What are the likely changes in mercury concentration in the Arctic atmosphere and ocean under future emissions scenarios?

Mercury bioaccumulation and assimilation in marine plankton in meltwater influenced fjords and shelf waters along the east coast of Greenland

The rapid melting of the Arctic cryosphere due to climate change will result in significant freshwater input into Arctic marine ecosystems. This might also cause the release of legacy mercury (Hg) stored in the cryosphere, increasing Hg concentration and its subsequent effects on the marine biota. However, there is scarce knowledge on the concentration of Hg in the lower trophic level organisms at the base of the Arctic pelagic food web. This is particularly important since these organisms modulate the transfer of Hg to higher trophic levels, including fish and marine mammals. We quantified the total Hg (THg) concentration in two plankton size classes (>200 and 50-200 μm) in coastal waters along the east Greenland coast and investigated the potential assimilation efficiency of both inorganic Hg (IHg) and methyl Hg (MeHg) in mesozooplankton and their faecal pellets in experimental incubations. The concentration of THg in plankton ranged from 12 to 109 ng (g dw)-1 without clear trends between geographic locations or between fjords and coastal areas. Also, the concentrations did not vary between the different plankton size fractions. MeHg concentrations were lower in the mesozooplankton faecal pellets than IHg, which may be due to the higher assimilation of MeHg than IHg in mesozooplankton tissue. Our results confirm that Arctic zooplankton assimilates MeHg more efficiently than IHg and may contribute significantly to the partitioning and cycling of different Hg types in Arctic marine ecosystems.

Mercury contamination and potential health risk to French seabirds: A multi-species and multi-site study

Mercury (Hg) is a naturally occurring highly toxic element which circulation in ecosystems has been intensified by human activities. Hg is widely distributed, and marine environments act as its main final sink. Seabirds are relevant bioindicators of marine pollution and chicks are particularly suitable for biomonitoring pollutants as they reflect contamination at short spatiotemporal scales. This study aims to quantify blood Hg contamination and identify its drivers (trophic ecology inferred from stable isotopes of carbon (δ13C) and nitrogen (δ15N), geographical location, chick age and species) in chicks of eight seabird species from 32 French sites representing four marine subregions: the English Channel and the North Sea, the Celtic Sea, the Bay of Biscay and the Western Mediterranean. Hg concentrations in blood ranged from 0.04 μg g-1 dry weight (dw) in herring gulls to 6.15 μg g-1 dw in great black-backed gulls. Trophic position (δ15N values) was the main driver of interspecific differences, with species at higher trophic positions showing higher Hg concentrations. Feeding habitat (δ13C values) also contributed to variation in Hg contamination, with higher concentrations in generalist species relying on pelagic habitats. Conversely, colony location was a weak contributor, suggesting a relatively uniform Hg contamination along the French coastline. Most seabirds exhibited low Hg concentrations, with 74% of individuals categorized as no risk, and < 0.5% at moderate risk, according to toxicity thresholds. However, recent work has shown physiological and fitness impairments in seabirds bearing Hg burdens considered to be safe, calling for precautional use of toxicity thresholds, and for studies that evaluate the impact of Hg on chick development.

Exploring Drivers of Historic Mercury Trends in Beluga Whales Using an Ecosystem Modeling Approach

While mercury occurs naturally in the environment, human activity has significantly disturbed its biogeochemical cycle. Inorganic mercury entering aquatic systems can be transformed into methylmercury, a strong neurotoxicant that builds up in organisms and affects ecosystem and public health. In the Arctic, top predators such as beluga whales, an ecologically and culturally significant species for many Inuit communities, can contain high concentrations of methylmercury. Historical mercury concentrations in beluga in the western Canadian Arctic's Beaufort Sea cannot be explained by mercury emission trends alone; in addition, they could potentially be driven by climate change impacts, such as rising temperatures and sea ice melt. These changes can affect mercury bioaccumulation through different pathways, including ecological and mercury transport processes. In this study, we explore key drivers of mercury bioaccumulation in the Beaufort Sea beluga population using Ecopath with Ecosim, an ecosystem modeling approach, and scenarios of environmental change informed by Western Science and Inuvialuit Knowledge. Comparing the effect of historical sea ice cover, sea surface temperature, and freshwater discharge time series, modeling suggests that the timing of historical increases and decreases in beluga methylmercury concentrations can be better explained by the resulting changes to ecosystem productivity rather than by those to mercury inputs and that all three environmental drivers could partially explain the decrease in mercury concentrations in beluga after the mid-1990s. This work highlights the value of multiple knowledge systems and exploratory modeling methods in understanding environmental change and contaminant cycling. Future work building on this research could inform climate change adaptation efforts and inform management decisions in the region.

