Arctic atmospheric mercury: Sources and changes

Mercury, methylmercury, and its fractions at the base of the trophic pyramid of the maritime Antarctic ecosystem of Admiralty Bay

Mercury (Hg) pollution in polar regions is a critical environmental concern, exacerbated by glacier melting due to climate change. This study investigated the impact of glacial meltwater on total mercury (THg), methylmercury (MeHg), and various Hg fractions levels in seawater, suspended particulate matter, and microplankton in Admiralty Bay, Antarctica. Stable isotope analyses of carbon and nitrogen complement Hg measurements, providing insights into food web dynamics and pollutant transfer. The average THg concentration in water samples from creeks, which may represent runoff from melting glaciers and snow, was 2.5 times higher than in sea water from Admiralty Bay. The proportion of methylmercury in total mercury varied depending on the environmental component: in water, it was 1.1 %; in SPM, 0.7 %; and in microplankton, 2.4 %. Increased microplankton biomass, which provides a larger surface area, enhanced the proportion of adsorbed HgF1, in microplankton, indicating that mercury adsorbs onto available planktonic surfaces. This research enhances our understanding of Hg cycling in Antarctic ecosystems and underscores the implications of climate change for Hg contamination, with potential effects on marine food webs and human health.

Elevated mercury wet deposition in the biodiversity hotspot of southwestern China

The West China Rain Zone (WCRZ), one of worldwide biodiversity hotspots, is vulnerable to pollutant exposure. Mercury (Hg), as a global toxic pollutant, could enter into this ecosystem by wet and dry deposition, potentially posing ecological risks. Therefore, it is essential to investigate the patterns, controlling factors, and source contributions of Hg deposition in this region. This study presents a three-year comprehensive analysis of atmospheric Hg wet deposition at Mt. Emei of this biodiversity hotspot region. Results revealed the elevated Hg concentrations with volume-weighted mean concentration (VWMC) of 15.6 ± 9.8 ng L-1 and deposition fluxes of 47.8 ± 4.3 μg m-2 in the WCRZ. The wet deposition flux was twice the magnitude of dry deposition flux in this region. This value exceeded the deposition levels observed in many other regions globally, with WCRZ deposition levels being 1.1-15.6 times that of other biodiversity hotspots worldwide. Source apportionment analysis revealed that Hg in wet deposition predominantly originated from local anthropogenic sources. The transboundary Hg of anthropogenic sources in South Asia contributed to ∼20% of Hg source contribution during winter periods. Finally, we suggest the elevated Hg wet deposition inducing a potentially ecological risk to wildlife in this biodiversity hotspot regions of Southwest China.

Mercury poisoning in women and infants inhabiting the Gangetic plains of Bihar: risk assessment

Mercury is a persistent, bio-accumulative, and hazardous contaminant. When released into the environment, it accumulates in water sediments, converting it to poisonous methylmercury that enters the food chain. The present study was carried out in habitations from the 11 districts of Bihar (India). In the study, n = 224 lactating women and their infants n = 172 infants participated. After obtaining the written informed consent, their breast milk, urine, and blood were collected for mercury estimation. The breastmilk content was measured in n = 181 subjects, in which 74% women had their breastmilk higher than the WHO permissible limit (< 1.7 μg/L), while 26% of the women had their breast milk below the permissible limit. The blood mercury content showed that 19% subjects had mercury content above the permissible limit [20 μg/L]. In urine mercury estimation, 49% women had mercury content above the permissible limit [10 μg/L], while, 51% women had the mercury content below the permissible limit. In the child's urine, 54% infants had their mercury content in urine above the permissible limit [10 μg/L] while 46% infants had content below the permissible limit. The study indicates that 20% of infants had the complete accumulation of mercury in their body which is highly toxic for them. However, the mercury content in the food (wheat) had the contamination with in the permissible limit [100 μg/kg]. There was a significant correlation found between the breastmilk and child's urine and mother's urine. The HQ study also correlates the mercury poisoning effect with 100% of the mother's and 66% of the infants exceeding the limit of non-carcinogenic risk. The Monte Carlo and multivariate study correlates the high health risk in the studied population due to mercury poisoning. The entire study concludes that population inhabitation in the Gangetic plains of Bihar are exposed to mercury poisoning which may be due to geogenic or anthropogenic sources. But, the levels of mercury contamination above the permissible limit could lead to neurogenerative changes in the lactating mothers and their infants. To control the present problem medical intervention is immediately required.

Photoreduction of mercuric bromides in polar ice

In the polar regions, which are vulnerable receptors of mercury pollution, atmospheric mercury depletion events (AMDEs) efficiently convert elemental mercury (Hg(0)) into oxidized mercury (Hg(II)) via bromine oxidation. Hg(II) subsequently deposits onto snow and sea ice. While field observations have shown that a large percentage of deposited mercury is re-emitted from the ice to the atmosphere by a photoinduced process, the fundamental photochemistry that drives the re-emission process remains unknown. Here, using multiconfigurational quantum chemistry, we find that the photoreduction of HgBr2, HgBr3-, and HgBr42- in ice is more efficient than in the gas phase. This results from the influence of water molecules on the molecular geometry and electronic structure of mercuric bromides in ice, which enhances the absorption intensities at wavelengths relevant in the troposphere (λ > 290 nm), as compared to gas phase. Kinetic modeling shows that ~30 to 60% of deposited mercury in AMDEs can be reemitted due to the photoreduction of mercuric bromides in ice, in agreement with field observations. Our results reveal a photoreduction mechanism of sunlight-induced excited state chemistry of mercuric bromides on ice. These findings strongly suggest that this chemistry should be incorporated into atmospheric models to account for ice-atmosphere mercury cycling in the polar environments, currently not considered.

