Global Mercury Cycle Research Articles

Enhancing Atmospheric Mercury Research in China to Improve the Current Understanding of the Global Mercury Cycle: The Need for Urgent and Closely Coordinated Efforts

The current understanding of the global mercury (Hg) cycle remains uncertain because Hg behavior in the environment is very complicated. The special property of Hg causes the atmosphere to be the most important medium for worldwide dispersion and transformation. The source and fate of atmospheric Hg and its interaction with the surface environment are the essential topics in the global Hg cycle. Recent declining measurement trends of Hg in the atmosphere are in apparent conflict with the increasing trends in global anthropogenic Hg emissions. As the single largest country contributor of anthropogenic Hg emission, China's role in the global Hg cycle will become more and more important in the context of the decreasing man-made Hg emission from developed regions. However, much less Hg information in China is available. As a global pollutant which undergoes long-range transport and is persistence in the environment, increasing Hg knowledge in China could not only promote the Hg regulation in this country but also improve the understanding of the fundamental of the global Hg cycle and further push the abatement of this toxin on a global scale. Then the atmospheric Hg research in China may be a breakthrough for improving the current understanding of the global Hg cycle. However, due to the complex behavior of Hg in the atmosphere, a deeper understanding of the atmospheric Hg cycle in China needs greater cooperation across fields.

Atmospheric mercury observations from Antarctica: seasonal variation and source and sink region calculations

Abstract. Long term atmospheric mercury measurements in the Southern Hemisphere are scarce and in Antarctica completely absent. Recent studies have shown that the Antarctic continent plays an important role in the global mercury cycle. Therefore, long term measurements of gaseous elemental mercury (GEM) were initiated at the Norwegian Antarctic Research Station, Troll (TRS) in order to improve our understanding of atmospheric transport, transformation and removal processes of GEM. GEM measurements started in February 2007 and are still ongoing, and this paper presents results from the first four years. The mean annual GEM concentration of 0.93 ± 0.19 ng m−3 is in good agreement with other recent southern-hemispheric measurements. Measurements of GEM were combined with the output of the Lagrangian particle dispersion model FLEXPART, for a statistical analysis of GEM source and sink regions. It was found that the ocean is a source of GEM to TRS year round, especially in summer and fall. On time scales of up to 20 days, there is little direct transport of GEM to TRS from Southern Hemisphere continents, but sources there are important for determining the overall GEM load in the Southern Hemisphere and for the mean GEM concentration at TRS. Further, the sea ice and marginal ice zones are GEM sinks in spring as also seen in the Arctic, but the Antarctic oceanic sink seems weaker. Contrary to the Arctic, a strong summer time GEM sink was found, when air originates from the Antarctic plateau, which shows that the summertime removal mechanism of GEM is completely different and is caused by other chemical processes than the springtime atmospheric mercury depletion events. The results were corroborated by an analysis of ozone source and sink regions.

An Analytical Method development for the Study of Chemical Species of Mercury in the Atmosphere


 
 
 Introduction: both natural and anthropogenic activities add mercury (Hg) to the atmosphere. The speciation and chemical transformation of mercury in the atmosphere can significantly influence how it is deposited on the earth’s surface. Methods: To better understand the impact of urban emissions on global mercury cycling, we developed an inexpensive technique for the reliable measurement of gaseous oxidized mercury (GOM) in air. This simple technique is based on a thermal decomposition-difference method previously developed by others for aircraft studies of gom in the remote troposphere. measurements of total atmospheric mercury (TAM) were made by decomposing all forms of mercury in ambient air to gaseous elemental mercury (GEM) at 500°c prior to detection using cold vapour atomic fluorescence spectroscopy (CVAFS). The amount of gom was determined through the difference between TAM and GEM values. results and discussion: a diurnal pattern was found for GEM, with the highest concentrations of Hg species found ranging from 2:00 to 5:00 pm and the lowest and most stable values from 9:00 pm to 6:00 am. The amount of GOM was estimated on the 5th floor balcony of pavillon prépresident-Kennedy at université de Québec à montréal to be 14.7 ± 10.3 ng∙m-3 (arithmetic mean from eight groups of Tam-gem differences in the afternoons of july 12 and 14, 2011 and 95% confidence interval). The inconsistent GOM result, in addition to a large error value, suggests the need for further investigation, and to compare the efficiency of this method to previously established methods to identify and quantify the mercury species in urban gom.
 
