Atmospheric Hg Deposition Research Articles

Net atmospheric mercury deposition to Svalbard: Estimates from lacustrine sediments

In this study we used lake sediments, which faithfully record Hg inputs, to derive estimates of net atmospheric Hg deposition to Svalbard, Norwegian Arctic. With the exception of one site affected by local pollution, the study lakes show twofold to fivefold increases in sedimentary Hg accumulation since 1850, likely due to long-range atmospheric transport and deposition of anthropogenic Hg. Sedimentary Hg accumulation in these lakes is a linear function of the ratio of catchment area to lake area, and we used this relationship to model net atmospheric Hg flux: preindustrial and modern estimates are 2.5 ± 3.3 μg m−2 y−1 and 7.0 ± 3.0 μg m−2 y−1, respectively. The modern estimate, by comparison with data for Hg wet deposition, indicates that atmospheric mercury depletion events (AMDEs) or other dry deposition processes contribute approximately half (range 0–70%) of the net flux. Hg from AMDEs may be moving in significant quantities into aquatic ecosystems, where it is a concern because of contamination of aquatic food webs.

Seasonal variations, speciation and possible sources of mercury in the snowpack of Zhadang glacier, Mt. Nyainqêntanglha, southern Tibetan Plateau

Ten snowpits were sampled at the Zhadang glacier during 2008 and 2011 to investigate the seasonal variations, speciation, and sources of mercury (Hg) in the southern Tibetan Plateau. In the 2008 snowpit, total Hg (HgT), particulate matter, most of major ions were found in higher concentrations during the non-monsoon season than in the monsoon season. Analysis of Hg speciation indicated that HgT in the 2011 snowpits was dominated by particulate-bound Hg (HgP). Most of particulate matter in the 2008 snowpit was dominated by fine particulates, indicating that the influx of particulate matter and HgP was probably occurring by long-range transportation via general atmospheric circulation. Analysis of dominant ion Ca2+ and alkaline pH values has suggested that the long-range transported HgP, originating from dust storm activities, may be the most important source for Hg in the Zhadang glacier snowpit during the non-monsoon season. Backward-trajectory analysis indicates the majority of the air masses arriving at the Zhandang glacier originated from the arid regions of northwestern India (e.g., Thar Desert), confirming that arid regions in central and southern Asia are likely the main sources of Hg being deposited in the Zhadang glacier snowpit. This study also suggests that ice core records from the Tibetan Plateau may be useful tools for interpreting long-term historical records of atmospheric Hg deposition, and reconstructing Hg biogeochemical cycling.

Tracing mercury seawater vs. atmospheric inputs in a pristine SE USA salt marsh system: Mercury isotope evidence

Salt marshes can be a significant source of MeHg in coastal marine organisms, however the sources and cycling of Hg in salt marsh sediments, and in coastal environments in general, remain unclear. We analyzed surface and cored sediments from a salt marsh and adjacent upland sand dune in Cabretta Island, Georgia, USA, for total mercury (HgT), Hg isotopes and trace metal concentrations to better constrain the sources of Hg in this coastal environment. HgT concentrations are lower in the upland sands (1–6ng/g) than in the marsh sediments (6–16ng/g). HgT shows a positive correlation with total organic content (TOC) and increasing proportion of fines in the sediments. Trace metal concentrations also show a positive correlation with HgT in the marsh sediments regardless of chemical affinity (i.e. chalcophile, siderophile or lithophile). All these data are consistent with surface adsorption (either directly on to sediments or on to organic matter) as a dominant mechanism of Hg and metals accumulation in the marsh sediments. The surface sediments show significant mass independent fractionation (MIF) of odd Hg isotopes: the upland dune sands have zero to slightly negative Δ199Hg (−0.07‰ to −0.14‰) and the marsh surface sediments have positive Δ199Hg (0.48‰ to 0.79‰). As in the surface samples, well-sorted sand layers in the cored sediments have low Hg concentrations and zero to slightly negative Δ199Hg, whereas fine particle-rich layers have higher Hg concentrations and positive Δ199Hg values. In the absence of any evidence for MIF of Hg isotopes by bacteria mediated methylation–demethylation reactions, the observed Hg isotope differences between marsh and upland sands can be explained by different sources of Hg. We suggest that local atmospheric Hg deposition dominates the Hg budget in the ombrotrophic upland sand, while the positive MIF in the marsh sediments are consistent with Hg dominantly of seawater origin. While in situ processes, like photoreduction and evasion can overprint the Hg depositional isotope signature, their effect on the sediments is currently unconstrained. Nevertheless, our data show that Hg isotopes can delineate different sources of Hg in a pristine coastal environment and at small spatial scales. Thus natural background isotope variability should be assessed as a baseline when Hg isotopes are used as tracers of Hg in anthropogenically-influenced sites.

