Mercury speciation and stable isotopic composition in marine vertebrates: new insights and perspectives

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). The combination of both values should allow to trace back sources and pathways of Hg and methylmercury (MeHg). But, so far, few studies have considered Hg isotopes in marine vertebrates. Thus, our general objective is to study Hg accumulation in marine predator species including, the European seabass, Dicentrarchus labrax, and the hooded seal, Cystophora cristata. By combining both in situ and experimental investigations, we aim to characterize the Hg profile (THg, MeHg and isotopy) of wild populations, to assess whether Hg isotopes differ between populations and could give indications on Hg sources, with special attention paid to differentiate local versus global Hg sources.