 

Mercury Cycling in an Urbanized Watershed: The Influence of Wind Distribution and Regional Subwatershed Geometry in Central Indiana, USA

The global cycle of mercury (Hg) is reasonably well-understood, as are some of the natural and anthropogenic sources of Hg to the atmosphere. Less well understood are the regional and local characteristics of Hg deposition and subsequent watershed-scale transport, important parameters for assessing human risk to various avenues of Hg exposure. This study employed a two-part strategy for understanding coupled deposition and transport processes in central Indiana (USA), including Indianapolis, a typical large city with multiple coal-fired electric utilities and other Hg emission sources. A spatial analysis of Hg concentrations in surface soils revealed elevated Hg proximal to many of the large emission sources, with a distribution aligned along a southwest-northeast axis corresponding to the mean wind direction in this region. This soil distribution suggests some local depositional impact from local utilities, with wind modification affecting the regional pattern. Post-depositional transport of Hg was assessed using a series of streambank sampling arrays as the White River and various tributaries travelled through the urban core of Indianapolis. Streambank sediments had peak Hg concentrations in the urban core, where several local sources are present and where a number of subwatersheds join the main trunk of the White River, suggesting local emission and/or rapid Hg transport from urban subwatersheds due to their relatively high proportion of impervious surfaces. High Hg values persist in White River sediments into rural areas tens of kilometers south of Indianapolis, raising concerns for anglers collecting fish in this apparently “pristine” environment.

Importance of vegetation type for mercury sequestration in the northern Swedish mire, Rödmossamyran

Even if mires have proven to be relatively reliable archives over the temporal trends in atmospheric mercury deposition, there are large discrepancies between sites regarding the magnitude of the anthropogenic contribution to the global mercury cycle. A number of studies have also revealed significant differences in mercury accumulation within the same mire area. This raises the question of which factors, other than mercury deposition, affect the sequestration of this element in peat. One such factor could be vegetation type, which has the potential to affect both interception and retention of mercury. In order to assess how small-scale differences in vegetation type can affect mercury sequestration we sampled peat and living plants along three transects on a northern Swedish mire. The mire has two distinctly different vegetation types, the central part consists of an open area dominated by Sphagnum whereas the surrounding fen, in addition to Sphagnum mosses, has an understory of ericaceous shrubs and a sparse pine cover. A few main patterns can be observed in our data; (1) Both peat and Sphagnum-mosses have higher mercury content (both concentration and inventory) in the pine-covered fen compared to the open Sphagnum area (100% and 71% higher for peat and plants, respectively). These differences clearly exceed the 33% difference observed for lead-210, which is considered as a good analogue for atmospheric mercury deposition. (2) The differences in mercury concentration between peat profiles within a single vegetation type can largely be attributed to differences in peat decomposition. (3) When growing side by side in the open Sphagnum area, the moss species Sphagnum subsecundum has significantly higher mercury concentrations compared to S. centrale (24 ± 3 and 18 ± 2 ng Hg g −1, respectively). Based on these observations we suggest that species composition, vegetation type and decomposition can affect the mercury sequestration in a peat record, and that any changes in these properties over time, or space, have the potential to modify the mercury deposition signal recorded in the peat.

