the chemical contaminant availability in sediment, the metal concentrations in gills and the estimation of PAH metabolites in their bile. Significant decreases in growth rates, morphometric index, RNA:DNA ratio and the lipid storage index, based on the ratio of the quantity of triacylglycerols on sterols (TAG:ST), were observed with increasing level of chemical contamination. This decrease in the fish's physiological status could be related to the significant increase of several metal concentrations in contaminated fish gills and the significant increase of PAH metabolites in bile. In a field situation, such a reduction in growth and energetic status of juvenile fish could dramatically decrease their over-winter survival in contaminated nursery grounds

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

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

Directed collective flow and azimuthal distributions in Ar-36+Al-27 collisions from 55 to 95 MeV/u

A 4 pi charged particle detector array with a low velocity threshold has been used to detect the products from reactions induced by Ar-36 on Al-27 at energies ranging from 55 to 95 MeV/u. Well characterized events were selected and sorted as a function of the impact parameter. Two methods were used for sorting these events with respect to their impact parameters and three methods were compared to determine the reaction plane. The transverse momentum analysis has been found to be the best method to extract the direction of the reaction plane for this system and for the experimental set-up used here. The energy of vanishing flow for central collisions has been found to be around 90-95 MeV/u. The azimuthal distributions of mid-rapidity particles exhibit a preferential in-plane emission and no squeeze-out effect