Effects of organic amendments on plant-parasitic nematode populations, root damage, and banana plant growth

Nematodes are major pests for crops, including banana. Environmentally friendly methods for managing plant-parasitic nematodes have to be developed, such as organic material application. Our study focuses on the impacts of several organic amendments on banana plants, considering mainly their effect on soil nitrogen supply and soil microbial biomass, and the consequences on plant-parasitic nematode impacts on the plants. A microcosm experiment for 13 weeks was conducted to evaluate four organic materials: sugarcane bagasse, sugarcane sludge, plant residues, and sewage sludge, compared to a control without organic amendment. Input of organic materials led to an important change on nitrogen resource, and plants grew better when the N availability was the highest, but better growth conditions did not necessarily reduce parasitic nematodes impacts on the roots. Damage on the roots depended on plant-parasitic nematode abundance. Three of four tested amendments exhibited a regulator effect on plant-parasitic nematode populations (bagasse, sugarcane sludge, and plant residues). Root growth was not the explanatory factor for this regulation. Only sugarcane sludge led to an overall positive effect on the plant, increasing its growth and reducing its parasitism pressure. The other organic materials exhibited an antagonism between the promoted plant growth and the reduced nematode populations

Effects of four organic amendments on banana parasitic nematodes and soil nematode communities

Plant-parasitic nematodes are injurious crop pests that have been managed mainly by chemical nematicides. However, safe and alternative methods such as those based on organic materials need to be developed. Our study has evaluated (i) the effects of four organic amendments with different biochemical compositions that are abundantly produced in the study area (Guadeloupe, French West Indies) on soil nematode communities and (ii) some of the suppression mechanisms of banana parasitic nematodes, especially those involving the soil food web. This study is based on a microcosm experiment comparing sugarcane bagasse, sugarcane sludge, plant residues and sewage sludge. All amendments except sewage sludge decreased the root abundances of plant-parasitic nematodes, by 96% in the case of sugarcane bagasse. For this treatment, soil densities of carnivorous nematodes were six times higher than the treatments without organic amendment. Plant residues and bagasse were mainly composed of materials that are difficult to decompose, namely cellulose and lignins. These organic materials favored a fungal decomposition pathway and permitted development of carnivorous nematode populations and increased the Channel Index (CI). Pratylenchus coffeae control after sugarcane refinery sludge application remains unexplained. Lastly, sewage sludge, composed mainly of easily degradable compounds, did not permit nematode control, and only bacterivorous nematode populations were enhanced by this treatment

Corrosion of Zirconium in the Context of the Spent Nuclear Fuel Reprocessing Plant

International audienceZirconium is used as material for various applications in spent nuclear fuel reprocessing plants involving concentrated nitric acid medium under highly corrosive oxidizing conditions. In such conditions, zirconium can show two different oxidation regimes as a function of potential. At high potentials, the oxidation current is relatively important (few $\mu$A/cm$^2$) and constant with time. A poorly protective black oxide layer (ZrO$_2$) is formed on the surface, which has a thickness of few micrometers. At low potentials, the oxidation current decreases with time and progressively tends to low values (few nA/cm$^2$). This protective effect has been attributed to the formation/growth of a nanometric oxide layer (ZrO$_2$) on the surface. The thickness evolution of this layer has been simultaneously estimated as a function of time by in-situ electrochemical methods (Electrochemical Impedance Spectroscopy (EIS) and coulometry) and by ex-situ X-ray Photoelectron Spectroscopy analyses (XPS). These experimental results have been successfully compared with an anodic oxide layer growth model based on the high field regime. The addition of small amounts of fluorine in nitric acid (a few tenths of millimoles per liter) modifies notably the corrosion processes. Three phases are observed in the corrosion mechanism:(1) a first incubation phase where the corrosion rate is negligible, (2) a second phase with a sharp increase of the corrosion rate (the SEM observations show a process of nucleation / growth /coalescence of pits) and (3) a third phase with a progressive decrease of the corrosion rate (corresponding to a generalized corrosion mechanism by an oxidation/complexation process limited by the supply of the reactive species

Single crystal and sintered alumina corrosion in liquid sodium

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Co-deposited layer characterisation and removal control by opticam emission spectroscopy coupled to nano-second laser ablation