Are Arctic Ocean ecosystems exceptionally vulnerable to global emissions of mercury? A call for emphasised research on methylation and the consequences of climate change

Environmental context. Mercury is a global contaminant that has entered Arctic food webs in sufficient quantity to put at risk the health of top predators and humans that consume them. Recent research has discovered a photochemical process unique to the Arctic that leads to mercury deposition on frozen surfaces after polar sunrise, but the connection between mercury deposition and entry into food webs remains tenuous and poorly understood. We propose here that the Arctic Ocean’s sensitivity to the global mercury cycle depends far more on neglected post-deposition processes that lead to methylation within the ice–ocean system, and the vulnerability of these processes to changes occurring in the cryosphere. Abstract. Emissions, atmospheric transport and deposition have formed the emphasis of recent research to understand Hg trends in Arctic marine biota, with the expressed objective of predicting how biotic trends might respond to emission controls. To answer the question of whether the Arctic Ocean might be especially vulnerable to global mercury (Hg) contamination and how biota might respond to emission controls requires a distinction between the supply of Hg from source regions and the processes within the Arctic Ocean that sequester and convert mercury to monomethyl Hg (MeHg). Atmospheric Mercury Depletion Events (AMDEs) provide a unique Hg deposition process in the Arctic; however, AMDEs have yet to be linked quantitatively with Hg uptake in marine food webs. The difficulty in implicating AMDEs or emissions to biotic trends lie in the ocean where several poorly understood processes lead to MeHg production and biomagnification. We propose that sensitivity of the Arctic Ocean’s ecosystem to Hg lies not so much in the deposition process as in methylation processes within the ocean, Hg inputs from large drainage basins, and the vulnerability these to climate change. Future research needs to be better balanced across the entire Hg cycle.

Global Biogeochemical Cycling of Mercury: A Review

Mercury pollution poses global human health and environmental risks. Although mercury is naturally present in the environment, human activities, such as coal burning, have increased the amount of mercury cycling among the land, atmosphere, and ocean by a factor of three to five. Emitted to the atmosphere in its elemental form, mercury travels worldwide before oxidizing to a form that deposits to ecosystems. In aquatic systems, mercury can convert into methylmercury, a potent neurotoxin. People and wildlife are exposed to methylmercury as it bioaccumulates up the food chain. Mercury continues to circulate in the atmosphere, oceans, and terrestrial system for centuries to millennia before it returns to deep-ocean sediments. Areas of uncertainty in the global biogeochemical cycle of mercury include oxidation processes in the atmosphere, land-atmosphere and ocean-atmosphere cycling, and methylation processes in the ocean. National and international policies have addressed direct mercury emissions, but further efforts to reduce risks face numerous political and technical challenges.

Effects of Glucan on Immunosuppressive Actions of Mercury

Global cycling of mercury results in the presence of mercury salts in the environment. The well-established negative effects of mercury on the immune system led us to the study whether natural immunomodulator glucan can overcome the immunosuppressive effects of mercury. Two types of mercury, thimerosal and mercury acetate, were administered in a dose of 2-8 mg/L of drinking water to mice. After 2 weeks, all mice exhibited profound suppression of both cellular (phagocytosis, natural killer cell activity, mitogen-induced proliferation, and expression of CD markers) and humoral (antibody formation and secretion of interleukin-6, interleukin-12, and interferon-gamma) responses. The mice were then fed with a diet containing a standard dose of glucan. Our results showed that simultaneous treatment with mercury and glucan resulted in significantly lower immunotoxic effects of mercury, which suggests that glucans can be successfully used as a natural remedy of low-level exposure to mercury.

Mechanism of Hg−C Protonolysis in the Organomercurial Lyase MerB

Demethylation is a key reaction in global mercury cycling. The bacterial organomercurial lyase, MerB, catalyzes the demethylation of a wide range of organomercurials via Hg-C protonolysis. Two strictly conserved cysteine residues in the active site are required for catalysis, but the source of the catalytic proton and the detailed reaction mechanism have not been determined. Here, the two major proposed reaction mechanisms of MerB are investigated and compared using hybrid density functional theory calculations. A model of the active site was constructed from an X-ray crystal structure of the Hg(II)-bound MerB product complex. Stationary point structures and energies characterized for the Hg-C protonolysis of methylmercury rule out the direct protonation mechanism in which a cysteine residue delivers the catalytic proton directly to the organic leaving group. Instead, the calculations support a two-step mechanism in which Cys96 or Cys159 first donates a proton to Asp99, enabling coordination of two thiolates with R-Hg(II). At the rate-limiting transition state, Asp99 protonates the nascent carbanion in a trigonal planar, bis thiol-ligated R-Hg(II) species to cleave the Hg-C bond and release the hydrocarbon product. Reactions with two other substrates, vinylmercury and cis-2-butenyl-2-mercury, were also modeled, and the computed activation barriers for all three organomercurial substrates reproduce the trend in the experimentally observed enzymatic reaction rates. Analysis of atomic charges in the rate-limiting transition state structure using Natural Population Analysis shows that MerB lowers the activation free energy in the Hg-C protonolysis reaction by redistributing electron density into the leaving group and away from the catalytic proton.