Toxicity of methylmercury in aquatic organisms and interaction with environmental factors and coexisting pollutants: A review

Mercury is a hazardous heavy metal that is distributed worldwide in aquatic ecosystems. Methylmercury (MeHg) poses significant toxicity risks to aquatic organisms, primarily through bioaccumulation and biomagnification, due to its strong affinity for protein thiol groups, which results in negative effects even at low concentrations. MeHg exposure can cause various physiological changes, oxidative stress, neurotoxicity, metabolic disorders, genetic damage, and immunotoxicity. To assess the risks of MeHg contamination in actual aquatic ecosystems, it is important to understand how MeHg interacts with environmental factors such as temperature, pH, dissolved organic matter, salinity, and other pollutants such as microplastics and organic compounds. Complex environmental conditions can cause potential toxicity, such as synergistic, antagonistic, and unchanged effects, of MeHg in aquatic organisms. This review focuses on demonstrating the toxic effects of single MeHg exposure and the interactive relationships between MeHg and surrounding environmental factors or pollutants on aquatic organisms. Our review also recommends further research on biological and molecular responses in aquatic organisms to better understand the potential toxicity of combinational exposure.

Upwelling Enhances Mercury Particle Scavenging in the California Current System

Coastal upwelling supplies nutrients supporting primary production while also adding the toxic trace metal mercury (Hg) to the mixed layer of the ocean. This could be a concern for human and environmental health if it results in the enhanced bioaccumulation of monomethylmercury (MMHg). Here, we explore how upwelling influences Hg cycling in the California Current System (CCS) biome through particle scavenging and sea-air exchange. We collected suspended and sinking particle samples from a coastal upwelled water parcel and an offshore non-upwelled water parcel and observed higher total particulate Hg and sinking flux in the upwelling region compared to open ocean. To further investigate the full dynamics of Hg cycling, we modeled Hg inventories and fluxes in the upper ocean under upwelling and non-upwelling scenarios. The model simulations confirmed and quantified that upwelling enhances sinking fluxes of Hg by 41% through elevated primary production. Such an enhanced sinking flux of Hg is biogeochemically important to understand in upwelling regions, as it increases the delivery of Hg to the deep ocean where net conversion to MMHg may take place.

Near surface oxidation of elemental mercury leads to mercury exposure in the Arctic Ocean biota

Atmospheric mercury (Hg(0), Hg(II)) and riverine exported Hg (Hg(II)) are proposed as important Hg sources to the Arctic Ocean. As plankton cannot passively uptake Hg(0), gaseous Hg(0) has to be oxidized to be bioavailable. Here, we measured Hg isotope ratios in zooplankton, Arctic cod, total gaseous Hg, sediment, seawater, and snowpack from the Bering Strait, the Chukchi Sea, and the Beaufort Sea. The Δ200Hg, used to differentiate between Hg(0) and Hg(II), shows, on average, 70% of Hg(0) in all biota and differs with seawater Δ200Hg (Hg(II)). Since Δ200Hg anomalies occur via tropospheric Hg(0) oxidation, we propose that near-surface Hg(0) oxidation via terrestrial vegetation, coastally evaded halogens, and sea salt aerosols, which preserve Δ200Hg of Hg(0) upon oxidation, supply bioavailable Hg(II) pools in seawater. Our study highlights sources and pathways in which Hg(0) poses potential ecological risks to the Arctic Ocean biota.