Unusual fractionation of both odd and even mercury isotopes in precipitation from Peterborough, ON, Canada

Once released into the atmosphere, mercury (Hg) is subject to long-range transport and a series of physico-chemical reactions before reentering terrestrial ecosystems. Though impressive progress has been made in understanding all aspects of Hg behavior in the atmosphere, many processes involved in the transformation and deposition of atmospheric Hg remain unidentified and source attribution is still an enormous challenge. Here, we examine the isotopic composition of Hg in precipitation collected during 2010 in Peterborough, ON, Canada and combine data on seasonal variations of mass-dependent (MDF) and mass-independent (MIF) fractionation with meteorological back-trajectory calculations to identify the Hg sources and to decipher Hg atmospheric transformation reactions. All precipitation samples displayed significant MDF (δ202Hg between −0.02‰ and −1.48‰) and MIF of odd isotopes (Δ199Hg varying from −0.29‰ to 1.13‰). We also report for the first time a seasonal variation of MIF of even Hg isotopes (Δ200Hg) in wet precipitation. Our results may suggest that photoreduction in droplets or on the surface layer of snow crystals induces odd Hg isotope anomalies, while mass independent fractionation of 200Hg is probably triggered by photo-initiated oxidation occurring on aerosol or solid surfaces in the tropopause. The observed seasonal variation of even Hg isotope MIF (Δ200Hg decrease with ambient temperature) is possibly a powerful tool for meteorological research and may aid in monitoring related climate changes.

Mercury sources and fate in the Gulf of Maine

Most human exposure to mercury (Hg) in the United States is from consuming marine fish and shellfish. The Gulf of Maine is a complex marine ecosystem comprising twelve physioregions, including the Bay of Fundy, coastal shelf areas and deeper basins that contain highly productive fishing grounds. Here we review available data on spatial and temporal Hg trends to better understand the drivers of human and biological exposures. Atmospheric Hg deposition from U.S. and Canadian sources has declined since the mid-1990s in concert with emissions reductions and deposition from global sources has increased. Oceanographic circulation is the dominant source of total Hg inputs to the entire Gulf of Maine region (59%), followed by atmospheric deposition (28%), wastewater/industrial sources (8%) and rivers (5%). Resuspension of sediments increases MeHg inputs to overlying waters, raising concerns about benthic trawling activities in shelf regions. In the near coastal areas, elevated sediment and mussel Hg levels are co-located in urban embayments and near large historical point sources. Temporal patterns in sentinel species (mussels and birds) have in some cases declined in response to localized point source mercury reductions but overall Hg trends do not show consistent declines. For example, levels of Hg have either declined or remained stable in eggs from four seabird species collected in the Bay of Fundy since 1972. Quantitatively linking Hg exposures from fish harvested from the Gulf of Maine to human health risks is challenging at this time because no data are available on the geographic origin of seafood consumed by coastal residents. In addition, there is virtually no information on Hg levels in commercial species for offshore regions of the Gulf of Maine where some of the most productive fisheries are located. Both of these data gaps should be priorities for future research.

Mercury Distribution and Deposition in Glacier Snow over Western China

Western China is home to the largest aggregate of glaciers outside the polar regions, yet little is known about how the glaciers in this area affect the transport and cycling of mercury (Hg) regionally and globally. From 2005 to 2010, extensive glacier snow sampling campaigns were carried out in 14 snowpits from 9 glaciers over western China, and the vertical distribution profiles of Hg were obtained. The Total Hg (THg) concentrations in the glacier snow ranged from <1 to 43.6 ng L(-1), and exhibited clear seasonal variations with lower values in summer than in winter. Spatially, higher THg concentrations were typically observed in glacier snows from the northern region where atmospheric particulate loading is comparably high. Glacier snowpit Hg was largely dependent on particulate matters and was associated with particulate Hg, which is less prone to postdepositional changes, thus providing a valuable record of atmospheric Hg deposition. Estimated atmospheric Hg depositional fluxes ranged from 0.74 to 7.89 μg m(-2) yr(-1), agreeing very well with the global natural values, but are one to two orders of magnitude lower than that of the neighboring East Asia. Elevated Hg concentrations were observed in refrozen ice layers in several snowpits subjected to intense melt, indicating that Hg can be potentially released to meltwater.