Assessing mercury exposure to water and fish of the Mackenzie watershed using a Bayesian network analysis

Bayesian Network Relative Risk Models (BN-RRM) were developed to assess recent (2005-2020) risk of mercury (Hg) exposure to the freshwater ecosystems of Great Slave Lake (GSL) and the Mackenzie River Basin (MRB) in the Canadian Northwest Territories. Risk is defined as the probability of a specified adverse outcome; here the adverse outcome was the probability of environmental Hg concentrations exceeding the Hg regulatory guidelines (thresholds values) established to protect the health of humans and aquatic biota. Environmental models and Hg monitoring studies were organized into a probabilistic (Bayesian network) model which considered six Hg input pathways, including atmospheric Hg deposition, Hg release from permafrost thaw, terrestrial to aquatic Hg transfer via soil erosion, and the proximity to mining, fossil fuel developments, and retrogressive permafrost thaw slumps (RPTS). Sensitivity analysis was used to assess spatial trends in influence of the sources to Hg concentrations in freshwater and in the tissue of five keystone fish species (lake whitefish, lake trout, northern pike, walleye, and burbot) which are essential for the health and food security of the people in the MRB. The risk to the health of keystone fish species, defined by toxicological dose-response curves, was generally low but greatest in GSL where fish size, mine proximity, and soil erosion were identified to be important explanatory variables. These BN-RRMs provide a probabilistic framework to integrate advances in Hg cycling modeling, identify gaps in Hg monitoring efforts, and calculate risk to environmental endpoints under alternative scenarios of mitigation measures. For example, the models predicted that the successful implementation of the Minamata Treaty, corresponding to 35%-60% reduction in atmospheric Hg deposition, would translate to a ∼1.2-fold reduction in fish Hg concentrations. In this way, these models can form the basis for a decision-support tool for comparing and ranking risk-reduction initiatives.

Mercury-Mediated Cardiovascular Toxicity: Mechanisms and Remedies

Mercury is a significant environmental pollutant and public health threat, primarily recognized for its neurotoxic effects. Increasing evidence also highlights its harmful impact on the cardiovascular system, particularly in adults. Exposure to mercury through contaminated soil, air, or water initiates a cascade of pathological events that lead to organ damage, including platelet activation, oxidative stress, enhanced inflammation, and direct injury to critical cells such as cardiomyocytes and endothelial cells. Endothelial activation triggers the upregulation of adhesion molecules, promoting the recruitment of leukocytes and platelets to vascular sites. These interactions activate both platelets and immune cells, creating a pro-inflammatory, prothrombotic environment. A key outcome is the formation of platelet-leukocyte aggregates (PLAs), which exacerbate thromboinflammation and endothelial dysfunction. These processes significantly elevate cardiovascular risks, including thrombosis and vascular inflammation. This study offers a comprehensive analysis of the mechanisms underlying mercury-induced cardiotoxicity, focusing on oxidative stress, inflammation, and cellular dysfunction.

Total gaseous mercury in Kathmandu, a South Asian metropolis: Temporal variations, sources apportionment and health risk assessment

South Asia is a global hotspot of air pollution gaining attention due to its severe implications, in which atmospheric mercury (Hg) could cause detrimental health effects in metropolitan areas. In this study, first-time year-round (January - December 2019) mean total gaseous mercury (TGM) concentration at Kathmandu, Nepal - a sub-tropical city in South Asia was reported at 9.9 ± 10.0 ng m-3. Seasonal TGM variation at Kathmandu showed highest concentration in winter (16.8 ± 16.9 ng m-3) and lowest in summer (2.9 ± 2.1 ng m-3). Generally higher daytime TGM concentration as opposed to night-time TGM indicated Hg build-up within atmospheric boundary layer due to low wind speed and high humidity. Events with high wind speed (> 30 m s-1) induced regional pollutant transport from nearby brick kilns and cement factories. Principal component analysis associated a major part of TGM with PM2.5 and CO and indicated the remarkable influence of fuel combustion and vehicular emissions. Backward trajectory and potential source contribution factor analysis further indicate the impact of regional Hg emissions and transboundary emissions from India towards Nepal, which expands beyond the Himalayas and the Tibetan Plateau. Prominent low-grade coal burning and kilning activities in winter spiked up TGM concentrations, resulting in the highest health quotient (HQ = 0.24) value, which could significantly impact public health. Our study presented the most comprehensive set of continuous annual atmospheric Hg monitoring data from Nepal in the South Asian region. The results serve as a baseline for regional atmospheric Hg levels and offer a critical reference for assessing and addressing air pollution concerns in Nepal as well as throughout South Asia.

Evaluating sources of mercury in Canada's Mackenzie River

Arctic rivers may be the largest net sources of mercury (Hg) to the Arctic Ocean, yet riverine sources of Hg remain poorly characterized compared to atmospheric processes. This article reviews the current state of knowledge on Hg inputs to the Mackenzie River and Valley in Northern Canada from six point and non-point sources. Point sources include the locations of mines, fossil fuel extraction facilities, and retrogressive permafrost thaw slumps. Non-point sources are assessed through models of Hg release from anthropogenic and wildfire-derived atmospheric Hg deposition (GEM-MACH-Hg), permafrost thaw (SiBCASA), and rainfall-induced soil erosion (RUSLE). Ongoing anthropogenic activity is likely a minor contributor to Hg levels in the Mackenzie Valley as production from the fossil fuel and mining industries have steadily declined over the past two decades. Conversely, Hg inputs from atmospheric deposition, permafrost thaw, and permafrost thaw slumps have increased due to climate change and the re-emission of legacy Hg. The widespread influence of atmospheric Hg deposition makes it the dominant source of Hg to both aquatic and terrestrial systems in the Mackenzie Valley, although soil erosion inputs, while higher, are restricted to regions of steep terrain. Climate-driven increases in terrestrial Hg release, particularly from permafrost degradation and erosion, are emerging as key localized drivers of Hg inputs in the Mackenzie Valley.