Effect of bromine chemistry on the atmospheric mercury cycle

Bromine chemistry is believed to play a major role in the atmospheric oxidation of elemental mercury (Hg0) to divalent mercury (HgII). However, its effect on the speciation of atmospheric mercury (Hg) has been mostly ignored in models of the fate and transport of mercury. We investigate the effect of bromine chemistry on Hg speciation for various reaction kinetics and environmental conditions with a box model. Bromine chemistry was also added to the chemical mechanism of a global chemical transport model, and simulations of the global mercury cycle were conducted with different sets of bromine reaction kinetics. The global model simulations conducted with bromine chemistry lead to Hg0 concentrations that are consistent with observations only if the pressure dependence of the kinetics of the oxidation of Hg0 by Br is taken into account. Bromine chemistry is found to reduce the overall lifetime of Hg by about 10%.

Determination of Henry’s law constant for elemental mercury

The assessment of the global mercury cycle involves estimations of the evasion of mercury form oceanic waters. In such estimations Henry’s law constant is often used. In this study the Henry’s law constant for elemental mercury has been re-determined in MQ water and artificial sea water. Moreover, for the first time it has been determined for 1.5 M sodium chloride (NaCl) solution which is of relevance for modeling of atmospheric waters at coastal locations. For all solutions, experiments has been conducted at five different temperatures between 278 and 308 K, using a novel technique, for mercury, based on direct measurements of the portioning of mercury between the aqueous and gaseous phase. Elemental mercury was extracted from the water column and the logarithm of the mass of extracted mercury was plotted against time. A dimensionless Henry’s law constant, defined as: k H ′ = [ Hg ( g ) ] / [ Hg ( aq ) ] was obtained from the slope of the curve. Almost no difference was observed in the values comparing the Milli-Q water and artificial sea water, however for the 1.5 M NaCl solution a salting-out effect was seen, i.e. the solubility of mercury in the water phase decreased. The decreased solubility will generate an increase in the value of Henry’s law constant.

Annual time-series analyses of total gaseous mercury measurement and its impact factors on the Gongga Mountains in the southeastern fringe of the Qinghai-Tibetan Plateau

Long-term monitoring programs for measurement of atmospheric mercury concentrations are presently recognized as powerful tools for local, regional and global studies of atmospheric long-range transport processes, and they could also provide valuable information about the impact of emission controls on the global budget of atmospheric mercury, their observance and an insight into the global mercury cycle. China is believed to be an increasing atmospheric mercury emission source. However, only a few measurements of mercury, to our knowledge, have been done in ambient air over China. The highly-time resolved atmospheric mercury concentrations have been measured at Moxi Base Station (102 degrees 72'E 29 degrees 92'N, 1640 in asl) of the Gongga Alpine Ecosystem Observation and Experiment Station of Chinese Academy of Sciences (CAS) from May 2005 to June 2006 by using a set of Automatic Atmospheric Mercury Speciation Analyzers (Tekran 2537A). Measurements were carried out with a time resolution 0 every 15 minutes. The overall average total gaseous mercury (TGM) covering the measurement periods was 4+/-1.38 ng.m(-3) (N=57310), which is higher than the global background level of approximately 1.5 similar to 2.0 ng.m(-3). The measurements in all seasons showed a similar diurnal change pattern with a high concentration during daytime relative to nighttime and maximum concentration near solar noon and minimum concentration immediately before sunrise. The presence of diurnal TGM peaks during spring and summer was found earlier than that during autumn and winter. When divided seasonally, it was found that the concentrations of TGM were highest in winter with 6.13 +/- 1.78 ng.m(-3) and lowest in summer with 3.17 +/- 0.67 ng.m(-3). There were no significant differences in TGM among wind sectors during each season. Whereas Hg generally exhibited significant correlations with the parameters, such as temperature, saturated vapor pressure, precipitation, ultraviolet radiation (LTV) and atmospheric pressure at the whole measurement stage, and the correlations varied seasonally. Our results suggest that the local or regional abundant geothermal activities, such as thermal spring, anthropogenic source processes and changes in meteorological conditions, regulate and affect Hg behavior in the study area.

