Impact de la matrice cimentaire sur le développement de biofilms dans les réseaux d’assainissement

Le milieu régnant dans les réseaux d’assainissement est agressif pour les matériaux et notamment pour les matériaux cimentaires. La présence de sulfure de dihydrogène (H2S) va permettre le développement de bactéries sulfo-oxydantes qui vont oxyder les molécules soufrées en acide sulfurique qui va réagir avec les matériaux cimentaires pour former des matériaux sans consistance ou expansifs pouvant provoquer une rupture de la structure. Tous les matériaux n’ont pas la même résistance vis-à-vis de ce milieu. Ainsi les bétons à base de ciment d’aluminate de calcium présentent une meilleure résistance que les bétons à base de ciment Portland. Nous nous sommes intéressés à un des paramètres pouvant expliquer cette différence à savoir une différence de colonisation des mortiers par les espèces microbiennes. Des échantillons de mortiers à base des deux types de ciment ont été placés dans une enceinte recréant les conditions des réseaux d’assainissement puis observés au microscope à épifluorescence avec une coloration Live/Dead puis en microscopie électronique à balayage. Il a ainsi pu être mis en évidence que les mortiers à base de ciment d’aluminate de calcium présentent un plus faible développement microbien. Ceci peut être expliqué par la présence d’ions aluminium, inhibiteur de la croissance bactérienne, et par la modification des propriétés de surface des mortiers par la formation d’un gel d’alumine

Liquid relative permeability through foam-filled porous media: Experiments

International audienceFor some applications involving liquid foams, such as soil remediation for example, the liquid relative permeability of the foam-filled porous medium is a crucial parameter as it sets the liquid flow rate at which active substances or nutrients (for bacteria) can be delivered deep into the medium. We are interested in the liquid relative permeability of foam-filled porous media, within the range of low liquid saturations, i.e., ≲ 20 vol % . We fill porous media (packed spherical grains) with different foams made from either alkyl polyglucosides (APG) or saponin, in such a manner that we obtain highly controlled samples in terms of the bubble-to-grain size ratio r and the liquid saturation. The liquid relative permeability of saponin samples exhibits an optimal value as a function of r, while it increases significantly for APG foams. The ratio of their relative permeability of APG/saponin reveals two regimes as a function of r: for r ≲ 0.25, the permeability ratio is equal to the ratio corresponding to the bulk foams, while for larger r values, the permeability ratio is increased by one order of magnitude. The foam microstructure changes a lot as the bubble-to-grain size ratio increases up to 0.5, so that a new liquid network is activated, made of surface channels and liquid bridges, the former connecting the latter even at low liquid saturation. These new liquid elements may greatly benefit foams with mobile interfaces such as APGs. One such issue would deserve a dedicated study to be elucidated

Detoxification of Pacific oyster

Contamination of shellfish by paralytic shellfish poisoning (PSP) toxins poses an economic threat to shellfish farmers. As contaminated shellfish cannot be harvested for long periods of time, it would be very useful to develop processes to optimise and shorten their detoxification. In this study, Pacific oysters Crassostrea gigas were first experimentally contaminated over a period of 13 days with a continuous flow of toxic Alexandrium minutum cultures at concentrations ranging from 150 to 200 cell ml-1 (toxin content after 13 days of contamination 438 $\mu$g STX equiv. 100 g−1 wet weight). Then, two different detoxification treatments were tested and showed detoxification rates greater than those observed in coastal environments. The first treatment consisted of feeding oysters on Skeletonema costatum, at a concentration of 2000 cell ml−1 to speed up detoxification rates. The second detoxification method used the same Skeletonema costatum diet, supplemented with silt particles at a concentration of 20 mg L−1. A control was also set up by placing contaminated oysters in seawater with no additional algal food. The detoxification experiment lasted 8 days. Toxin contents were analysed by liquid chromatography with fluorescence detection (LC-FD). The S. costatum diet significantly reduced the time needed for oysters to reach the sanitary threshold (80 $\mu$g STX equiv. 100 g−1 wet weight), but no effect of the silt supplement could be demonstrated conclusively. These different detoxification methods did not influence toxin biotransformations as observed in oyster tissues, i.e. epimerisation and decarbamoylation of gonyautoxins 2 and 3

Influence of Crassostrea gigas (Thunberg) sexual maturation stage and ploidy on uptake of paralytic phycotoxins.