Declines in anthropogenic mercury emissions in the Global North and China offset by the Global South

Human activities have emitted substantial mercury into the atmosphere, significantly impacting ecosystems and human health worldwide. Currently, consistent methodologies to evaluate long-term mercury emissions across countries and industries are scant, hindering efforts to prioritize emission controls. Here, we develop a high-spatiotemporal-resolution dataset to comprehensively analyze global anthropogenic mercury emission patterns. We show that global emissions increased 330% during 1960-2021, with declines in developed Global North countries since the 1990s and China since the 2010s completely offset by rapid growth in Global South countries (excluding China). Consequently, global emissions have continued to rise slightly since the 2013 Minamata Convention. In 2021, Global South countries produced two-thirds of global emissions, despite comprising only one-fifth of the global economy. We predict that, although large uncertainties exist, continued emission growth in Global South countries under a business-as-usual scenario could increase 10%-50% global mercury emissions by 2030. Our findings demonstrate that global control of anthropogenic mercury emissions has reached a critical juncture, highlighting the urgent need to target reductions in Global South countries to prevent worsening health and environmental impacts.

Enhanced mercury deposition in Arctic Alaskan lake sediments coincides with early Holocene hydroclimate shift

Substantial amounts of mercury (Hg) are projected to be released into Arctic watersheds as permafrost thaws amid warmer and wetter conditions. This may have far-reaching consequences because the highly toxic methylated form of Hg biomagnifies rapidly in ecosystems. However, understanding how climate change affects Hg dynamics in permafrost regions is limited due to the lack of long-term Arctic Hg records. Using a 27-ka Hg sediment record from Burial Lake, northwestern Alaska, we examine how well-characterized temperature, precipitation, and vegetation shifts affected Hg mobilization in a catchment underlain by permafrost. During the Last Glacial Maximum (29.6-19.6 ka), Hg concentrations (63 ± 5 μg/kg) and Hg flux (8.6 ± 2.2 μg m-2 yr-1) remain relatively stable. Abrupt warming trends, starting at 17.6 ka, do not coincide with Hg levels. After 15 ka, the ecosystem transitions to shrub tundra, Hg concentrations (101.2 μg/kg) peak at 14.2 ka, while flux (5.3 ± 1.3 μg m-2 yr-1) declines and stabilizes. At ~11 ka, increased precipitation coincides with a 72 % rise in Hg concentrations and a 32 % increase in Hg flux compared to average Hg levels since 15 ka. These results suggest that summer rainfall was the primary driver of Hg mobilization from the catchment, while the vegetation shift influenced lake sediment Hg concentrations. At 1990 CE, peak Hg levels represent an 88 % increase in Hg concentrations (196.3 μg/kg) and a sixfold rise in Hg flux (38.1 μg m-2 yr-1) above background levels, underscoring the need for further research to understand Hg dynamics driven by anthropogenic Hg emissions and climate change.

Oceanic evasion fuels Arctic summertime rebound of atmospheric mercury and drives transport to Arctic terrestrial ecosystems

Mercury (Hg) contamination poses a persistent threat to the remote Arctic ecosystem, yet the mechanisms driving the pronounced summer rebound of atmospheric gaseous elemental Hg (Hg0) and its subsequent fate remain unclear due to limitations in large-scale seasonal studies. Here, we use an integrated atmosphere-land-sea-ice-ocean model to simulate Hg cycling in the Arctic comprehensively. Our results indicate that oceanic evasion is the dominant source (~80%) of the summer Hg0 rebound, particularly driven by seawater Hg0 release facilitated by seasonal ice melt (~42%), with further contributions from anthropogenic deposition and terrestrial re-emissions. Enhanced Hg0 dry deposition across the Arctic coastal regions, especially in the Arctic tundra, during the summer rebound highlights the potential transport of Hg from the pristine Arctic Ocean to Arctic terrestrial ecosystems. Arctic warming, with a transition from multi-year to first-year ice and tundra greening, is expected to amplify oceanic Hg evasion and intensify Hg0 uptake by the Arctic tundra due to increased vegetation growth, underlining the urgent need for continued research to evaluate Hg mitigation strategies effectively in the context of a changing Arctic.

Trace elements in Alaska's ice seals in the 2000s and 2010s

Ringed (Pusa hispida), bearded (Erignathus barbatus), spotted (Phoca largha), and ribbon (Histriophoca fasciata) seals are ice-associated seals that are important subsistence resources for coastal Alaska Native people. These seals are also mid- to upper trophic level Arctic predators and primary prey of polar bears (Ursus maritimus). We analyzed concentrations of 19 trace elements in seal liver, kidney, muscle, and blubber, including arsenic, cadmium, lead, mercury, and vanadium due to their potential toxicity. We also measured monomethyl mercury, the more biologically available and toxic form of mercury, in a subsample of seals. We tested for differences in elemental concentrations by seal sex, age, and two periods, 2003-2007 and 2011-2016, to detect environmental trends, assess seal health, and explore trace elements in seal tissues as indicators of seal diet. Trace element concentrations were within ranges that were similar or below that previously measured for these species throughout their range in the Arctic and subarctic. We found relationships between concentration and seal sex or age, as well as differences between periods, with a notable decline over time in magnesium for bearded seal liver and kidney, and ringed and spotted seal liver. Relative concentrations of methyl mercury and total mercury among the four seal species matched known patterns of piscivory and pelagic feeding. Cadmium concentrations were highest in bearded and ribbon seals, possibly due to greater benthic feeding and consumption of squid, respectively. Tissue trace element concentrations from sick seals collected during the 2011-2016 Northern Alaska Pinnipeds Unusual Mortality Event did not differ from those of healthy subsistence harvested seals. Our analysis of trace elements in four Alaskan ice seal species can inform toxicological risk assessments regarding non-essential elements of concern and assessments of nutritional benefits regarding essential elements for seals and for the people and polar bears that eat them.