The role of terrestrial vegetation in atmospheric Hg deposition: Pools and fluxes of spike and ambient Hg from the METAALICUS experiment

[1] As part of the Mercury Experiment to Assess Atmospheric Loading in Canada and the U.S. (METAALICUS), different stable Hg(II) isotope spikes were applied to the upland and wetland areas of a boreal catchment between 2001 and 2006 to examine retention of newly deposited Hg(II). In the present study, a Geographical Information Systems (GIS)-based approach was used to quantify canopy and ground vegetation pools of experimentally applied upland and wetland spike Hg within the METAALICUS watershed over the terrestrial loading phase of the experiment. A chemical kinetic model was also used to describe the changes in spike Hg concentrations of canopy and ground vegetation over time. An examination of the fate of spike Hg initially present on canopy vegetation using a mass balance approach indicated that the largest percentage flux from the canopy over one year post-spray was emission to the atmosphere (upland: 45%; wetland: 71%), followed by litterfall (upland: 14%; wetland: 10%) and throughfall fluxes (upland: 12%; wetland: 9%) and longer term retention of spike in the forest canopy (11% for both upland and wetland). Average half-lives (t1/2) of spike on deciduous (110 ± 30 days) and coniferous (180 ± 40 days) canopy and ground vegetation (890 ± 620 days) indicated that retention of new atmospheric Hg(II) on terrestrial (especially ground) vegetation delays downward transport of new atmospheric Hg(II) into the soil profile and runoff into lakes.

Gas-particle partitioning of atmospheric Hg(II) and its effect on global mercury deposition

Abstract. Atmospheric deposition of Hg(II) represents a major input of mercury to surface environments. The phase of Hg(II) (gas or particle) has important implications for deposition. We use long-term observations of reactive gaseous mercury (RGM, the gaseous component of Hg(II)), particle-bound mercury (PBM, the particulate component of Hg(II)), fine particulate matter (PM2.5), and temperature (T) at five sites in North America to derive an empirical gas-particle partitioning relationship log10(K−1) = (10±1)–(2500±300)/T where K = (PBM/PM2.5)/RGM with PBM and RGM in common mixing ratio units, PM2.5 in μg m−3, and T in K. This relationship is within the range of previous work but is based on far more extensive data from multiple sites. We implement this empirical relationship in the GEOS-Chem global 3-D Hg model to partition Hg(II) between the gas and particle phases. The resulting gas-phase fraction of Hg(II) ranges from over 90 % in warm air with little aerosol to less than 10 % in cold air with high aerosol. Hg deposition to high latitudes increases because of more efficient scavenging of particulate Hg(II) by precipitating snow. Model comparison to Hg observations at the North American surface sites suggests that subsidence from the free troposphere (warm air, low aerosol) is a major factor driving the seasonality of RGM, while elevated PBM is mostly associated with high aerosol loads. Simulation of RGM and PBM at these sites is improved by including fast in-plume reduction of Hg(II) emitted from coal combustion and by assuming that anthropogenic particulate Hg(p) behaves as semi-volatile Hg(II) rather than as a refractory particulate component. We improve the simulation of Hg wet deposition fluxes in the US relative to a previous version of GEOS-Chem; this largely reflects independent improvement of the washout algorithm. The observed wintertime minimum in wet deposition fluxes is attributed to inefficient snow scavenging of gas-phase Hg(II).

Differential exposure of alpine ospreys to mercury: Melting glaciers, hydrology or deposition patterns?

Mercury (Hg) is a global contaminant impacting even remote environments. In alpine watersheds, glacial meltwater is a source of Hg, which accumulated in glaciers during the 1960–1980 cooling cycle. The considerable variation observed for Hg exposure of alpine animals in proximal watersheds could result from differences among those watersheds in Hg loading from glacial meltwater. Alternatively, variation may be the result of hydrology, atmospheric Hg deposition patterns, or food web characteristics. To examine those possibilities, we measured Hg in ospreys (Pandion haliaetus), apex predators in 15 watersheds in western Canada. Mercury levels in feathers of nestlings increased with increasing modeled atmospheric deposition rates and decreased with lake size. In eggs mercury decreased with δ13C, an indicator of food web structure, and with pH and elevation. Thus, Hg levels in chicks were strongly associated with local patterns relevant when the chicks were growing (e.g. the period post-snow melt: Hg deposition, lake size) while Hg levels in eggs were weakly associated with local patterns relevant during the snow melt (elevation, δ13C), with the remainder of the Hg variation in eggs determined by other factors such as possible Hg accumulation by the adult elsewhere. Modeled atmospheric deposition from prevailing upwind locations including Asia, followed by runoff into small lakes, were related to Hg patterns in osprey, with little apparent role for recent melting of glaciers. Our study highlights the importance of physical patterns to the environmental chemistry of top predators.

