Sourcing and dynamic of mercury in Arctic true seals

Mercury (Hg) is considered one of the top 10 chemicals of modern public health concern. After the implementation of the Minamata convention in 2017, efforts were mostly directed to the understanding of Hg cycling in marine environment impacted by climate change. The Arctic region is a hotspot of Hg contamination studies, being a major sink and source for the global Hg cycle. Although evidences exist about a shift in Hg bioaccumulation in Arctic wildlife over time, scientists were not able to effectively link it with climate change. The remote position of some regions of the Arctic brought to a paucity of data. For example, Total-Hg (THg) temporal and spatial trends in marine and terrestrial predators living in the Greenland Sea are wildly missing. Forecasting of future THg trends is especially important for Arctic marine predators like marine mammals, whose Hg concentrations often surpass suggested toxicological thresholds.
The assessment of Hg sources and pathways in the marine environment, remains a complex challenge despite its recognized toxicity, both for wildlife and humans. Stable isotope ratios of carbon (C), nitrogen (N), sulphur (S) and Hg are valid tracers of Arctic marine predators’ trophic ecology, as well as Hg sourcing and cycling in the ocean. They are often studied separately, leaving the interpretation of the data at times incomplete and limiting the understanding of the complexity of the natural world.
The main goal of this work was to understand the main factors governing Hg pollution of marine predators in a changing Arctic. We focused on Greenland Sea true seals because of their diverse trophic ecologies and distribution. The hooded seal Cystophora cristata, harp seal Pagophilus groenlandicus and the ringed seal Pusa hispida are the most common specie in the area. As such they represent the main food source of local apex predators like polar bears and humans.
We applied a multivariate approach integrating C, N and S stable isotopes as proxies of seal ecology, Hg stable isotopes as proxies of Hg sources and Hg concentrations as proxies of levels of exposure. We set 3 specific questions: (1) which are the main sources of Hg in Arctic marine predators? (2) Which factors influence the most Hg bioaccumulation and biomagnification in Arctic marine food webs? And (3) Which consequences can be drawn for the health of Arctic marine food webs in the framework of climate change?
Our main findings indicate that (1) local Hg sources are far more important in governing Hg bioaccumulation and biomagnification in Arctic marine food webs, than environmental Hg levels; and (2) while environmental change at global levels is determining a decrease in Hg emissions and accumulation in marine species from oceanic food webs, ongoing changes across Arctic coasts are enhancing the risk of Hg exposure to inshore food webs.