Accelerated weathering of cementitious matrix for the development of an accelerated laboratory test of biodeterioration

International audienceCement based materials are porous, may contain organic adjuvants, and thus possesses an important primary bioreceptivity. To preserve constructions from fungal colonization and to act efficiently against fungal biodeterioration, it is necessary to have a better understanding of biodeterioration mechanisms and its effects on materials properties. An accelerated laboratory test which allows us to compare the growth of three fungal strains and the aesthetic biodeterioration of a cementitious matrix was developed. As the surface pH of the fresh cement specimen is too high to allow fungal growth (pH ~12), accelerating weathering of the matrix, consisting of the combination of carbonation and leaching, was performed to reduce the matrix alkalinity. XRD analyses and SEM observations pointed out that the matrix surface is progressively covered by a calcium carbonate layer as the weathering increases. Results point out that the microbial growth occurs on matrix with a surface composition more like a limestone than a cementitious one

Effect of the Chemical Composition of Building Materials on Algal Biofouling

International audienceThe main cause of aesthetical deterioration of outdoor exposed building materials is the colonization by microorganisms. This phenomenon depends on factors such as geographical situation, environmental conditions and surface state of the substrate. Several researches have been devoted to the study of the effect of porosity, roughness and surface treatment on the biofouling of building materials. However, none of them has addressed the influence of cement composition. The main objective of this study is thus to highlight the influence of the composition of the material on its biocolonization by algae. The green alga Klebsormidium flaccidum was chosen because of its representativeness in France. It is indeed the species the most frequently identified and isolated from samples taken on sites. In order to characterize the influence of the composition of building materials on their biofouling, the behavior of mortars prepared with two types of Portland cement and two types of calcium aluminates cement is studied. The biofouling is followed by measuring the covering rate thanks to image analysis. This work is realized both on samples exposed outdoor and on samples tested in a laboratory bench. Obtained results prove that the composition of cementitious materials is a determining factor

Phytostabilisation d'un site pollué par les éléments traces : opération pilote et pérennité du traitement

National audienceGrâce à l'utilisation combinée de plantes et d'agents immobilisants, la phytostabilisation assistée limite les risques associés à un sol contaminé en réduisant la biodisponibilité des polluants. Le rôle des plantes est de réduire le lessivage et l'érosion. En Europe et dans le monde, de nombreux sites ont déjà été phytostabilisés avec succès. Cependant, peu de projets de phytostabilisation associent une surface et une durée d'expérimentation suffisantes pour établir l'efficacité sur le long terme et en conditions réelles d'une telle pratique pour la gestion d'un site pollué. La nécessité de conduire des opérations pilotes sur une longue durée a été ainsi mise en avant par la communauté scientifique. L'objectif de ce projet mené sur un dispositif pilote mis en place en 2002 est d'estimer l'efficacité dans le temps d'une phytostabilisation assistée appliquée à un sédiment pollué par les éléments traces (Cd, Zn, Pb, Cu, As). Les paramètres suivis dans cette étude sont liés aux plantes initialement semées, aux espèces végétales venues spontanément coloniser le dispositif, aux agents immobilisants utilisés et aux caractéristiques physico-agronomiques de la matrice polluée. Une synthèse des résultats obtenus sur 7 années de suivi sera présentée lors du colloque

Metal immobilization and soil amendment efficiency at a contaminated sediment landfill site: a field study focusing on plants, springtails, and bacteria

International audienceMetal immobilization may contribute to the environmental management strategy of dredged sediment landfill sites contaminated by metals. In a field experiment, amendment effects and efficiency were investigated, focusing on plants, springtails and bacteria colonisation, metal extractability and sediment ecotoxicity. Conversely to hydroxylapatite (HA, 3% DW), the addition of Thomas Basic Slag (TBS, 5% DW) to a 5-yr deposited sediment contaminated with Zn, Cd, Cu, Pb and As resulted in a decrease in the 0.01 M Ca(NO(3))(2)-extractable concentrations of Cd and Zn. Shoot Cd and Zn concentration in Calamagrostis epigejos, the dominant plant species, also decreased in the presence of TBS. The addition of TBS and HA reduced sediment ecotoxicity and improved the growth of the total bacterial population. Hydroxylapatite improved plant species richness and diversity and decreased antioxidant enzymes in C. Epigejos and Urtica dïoica. Collembolan communities did not differ in abundance and diversity between the different treatments

An in-situ and laboratory study of the effect of the intrinsic properties of mortars on their potential bioreceptivity

International audienceThis study aims to clarify the effect of mortar intrinsic properties (porosity, roughness and carbonation level) on its ability to biofouling. Two scales experimental tests, an accelerated fouling in laboratory and a natural fouling in the real-world, were set-up. The first one was conducted in a closed device allowing a periodic sprinkling of an algal suspension on the samples surface. The outdoor test samples were exposed in a park at Grenoble (France). The colonization rate of the sample surface was evaluated by image analysis. The results show that the impact of each intrinsic parameter is quite different as function of the test. The porosity has no influence on the algal colonization of the samples exposed in indoor whereas a high porosity seems to increase slightly the bioreceptivity of ones exposed outdoor. The roughness, in both tests, promoted the microorganisms attachment and so their colonization. However, the discrimination of roughness grades is higher in the laboratory test than in the in-situ one. The surface pH significantly influences on the accelerated biofouling but not on the in-situ one. These dissimilarities result from the difference in experimental configurations of the two tests. Thus the laboratory test should be adjusted to be more suitable and to allow an extrapolation of results

Influence of the intrinsic characteristics of mortars on their biofouling by pigmented organisms: Comparison between laboratory and field-scale experiments.

