[en] Many of the biophysical processes involved in the scope of desertification depend on the hydric characteristics of the soils the impact on vegetation cover. To protect soils against desertification, it is necessary to understand how some of these characteristics (such as water storage) interact in a complex and integrated chain of degradation processes. Several works have been developed to contribute to the definition of a Index of Desertification Susceptibility (DSI) expressed as a function of several components, climatic, edaphic, vegetative and slope. However, the various built-in edaphic components already defined, leave aside the water retention in soil. Furthermore, these components only focus on the characteristics of the uppermost surface soil layer (A-layer). In fact, desertification is simultaneously cause and consequence of the depleted soil water retention with a positive feedback of the plant life and on the hydrological cycle. (Author) 10 refs.

[en] This sheet summarizes the behavior of the chemical element in the main compartments of terrestrial and aquatic ecosystems, under the following two assumptions. Isotopic discrimination is negligible, which is the case for most of the elements discussed. When the element has stable isotopes, the analogy in behavior between its stable and radioactive isotopes is implicitly accepted, bearing in mind, however, that for naturally occurring elements, the chemical form and emission medium of anthropogenic discharges are likely to involve transfer pathways and processes other than those identified for the naturally stable element. The radioactive isotope(s) designated in the heading of the data sheet correspond to radionuclides of major radioecological importance, in terms of quantities and persistence in the environment. Other isotopes, whether radioactive or stable, may also be cited. The information, which is deliberately simplified, is intended to reflect the state of knowledge on the subject at the time of updating, and to propose values for the main radioecological parameters used to estimate transfers in the environment, and more particularly within the food chain

[en] The Nb(III) complex [Cp'Nb(CO)₂Cl₂]₂ (1, Cp' = C₅H₄Me) undergoes decarbonylation in refluxing THF to give a dark brown paramagnetic compound believed to be Cp'₃Nb₃Cl₆(μ₃-O) (2). Compound 2 reacts with atmospheric oxygen to produce Cp'₃Nb₃Cl₃(μ₂-Cl)₃(μ₃-O)(μ₃-OH) (3) and with chlorinated hydrocarbons to form Cp'₃Nb₃Cl₃(μ₂-Cl)₃(μ₃-O)(μ₃-Cl) (4). Compounds 3 and 4 are paramagnetic. X-ray structure determinations show that each of these clusters has one short Nb-Nb distance of ca. 2.92 angstrom corresponding to a Nb-Nb bond and two long Nb···Nb distances near 3.28 (3) or 3.39 angstrom (4). The Nb₃ triangle is bridged by Cl atoms along each edge and is capped by a μ₃-oxo ligand and a μ₃-hydroxo (3) or μ₃-chloro ligand (4) on opposite sides of the Nb₃ plane. Terminal Cp and Cl ligands complete the coordination sphere about each Nb atom. Crystal data: for 3, a = 7.210 (2) angstrom, b = 26.097 (7) angstrom, c = 12.518 (3) angstrom, β = 94.18 (2)degree, space group P2₁/n, Z = 4, V = 2349 angstrom ³, ρ_calcd = 2.06 g/mL, R = 0.039 and R_w = 0.054 on 2551 reflections with I > 3σ(I); for 4, a = 7.620 (1) angstrom, b = 15.108 (4) angstrom, c = 21.670 (6) angstrom, α = 87.45 (2)degree, β = 93.68 (2)degree, γ = 104.01 (2)degree, space group P1, Z = 4, V = 2414 (1) angstrom ³, ρ_calcd = 2.01 g/mL, R = 0.065 and R_w = 0.055 on 2424 reflections with I > 3σ(I). 6 references, 3 figures, 4 tables

[en] The radioactive isotopes of cesium and strontium may be deposited on urban surfaces in the case of an accidental atmospheric discharge from a nuclear facility and thus imply a health hazard. In order to handle the decontamination of these surfaces, we have carried out experiments under controlled conditions on tiles and concrete and we have studied the physical and chemical mechanisms at the solid-liquid interface. The deposition of radionuclides was carried out in the form of aerosols indicating an accidental source term. Their desorption by rainwater is low in all cases, of the order of 5-6% for cesium for any material and 29 and 12% for strontium on tile and concrete, respectively. The low desorption values of cesium may be explained by the strong bonding that occurs with the silicates constituting the tile due to virtually irreversible processes of exchange of ions and by the formation of insoluble complexes with the C-S-H gel of concrete. The strontium-tile bonds are weaker, while strontium precipitates with the carbonates of concrete in the form of SrCO₃. In view of these characteristics, washing solutions with high concentrations of chloride and oxalate of ammonium chosen for their ion-exchanging and sequestering properties were tested on these surfaces. The desorption of cesium improved strongly since it reached 70% on tile and 90% on concrete after 24 h of contact, which is consistent with our knowledge of the bonds between this element and the surfaces. Strontium, given the greater complexity of physical and chemical forms that it may take is less well desorbed. The ammonium chloride improves the desorption (50% and 40%, for tile and concrete, respectively) but the oxalate, while it does not affect desorption on the tiles, decreases that on the concrete since by strongly etching the concrete, it causes the release of carbonate ions that precipitate with strontium

