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[Departement_IRSTEA]Territoires [TR1_IRSTEA]DTAM; International audience; The book deals with a long term pollution problem, generated by the former use of organochlorine pesticides. Through a case study of the chlordecone pollution in the French West Indies, the authors illustrate a global and systemic mobilization of research institutions and public services. This "management model", together with its major results, the approach and lessons to be learned, could be useful to other situations. This book gathers all the works that have been carried out over the last ten years or more and links them to decision makers’ actions and stakeholders’ expectations. This reference fills a gap in the literature on chronic pollution.

Chlordecone, an organochlorine insecticide, pollutes soils and contaminates crops and water resources and is biomagnified by food chains. As chlordecone is partly trapped in the soil, one possible alternative to decontamination may be to increase its containment in the soil, thereby reducing its diffusion into the environment. Containing the pesticide in the soil could be achieved by adding compost because the pollutant has an affinity for organic matter. We hypothesized that adding compost would also change soil porosity, as well as transport and containment of the pesticide. We measured the pore features and studied the nanoscale structure to assess the effect of adding compost on soil microstructure. We simulated changes in the transport properties (hydraulic conductivity and diffusion) associated with changes in porosity. During compost incubation, the clay microstructure collapsed due to capillary stresses. Simulated data showed that the hydraulic conductivity and diffusion coefficient were reduced by 95 and 70 % in the clay microstructure, respectively. Reduced transport properties affected pesticide mobility and thus helped reduce its transfer from the soil to water and to the crop. We propose that the containment effect is due not only to the high affinity of chlordecone for soil organic matter but also to a trapping mechanism in the soil porosity.

Crisis Management of Chronic Pollution: Contaminated Soil and Human Health deals with a long term pollution problem, generated by the former use of organochlorine pesticides. Through a case study of the chlordecone pollution in the French West Indies, the authors illustrate a global and systemic mobilization of research institutions and public services. This "management model", together with its major results, the approach and lessons to be learned, could be useful to other situations. This book gathers all the works that have been carried out over the last ten years or more and links them to decision makers' actions and stakeholders' expectations. This reference fills a gap in the literature on chronic pollution.

International audience

Thermo-stable, operationally defined soil protein, known as glomalin, may make an important contribution to carbon storage in soils. The term glomalin is used because this putative protein, or group of proteins, was originally thought to be produced only by Glomus fungi. There is currently little information on the glomalin-related soil protein (GRSP) content of tropical soils, particularly allophanic soils that are known to have different carbon dynamics to temperate climate soils. We have measured the Bradford-reactive GRSP content of soils sampled from forests and grasslands on the tropical island of Martinique and compared the observations with soil composition. Two operationally defined fractions of GRSP were measured, namely easily-extractable and total GRSP. The contents of GRSP in moist soils were in the range of 2-36 g kg(-1), accounting for about 8% of soil organic carbon, and were greater in topsoils than in corresponding subsoils. Both the GRSP contents and the fraction of soil organic carbon attributed to GRSP were greater than those reported for temperate climate soils. Both total and easily extractable GRSP contents were positively correlated to soil organic carbon content. The fraction of soil organic carbon that could be attributed to soil protein decreased with increasing allophane content for allophanic soils. No other trends of GRSP content with soil properties or land use were found. GRSP extraction was decreased about seven-fold by air-drying of soils, confirming the irreversible change in the soil microstructure of allophanic soils. Total and easily extractable GRSP were correlated and we conclude that both are good probes of thermo-stable soil protein content for these soils. No attempt was made to verify the fungal origin of the protein detected.

Allophanic soils are interesting in terms of environmental properties especially because of their potentialities as sinks for "greenhouse gases" by the way of C sequestration. These volcanic soils contain amorphous clays (allophanes) and exhibit higher organic carbon content than the one measured in other clay soils. We measured the C content of a set of allophanic soils and showed that the C content is positively correlated to the allophane content. We also measured the part of organic matter transformed into CO2 during a respiration experiment and showed that the decomposition is lowered as the soils allophane content increases. Allophane aggregates are very close to the synthetic gels: high specific surface area large pore volume, fractal structure, large water content and important irreversible shrinkage during drying. In this work we characterized by Small Angle X-Ray Scattering (SAXS) the fractal structure of the allophane aggregates at the nano scale. We hypothesized that the peculiar structure and the associated low accessibility of the allophanic soils could explain the high organic carbon content and the associated poor transformation into CO2. The tortuous structure of the allophane aggregates plays the role of a labyrinth which fix and traps soil organic carbon.