Patterns and trends of atmospheric mercury in the GMOS network: Insights based on a decade of measurements

The Global Mercury Observation System (GMOS) network, initially a five-year project (2010-2015) funded by the European Commission, continued as a GEO Flagship program to support the Global Observation System for Mercury (GOS4M). GMOS was envisioned as a coordinated global observing system to monitor atmospheric mercury (Hg) on a global scale, to support and evaluate the effective implementation of the Minamata Convention on Mercury (MCM). Twenty-eight ground-based stations have participated in monitoring activities, following GMOS sampling protocols and related data quality control management. The GMOS network provides representative coverage of all latitudes, from the Northern Hemisphere to the Southern Hemisphere including the Arctic Circle, Antarctica, and the Tropical Zone. This work presents atmospheric Hg data, available as Total Gaseous Mercury (TGM) or Gaseous Elemental Mercury (GEM) concentrations, recorded within the GMOS network from 2011 to 2020. TGM/GEM concentrations were analysed in terms of their variability along latitudinal areas, considering their comparability, temporal trends and patterns. The main results confirmed a clear gradient of TGM/GEM concentrations between the northern (1.58 ± 0.31 ng/m3) and southern (0.97 ± 0.14 ng/m3) hemispheres. Decreasing trends in TGM/GEM levels were found to be strongly significant only for selected remote stations with at least 5 years of data coverage. Seasonality in atmospheric TGM/GEM concentrations was observed to increase with latitude and is greater at inland sites than at coastal sites.

Organic matter is a predominant control on total mercury concentration of near-surface lake sediments across a boreal to low Arctic tundra transect in northern Canada

Mercury (Hg) is a bioavailable and toxic element with concentrations that are persistently high or rising in some Arctic and subarctic lakes despite reduced atmospheric emissions in North America. This is due to rising Hg emissions to the atmosphere outside of North America, enhanced sequestration of Hg to sediments by climate-mediated increases in primary production, and ongoing release of Hg from terrestrial reservoirs. To evaluate the influence of organic matter and other parameters on Hg accumulation in northern lakes, near-surface sediments were sampled from 60 lakes across a boreal to shrub tundra gradient in the central Northwest Territories, Canada. The organic matter of the lake sediments, assessed using programmed pyrolysis and petrology, is composed of a mixture of terrestrial, aquatic, and inert organic matter. The proportion of algal-derived organic matter is higher in sediments of lakes below treeline relative to shrub tundra sites. Total sedimentary Hg concentration is correlated to all organic matter constituents but is unrelated to latitude or lake position below or above treeline. The concentrations of Ag, Ca, P, S, U, Ti, Y, Cd, and Zn are also strong predictors of total sedimentary Hg concentration, indicating input from a common geogenic source and/or common sequestration pathways associated with organic matter. Catchment area is a strong negative predictor of total sedimentary Hg concentration, particularly in lakes above treeline, possibly due to retention capacity of Hg and other elements in local sinks. This research highlights the complexity of controls on Hg sequestration in sediment and shows that while organic matter is a strong predictor of total sedimentary Hg concentration on a landscape scale and across extreme gradients in climate and associated vegetation and permafrost, other factors such as catchment area and sources from mineralized bedrock are also important.

Differences in mercury (THg) levels in Brown booby (Sula leucogaster) feathers from two environmentally distinct Brazilian archipelagos

Mercury pollution is a matter of global concern due to its detrimental effects on ecosystems and human well-being. Seabirds generally occupy high levels within trophic chains and are often used as valuable indicators of marine pollution, including mercury contamination. We examined the concentrations of total mercury (THg) in the ventral feathers of Brown boobies (Sula leucogaster) from two distinct Brazilian archipelagos: one coastal and subtropical (Moleques do Sul) and one tropical and oceanic (São Pedro and São Paulo). We hypothesized that there would be differentiation in mercury levels between these archipelagos due to differences in geographical location and environmental conditions, where higher Hg levels would be found in Brown boobies from the coastal one since they are more exposed to anthropogenic sources from the continent. Additionally, we also investigated whether there were any differences in mercury levels based on sex and age. We found significantly higher THg levels in Brown boobies from São Pedro and São Paulo compared to those from Moleques do Sul, indicating differential levels of exposure to mercury sources. No significant differences between sexes or age classes, although juvenile individuals showed the lowest values. We suggest that the THg higher levels found in individuals from São Pedro e São Paulo can be due to the geological peculiarities of this archipelago, formed by mantle peridotites considered mercury hotspots. Our findings emphasize the importance of considering spatial and environmental factors in mercury biomonitoring and highlight the potential use of seabird feathers as a proxy for mercury contamination in marine environments.

Harvester selection and observed mercury levels in Eastern Beaufort Sea and Western Hudson Bay beluga whales (Delphinapterus leucas)