Can Mercury Influence Carbon Dioxide Levels? Implications for the Implementation of the Minamata Convention on Mercury

The Paris Agreement and the Minamata Convention on Mercury are two of the most important environmental conventions being implemented concurrently, with a focus on reducing carbon and mercury emissions, respectively. The relation between mercury and carbon influences the interactions and outcomes of these two conventions. This perspective investigates the link between mercury and CO2, assessing the consequences and exploring the policy implications of this link. We present scientific evidence showing that mercury and CO2 levels are negatively correlated under natural conditions. As a result of this negative correlation, the CO2 level under the current mercury reduction scenario is predicted to be 2.4-10.1 ppm higher than the no action scenario by 2050, equivalent to 1.0-4.8 years of CO2 increase due to human activity. The underlying causations of this negative correlation are complex and need further research. Economic analysis indicates that there is a trade-off between the benefits and costs of mercury reduction actions. As reducing mercury emission may inadvertently undermine efforts to achieve climate goals, we advocate for devising a coordinated implementation strategy for carbon and mercury conventions to maximize synergies and reduce trade-offs.

Climate change dynamics and mercury temporal trends in Northeast Arctic cod (Gadus morhua) from the Barents Sea ecosystem

The Northeast Arctic cod (Gadus morhua) is the world's northernmost stock of Atlantic cod and is of considerable ecological and economic importance. Northeast Arctic cod are widely distributed in the Barents Sea, an environment that supports a high degree of ecosystem resiliency and food web complexity. Here using 121 years of ocean temperature data (1900-2020), 41 years of sea ice extent information (1979-2020) and 27 years of total mercury (Hg) fillet concentration data (1994-2021, n = 1999, ≥71% Methyl Hg, n = 20) from the Barents Sea ecosystem, we evaluate the effects of climate change dynamics on Hg temporal trends in Northeast Arctic cod. We observed low and consistently stable, Hg concentrations (yearly, least-square means range = 0.022-0.037 mg/kg wet wt.) in length-normalized fish, with a slight decline in the most recent sampling periods despite a significant increase in Barents Sea temperature, and a sharp decline in regional sea ice extent. Overall, our data suggest that recent Arctic amplification of ocean temperature, "Atlantification," and other perturbations of the Barents Sea ecosystem, along with rapidly declining sea ice extent over the last ∼30 years did not translate into major increases or decreases in Hg bioaccumulation in Northeast Arctic cod. Our findings are consistent with similar long-term, temporal assessments of Atlantic cod inhabiting Oslofjord, Norway, and with recent investigations and empirical data for other marine apex predators. This demonstrates that Hg bioaccumulation is highly context specific, and some species may not be as sensitive to current climate change-contaminant interactions as currently thought. Fish Hg bioaccumulation-climate change relationships are highly complex and not uniform, and our data suggest that Hg temporal trends in marine apex predators can vary considerably within and among species, and geographically. Hg bioaccumulation regimes in biota are highly nuanced and likely driven by a suite of other factors such as local diets, sources of Hg, bioenergetics, toxicokinetic processing, and growth and metabolic rates of individuals and taxa, and inputs from anthropogenic activities at varying spatiotemporal scales. Collectively, these findings have important policy implications for global food security, the Minamata Convention on Mercury, and several relevant UN Sustainable Development Goals.

Global change effects on biogeochemical mercury cycling

Past and present anthropogenic mercury (Hg) release to ecosystems causes neurotoxicity and cardiovascular disease in humans with an estimated economic cost of $117 billion USD annually. Humans are primarily exposed to Hg via the consumption of contaminated freshwater and marine fish. The UNEP Minamata Convention on Hg aims to curb Hg release to the environment and is accompanied by global Hg monitoring efforts to track its success. The biogeochemical Hg cycle is a complex cascade of release, dispersal, transformation and bio-uptake processes that link Hg sources to Hg exposure. Global change interacts with the Hg cycle by impacting the physical, biogeochemical and ecological factors that control these processes. In this review we examine how global change such as biome shifts, deforestation, permafrost thaw or ocean stratification will alter Hg cycling and exposure. Based on past declines in Hg release and environmental levels, we expect that future policy impacts should be distinguishable from global change effects at the regional and global scales.

