Transport Of Hg Research Articles

Integrated watershed process model for evaluating mercury sources, transport, and future remediation scenarios in an industrially contaminated site

We used the Soil Water Assessment Tool (SWAT) as a framework to develop an empirical Hg flux model for Upper East Fork Poplar Creek (UEFPC), a Hg-contaminated watershed in Oak Ridge, Tennessee. By integrating long-term Hg monitoring data with simulated flow and suspended solid loads in a site-specific empirical Hg transport model, we (1) quantified the spatial, temporal, and flow regime controls on daily Hg flux (adjusted R2 = 0.82) and (2) made predictions about Hg flux under future climate, land use, and management scenarios. We found that 62.79% of the average daily Hg flux in the watershed is currently driven by base flow, whereas variability in Hg flux is driven by storm and extreme flow. We estimate an average annual Hg flux of 28.82 g day-1 leaving the watershed under baseline precipitation, with an estimated 43.73% reduction in daily Hg flux under drought conditions and a 296% increase in daily Hg flux in extreme precipitation scenarios. We estimated that a new mercury treatment facility would result in a 24.7% reduction in Hg flux under baseline conditions and a 33.4% reduction under extreme precipitation scenarios. The study demonstrated the merit of this approach, which can be replicated for sites where information on flow, suspended solids, and Hg concentrations is available.

Effects of photo-irradiation on mercury binding to dissolved organic matter: Insights from FT-IR and synchronous fluorescence two-dimensional correlation spectroscopy

The binding interactions between Hg and dissolved organic matter (DOM) affect the fate and transport of Hg in the aquatic environment. Here, we investigate the effects of photo-irradiation on the binding characteristics of dissolved organic matter with Hg(II) using FT-IR and synchronous fluorescence two-dimensional correlation spectroscopy (2D-COS). Results showed that the binding of Hg(II) onto humic acid (HA) followed the order of humic-like fraction > fulvic-like fraction > protein-like fraction and photo-irradiation did not affect this order. The binding affinity of each site within the fluorescent fraction was affected by the photoreaction patterns. Pre-irradiation of HA before Hg(II) binding changed its structures and binding ability. UV irradiation showed a more obvious effect on Hg(II)-HA complexes than solar irradiation, and UV irradiation enhanced the reactivity of aromatic groups of HA. The amine or amide N–H of HA played a leading role in binding with Hg(II) in the dark, whereas the aromatic amine C–N became dominant after UV irradiation. In fulvic acid (FA), the aromatic hydrogen C–H played a leading role in Hg(II) binding in the dark, but solar irradiation promoted the binding ability of polysaccharide C–O and the carboxyl CO became dominant after UV irradiation. The response sensitivity of the fulvic-like fraction to Hg(II) was higher than that of the protein-like fraction in FA. Multiple types of sites binding to Hg(II) were verified in the fulvic-like fraction and protein-like fraction of FA. These findings provide new insight into photo-induced structural changes of DOM upon Hg binding.

Effects of temperature and relative humidity on the partitioning of atmospheric oxidized mercury at a high-altitude mountain background site in Taiwan

Gas-particle partitioning of oxidized mercury (Hg) plays an important role in governing the speciation, transport and deposition of atmospheric Hg. Although studies on gas-particle partitioning of oxidized Hg have been conducted at some urban sites, comparable studies at remote mountain sites are still limited. This study analyzes multi-year (2014–2016) data of speciated atmospheric Hg concentrations from Lulin Atmospheric Background Station (LABS, 2862 m above sea level), Taiwan, to explore the factors that influence the gas-particle partitioning of atmospheric oxidized Hg. Mean concentrations (±S.D.) of gaseous elemental mercury (GEM), gaseous oxidized mercury (GOM), and particulate-bound mercury (PBM) were 1.54 ± 0.34 ng m−3, 14.5 ± 26.5 pg m−3, and 5.0 ± 12.0 pg m−3, respectively. In addition, our results indicated that the partitioning of Hg(II) toward particles was favored in the upper free troposphere and/or lower stratosphere. Both temperature (T) and relative humidity (RH) were found to strongly affect the gas-particle partitioning of oxidized Hg. Significant negative correlations between the partitioning coefficient (Kp) and T were obtained for all seasons, but peaked in summer. When RH<30%, Kp decreased with increasing RH. However, Kp and RH were positively correlated when RH>30%. Two empirical Kp-T and Kp-T-RH regression equations: log(1/Kp) = 15.0 – 3887.6(1/T) and log(1/Kp) = 17.92 – 4390.0(1/T) – 0.016RH were developed for free tropospheric air downwind of continental East Asia, which could be implemented in a chemical transport model to improve our understanding of the Hg biogeochemical cycle.