Sensitivity of the global atmospheric cycle of mercury to emissions

Abstract A systematic investigation of the impact of current uncertainties in Hg emissions from specific source categories on global air Hg concentrations is presented. First, the uncertainties in different emission source categories are discussed and then the results of a base simulation and three sensitivity simulations conducted with a global chemical transport model for mercury (CTM-Hg) are presented. The total Hg emissions in the four scenarios range from 6600 to 9400 Mg/a. The sensitivity studies investigate the impact of the range in uncertainty in natural emissions, emissions of previously deposited Hg, and anthropogenic emissions both in China and worldwide, while taking into account constraints imposed by available data (current/pre-industrial emission ratio of 2–4). In one case, natural emissions and emissions of previously deposited Hg were changed to represent a mid point of the range of values found in the literature. This lead to a 16% increase in background emissions, i.e., natural emissions and emissions of previously deposited Hg combined. Increasing natural emissions by 16% or Chinese anthropogenic emissions by 100% yielded atmospheric Hg concentrations comparable with those measured across the globe without any changes to the atmospheric chemistry. Increasing natural emissions and emissions of previously deposited Hg by 16% and all anthropogenic emissions by 100% as compared to the base scenario yielded atmospheric Hg concentrations that were not compatible with measurements and changes in the chemical behavior of Hg in the atmosphere would be required to yield results that are consistent with observed Hg concentrations. The current uncertainty in total Hg emissions at the global scale is placed at about a factor of two.

Sources, fate and transport of atmospheric mercury from Asia

Environmental context. Mercury is a global problem and more than half of all anthropogenic emissions are from Asia. In this paper we review the sources of mercury coming from Asia, the environmental fate of these emissions and their global transport. Asian emissions of mercury are responsible for a small, but significant share of the mercury that deposits throughout the world, especially in the northern hemisphere. Abstract. Asian anthropogenic emissions of mercury to the atmosphere contribute 54% of all anthropogenic emissions. For this reason, it is important to understand how these emissions impact both the regional and global mercury cycle. The largest share of mercury emissions in Asia is due to coal combustion and smelting. Approximately half of the Asian anthropogenic emissions are emitted as Hg0. The remainder are emitted as gaseous Hg2+ compounds and particle-bound Hg (PHg). These latter forms of Hg are susceptible to relatively rapid removal from the atmosphere. The Asian emissions lead to very high concentrations of airborne Hg in urban and rural areas of Asia. Modelling the fate and transport of the Asian emissions using the Goddard Earth Observing System (GEOS)-Chem model of global tropospheric chemistry shows that these emissions are associated with high deposition of Hg within Asia, but there is little data with which to evaluate this model result. Observations downwind of Asia show that Hg0 is the dominant form in Asian plumes, with generally small, but variable amounts of other forms. Thus we conclude that most of the Asian Hg2+ and PHg have been removed in the source region. In addition, downwind observations show that total emissions are significantly larger than indicated by the anthropogenic emission inventory. This likely reflects either an underestimate of the anthropogenic emissions or emissions of Hg from land. Plumes containing enhancements in Asian Hg0, but not other species, have been detected as far away as North America. Because only Asian Hg0 is transported long distances, the deposition is distributed relatively uniformly in the northern hemisphere. In North America, Asian anthropogenic emissions account for 7–20% of all deposition, with an average of 16%.