Mercury in marine biota has been extensively studied across Inuit Nunaat because it bioaccumulates and biomagnifies in high trophic level species, such as the beluga whale (Delphinapterus leucas), or qilalugaq in Inuktut. Qilalugaait (pl) are a staple in many coastal Inuit communities, including Tuktoyaktuk, Northwest Territories and Arviat, Nunavut. We examine how total mercury (THg) concentrations in two beluga populations are influenced by biased sampling resulting from local harvester preferences. We examined historical THg in skin, muscle, and liver (1980's to 2022) together with local qualitative interviews from two beluga-harvesting communities. Age and length bins were used to compare similar sized and aged whales between locations, where males (350 - 400 cm, and 20-30 years) and females (330-400 cm, and 15-30 years) were segregated. The interviews revealed distinct preferences whereby harvesters in Tuktoyaktuk actively sought larger (length) male whales, whereas harvesters in Arviat, selected wide and even range across size and sex. These local preferences were also evident in the historical dataset, with the median age and lengths were 31 years and 389.0 cm in Tuktoyaktuk (n = 461) and 23 and 336.0 cm in Arviat (n = 146). For males, mean and median THg concentrations were higher in beluga harvested from Tuktoyaktuk than Arviat in all three tissues with age and lengths combined, yet in the selected age and length bins, there was no difference in mean and median THg in the muscle tissue, and in median liver THg. There were significant differences in mean and median skin THg and in mean liver THg concentrations between males. In female whales, THg concentrations did not differ between Tuktoyaktuk and Arviat (in ages and lengths combined and in selected age bins across all tissues), excluding median muscle THg concentration. This study indicated that differences in THg concentrations that were previously observed resulted from hunter preferences in these two communities.

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.

Quantifying soil accumulation of atmospheric mercury using fallout radionuclide chronometry

Soils are a principal global reservoir of mercury (Hg), a neurotoxic pollutant that is accumulating through anthropogenic emissions to the atmosphere and subsequent deposition to terrestrial ecosystems. The fate of Hg in global soils remains uncertain, however, particularly to what degree Hg is re-emitted back to the atmosphere as gaseous elemental mercury (GEM). Here we use fallout radionuclide (FRN) chronometry to directly measure Hg accumulation rates in soils. By comparing these rates with measured atmospheric fluxes in a mass balance approach, we show that representative Arctic, boreal, temperate, and tropical soils are quantitatively efficient at retaining anthropogenic Hg. Potential for significant GEM re-emission appears limited to a minority of coniferous soils, calling into question global models that assume strong re-emission of legacy Hg from soils. FRN chronometry poses a powerful tool to reconstruct terrestrial Hg accumulation across larger spatial scales than previously possible, while offering insights into the susceptibility of Hg mobilization from different soil environments.

Seabirds reveal mercury distribution across the North Atlantic

Mercury (Hg) is a heterogeneously distributed toxicant affecting wildlife and human health. Yet, the spatial distribution of Hg remains poorly documented, especially in food webs, even though this knowledge is essential to assess large-scale risk of toxicity for the biota and human populations. Here, we used seabirds to assess, at an unprecedented population and geographic magnitude and high resolution, the spatial distribution of Hg in North Atlantic marine food webs. To this end, we combined tracking data of 837 seabirds from seven different species and 27 breeding colonies located across the North Atlantic and Atlantic Arctic together with Hg analyses in feathers representing individual seabird contamination based on their winter distribution. Our results highlight an east-west gradient in Hg concentrations with hot spots around southern Greenland and the east coast of Canada and a cold spot in the Barents and Kara Seas. We hypothesize that those gradients are influenced by eastern (Norwegian Atlantic Current and West Spitsbergen Current) and western (East Greenland Current) oceanic currents and melting of the Greenland Ice Sheet. By tracking spatial Hg contamination in marine ecosystems and through the identification of areas at risk of Hg toxicity, this study provides essential knowledge for international decisions about where the regulation of pollutants should be prioritized.

Development of a green and low-cost method to determine mercury content in sediments affected by oil spill on the Brazilian coast

Tons of crude oil were found on the Brazilian coast in 2019, and studies assessing its chemical composition are still scarce. This study aimed to develop a new and simple technique of cold vapor generation using infrared irradiation coupled with atomic absorption spectrometry to determine mercury content in sediments contaminated by crude oil. Experimental conditions were evaluated, including formic acid concentration, reactor temperature, and carrier gas flow rate. The accuracy of the method was validated by comparison with mercury contents in a certified reference material (PACS-2). The detection limit was found to be 0.44 μg kg-1. The developed method was applied to determine the total mercury content in marine sediment samples collected from beaches in Ceará State. Mercury concentrations ranged from 0.41 to 0.95 mg kg-1. The proposed method is efficient, simple, low-cost, and adequate for its purpose.

Climate and industrial pollution determine the seasonal and spatial mercury variations in the China's Weihe River

Natural processes and human activities impact mercury (Hg) pollution in rivers. Investigating the individual contributions and interactions of factors affecting variations in Hg concentrations, particularly under climate change, is crucial for safeguarding watershed ecosystems and human health. We collected 381 water samples from China's Weihe River Basin (WRB) during dry and wet seasons to assess the total Hg (THg) concentration. Results revealed high Hg concentrations in the WRB (0.1-2200.9 ng/L, mean 126.2 ± 335.5 ng/L), with higher levels during the wet season (wet season: 249.1 ± 453.5 ng/L, dry season: 12.7 ± 14.0 ng/L), particularly in the mainstream and southern tributaries of the Weihe River. Industrial pollution (contributing 26.2 %) and precipitation (contributing 33.5 %) drove spatial heterogeneity in THg concentrations during the dry and wet seasons, respectively. Notably, combined explanatory power increased to 47.9 % when interaction was considered, highlighting the amplifying effect of climate change, particularly precipitation, on the impact of industrial pollution. The middle and downstream of the Weihe River, especially the Guanzhong urban agglomeration, were identified as high-risk regions for Hg pollution. With ongoing climate change the risk of Hg exposure in the WRB is expected to escalate. This study lays a robust scientific foundation for the effective management of Hg pollution in analogous river systems worldwide.