International audienceOptical emission spectroscopy coupled with laser ablation has been used to characterise plasma facing components. First results of feasibility studies have shown that specific lines of metallic impurities can be used to discriminate co-deposited layer from substrate (graphite). Recording these lines shot by shot allows to follow in real-time co-deposited layer removal and to evaluate co-deposited layer thickness. It is also possible to evaluate, with this technique, impurity profiles versus depth. Furthermore, last experiments have permitted to record a Hydrogen line indicating that such a technique could be implemented in-situ, in a tokamak, to localise and quantify tritium retention

Irradiation effects in hydrated zirconium molybdate

International audienceHydrated zirconium molybdate is a precipitate formed during the process of spent nuclear fuel dissolution. In order to study the radiation stability of this material, we performed gamma and electron irradiation in a dose range of 10–100 kGy. XRD patterns showed that the crystalline structure is not affected by irradiation. However, the yellow original sample exhibits a blue–grey color after exposure. The resulting samples were analyzed by means of EPR and diffuse reflectance spectroscopy. Two sites for trapped electrons were evidenced leading to a d1 configuration responsible for the observed coloration. Moreover, a third defect corresponding to a hole trapped on oxygen was observed after electron irradiation at low temperature

Cobalt distribution in keratinocyte cells indicates nuclear and perinuclear accumulation and interaction with magnesium and zinc homeostasis

Cobalt is knownto be toxic at high concentration, to induce contact dermatosis, and occupational radiation skin damage because of its use in nuclear industry.We investigated the intracellular distribution of cobalt in HaCaThumankeratinocytes as a model of skin cells, and its interaction with endogenous trace elements. Direct micro-chemical imaging based on ion beam techniques was applied to determine the quantitative distribution of cobalt in HaCaT cells. In addition, synchrotron radiation X-ray fluorescence microanalysis in tomography mode was performed, for the first time on a single cell, to determine the 3D intracellular distribution of cobalt. Results obtained with these micro-chemical techniques were compared to a more classical method based on cellular fractionation followed by inductively coupled plasma atomic emission spectrometry (ICP-AES) measurements. Cobalt was found to accumulate in the cell nucleus and in perinuclear structures indicating the possible direct interaction with genomic DNA, and nuclear proteins. The perinuclear accumulation in the cytosol suggests that cobalt could be stored in the endoplasmic reticulum or the Golgi apparatus. The multi-elemental analysis revealed that cobalt exposure significantly decreased magnesium and zinc content, with a likely competition of cobalt for magnesium and zinc binding sites in proteins. Overall, these data suggest a multiform toxicity of cobalt related to interactions with genomic DNA and nuclear proteins, and to the alteration of zinc and magnesium homeostasis

Assessment of exposure to airborne carbon nanotubes by laser-induced breakdown spectroscopy analysis of filter samples

International audienceExposure assessment is a key step in the evaluation of the risk induced by the handling of engineered nanomaterials. It is a very complex task, because several properties of nanoparticles are assumed to have an effect on their hazards. For exposure monitoring at the workplace, real-time onsite measurements are commonly implemented to measure the particles size and number density, whereas the sampled material is subsequently analysed by electron microscopy. A complementary approach would consist in doing onsite chemical analysis of the filter samples, in order to routinely monitor a potential chronic exposure. Laser-induced breakdown spectroscopy (LIBS) has distinctive advantages for this purpose. Therefore, this work aims at evaluating the performances of LIBS to assess the exposure to airborne carbon nanotubes (CNTs) at the workplace. As carbon is a ubiquitous element in the environment, our strategy was to target metal impurities in CNTs, aluminum and iron in our case. Then, we proceeded in three steps. First, we optimized the choice of the filter type to get the lowest detection limit for both elements. Secondly, this filter was used to quantitatively measure deposited CNTs. Eventually, we conducted an onsite measurement campaign in an industrial CNT production plant to evaluate the exposure in a real situation. We demonstrated that we could reach a detection limit for CNTs compliant with the current NIOSH recommendation of 1 μg m−3, and that the detected CNTs during the onsite campaign in areas accessible to workers were at an extremely low concentration, several orders of magnitude lower than this recommendation