Increased atmospheric deposition of mercury in reference lakes near major urban areas

Atmospheric deposition of Hg is the predominant pathway for Hg to reach sensitive ecosystems, but the importance of emissions on near-field deposition remains unclear. To better understand spatial variability in Hg deposition, mercury concentrations were analyzed in sediment cores from 12 lakes with undeveloped watersheds near to (<50 km) and remote from (>150 km) several major urban areas in the United States. Background and focusing corrected Hg fluxes and flux ratios (modern to background) in the near-urban lakes (68 ± 6.9 μg m −2 yr −1 and 9.8 ± 4.8, respectively) greatly exceed those in the remote lakes (14 ± 9.3 μg m −2 yr −1 and 3.5 ± 1.0) and the fluxes are strongly related to distance from the nearest major urban area ( r 2 = 0.87) and to population and Hg emissions within 50–100 km of the lakes. Comparison to monitored wet deposition suggests that dry deposition is a major contributor of Hg to lakes near major urban areas.

Assessment of mercury and selenium concentrations in captive bottlenose dolphin's (Tursiops truncatus) diet fish, blood, and tissue

Concentrations of total mercury (Hg) and selenium (Se) were determined in diet fish and whole blood and tissue samples from seven bottlenose dolphins (Tursiops truncatus) housed at the National Aquarium Baltimore (NAB). In addition, concentrations of monomethylmercury (CH3Hg+) were determined in diet fish and dolphins' tissue samples. The data were compared with the values found in wild populations to better understand how the dietary Hg and Se uptake rates affect the Hg and Se levels in dolphins. The diet fish total Hg concentrations ranged between 14 and 47ngg−1 and were markedly lower than for similar fish found in Florida, South Carolina, and other aquaria. CH3Hg+ accounted for 85 to 91% of the total Hg found in diet fish. The diet fish Se concentrations ranged between 270 and 800ngg−1, indicating excess molar concentrations of Se over Hg. The Hg concentration range in the blood of NAB dolphins was 27–117ngg−1 and the concentrations were about one order of magnitude and several factors lower than the concentrations found in the blood of wild bottlenose dolphins in Florida and in South Carolina, respectively. The total Hg and CH3Hg+ in tissue samples were also significantly lower than the reported values obtained from wild populations of bottlenose dolphins. The differences in the Hg concentrations in the dolphins' blood may be due to the different levels of Hg atmospheric deposition in the area where the dolphins' diet fish were found. The Se concentration range in the blood of NAB dolphins was 221–297ngg−1 which was two factors lower than the values found in wild populations. The lower Hg levels, as well as higher Se:Hg molar ratios in the blood of NAB dolphins, suggest that NAB dolphins may be less susceptible to the potential neurotoxicity from the CH3Hg+ in their blood.

Recent paleorecords document rising mercury contamination in Lake Tanganyika

Abstract Recent Lake Tanganyika Hg deposition records were derived using 14C and excess 210Pb geochronometers in sediment cores collected from two contrasting depositional environments: the Kalya Platform, located mid-lake and more removed from watershed impacts, and the Nyasanga/Kahama River delta region, located close to the lake’s shoreline north of Kigoma. At the Kalya Platform area, pre-industrial Hg concentrations are 23 ± 0.2 ng/g, increasing to 74 ng/g in modern surface sediment, and the Hg accumulation rate has increased from 1.0 to 7.2 μg/m2/a from pre-industrial to present, which overall represents a 6-fold increase in Hg concentration and accumulation. At the Nyasanga/Kahama delta region, pre-industrial Hg concentrations are 20 ± 3 ng/g, increasing to 46 ng/g in surface sediment. Mercury accumulation rate has increased from 30 to 70 μg/m2/a at this site, representing a 2–3-fold increase in Hg concentration and accumulation. There is a lack of correlation between charcoal abundance and Hg accumulation rate in the sediment cores, demonstrating that local biomass burning has little relationship with the observed Hg concentration or Hg accumulation rates. Examined using a sediment focusing-corrected mass accumulation rate approach, the cores have similar anthropogenic atmospheric Hg deposition profiles, suggesting that after accounting for background sediment concentrations the source of accumulating Hg is predominantly atmospheric in origin. In summary, the data document an increase of Hg flux to the Lake Tanganyika ecosystem that is consistent with increasing watershed sediment delivery with background-level Hg contamination, and regional as well as global increases in atmospheric Hg deposition.