Insights into the reduction of methylmercury accumulation in rice grains through biochar application: Hg transformation, isotope fractionation, and transcriptomic analysis

Methylmercury (MeHg), a potent neurotoxin, easily moves from the soil into rice plants and subsequently accumulates within the grains. Although biochar can reduce MeHg accumulation in rice grains, the precise mechanism underlying biochar-mediated responses to mercury (Hg) stress, specifically regarding MeHg accumulation in rice, remains poorly understood. In the current study, we employed a 4% biochar amendment to remediate Hg-contaminated paddy soil, elucidate the impacts of biochar on MeHg accumulation through a comprehensive analysis involving Hg isotopic fractionation and transcriptomic analyses. The results demonstrated that biochar effectively lowered the levels of MeHg in paddy soils by decreasing bioavailable Hg and microbial Hg methylation. Furthermore, biochar reduced the uptake and translocation of MeHg in rice plants, ultimately leading to a reduction MeHg accumulation in rice grains. During the process of total mercury (THg) uptake, biochar induced a more pronounced negative isotope fractionation magnitude, whereas the effect was less pronounced during the upward transport of THg. Conversely, biochar caused a more pronounced positive isotope fractionation magnitude during the upward transport of MeHg. Transcriptomics analyses revealed that biochar altered the expression levels of genes associated with the metabolism of cysteine, glutathione, and metallothionein, cell wall biogenesis, and transport, which possibly enhance the sequestration of MeHg in rice roots. These findings provide novel insights into the effects of biochar application on Hg transformation and transport, highlighting its role in mitigating MeHg accumulation in rice.

Tracing the footprints of Arctic pollution: Spatial variations in toxic and essential elements in Svalbard reindeer (Rangifer tarandus platyrhynchus) faeces

The Arctic is an accumulation zone of long-range transported pollution. In addition, local anthropogenic activities further contribute to regional pollution levels. The Svalbard reindeer (Rangifer tarandus platyrhynchus) is a suitable organism for studying and monitoring exposure to anthropogenic pollutants at the base of the terrestrial Arctic food web, and reindeer faeces have been promoted as non-invasive means of biomonitoring contaminant exposure. This study used HR-ICP-MS to analyse levels and composition of 16 elements in Svalbard reindeer faeces (n = 96) and soil (n = 9) from two locations on Svalbard, with the aim to assess whether local anthropogenic pollution influences element bioavailability. One of the sampling areas, the Nordenskiöld coast, is situated on the west coast of Spitsbergen, close to the Arctic Ocean and relatively far from local anthropogenic sources. The other sampling area, Adventdalen, is located further inland and close to Longyearbyen, the largest settlement of the archipelago. There was a significant difference in faecal elemental concentration and composition between the Adventdalen and Nordenskiöld coast reindeer populations. Elements of geogenic origin (e.g., Al, Cu and Fe) were found at higher levels in faeces from Adventdalen. In comparison, levels of Ca, Se and the toxic elements Cd and Pb were higher in faecal samples from the Nordenskiöld coast. The significantly higher levels of faecal Cd and Pb at Nordenskiöld coast may be due to marine input, dietary differences between the populations, or possible anthropogenic influence from the nearby settlement of Barentsburg. There was, however, a decoupling in elemental composition between faecal and soil samples, which may derive from a selective vegetational uptake of elements from the soil. The results suggest that reindeer are exposed to a range of elements and that faeces can be used to monitor the exposure to bioavailable environmental levels of both essential and toxic elements in terrestrial ecosystems.

Mercury at the top of the world: A 31-year record of mercury in Arctic char in the largest High Arctic lake, linked to atmospheric mercury concentrations and climate oscillations

Lake Hazen, the largest lake north of the Arctic circle, is being impacted by mercury (Hg) pollution and climate change. The lake is inhabited by two morphotypes of land-locked Arctic char (Salvelinus alpinus), a sensitive indicator species for pollution and climatic impacts. The objectives of this study were to describe the trends in Hg concentration over time and to determine the relationship of climate to length-at-age and Hg concentrations in each char morphotype, as well as the relationship to atmospheric Hg measurements at a nearby monitoring station. Results for Hg in char muscle were available from 20 sampling years over the period 1990 to 2021. We found significant declines in Hg concentrations for both morphotypes during the 31-year study period. Increased rain and earlier freeze-up of lake ice during the summer growing season was linked to increased length-at-age in both char morphotypes. For the large morphotype, higher total gaseous Hg in the fall and winter seasons was related to higher concentrations of Hg in char, while increased glacial runoff was related to decreases in char Hg. For the small morphotype char, increased snow and snow accumulation in the fall season were linked to declines in char Hg concentration. The Atlantic Multidecadal Oscillation and Arctic Oscillation were positively related to the large char Hg trend and Arctic Oscillation was positively related to the small char Hg trend. Significant trend relationships between atmospheric Hg and Hg in biota in remote regions are rare and uniquely valuable for evaluation of the effectiveness of the Minamata Convention and related monitoring efforts.

Isotopic Characterization of Mercury Atmosphere-Foliage and Atmosphere-Soil Exchange in a Swiss Subalpine Coniferous Forest

To understand the role of vegetation and soil in regulating atmospheric Hg0, exchange fluxes and isotope signatures of Hg were characterized using a dynamic flux bag/chamber at the atmosphere-foliage/soil interfaces at the Davos-Seehornwald forest, Switzerland. The foliage was a net Hg0 sink and took up preferentially the light Hg isotopes, consequently resulting in large shifts (-3.27‰) in δ202Hg values. The soil served mostly as net sources of atmospheric Hg0 with higher Hg0 emission from the moss-covered soils than from bare soils. The negative shift of δ202Hg and Δ199Hg values of the efflux air relative to ambient air and the Δ199Hg/Δ201Hg ratio among ambient air, efflux air, and soil pore gas highlight that Hg0 re-emission was strongly constrained by soil pore gas evasion together with microbial reduction. The isotopic mass balance model indicates 8.4 times higher Hg0 emission caused by pore gas evasion than surface soil photoreduction. Deposition of atmospheric Hg0 to soil was noticeably 3.2 times higher than that to foliage, reflecting the high significance of the soil to influence atmospheric Hg0 isotope signatures. This study improves our understanding of Hg atmosphere-foliage/soil exchange in subalpine coniferous forests, which is indispensable in the model assessment of forest Hg biogeochemical cycling.

