La contamination des sols agricoles par la chlordécone menace la durabilité de l’élevage de plein air aux Antilles. Afin de maintenir ce dernier tout en protégeant les consommateurs de denrées animales d’origine terrestre, plusieurs stratégies sont étudiées. Ces travaux de thèse sont focalisés sur l’une d’entre elles qui consiste à séquestrer la chlordécone afin de réduire significativement sa biodisponibilité pour l’animal. La démarche expérimentale a été réalisée par étape, elle s’appuie sur trois piliers : des matières séquestrantes carbonées de type biochar ou charbon activé, l’utilisation de sols artificiels et sur le concept de biodisponibilité relative pour évaluer les performances de séquestration. Les essais conduits avec du charbon activé (à base de noyaux de dattes, de coco ou de lignite) ont montré une séquestration de la chlordécone en milieu aqueux ou chez l’animal, mais pour ce dernier cela ne fonctionne que si la chlordécone et la matrice séquestrante ont eu un temps de contact prolongé (ou maturation) avec l’ingestion par l’animal. Ces résultats montrent l’intérêt d’une séquestration in situ, à savoir directement dans le sol contaminé susceptible d’être ingéré par les animaux. Comme le charbon activé a un coût élevé, des matières carbonées a priori moins coûteuses ont été testées : des biochars à base de diverses essences de bois. Ces biochars produits à deux températures de pyrolyse (500 et 700°C) ont été caractérisés d’un point de vue physique (porosité) et sélectionnés via un test in vitro de disponibilité environnementale. Les tests in vivo (sur porcelets) n’ont pas montré que ces biochars sélectionnés étaient aptes à séquestrer efficacement la chlordécone, puisque la biodisponibilité relative n’était pas différente de un (référence = sol standard sans matière organique). La présence de tourbe dans le sol artificiel ne s’oppose pas au piégeage par les matrices carbonées exogènes. Le test in vitro utilisé et le test in vivo donnent des tendances équivalentes de réduction de la biodisponibilité relative, ce qui est intéressant dans une logique de validation du test in vitro. Ces résultats positifs montrent que la stratégie de séquestration par des matériaux hautement carbonés est possible, requiert des propriétés de microporosité et d’accès aux pores proches de celles d’un charbon activé, mais contingents des conditions expérimentales mises en œuvre ils doivent être poursuivis et validés sur des sols dits naturels / The contamination of agricultural soils by chlordecone threatens the sustainability of outdoor farming in the West Indies. In order to maintain the latter while protecting consumers of terrestrial animal products, several strategies are being studied. This thesis is focused on one of them which consists of sequestering chlordecone in order to significantly reduce its bioavailability for the animal. The experimental approach was carried out in stages, based on three pillars: biochar or activated carbon as sequestering materials, the use of artificial soils and the concept of relative bioavailability to assess sequestration performance. Tests conducted with activated charcoal (based on dates kernels, coconut or lignite) have shown that chlordecone is sequestered in an aqueous medium or in animals, but for the latter it only works if chlordecone and sequestering matrix had a prolonged contact time (or maturation) with ingestion by the animal. These results show the interest of in situ sequestration, ie directly in the contaminated soil likely to be ingested by the animals. As activated charcoal has a high cost, a priori less expensive carbonaceous materials have been tested: biochars based on various wood species. These biochars produced at two pyrolysis temperatures (500 and 700 ° C) were characterized from a physical point of view (porosity) and selected via an in vitro environmental availability test. In vivo tests (on piglets) did not show that these selected biochars were able to effectively sequester chlordecone, since the relative bioavailability was not different from one (reference = standard soil without organic matter). The presence of peat in the artificial soil does not prevent trapping by exogenous carbonaceous matrices. The in vitro test used and the in vivo test give equivalent tendencies to reduce the relative bioavailability, which is interesting in a logic of validation of the in vitro test. These positive results show that the strategy of sequestration by highly carbonaceous materials is possible, requires properties of microporosity and access to pores close to those of an activated carbon, but contingent on the experimental conditions implemented, they must be continued and validated on natural soils

Organic matter is ubiquitous in the environment and exists in many different forms. Reactions involving organic matter are diverse and many have significant economic and environmental implications. In this research, calorimetric techniques were used to study organic- inorganic reactions in two different systems. The primary objectives were to elucidate potential mechanism(s) by which: (i) natural organic matter (NOM) influences strength development in lime-stabilized soils, and; (ii) plant-derived biochars reacts with cations in aqueous environments. Natural organic matter influenced strength development in lime-stabilized soils through the direct inhibition of the formation of pozzolanic reaction products. The degree of inhibition was dependent mainly on the type of pozzolanic reaction product, and the amount and source of organic matter. The formation of the pozzolanic reaction product, calcium silicate hydrate II (CSH2) was less affected by NOM, than was the formation of CSH1. For a given pozzolanic product, the inhibition increased with NOM content. The effect of organic matter source followed the order fulvic acid> humic acid&gt; lignite. Formation of CSH pozzolanic reaction products decreased by 50-100%, 20-80% and 20-40% in the presence of ?2% fulvic acid, humic acid and lignite, respectively. Cation interactions with plant-derived biochars were complex and depended both on the nature of the cation and biochar surface properties. Reactions involving the alkali cation, K+; occurred via electrostatic ion exchange, on deprotonated functional groups located on the biochar surface and; were exothermic with molar heats of reaction (?Hads) between -3 and -8 kJ mol-1. In contrast, reactions involving the transition metal cation, Cd2+ were endothermic with delta Hads between +10 and +30 kJ mol-1. Reaction mechanism(s) for Cd2+ varied from ion exchange/surface complexation in biochars formed at <350 oC, to an ion exchange/surface complexation/diffusion-controlled mechanism in biochars formed at >/=350 oC. For a given cation, differences in sorption characteristics were attributable to temperature-dependent or plant species dependent variations in the properties of the biochars.