Studies on Nusselt and Sherwood number for diffusion-advective convection during physical vapor transport of Hg 2 Br 2

Studies on Nusselt and Sherwood number for diffusion-advective convection during physical vapor transport of Hg 2 Br 2

Assessment of mercury levels in modern sediments of the East Siberian Sea

Mercury (Hg) is an important environmental indicator of anthropogenic pollution. In this study, the Hg content in the bottom sediments of the East Siberian Sea was observed to range from 13 to 92 ppb, with an average of 36 ppb. Facies dependence was also observed and expressed as an increase in the Hg concentration in fine-sized sediments on the shelf edge and continental slope, compared to that in the sandy silts and sands of the inner shelf. The Hg accumulation in bottom sediments of the eastern part has increased over the past 150 years due to an increase in global emissions of anthropogenic Hg, which is caused by the transboundary transport of Hg to the Arctic. Moreover, changes in the Hg value, which occur due to the plankton arriving at the bottom sediments because of changes in hydrology and primary production, are thought to be associated with global warming.

APPLICATION OF COUPLED HEC-HMS AND US EPA WASP FOR TRANSPORT MODELLING OF MERCURY IN THE MINING-IMPACTED AMBALANGA RIVER

This study provides a simulation of mercury (Hg) transport in water and sediments in the mining-impacted Ambalanga River located in Upper Agno Subbasin in the Philippines. The Hydrologic Engineering Center - Hydrologic Modeling System (HEC-HMS) and Water Quality Analysis Simulation Program (WASP) of the US Environmental Protection Agency (EPA) were coupled to handle both hydrologic modelling and total Hg transport processes, respectively, for 12 months in the year 2014. Watershed delineation from Digital Elevation Model, rainfall and streamflow data from the local weather bureau, and dam operational data were used to develop the hydrological model. The calibrated HEC-HMS model satisfactorily simulated the flow in the river and its tributaries, which is then used as an input to the Hg transport model. The Ambalanga subbasin was conceptually divided into 29 segments in WASP to represent the water column and the surface benthic sediment. Time-variable sediment and Hg load were applied to the upstream of Ambalanga River. Total Hg concentration in water and sediments at five sampling locations along the Ambalanga River and two sampling locations along the Upper Agno River were measured in 2014-2015, in addition to the Hg monitoring data from the local environmental bureau. The gathered data were used to validate the WASP model, and results show that it was able to reasonably simulate the Hg fate and transport. Simulation results showed a downward trend in Hg concentration in surface water and sediments from upstream to downstream, while Hg in sediments was observed to stabilize over time. The model was further utilized to come up with exceedance curves of Hg in water and sediments as a result of the river’s response to different Hg loading from the known point sources. The exceedance curves derived from the model were used to determine the maximum permissible Hg loading to the river and identify pollution load reduction measures for river rehabilitation.

Katabatic Wind and Sea-Ice Dynamics Drive Isotopic Variations of Total Gaseous Mercury on the Antarctic Coast.

Clarifying the sources and fates of atmospheric mercury (Hg) in the Antarctic is crucial to understand the global Hg circulation and its impacts on the fragile ecosystem of the Antarctic. Herein, the annual variations in the isotopic compositions of total gaseous Hg (TGM), with 5-22 days of sampling duration for each sample, were presented for the first time to provide isotopic evidence of the sources and environmental processes of gaseous Hg around the Chinese Great Wall Station (GWS) in the western Antarctic. Different from the Arctic tundra and lower latitude areas in the northern hemisphere, positive δ202Hg (0.58 ± 0.21‰, mean ± 1SD) and negative Δ199Hg (-0.30 ± 0.10‰, mean ± 1SD) in TGM at the GWS indicated little impact from the vegetation-air exchange in the Antarctic. Correlations among TGM Δ199Hg, air temperature, and ozone concentrations suggested that enhanced katabatic wind that transported inland air masses to the continental margin elevated TGM Δ199Hg in the austral winter, while the surrounding marine surface emissions controlled by sea-ice dynamics lowered TGM Δ199Hg in the austral summer. The oxidation of Hg(0) might elevate Δ199Hg in TGM during atmospheric Hg depletion events but have little impact on the seasonal variations of atmospheric Hg isotopes. The presented atmospheric Hg isotopes were essential to identify the transport and transformation of atmospheric Hg and further understand Hg cycling in the Antarctic.

Mercury contamination at Vembanad Lake and near-shore regions in the southwest coast of India

Mercury (Hg) contamination in aquatic systems is a universal concern because of its persistence, bioaccumulation, toxicity, and trans-boundary nature. The current study focuses on monitoring the fate and transport of Hg in aquatic matrices such as water, interstitial water, sediment and fish in a tropical coastal ecosystem. The cold vapour atomic fluorescence spectrometer was used for the Hg analysis. The study assessed the fractionation of Hg and its methylation potential in sediments. The high Hg concentration in fish tissues showed the ineffectiveness of biogeochemical control over the methyl Hg mobility and bioavailability through the food web. Research results indicate that the accumulation potential of Hg subsequently increases along the food chain. The conducive physico-chemical environment at the sediment–water interface supports chemical transformations/transport of Hg from one matrix to the next. The fate of Hg in the lake has also been discussed based on the data generated.