The Marginal Ice Zone as a dominant source region of atmospheric mercury during central Arctic summertime

Atmospheric gaseous elemental mercury (GEM) concentrations in the Arctic exhibit a clear summertime maximum, while the origin of this peak is still a matter of debate in the community. Based on summertime observations during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition and a modeling approach, we further investigate the sources of atmospheric Hg in the central Arctic. Simulations with a generalized additive model (GAM) show that long-range transport of anthropogenic and terrestrial Hg from lower latitudes is a minor contribution (~2%), and more than 50% of the explained GEM variability is caused by oceanic evasion. A potential source contribution function (PSCF) analysis further shows that oceanic evasion is not significant throughout the ice-covered central Arctic Ocean but mainly occurs in the Marginal Ice Zone (MIZ) due to the specific environmental conditions in that region. Our results suggest that this regional process could be the leading contributor to the observed summertime GEM maximum. In the context of rapid Arctic warming and the observed increase in width of the MIZ, oceanic Hg evasion may become more significant and strengthen the role of the central Arctic Ocean as a summertime source of atmospheric Hg.

Toxic elements in arctic and sub-arctic brown bears: Blood concentrations of As, Cd, Hg and Pb in relation to diet, age, and human footprint

Contamination with arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb) is a global concern impairing resilience of organisms and ecosystems. Proximity to emission sources increases exposure risk but remoteness does not alleviate it. These toxic elements are transported in atmospheric and oceanic pathways and accumulate in organisms. Mercury accumulates in higher trophic levels. Brown bears (Ursus arctos), which often live in remote areas, are long-lived omnivores, feeding on salmon (Oncorhynchus spp.) and berries (Vaccinium spp.), resources also consumed by humans. We measured blood concentrations of As, Cd, Hg and Pb in bears (n = 72) four years and older in Scandinavia and three national parks in Alaska, USA (Lake Clark, Katmai and Gates of the Arctic) using high-resolution, inductively-coupled plasma sector field mass spectrometry. Age and sex of the bears, as well as the typical population level diet was associated with blood element concentrations using generalized linear regression models. Alaskan bears consuming salmon had higher Hg blood concentrations compared to Scandinavian bears feeding on berries, ants (Formica spp.) and moose (Alces). Cadmium and Pb blood concentrations were higher in Scandinavian bears than in Alaskan bears. Bears using marine food sources, in addition to salmon in Katmai, had higher As blood concentrations than bears in Scandinavia. Blood concentrations of Cd and Pb, as well as for As in female bears increased with age. Arsenic in males and Hg concentrations decreased with age. We detected elevated levels of toxic elements in bears from landscapes that are among the most pristine on the planet. Sources are unknown but anthropogenic emissions are most likely involved. All study areas face upcoming change: Increasing tourism and mining in Alaska and more intensive forestry in Scandinavia, combined with global climate change in both regions. Baseline contaminant concentrations as presented here are important knowledge in our changing world.

Elevated methylmercury in Antarctic surface seawater: The role of phytoplankton mass and sea ice

Methylmercury is a neurotoxin that is biomagnified in marine food webs. Its distribution and biogeochemical cycle in Antarctic seas are still poorly understood due to scarce studies. Here, we report the total methylmercury profiles (up to 4000 m) in unfiltered seawater (MeHg_T) from the Ross Sea to the Amundsen Sea. We found high MeHg_T levels in oxic unfiltered surface seawater (upper 50 m depth) in these regions. It was characterized by an obviously higher maximum concentration level of MeHg_T (up to 0.44 pmol/L, at a depth of 3.35 m), which is higher than other open seas (including the Arctic Ocean, the North Pacific Ocean and the equatorial Pacific), and a high MeHg_T average concentration in the summer surface water (SSW, 0.16 ± 0.12 pmol/ L). Further analyses suggest that the high phytoplankton mass and sea-ice fraction are important drivers of the high MeHg_T level that we observed in the surface water. For the influence of phytoplankton, the model simulation showed that the uptake of MeHg by phytoplankton would not fully explain the high levels of MeHg_T, and we speculated that high phytoplankton mass may emit more particulate organic matter as microenvironments that can sustain Hg in-situ methylation by microorganisms. The presence of sea-ice may not only harbor a microbial source of MeHg to surface water but also trigger increased phytoplankton mass, facilitating elevation of MeHg in surface seawater. This study provides insight into the mechanisms that impact the content and distribution of MeHg_T in the Southern Ocean.

Diet and landscape characteristics drive spatial patterns of mercury accumulation in a high-latitude terrestrial carnivore

Limited information exists on mercury concentrations and environmental drivers of mercury bioaccumulation in high latitude terrestrial carnivores. Spatial patterns of mercury concentrations in wolverine (Gulo gulo, n = 419) were assessed across a 1,600,000 km2 study area in relation to landscape, climate, diet and biological factors in Arctic and boreal biomes of western Canada. Hydrogen stable isotope ratios were measured in wolverine hair from a subset of 80 animals to assess the spatial scale for characterizing environmental conditions of their habitat. Habitat characteristics were determined using GIS methods and raster datasets at two scales, the collection location point and a 150 km radius buffer, which was selected based on results of a correlation analysis between hydrogen stable isotopes in precipitation and wolverine hair. Total mercury concentrations in wolverine muscle ranged >2 orders of magnitude from 0.01 to 5.72 μg/g dry weight and varied geographically, with the highest concentrations in the Northwest Territories followed by Nunavut and Yukon. Regression models at both spatial scales indicated diet (based on nitrogen stable isotope ratios) was the strongest explanatory variable of mercury concentrations in wolverine, with smaller though statistically significant contributions from landscape variables (soil organic carbon, percent cover of wet area, percent cover of perennial snow-ice) and distance to the Arctic Ocean coast. The carbon and nitrogen stable isotope ratios of wolverine muscle suggested greater mercury bioaccumulation could be associated with feeding on marine biota in coastal habitats. Landscape variables identified in the modelling may reflect habitat conditions which support enhanced methylmercury transfer to terrestrial biota. Spatially-explicit estimates of wet atmospheric deposition were positively correlated with wolverine mercury concentrations but this variable was not selected in the final regression models. These landscape patterns provide a basis for further research on underlying processes enhancing methylmercury uptake in high latitude terrestrial food webs.