Mercury concentrations in snapping turtles (Chelydra serpentina) correlate with environmental and landscape characteristics

Mercury (Hg) deposited onto the landscape can be transformed into methylmercury (MeHg), a neurotoxin that bioaccumulates up the aquatic food chain. Here, we report on Hg concentrations in snapping turtles (Chelydra serpentina) across New York State, USA. The objectives of this study were to: (1) test which landscape, water, and biometric characteristics correlate with total Hg (THg) concentrations in snapping turtles; and (2) determine whether soft tissue THg concentrations correlate with scute (shell) concentrations. Forty-eight turtles were sampled non-lethally from ten lakes and wetlands across New York to observe patterns under a range of ecosystem variables and water chemistry conditions. THg concentrations ranged from 0.041 to 1.50 μg/g and 0.47 to 7.43 μg/g wet weight of muscle tissue and shell, respectively. The vast majority of mercury (~94%) was in the MeHg form. Sixty-one percent of turtle muscle samples exceeded U.S. Environmental Protection Agency (U.S. EPA) consumption advisory limit of 0.3 μg Hg/g for fish. Muscle THg concentrations were significantly correlated with sulfate in water and the maximum elevation of the watershed. Shell THg concentrations were significantly correlated with the acid neutralizing capacity (ANC) of water, the maximum elevation of the watershed, the percent open water in the watershed, the lake to watershed size, and various forms of atmospheric Hg deposition. Thus, our results demonstrate that THg concentrations in snapping turtles are spatially variable, frequently exceed advisory limits, and are significantly correlated with several landscape and water characteristics.

A global model of mass independent mercury stable isotope fractionation

Mass independent fractionation (MIF) of stable isotopes associated with terrestrial geochemical processes was first observed in the 1980s for oxygen and in the 1990s for sulfur isotopes. Recently mercury (Hg) was added to this shortlist when positive odd Hg isotope anomalies were observed in biological tissues. Experimental work identified photoreduction of aquatic inorganic divalent Hg II and photodegradation of monomethylmercury species as plausible MIF inducing reactions. Observations of continental receptors of atmospheric Hg deposition such as peat, lichens, soils and, indirectly, coal have shown predominantly negative MIF. This has led to the suggestion that atmospheric Hg has negative MIF signatures and that these are the compliment of positive Hg MIF in the aquatic environment. Recent observations on atmospheric vapor phase Hg 0 and Hg II in wet precipitation reveal zero and positive Hg MIF respectively and are in contradiction with a simple aquatic Hg II photoreduction scenario as the origin for global Hg MIF observations. This study presents a synthesis of all terrestrial Hg MIF observations, and these are integrated in a one-dimensional coupled continent-ocean–atmosphere model of the global Hg cycle. The model illustrates how Hg MIF signatures propagate through the various Earth surface reservoirs. The scenario in which marine photoreduction is the main MIF inducing process results in negative atmospheric Δ 199Hg and positive ocean Δ 199Hg of −0.5‰ and +0.25‰, yet does not explain atmospheric Hg 0 and Hg II wet precipitation observations. Alternative model scenarios that presume in-cloud aerosol Hg II photoreduction and continental Hg II photoreduction at soil, snow and vegetation surfaces to display MIF are necessary to explain the ensemble of natural observations. The model based approach is a first step in understanding Hg MIF at a global scale and the eventual incorporation of Hg stable isotope information in detailed global mercury chemistry and transport models.