Special issue on the AMAP 2021 assessment of mercury in the Arctic

This Editorial presents an overview of the Special Issue on advances in Arctic mercury (Hg) science synthesized from the 2021 assessment of the Arctic Monitoring and Assessment Programme (AMAP). Mercury continues to travel to Arctic environments and threaten wildlife and human health in this circumpolar region. Over the last decade, progress has been achieved in addressing policy-relevant uncertainties in environmental Hg contamination. This includes temporal trends of Hg, its transport to and within the Arctic, methylmercury cycling, climate change influences, biological effects of Hg on fish and wildlife, human exposure to Hg, and forecasting of Arctic responses to different future scenarios of anthropogenic Hg emissions. In addition, important contributions of Indigenous Peoples to Arctic research and monitoring of Hg are highlighted, including through projects of knowledge co-production. Finally, policy-relevant recommendations are summarized for future study of Arctic mercury. This series of scientific articles presents comprehensive information relevant to supporting effectiveness evaluation of the United Nations Minamata Convention on Mercury.

Arctic atmospheric mercury: Sources and changes

Global anthropogenic and legacy mercury (Hg) emissions are the main sources of Arctic Hg contamination, primarily transported there via the atmosphere. This review summarizes the state of knowledge of the global anthropogenic sources of Hg emissions, and examines recent changes and source attribution of Hg transport and deposition to the Arctic using models. Estimated global anthropogenic Hg emissions to the atmosphere for 2015 were ~2220 Mg, ~20% higher than 2010. Global anthropogenic, legacy and geogenic Hg emissions were, respectively, responsible for 32%, 64% (wildfires: 6-10%) and 4% of the annual Arctic Hg deposition. Relative contributions to Arctic deposition of anthropogenic origin was dominated by sources in East Asia (32%), Commonwealth of Independent States (12%), and Africa (12%). Model results exhibit significant spatiotemporal variations in Arctic anthropogenic Hg deposition fluxes, driven by regional differences in Hg air transport routes, surface and precipitation uptake rates, and inter-seasonal differences in atmospheric circulation and deposition pathways. Model simulations reveal that changes in meteorology are having a profound impact on contemporary atmospheric Hg in the Arctic. Reversal of North Atlantic Oscillation phase from strongly negative in 2010 to positive in 2015, associated with lower temperature and more sea ice in the Canadian Arctic, Greenland and surrounding ocean, resulted in enhanced production of bromine species and Hg(0) oxidation and lower evasion of Hg(0) from ocean waters in 2015. This led to increased Hg(II) (and its deposition) and reduced Hg(0) air concentrations in these regions in line with High Arctic observations. However, combined changes in meteorology and anthropogenic emissions led to overall elevated modeled Arctic air Hg(0) levels in 2015 compared to 2010 contrary to observed declines at most monitoring sites, likely due to uncertainties in anthropogenic emission speciation, wildfire emissions and model representations of air-surface Hg fluxes.

The impact of mercury contamination on human health in the Arctic: A state of the science review

The 2021 Arctic Monitoring and Assessment Programme (AMAP) Mercury (Hg) Assessment is motivated by Arctic populations, and most notably Indigenous Peoples in the region, who are particularly vulnerable to Hg pollution. The objective of this review paper is to answer the following AMAP policy-relevant question: what is the human health impact of Hg pollution in the Arctic? In doing so, this state of the science review paper builds on information published 10 years ago in the last AMAP Hg assessment. The synthesized results demonstrate that: a) global influences (e.g., sources and transport pathways, biogeochemical processes, climate change, globalization) drive Hg exposures into human communities; b) Hg exposures are realized through dietary intake of certain country food items, and that new exposure science approaches are helping to deepen understandings; c) the nutritional and cultural benefits of country foods are immense, though a dietary transition is underway raising concerns over metabolic syndrome and broader issues of food security as well as cultural and social well-being; d) blood Hg measures are among the highest worldwide based on the results of human biomonitoring studies; e) Hg exposures are associated with adverse health outcomes across life stages (e.g., neurodevelopmental outcomes in young children to cardiovascular disease in adults); and f) risk communication needs to be balanced, targeted and clear, culturally appropriate, and be done collaboratively. These synthesized findings are particularly timely and policy-relevant given that the Minamata Convention entered into legal force worldwide in 2017 as a regulatory scheme to reduce the use and environmental release of Hg in order to protect human health and the environment. The Convention was influenced by health concerns raised by northern populations as indicated in the preamble text which makes reference to "the particular vulnerabilities of Arctic ecosystems and Indigenous communities".