International audienceThe purpose of this study was to assess paralytic phycotoxin uptake in diploid and triploid oysters at two stages of their sexual cycle corresponding to their status in early summer (June) and winter (November). Samples of diploid and triploid oysters were exposed to a toxic culture of Alexandrium minutum for 4 days in each season. No significant differences in filtration or clearance rates were observed during either November or June experiments. When diploid oysters were at resting stage (November), toxin uptake showed no significant difference between the ploidy classes. In contrast, when the diploid oysters were at the peak of their sexual maturation (June), the triploid oysters were seen to accumulate almost double the amount of paralytic toxins as the diploid ones

Effects of Alexandrium minutum exposure upon physiological and hematological variables of diploid and triploid oysters, Crassostrea gigas.

International audienceThe effects of an artificial bloom of the toxin-producing dinoflagellate, Alexandrium minutum, upon physiological parameters of the Pacific oyster, Crassostrea gigas, were assessed. Diploid and triploid oysters were exposed to cultured A. minutum and compared to control diploid and triploid oysters fed T.Isochrysis. Experiments were repeated twice, in April and mid-May 2007, to investigate effects of maturation stage on oyster responses to A. minutum exposure. Oyster maturation stage, Paralytic Shellfish Toxin (PST) accumulation, as well as several digestive-gland and hematological variables, were assessed at the ends of the exposures. In both experiments, triploid oysters accumulated more PSTs (approximately twice) than diploid oysters. Significant differences, in terms of phenoloxidase activity (PO) and reactive oxygen species (ROS) production of hemocytes, were observed between A. minutum-exposed and non-exposed oysters. PO in hemocytes was lower in oysters exposed to A. minutum than in control oysters in an early maturation stage (diploids and triploids in April experiment and triploids in May experiment), but this contrast was reversed in ripe oysters (diploids in May experiment). In the April experiment, granulocytes of oysters exposed to A. minutum produced more ROS than those of control oysters; however, in the May experiment, ROS production of granulocytes was lower in A. minutum-exposed oysters. Moreover, significant decreases in free fatty acid, monoacylglycerol, and diacylglycerol contents in digestive glands of oysters exposed to A. minutum were observed. Concurrently, the ratio of reserve lipids (triacylglycerol, ether glycerides and sterol esters) to structural lipids (sterols) decreased upon A. minutum exposure in both experiments. Also, several physiological responses to A. minutum exposure appeared to be modulated by maturation stage as well as ploidy of the oysters

Shellfish and residual chemical contaminants: hazards, monitoring, and health risk assessment along French coasts

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Effects of Alexandrium minutum exposure on nutrition-related processes and reproductive output in oysters Crassostrea gigas.

International audienceThis study assessed the effects of an artificial bloom of the toxin-producing dinoflagellate, Alexandrium minutum, upon nutrition related processes and reproductive output of the Pacific oyster, Crassostrea gigas. Oysters were exposed to A. minutum, Paralytic Shellfish Toxins (PST) producer and compared to a control batch of oysters fed Isochrysis galbana clone Tahitian (T.Iso). The experiment was performed in June 2008, when oysters were found ripe. Several physiological variables of oysters, such as PSTs accumulation, digestive gland and histological observations as well as spermatozoa quality, were measured at the end of the exposure. Results indicate that the digestive gland was greatly impacted upon A. minutum exposure. Monoacylglycerol and diacylglycerol contents as well as phospholipids (mainly phosphatidylcholine) drastically decreased in the digestive gland of oysters exposed to A. minutum compared to control oysters. At the same time, many oysters exposed to the harmful microalgae presented a strong inflammatory response in different tissues of the digestive gland: in intestine as well as in digestive ducts and tubules. Spermatozoa in oysters exposed to A. minutum were morphologically and functionally modified compared to spermatozoa of control oysters. Indeed, spermatozoa were less motile and had lower ATP content in oysters exposed to A. minutum. Meanwhile, spermatozoa produced by control oysters showed higher percentage of mortality and relative DNA content than those produced by A. minutum exposed oysters. Finally, the characteristics of the mitochondria of spermatozoa also appeared to be modified upon A. minutum exposure. The results of this study suggests that an exposure of oysters to A. minutum, reducing energy status and motility of spermatozoa associated to morphological changes at the cellular and sub-cellular levels, can have consequences on spermatozoa fertility and reproduction success

Impact of hemp shiv extractives on hydration of Portland cement

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