Mercury in the Southern Ocean

We present here the first mercury speciation study in the water column of the Southern Ocean, using a high-resolution south-to-north section (27 stations from 65.50°S to 44.00°S) with up to 15 depths (0–4440 m) between Antarctica and Tasmania (Australia) along the 140°E meridian. In addition, in order to explore the role of sea ice in Hg cycling, a study of mercury speciation in the “snow–sea ice–seawater” continuum was conducted at a coastal site, near the Australian Casey station (66.40°S; 101.14°E). In the open ocean waters, total Hg (Hg T) concentrations varied from 0.63 to 2.76 pmol L −1 with “transient-type” vertical profiles and a latitudinal distribution suggesting an atmospheric mercury source south of the Southern Polar Front (SPF) and a surface removal north of the Subantartic Front (SAF). Slightly higher mean Hg T concentrations (1.35 ± 0.39 pmol L −1) were measured in Antarctic Bottom Water (AABW) compared to Antarctic Intermediate water (AAIW) (1.15 ± 0.22 pmol L −1). Labile Hg (Hg R) concentrations varied from 0.01 to 2.28 pmol L −1, with a distribution showing that the Hg T enrichment south of the SPF consisted mainly of Hg R (67 ± 23%), whereas, in contrast, the percentage was half that in surface waters north of PFZ (33 ± 23%). Methylated mercury species (MeHg T) concentrations ranged from 0.02 to 0.86 pmol L −1. All vertical MeHg T profiles exhibited roughly the same pattern, with low concentrations observed in the surface layer and increasing concentrations with depth up to an intermediate depth maximum. As for Hg T, low mean MeHg T concentrations were associated with AAIW, and higher ones with AABW. The maximum of MeHg T concentration at each station was systematically observed within the oxygen minimum zone, with a statistically significant MeHg T vs Apparent Oxygen Utilization (AOU) relationship ( p < 0.001). The proportion of Hg T as methylated species was lower than 5% in the surface waters, around 50% in deep waters below 1000 m, reaching a maximum of 78% south of the SPF. At Casey coastal station Hg T and Hg R concentrations found in the “snow–sea ice–seawater” continuum were one order of magnitude higher than those measured in open ocean waters. The distribution of Hg T there suggests an atmospheric Hg deposition with snow and a fractionation process during sea ice formation, which excludes Hg from the ice with a parallel Hg enrichment of brine, probably concurring with the Hg enrichment of AABW observed in the open ocean waters. Contrastingly, MeHg T concentrations in the sea ice environment were in the same range as in the open ocean waters, remaining below 0.45 pmol L −1. The MeHg T vertical profile through the continuum suggests different sources, including atmosphere, seawater and methylation in basal ice. Whereas Hg T concentrations in the water samples collected between the Antarctic continent and Tasmania are comparable to recent measurements made in the other parts of the World Ocean (e.g., Soerensen et al., 2010), the Hg species distribution suggests distinct features in the Southern Ocean Hg cycle: (i) a net atmospheric Hg deposition on surface water near the ice edge, (ii) the Hg enrichment in brine during sea ice formation, and (iii) a net methylation of Hg south of the SPF.

Bioavailable Mercury Cycling in Polar Snowpacks

Polar regions are subject to contamination by mercury (Hg) transported from lower latitudes, severely impacting human and animal health. Atmospheric Mercury Depletion Events (AMDEs) are an episodic process by which Hg is transferred from the atmospheric reservoir to arctic snowpacks. The fate of Hg deposited during these events is the subject of numerous studies, but its speciation remains unclear, especially in terms of environmentally relevant forms such as bioavailable mercury (BioHg). Here, using a bacterial mer-lux biosensor, we report the fraction of newly deposited Hg at the surface and at the bottom of the snowpack that is bioavailable. Snow samples were collected over a two-month arctic field campaign in 2008. In surface snow, BioHg is related to atmospheric Hg deposition and snow fall events were shown to contribute to higher proportions of BioHg than AMDEs. Based on our data, AMDEs represent a potential source of 20 t.y(-1) of BioHg, while wet and dry deposition pathways may provide 135-225 t.y(-1) of BioHg to Arctic surfaces.

A 1955–2004 record of Hg contamination in Dianshan Lake sediments, Shanghai

Measuring Hg levels of water sediments is one of the primary routes to assess the trend of the contamination. Little work has been carried out in the Yangtze Delta to track the trend of mercury contamination caused by Shanghai, which is one of the fastest growing economies in the world today. The mercury concentration in the sedimentary cores from Dianshan Lake, Shanghai is studied here. Results show that mercury transported to Dianshan Lake from emissions of coal combustion and non-coal sources in the Yangtze Delta was greater after 1979. We found also that before 1979 mercury levels changed less with time than after 1979. Before 1967 Hg levels were more variable than in the 1970s. Moreover, the mercury dissolved in river water and bound to particles of water that flow past downtown Shanghai is different from that observed in Dianshan Lake, which is located in upper Shanghai. This indicates that atmospheric Hg deposition is probably the main source of mercury in Dianshan Lake. These results are important for the establishment of environmental protections and pollution treatment proposals for mercury in similar areas of the world, as well as in Shanghai.

