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Influence de la matrice sol sur la biodisponibilitté orale des Polluants Organiques Persistants chez les ruminants laitiers

Abstract : Persistent Organic Pollutants (PoP) can be accumulated through the memory effect of soil. Ruminants can therefore be exposed to the PoP through involuntary ingestion of the contaminated soil. On pasture, soil ingested by ruminants can reach 800 g of soil per day. But PoP interact with the soil particles, leading to the formation of strong bonds which can decrease their bioavailability. Therefore, we developed several approaches in order to determine the bioavailability of soil-bound PoP. Indeed, more precision on the impact of soil on the bioavailability of the contaminants is essential to assess the transfer to the animal products. The investigations focused on two PoP families: the Polycyclic Aromatic Hydrocarbons (PAH) which are readily cleared and the PolyChloroBiphenyls (PCB) which are poorly metabolized. For the PCB, the relative bioavailability was estimated by comparing the values of the transfer coefficients or « Carry-Over Rates » obtained after soil ingestion, with that those obtained in the literature with other food matrices such as hay. The second study was conducted in order to calculate the bioavailability of soil-bound PAH. This experimental approach lay in comparing soil matrix with the reference matrix (oil) through the urinary excretion of the major hydroxylated PAH metabolites. The last investigation focused on the statistical combination of the results of several studies that address a set of related research on the role of organic matter (organic carbon) on the bioaccessibility of the PAH in the gastro-intestinal tract. The results of the studies performed show that soil has limited impact on the PoP bioavailability in ruminants. However, the lipophilicity of PoP seems to play a role in regulating their bioavailability. Indeed, soil impact is not significant for Phenanthrene (three-ring molecule), whereas the bioavailability of Pyrene is estimated at 50 % (four-ring molecule). The bioaccessibility in the gastro-intestinal tract is a component of the bioavailability; it was estimated for PAH at between 0.2 and 46%, and seems to be led by the concentration of PAH and the organic carbon content in soil. These results suggest that soil matrix deserves some special focus because its properties of geoaccumulation may increase the risk of transfer of PoP to the ruminant. The geosorbant property of soil, which explains its role as environmental reservoir of PoP, does not appear enough to avoid contamination of animal products, in the conditions of the lactating ruminant digestif tract. Particular attention should be paid to soil in the scenarios of risk assessment
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Fayçal Ounnas. Influence de la matrice sol sur la biodisponibilitté orale des Polluants Organiques Persistants chez les ruminants laitiers. Science des sols. Institut National Polytechnique de Lorraine, 2011. Français. ⟨NNT : 2011INPL042N⟩. ⟨tel-01749529⟩



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