Lacs Aquitains et mercure

In 2013, a study of ANSES (French Agency for Food, Environmental and Occupational Health & Safety) on mercury (Hg) contamination of fish from the four largest Aquitaine Lakes (Hourtin-Carcans, Lacanau, Cazaux-Sanguinet and Parentis-Biscarrosse Lakes) showed that zander (Sander lucioperca), a carnivorous fish from Hourtin-Carcans and Lacanau Lakes had Hg levels exceeding the current consumption guideline (0.5 mg Hg. kg-1 wet weight). Following this contamination, a prefectural decree banned the consumption of zander caught in these lakes. The aim of this study was to understand the source of this contamination. The results of the project show an increasing Hg concentration gradient from the southernmost lake to north in the flesh of carnivorous fishes. Atmospheric Hg concentrations measured locally and accumulated in terrestrial bryophytes (mosses) around lakes are characteristic of so-called "remote and pristine" environments from all significant sources of contamination. Other factors that may explain this gradient of contamination in fish have been studied, such as the role of aquatic plants. None of the factors studied can explain differences among lakes. On the other hand, a significant south-north sulphate gradient has been found in the water and sediments of the four lakes. The presence of sulphate promotes the development of sulphate-reducing microorganisms in part responsible for the production of methylmercury. This increased production of methylmercury in the northern lakes (Hourtin-Carcans and Lacanau Lakes) seems responsible for the greatest accumulation of this metal in the carnivorous fishes of these lakes. The development of these microorganisms takes place mainly in the biofilm present on the surface of plants and organic sediment, also called periphyton. High sulphate concentrations resulted from agricultural activity in the Hourtin-Carcans Lake catchment. Our study found that it is strongly discouraged to consume carnivorous fishes from Hourtin-Carcans and Lacanau Lakes for vulnerable people (pregnant women and children). En 2013, une étude de l'ANSES sur la contamination par le mercure (Hg) des poissons des quatre plus grands lacs aquitains (Hourtin-Carcans, Lacanau, Cazaux-Sanguinet et Parentis-Biscarrosse) a montré que les concentrations de mercure chez le sandre (Sander lucioperca) des lacs d’Hourtin-Carcans et de Lacanau dépassaient la recommandation alimentaire de l’OMS de 0,5 mg Hg.kg-1 poids frais (WHO 1990). Cette contamination p