International audienceBiodeterioration of mortars by the photosynthetic microorganisms is affected by their intrinsic properties such as porosity, roughness and surface pH. The influence of these parameters was examined using an accelerated fouling test in laboratory and a natural fouling test in the real-world ( in situ). Based on color measurement and image analysis, the impact of each intrinsic parameter was evaluated. The results differed from a scale to the other one. No influence of porosity was measured on the algal colonization rate in the laboratory test whereas, a high porosity seemed to increase slightly the bioreceptivity of the mortars exposed outdoor. The roughness, in both tests, promoted the microbial colonization. However, the discrimination of roughness grades was better in the laboratory test than in the in situ one. The surface pH influenced remarkably on the accelerated biofouling test but not on the in situ one. These dissimilarities resulted from the differences in experimental configurations of the two tests

Impact des produits phytosanitaires sur la diversité spécifique et fonctionnelle de la microflore du sol : ecas du dinitro-o-cresol

The impact of herbicides on the soil microflora was studied through the effect of a model molecule : the DNOC. We first considered the influence of the DNOC on the growth of pure strains of microorganisms selected in 3 microbial groups. Two of the three were defined by their taxonomic position (Rhizobia and Pseudomonas), the third by its functional ability to degrade 2.4-D. This approach showed that Rhizobia were sensitive, pseudomonas were resistant and 2.4-D degraders had very different responses to DNOC. This suggests that, in the soil, 2.4-D degraders may be exposed to important modifications in their diversity with functional consequences. But, this approach cannot reflect what really happens in the soil where physico-chemical and biological protections probably limit the impact of pollutants. That is the reason why, in a second time, we studied the DNOC impact on the structure of two subsets of the soil microbial community : bacteria growing on a non-selective medium and on a medium with 2.4-D as the main carbon and energy source. We can clearly see that DNOC has destructurating effects on both groups : a diminution of the number of species and a selection of gram negative bacteria. The only difference is in the velocity of the answer which occurs as soon as 7 days for the "total population" and 14 days for the "2.4-D degraders". Moreover, diversity indices calculated on both morphologic and genetic criteria vary similarly for both populations. We showed a long term based but irreversible convergence of the evolution of control and treated soil samples towards a diminution of the number of microbial species. The DNOC effect ont the metabolic diversity of the total population and on 2.4-D degraders was then studied. We studied showed that DNOC presence in the soil could modify the metabolic signature of a microbial community defined by the ability to degrade different substrates. The effect is such, that we could consider it as a possible indicator of the ecotoxicological impact of toxic molecules. Functional changes due to the presence of a biocidaal molecule were investigated through its effect on the 2.4-D degradation in micro-samples. DNOC inhibits the degradation even at low doses where a stepwise effect is observed. This work demonstrates that the soil microbial population reacts to the presence of a chemical pollutant such as the DNOC by a functional and specific adaptationL'impact des pesticides sur la microflore du sol a été envisage par l'étude de l'effet d'un pesticide, le DNOC, pris comme polluant modèle. Nous avons tout d'abord considéré l'influence du DNOC sur la croissance de souches pures de micro-organismes choisies dans trois groupes microbiens. Deux d'entre eux ont une définition taxonomique, les rhizobium et les pseudomonas alors que le 3e a une définition fonctionnelle ; il s'agit des micro-organismes dégradant le 2,4-d. Cette approche a permis de mettre en évidence la sensibilité de micro-organismes sensibles tels que les rhizobium ou la résistance des pseudomonas au dnoc. Elle a également révélé une grande diversité de réponses des souches dégradant le 2,4-d suggérant que dans le sol la communauté dégradante est susceptible d'être exposée à des modifications importantes de composition dont les conséquences fonctionnelles sont probablement loin d'être négligeables. Cependant, cette approche trop simplificatrice ne reflète pas ce qui se passe réellement dans le sol ou des mécanismes de protection physico-chimiques et biologiques tendent probablement à limiter l'impact réel des polluants. C'est pourquoi, dans la seconde partie, nous avons étudié l'impact du DNOC sur la structure de deux sous-ensembles de la communauté bactérienne du sol, les bactéries cultivables sur milieu non sélectif et sur milieu dans lequel le 2,4-d constitue la principale source de carbone et d'énergie. Il ressort clairement de cette étude que le DNOC a des effets déstructurant qui se manifestent sur les deux groupes microbiens considérés. Il apparait nettement que le DNOC, à la dose la plus élevée (c = 50 mg kg-1) contribue à la diminution du nombre d'espèces de la microflore totale cultivable et de la microflore se développant sur milieu 2,4-d avec sélection d'une microflore gram-. L'effet du DNOC a ensuite été étudié au travers de ces conséquences sur la diversité métabolique de l'ensemble des bactéries cultivables et sur l'efficacité fonctionnelle des bactéries dégradant le 2,4-d. Nous avons montré que la présence dans le sol du dnoc était susceptible de modifier la signature métabolique d'une communauté microbienne au travers d'un profil d'utilisation de différents substrats carbones. Ces modifications sont suffisamment marquantes pour être considérées comme de possibles indicateurs de l'impact écotoxicologique de composés chimiques toxiques. Les changements fonctionnels liés à la présence d'un biocide dans le sol ont été appréciés par l'action qu'il exerce sur le déroulement d'une fonction particulière, la dégradation du 2,4-d en considérant comme entités fonctionnelles des microéchantillons de sol. Un traitement au DNOC s'avère pénalisant même à faible dose ou une plus grande progressivité de l'effet est observé. Ce travail démontre que certaines agressions chimiques telles que celles qui résultent de la présence du DNOC provoquent au sein de la microflore du sol des réajustements spécifiques et des adaptations fonctionnelles relativement prononcée