Human impacts on open ocean mercury concentrations

We develop an empirically constrained multicompartment box model for mercury cycling in open ocean regions to investigate changes in concentrations resulting from anthropogenic perturbations of the global mercury cycle. Using Monte Carlo simulations, we explicitly consider the effects of variability in measured parameters on modeled seawater concentrations. Our simulations show that anthropogenic enrichment in all surface (25%) and deep ocean waters (11%) is lower than global atmospheric enrichment (300–500%) and varies considerably among geographic regions, ranging from >60% in parts of the Atlantic and Mediterranean to <1% in the deep Pacific. Model results indicate that open ocean mercury concentrations do not rapidly equilibrate with atmospheric deposition and on average will increase if anthropogenic emissions remain at their present level. We estimate the temporal lag between changes in atmospheric deposition and ocean mercury concentrations will vary from decades in most of the Atlantic up to centuries in parts of the Pacific.

Mercury Depletion Events in the Troposphere in Mid-Latitudes at the Dead Sea, Israel

The occurrence of mercury depletion events (MDE) in the Polar Regions during the spring periods has raised global concern due to the biomagnifications of the deposited mercury into the aquatic food chain. However, it now appears that MDE is not limited to the Polar Regions and can also occur at mid-latitudes. Diurnal cycles of mercury, ozone, and BrO behavior based on short-time resolution measurements are presented for the Dead Sea, Israel, for Summer 2006. The results show that mercury depletion events occur almost daily, accompanied always by the presence of BrO and concurrent ozone destruction. The intensity of the MDE corresponded to increasing BrO levels. Mercury depletions of more than 40% were observed when BrO levels rose above 60-70 ppt. Based on the present measurements and supported bytheoretical considerations, it appears that BrOx (BrO + Br) is the primary species responsible for the mercury depletion at the Dead Sea. The present study also suggests, especially at low ozone levels, that the Br atom may play a major role in conversion of the gaseous elemental mercury to the reactive species, HgBr2. The implications of the present study are that even at low BrO levels (<10 ppt), mercury depletion may well occur at other mid-latitude sites and thus needs to be taken into consideration in the global mercury cycle.

Antarctic polar plateau snow surface conversion of deposited oxidized mercury to gaseous elemental mercury with fractional long-term burial

The role of the vast Antarctic polar plateau in the global mercury cycle was previously relatively unknown. Here, for the first time, mercury concentrations in snow and air, combined with vertical flux measurements at the South Pole (November–December 2003 and November 2005) have provided considerable insight into the cycling of this element through the Antarctic environment. These insights include observations showing atmospheric oxidized mercury depositing to the snow pack, subsequent photoreduction, and emissions of gaseous elemental mercury from the snow pack. Oxidized mercury (e.g., reactive gaseous mercury and fine particulate mercury) showed high concentrations (100–1000 pg m −3) in the near-surface air, with these concentrations strongly correlated with vertical mixing rates and showing rapid surface deposition. This suggests that the troposphere over Antarctica is enhanced in oxidized mercury, with mercury cycling between elemental and oxidized states, and between the atmosphere and snow pack. Based on these limited measurements at South Pole, we estimate that the Antarctic polar plateau could sequester as much as 60 metric tons of Hg annually. These data also suggest that there could be a seasonal cycling of atmospheric mercury oxidation, deposition, and re-emission via photoreduction of 490 metric tons annually. This cycling is restricted to the annual sunlit period and peaks 3–4 weeks after solar maximum. To our knowledge, these provisional values represent the first estimates of the mercury balance and cycling for the extensive Antarctic polar plateau.