Atmospheric Hg(p) concentrations at various particles sizes before (2018-2019) and during (2019-2020 and 2020-2021) COVID-19 occurred periods in Taichung, Taiwan

The main goal of this study is to compare concentrations of atmospheric Hg(p) for various particles sizes Total Suspended Particulates (TSP), PM₁₈, PM₁₀, PM_2.5, PM₁, PM_<1 before (2018-2019) and during (2019-2020 and 2020-2021) COVID-19 occurred periods in central Taiwan. In addition, test the statistical differences concentrations of Hg(p) for various particles sizes before and during COVID-19 occurred periods in central Taiwan. Finally, calculate the Hg(p) health risk assessment before and during COVID-19 occurred period in central Taiwan.The result indicated that the mean Hg(p) concentrations in TSP and PM_2.5 were higher during (2020-2021) the COVID-19 occurred period than that of the mean Hg(p) concentrations in TSP and PM_2.5 before the COVID-19 occurred period. In addition, the Hg(p)concentrations PM₁₈, PM₁₀, PM_2.5, PM₁ and PM_<1 were all increased during the COVID-19 occurred period. The Hg(p) concentrations in TSP were decreased during (2019-2020) the COVID-19 occurred period when compared with that of the before the COVID-19 occurred period. Moreover, significant mean Hg(p) concentrations differences were existed at PM₁₈, PM₁₀ and PM_2.5 before and during (2020-2021) COVID-19 occurred periods. Finally, the HQ and HI values for Hg(p) were both increased during COVID-19 occurred periods when compared with before COVID-19 occurred period in this study.

Mercury contamination and potential health risks to Arctic seabirds and shorebirds

Since the last Arctic Monitoring and Assessment Programme (AMAP) effort to review biological effects of mercury (Hg) on Arctic biota in 2011 and 2018, there has been a considerable number of new Arctic bird studies. This review article provides contemporary Hg exposure and potential health risk for 36 Arctic seabird and shorebird species, representing a larger portion of the Arctic than during previous AMAP assessments now also including parts of the Russian Arctic. To assess risk to birds, we used Hg toxicity benchmarks established for blood and converted to egg, liver, and feather tissues. Several Arctic seabird populations showed Hg concentrations that exceeded toxicity benchmarks, with 50 % of individual birds exceeding the "no adverse health effect" level. In particular, 5 % of all studied birds were considered to be at moderate or higher risk to Hg toxicity. However, most seabirds (95 %) were generally at lower risk to Hg toxicity. The highest Hg contamination was observed in seabirds breeding in the western Atlantic and Pacific Oceans. Most Arctic shorebirds exhibited low Hg concentrations, with approximately 45 % of individuals categorized at no risk, 2.5 % at high risk category, and no individual at severe risk. Although the majority Arctic-breeding seabirds and shorebirds appeared at lower risk to Hg toxicity, recent studies have reported deleterious effects of Hg on some pituitary hormones, genotoxicity, and reproductive performance. Adult survival appeared unaffected by Hg exposure, although long-term banding studies incorporating Hg are still limited. Although Hg contamination across the Arctic is considered low for most bird species, Hg in combination with other stressors, including other contaminants, diseases, parasites, and climate change, may still cause adverse effects. Future investigations on the global impact of Hg on Arctic birds should be conducted within a multi-stressor framework. This information helps to address Article 22 (Effectiveness Evaluation) of the Minamata Convention on Mercury as a global pollutant.

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.

Climate change and mercury in the Arctic: Biotic interactions

Global climate change has led to profound alterations of the Arctic environment and ecosystems, with potential secondary effects on mercury (Hg) within Arctic biota. This review presents the current scientific evidence for impacts of direct physical climate change and indirect ecosystem change on Hg exposure and accumulation in Arctic terrestrial, freshwater, and marine organisms. As the marine environment is elevated in Hg compared to the terrestrial environment, terrestrial herbivores that now exploit coastal/marine foods when terrestrial plants are iced over may be exposed to higher Hg concentrations. Conversely, certain populations of predators, including Arctic foxes and polar bears, have shown lower Hg concentrations related to reduced sea ice-based foraging and increased land-based foraging. How climate change influences Hg in Arctic freshwater fishes is not clear, but for lacustrine populations it may depend on lake-specific conditions, including interrelated alterations in lake ice duration, turbidity, food web length and energy sources (benthic to pelagic), and growth dilution. In several marine mammal and seabird species, tissue Hg concentrations have shown correlations with climate and weather variables, including climate oscillation indices and sea ice trends; these findings suggest that wind, precipitation, and cryosphere changes that alter Hg transport and deposition are impacting Hg concentrations in Arctic marine organisms. Ecological changes, including northward range shifts of sub-Arctic species and altered body condition, have also been shown to affect Hg levels in some populations of Arctic marine species. Given the limited number of populations and species studied to date, especially within Arctic terrestrial and freshwater systems, further research is needed on climate-driven processes influencing Hg concentrations in Arctic ecosystems and their net effects. Long-term pan-Arctic monitoring programs should consider ancillary datasets on climate, weather, organism ecology and physiology to improve interpretation of spatial variation and time trends of Hg in Arctic biota.