Aerogels produced hypercritical drying of gels from hydrolysis of TMOS in various pH conditions and subjected to a densification process were studied by SAXS using LURE synchrotron facility. The evaluation of scattering data combined with BET measurements leads to a model of aerogels consisting of a light density matrix in which meso- and macro-pores are embedded. No fractal features we observed for the gels, the Porod's limit having an exponent n=4. This could mean that either these aerogels are not fractals or that the SAXS method suffers from an inherent ambiguity for fractal dimension D=3.

International audience; Chlordecone (CLD) is an organochlorine insecticide that was used from 1972 to 1993 in the French West Indies (FWI) to control the populations of black weevil in banana plantations. This pesticide, with recognized neurotoxic, endrocrine, reproductive and carcinogenic effects, is nowadays responsible of an unprecedented sanitary, economic and social crisis in FWI. Thanks to the management options taken in the past years by the authorities to avoid the population dietary exposure the crisis is fortunately essentially contained. A final solution to the problem would consist however to eliminate the source of CLD responsible for the diffuse pollution of all the FWI environmental compartments and related food resources and so to destroy the stock of CLD still presents in the soils. One of the cheapest and most environmental friendly destruction methods corresponds to microbial degradation. Such a mode of destruction seems to be particularly appropriate in the case of FWI since it can often be implemented in situ, using techniques (e.g., watering; addition of nutrients, labile organic matter, microorganisms) that are fairly easy to incorporate into existing agricultural practices. The latter is important as the pollution is estimated to cover some 19,000 ha of arable lands. Until now however there is no evidence of natural attenuation in the environments impacted by chlordecone and so of the possibility to stimulate the rate of the process. The reason usually advocated to explain this apparent absence of degradation in the environment is the peculiar chemical structure of CLD (bishomocubane “cage” structure with a high steric hindrance caused by the 10 chlorine atoms bound to the cage), coupled to its low aqueous solubility (3 mg/l at 20°C) and high hydrophobicity (Log Kow 20°C, pH 7 = 4.5) that would make it refractory to degradation. In this chapter through a thermodynamic approach, we demonstrate that there is no energetic reason why the structure of CLD should not be amenable to microbial degradation and we propose some possible reasons for the apparent absence of CLD degradation in FWI and what could be done to reverse the situation.; La chlordécone (CLD) est un insecticide organochloré utilisé de 1972 à 1993 dans les Antilles françaises pour lutter contre les populations de charançon noir dans les bananeraies. Ce pesticide, aux effets neurotoxiques, endocriniens, reproductifs et cancérigènes reconnus, est actuellement responsable d’une crise sanitaire, économique et sociale sans précédent en Guadeloupe et en Martinique. Grâce aux options de gestion prises ces dernières années par les autorités pour éviter l'exposition alimentaire de la population, la crise est heureusement essentiellement contenue. Une solution définitive au problème consisterait à éliminer la source de CLD responsable de la pollution diffuse de tous les compartiments environnementaux des Antilles et des ressources alimentaires associées et donc à détruire le stock de CLD encore présent dans les sols. L'une des méthodes de destruction les moins chères et les plus respectueuses de l'environnement correspond à la dégradation microbienne. Un tel mode de destruction semble être particulièrement approprié au cas des Antilles, car il peut souvent être mis en œuvre in situ, en utilisant des techniques (par exemple, arrosage; ajout d'éléments nutritifs, matière organique labile, microorganismes) qui sont assez faciles à intégrer aux pratiques agricoles existantes. Ce dernier point est important car on estime que la pollution couvre environ 19 000 ha de terres arables. Jusqu'à présent cependant, il n'y avait aucune preuve d'atténuation naturelle dans les environnements affectés par la chlordécone et donc de la possibilité de stimuler le rythme du processus. La raison généralement invoquée pour expliquer cette apparente absence de dégradation dans l’environnement est la structure chimique particulière de la CLD (structure en forme de «cage» bishomocubane avec un fort encombrement stérique causé par les 10 atomes de chlore liés à la cage), couplée à sa faible solubilité dans l’eau (3 mg / l à 20 ° C) et une hydrophobie élevée (Log Kow 20 ° C, pH 7 = 4,5) qui la rendraient réfractaire à la dégradation. Dans ce chapitre, au moyen d'une approche thermodynamique, nous démontrons qu’aucune raison énergétique ne justifie que la structure de la CLD ne soit pas accessible à une dégradation microbienne et nous proposons des raisons possibles à l’absence apparente de dégradation de la CLD aux Antilles et ce qui pourrait être fait pour inverser la situation.