Air‐sea exchange in the global mercury cycle

We present results from a new global atmospheric mercury model coupled with a mixed layer slab ocean. The ocean model describes the interactions of the mixed layer with the atmosphere and deep ocean, as well as conversion between elemental, divalent, and nonreactive mercury species. Our global mean aqueous concentrations of 0.07 pM elemental, 0.80 pM reactive, and 1.51 pM total mercury agree with observations. The ocean provides a 14.1 Mmol yr−1 source of mercury to the atmosphere, at the upper end of previous estimates. Re‐emission of previously deposited mercury constitutes 89% of this flux. Ocean emissions are largest in the tropics and downwind of industrial regions. Midlatitude ocean emissions display a large seasonal cycle induced by biological productivity. Oceans contribute 54% (36%) of surface atmospheric mercury in the Southern (Northern) Hemisphere. We find a large net loss of mercury to the deep ocean (8.7 Mmol yr−1), implying a ∼0.7%/year increase in deep ocean concentrations.

Mercury species in lymphoid and non-lymphoid tissues after exposure to methyl mercury: Correlation with autoimmune parameters during and after treatment in susceptible mice

Methylmercury (MeHg) is present in the environment as a result of the global cycling of mercury, although anthropogenic sources may dramatically increase the availability in confined geographical areas. Accumulation of MeHg in the aquatic food chain is the dominating way of exposure in mammals, which accumulate MeHg in all organs, including the brain. Demethylation has been described in the organs, especially in phagocytic cells, but mainly in the flora of the intestinal tract. While most of the inorganic mercury (Hg 2+) formed in the intestine is excreted, a fraction is reabsorbed which together with the local demethylation increases the organ Hg 2+ concentration. MeHg is a well-known immunosuppressive agent, while Hg 2+ is associated with immunostimulation and autoimmunity especially in genetically susceptible rodents, creating a syndrome, i.e. mercury-induced autoimmunity (HgIA). This study aimed at exploring the effect of MeHg with regard to HgIA, and especially the immunological events after stopping treatment, correlated with the presence of MeHg and Hg 2+ in the organs. Treatment of A.SW mice for 30 days with 4.2 mg MeHg/L drinking water (corresponding to approximately 420 μg Hg/kg body weight/day) caused all the HgIA features observed after primary treatment with inorganic Hg, except systemic immune complex deposits. The total Hg concentration was 5-fold higher in the kidneys as compared with lymph nodes, but the fraction of Hg 2+ was similar (17–20%). After stopping treatment, the renal and lymph node MeHg concentration declined according to first order kinetics during the initial 4–6 weeks, but then slower. A similar decline in the organ Hg 2+ concentration occurred during the initial 2 weeks after stopping treatment but then ceased, causing the Hg 2+ concentration to exceed that of MeHg in the lymph nodes and kidneys after 3 and 8 weeks, respectively. The selective increase in lymph node Hg 2+ fraction is likely to be due to demethylation of MeHg in the macrophage-rich lymphoid tissue. The major autoantibody in HgIA, anti-fibrillarin antibodies, tended to increase during the initial 6 weeks after stopping treatment, while all other HgIA features including antichromatin antibodies declined to control levels after 2–4 weeks. This indicates differences in either dose requirement or induction mechanisms for the different HgIA parameters. The selective accumulation of Hg 2+ in lymph nodes following MeHg treatment should be taken into account when the effect of MeHg on the immune system is evaluated.

Wildfires threaten mercury stocks in northern soils

With climate change rapidly affecting northern forests and wetlands, mercury reserves once protected in cold, wet soils are being exposed to burning, likely triggering large releases of mercury to the atmosphere. We quantify organic soil mercury stocks and burn areas across western, boreal Canada for use in fire emission models that explore controls of burn area, consumption severity, and fuel loading on atmospheric mercury emissions. Though renowned as hotspots for the accumulation of mercury and its transformation to the toxic methylmercury, boreal wetlands might soon transition to hotspots for atmospheric mercury emissions. Estimates of circumboreal mercury emissions from this study are 15‐fold greater than estimates that do not account for mercury stored in peat soils. Ongoing and projected increases in boreal wildfire activity due to climate change will increase atmospheric mercury emissions, contributing to the anthropogenic alteration of the global mercury cycle and exacerbating mercury toxicities for northern food chains.