Atmospheric distribution and deposition of mercury in the Idrija Hg mine region, Slovenia

The atmospheric distribution and deposition of Hg in the area of the former Idrija Hg-mine, Slovenia, were investigated. Mapping of air Hg 0 concentrations was performed to assess the spatial distribution and major sources of mercury to the atmosphere in the area. In addition, analyses of mercury speciation in the air over Idrija were performed during a 4-day sampling campaign in September 2006 to better understand the fate and transformation of Hg in the atmosphere of this specific mercury polluted site. The speciation results were then compared to the results of mercury speciation in the wet and throughfall deposition sampled on a precipitation event basis from October 2006 to September 2007. The Hg 0 concentration in air was mostly below 10 ng m −3, with the highest concentration in the area of the former smelter complex exceeding 5000 ng m −3. Mercury-bearing airborne particles (TPM) seem to dominate the atmospheric Hg deposition, which revealed noticeable variations between precipitation events (11–76 ng m −2 day −1), mostly as a function of the amount of precipitation. Hg in precipitation was largely (∼50%) associated with the particulate phase (THg P). No correlation was found between the THg P and the dissolved phases (THg D), suggesting that particulate phase Hg is mostly the result of dry deposition. In the throughfall, significantly higher (2–10 fold) Hg concentrations than in associated event precipitation were observed, mostly due to Hg in the particulate phase (∼70% THg). As shown by SEM/EDXS microscopy, an important amount of mercury in the precipitation and throughfall samples is due to the presence of cinnabar particles as a result of the aeolian erosion of cinnabar-containing surfaces in the area.

Vertical transport of anthropogenic mercury in the ocean

We investigate the vertical transport of mercury (Hg) within the ocean using a simple box diffusion model to represent vertical water transport coupled with a particulate Hg flux. The particulate flux assumes that the Hg content of marine particles is proportional to the Hg concentration of surface waters via a sorption equilibrium constant, Kd. The model is forced with the observed factor of 3 increase in atmospheric Hg deposition over the industrial era. The modeled vertical profile of oceanic Hg shows a subsurface maximum at ∼500 m depth due to remineralization of Hg bound to sinking organic particles, consistent with observations. Model results indicate that surface (top 100 m) concentrations of Hg have increased by 150% since preindustrial times. Over the past 150 years, 280 Mmol of anthropogenic Hg have accumulated in the ocean, representing a 18% increase in the total oceanic Hg content. We find that 36% of the anthropogenic Hg occurs in the top 400 m and only 7% occurs below 1500 m. Over the industrial era, we find that 14% of cumulative anthropogenic emissions have accumulated in the ocean. Our model results show that half of the accumulation of anthropogenic Hg in the ocean is due to sinking on particulates. A sensitivity analysis indicates that the model results are most dependent on the value of Kd.

Measurement of surface mercury fluxes at active industrial gold mines in Nevada (USA)

Mercury (Hg) may be naturally associated with the rock units hosting precious and base metal deposits. Active gold mines are known to have point source releases of Hg associated with ore processing facilities. The nonpoint source release of Hg to the air from the large area (hundreds to thousands of hectares) of disturbed and processed material at industrial open pit gold mines has not been quantified. This paper describes the field data collected as part of a project focused on estimating nonpoint source emissions of Hg from two active mines in Nevada, USA. In situ Hg flux data were collected on diel and seasonal time steps using a dynamic flux chamber from representative mine surfaces. Hg fluxes ranged from < 1500 ng m −2 day −1 for waste rock piles (0.6–3.5 μg g −1) to 684,000 ng m −2 day −1 for tailings (2.8–58 μg g −1). Releases were positively correlated with material Hg concentrations, surface grain size, and moisture content. Highest Hg releases occurred from materials under active cyanide leaching and from tailings impoundments containing processed high-grade ore. Data collected indicate that as mine sites are reclaimed and material disturbance ceases, emissions will decline. Additionally local cycling of atmospheric Hg (deposition and re-emission) was found to occur.