Évaluation du niveau de contamination chimique et de la qualité des ressources vivantes aquatiques

Abstract : Much appreciated by consumers for its nutritional qualities, seafood plays an important role in human diet. Consumer confidence in the quality of these foodstuffs is nevertheless affected by concerns about risks associated with exposure to chemical contaminants and the freshness of these products. If the first of these is the result of pollution resulting from increasing human activities along coastlines, the second is linked to the highly perishable nature of these products. An evaluation of the levels of chemical contaminants in seafood and of its freshness is therefore a necessity. It is within this context that the work presented in this thesis was carried out. Two principal objectives were targeted in the present study. The first objective of this work was to evaluate the spatial and seasonal variability of seafood contamination by elements (including metals) and organic pollutants (PAHs and PCBs) along the Senegalese coast. We studied 7 marine species representative of different trophic level (a green macro algae, a bivalve mollusc, a crustacean and 4 species of fish) sampling them along the coastline at 5 sites representing different human activity pressur. The result of this study showed that contamination levels varied with species, underlining the importance of a multi-species approach to study contamination in the marine environment. Variations between sites were also observed. Sites with the greatest human activity, such as Soumbédioune and Rufisque, were also those where the highest levels of contaminants in seafood were found. The levels of contamination measured along the Senegalese coast, of both elements and organic pollutants, were inferior or of the same order of magnitude as those reported from other West African sites or from other regions of the globe. The risks associated with eating theseseafood products were low, with contaminant levels generally below the admissible limits (EU) for human consumption. Only a few samples of certain species (mussels, sardines) exceeded these limits at Soumbédioune and Rufisque. The second objective of this study was to develop methods to evaluate the freshness of fish fillets, and to distinguish fresh fillets from previously frozen ones. The methods developed were based upon a measure of cellular permeability within the fish muscle tissue. The conservation of fish fillets ar 4°C results in increased permeability of cells over time, measurable by studying the liberation of intra-cytoplasmic enzymes or the increasing permeability of cells to fluorescent colouring agents. The measurements of lactate dehydrogenase (LDH) is doubly interesting in this contex : on the one hand it enables a measure of cell lysis, and so the level of alteration of the fillets over time, to be established. It also, thanks to its sensitivity to freezing, to better distinguish fresh fillets from those that have been frozen then thawed.
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Mamadou Diop. Évaluation du niveau de contamination chimique et de la qualité des ressources vivantes aquatiques. Biochimie [q-bio.BM]. Université du Littoral Côte d'Opale; Université Cheikh Anta Diop de Dakar, 2016. Français. ⟨NNT : 2016DUNK0435⟩. ⟨tel-02177141⟩

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