392 - Mercury isotopes to identify the dynamics of dietary methylmercury in rainbow trout after selenium species supplementation

Methylmercury (MeHg) bioaccumulates and biomagnifies along the food chain. Aquatic species can metabolise this neurotoxic compound by different pathways such as demethylation, excretion or biomineralisation into inert mercury selenide nanoparticles (HgSe NPs). These transformations strongly depend on the tissue, but also on the compounds involved. Selenium (Se) has been largely evoked as antagonist of Hg toxicity, however this mechanism is not completely understood so far. Hg stable isotopes can undergo two types of fractionation: mass-dependent fractionation (MDF) and mass-independent fractionation (MIF). Hg isotopic fractionation provides information on the metabolic pathway of Hg in relation to different diets and feeding intake . This work presents a novel approach to investigate dietary MeHg dynamics in model aquaculture fish tissues (Rainbow trout) after supplementation with the most dietary relevant Se species. Fish were fed MeHg (2 µg of Hg per g) in seven different diets, ranging from vegetable to tuna, enriched with organic and inorganic Se species (1.5 µg of Se/g as selenite or hydroxy-selenomethionine). Sampling was performed at 0, 7, 21, 84 and 168 days of treatment. Fish tissues collected were liver, kidney, muscle, brain and blood in order to assess tissue-dependent Hg isotopic patterns. The results of the kinetic study showed a fast incorporation of the new dietary source of MeHg reflecting its high bioaccumulation rate. MeHg-containing diets exhibit the isotopic fingerprint of Hg in the diet already after 7 days of treatment. Different Hg incorporation rates have been also evidenced by Hg isotopes, depending on the Se species supplemented in the diet. This study shows the influence of Se species in Hg metabolism in different fish tissues, elucidated by Hg stable isotope analysis.

Authors: Silvia Queipo-Abad