[en] The interactions of soil disaggregation with radionuclide erosion were studied under controlled conditions in the laboratory on samples from a loamy silty-sandy soil. The fate of ¹³⁴Cs and ⁸⁵Sr was monitored on soil aggregates and on small plots, with time resolution ranging from minutes to hours after contamination. Analytical experiments reproducing disaggregation mechanisms on aggregates showed that disaggregation controls both erosion and sorption. Compared to differential swelling, air explosion mobilized the most by producing finer particles and increasing five-fold sorption. For all the mechanisms studied, a significant part of the contamination was still unsorbed on the aggregates after an hour. Global experiments on contaminated sloping plots submitted to artificial rainfalls showed radionuclide erosion fluctuations and their origin. Wet radionuclide deposition increased short-term erosion by 50% compared to dry deposition. A developed soil crust when contaminated decreased radionuclide erosion by a factor 2 compared to other initial soil states. These erosion fluctuations were more significant for ¹³⁴Cs than ⁸⁵Sr, known to have better affinity to soil matrix. These findings confirm the role of disaggregation on radionuclide erosion. Our data support a conceptual model of radionuclide erosion at the small plot scale in two steps: (1) radionuclide non-equilibrium sorption on mobile particles, resulting from simultaneous sorption and disaggregation during wet deposition and (2) later radionuclide transport by runoff with suspended matter

No abstract available

[en] This paper presents a summarized review of the knowledge relative to the behaviour of radio-cobalt in the terrestrial environment. The chemistry of cobalt in soils is closely connected to that of iron and manganese. It is more soluble in acidic conditions. In soils, 5 to 10 % of total cobalt may be hydrosoluble or easily extractable, and the main part of cobalt may be either weakly absorbed on clays or complexed with humic acids. The importance of cobalt absorption by the roots of plants depends mainly on the pH of the soil, on the presence of other elements such as iron, aluminium or calcium and to a lesser extent on the soil texture and organic matter content. Results concerning foliar transfer are sparse and very variable. For a single foliar contamination it depends on the vegetative stage of the plant at the time of deposit. As for other elements, the transfer resulting from a deposit onto aerial parts of the plants is more important tan the root uptake, for a similar deposition. In comparison to raw products, food processing results in lowering the residual activity of foods down to 50 %. (author)

[en] The decrease of radioactivity for ¹³⁴Cs, ⁸⁵Sr, ¹⁰⁶Ru, ⁵⁷Co, ^110mAg during food processing was measured. Washing and bleaching vegetables directly contaminated by a single aerosol deposit led to a radioactivity decrease (depending on the vegetable, the radionuclide and the time of deposition) up to 90% for caesium. The efficiency of these processes was less important when the vegetables were contaminated by root transfer, except for peeling of root vegetables. Canning of vegetables indirectly contaminated by caesium, strontium, cobalt and ruthenium, after paring and bleaching, was rather interesting with residual radioactivity varying from 30 to 50% for green beans and from 5 to 20% for carrots. Measurements of stable caesium and strontium in cereals before and after industrial processing showed an important activity decrease; retention factors varied from 0.1 to 0.2 for wheat milling and 0.1 to 0.4 for rice processing. (authors). 6 refs., 9 tabs., 1 figs

[en] From 1988 to 1993, the Nuclear Safety and Protection Institute (Institut de Protection et de Surete Nucleaire -- IPSN) conducted experimental programs focused on transfers to vegetation following accidental localized deposits of radioactive aerosols. In relation to vegetable crops (fruit, leaves, and root vegetables) and meadow grass these experiments have enabled a determination of the factors involved in the transfer of cesium, strontium, and ruthenium at successive harvests, or cuttings, in respect of various time lags after contamination. The dynamic modeling given by these results allows an evaluation of changes in the mass activity of vegetables and grass during the months following deposit. It constitutes part of the ASTRAL post-accident radioecology model

[en] In case of accidental radioactive discharges, the drinking water would not represent the first concern for the definition of the total radiological risk; however, it would generally constitute the first concern of the consumer. The purpose of the results come from experiments carried out in laboratory and were to evaluate the efficiency of two type of processing of drinking water on the elimination of the radionuclides cesium and strontium. Therefore, a catchment water was contaminated with radioactive aerosols representative of an accident. Then, it was made potable on the one hand, using a traditional process (clarification and filtration on sand then on activated carbon), and on the other hand, by a less traditional but easily integrable technique within an already existing process, in which sand is replaced by zeolite. The performance at the end of the processing using sand is average for cesium (from 67 to 73 % according to the type of coagulant injected) and becomes frankly poor for strontium (between 46 and 51 %). The results obtained with the process including of zeolite are very satisfactory. The performance at the end of the processing as well reach 99 % for strontium as for cesium whatever the type of coagulant used. The present study thus made it possible to show the insufficiency of the processing known as 'traditional' of drinking water towards to the elimination of the radionuclides cesium and strontium, but also to outline the features of a new process still to improve radioactive decontamination of water. (authors)