| Summary: | Mercury (Hg) is a persistent toxic compound whose amount in the global biosphere has at least tripled since industrialization. Recently, the study of the seven Hg stable isotopes has emerged as a new promising technique affording to explore the Hg cycle both in situ and in laboratory. Mercury stable isotopes display both mass dependent fractionation (MDF, reported as δ202Hg) and mass independent fractionation (MIF, reported as Δ199Hg and Δ201Hg). Our recent findings about Hg accumulation in the European seabass, Dicentrarchus labrax, showed how the combination of Hg isotopic values with Hg speciation allow tracing back Hg environmental sources as well as metabolic pathways within the organisms. However, such interpretation gets more complicated in more physiologically complex animals such as seals. With the aim of study basal Hg kinetic in an top predator without the influence of distribution and diet specialization, we measured T-Hg levels, speciation and isotopic composition in 6 captive pups of hooded seals, Cystophora cristata, and their diet the Norwegian herring Clupea harengus. The main objective was to select the tissue in which the information about Hg pathways would be conserved, leading to the optimal tracing of Hg sources along the food web. MMHg ranged between 84 to 98% in hair, 74 to 95% in muscle, 7 to 38% in liver and 4 to 27% in kidney. A significant 202Hg enrichment resulted between seal hair and herring (p = 0.011), indicating important MDF between the ingested prey and these tissues. Instead, a significant MIF (Δ199Hg and Δ201 values) was observed only between seals’ kidney and herring (p = 0.0003). Our results showed that hair represents the best tissue for the analysis of Hg biomagnification along food webs; and that with the exception of kidney, MIF signal is conserved in all tissues during assimilation of prey items. SODYMARS
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