Environmental Partitioning, Spatial Distribution, and Transport of Atmospheric Mercury (Hg) Originating from a Site of Former Chlor-Alkali Plant

Mercury (Hg) is one of the trace toxic and bioaccumulative global pollutants, and due to its long atmospheric lifetime, it presents a significant global challenge. The present study (1) utilizes total gaseous mercury (TGM) measurements made around a former Hg-cell chlor-alkali plant (CAP) located in Pavlodar, Kazakhstan, and predicts the spatial distribution of Hg over its premises and the nearby city. It then (2) estimates the environmental repartition of Hg deposited by the CAP using three fugacity models of varying complexity: Level I, QWASI, and HERMES. Finally, it (3) predicts long-range Hg transport via forward trajectory-based cluster analysis. The atmospheric Hg levels measured in Pavlodar and around Lake Balkyldak were elevated: in the range of 1–37 ng/m3 with an urban background level at 4.9 ng/m3. Specifically, concentrations up to 37 ng/m3 close to Lake Balkyldak and up to 22 ng/m3 nearby the city’s industrial zone (where the CAP was located) had been observed. Interpolation maps created using kriging also suggest these locations as the primary sources of atmospheric Hg in the city. The Level I fugacity model indicated that almost all of Hg is expected to end up in the atmosphere. The modeling results obtained using more complex QWASI and HERMES models showed that some significant quantity of Hg would still be associated with the sediments of Lake Balkyldak (a large wastewater discharge pond nearby the CAP). The forward trajectory-based cluster analysis method revealed the long-range atmospheric transportation routes and local, regional, and global impact zones. Furthermore, a source-receptor relationship using air transportation pathways to identify “areas of impact” was addressed. During both heating and non-heating seasons, the frequency-based analysis identified the distribution of Hg reaching the territories of Mongolia, northwest China, southwest Kazakhstan. The Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT-4) model forward trajectory analysis has confirmed similar patterns during heating and non-heating seasons, except with shorter impact distances during the non-heating period. Even though the CAP was closed more than 30 years ago and those past remediation efforts cleaned up the site, the residual Hg pollution seems significant and should be further investigated in different environmental media.

Role of organic matter and microbial communities in mercury retention and methylation in sediments near run-of-river hydroelectric dams

Run-of-river power plants (RoRs) are expected to triple in number over the next decades in Canada. These structures are not anticipated to considerably promote the mobilization and transport of mercury (Hg) and its subsequent microbial transformation to methylmercury (MeHg), a neurotoxin able to biomagnify in food webs up to humans. To test whether construction of RoRs had an effect on Hg transport and transformation, we studied Hg and MeHg concentrations, organic matter contents and methylating microbial community abundance and composition in the sediments of a section of the St. Maurice River (Quebec, Canada). This river section has been affected by the construction of two RoR dams and its watershed has been disturbed by a forest fire, logging, and the construction of wetlands. Higher total Hg (THg) and MeHg concentrations were observed in the surface sediments of the flooded sites upstream of the RoRs. These peaks in THg and MeHg were correlated with organic matter proportions in the sediments (r2 = 0.87 and 0.82, respectively). In contrast, the proportion of MeHg, a proxy for methylation potential, was best explained by the carbon to nitrogen ratio suggesting the importance of terrigenous organic matter as labile substrate for Hg methylation in this system. Metagenomic analysis of Hg-methylating communities based on the hgcA functional gene marker indicated an abundance of methanogens, sulfate reducers and fermenters, suggesting that these metabolic guilds may be primary Hg methylators in these surface sediments. We propose that RoR pondages act as traps for sediments, organic matter and Hg, and that this retention can be amplified by other disturbances of the watershed such as forest fire and logging. RoR flooded sites can be conducive to Hg methylation in sediments and may act as gateways for bioaccumulation and biomagnification of MeHg along food webs, particularly in disturbed watersheds.

Bog and lake sediment archives reveal a lagged response of subarctic lakes to diminishing atmospheric Hg and Pb deposition

We used a flux deconstruction approach on peat and sediment archives of four bogs and five lakes from two subarctic taiga ecoregions of the Northwest Territories (Canada) to distinguish the atmospheric and catchment-based responses to changing metal pollution emissions over the last 2000 years. Bogs tracked the atmospheric signal, whereas lake sediments provided a mixed atmospheric and catchment-based response. Anthropogenic mercury (Hg) and lead (Pb) contamination was identified in lake sediment and bog records from the mid-1800s onward and increased rapidly after ca. 1900. Long-range transport of Hg and Pb was likely the dominant source of the post-1900 enrichment in lake sediments, with minor contributions from local mining, mostly between 1950 and 1970. Bogs and sediment records of small lakes on the Taiga Plains showed that atmospheric deposition peaked in the late 1990s for Pb and in the 1970s for Hg. In contrast, the Pb and Hg accumulation rates in Taiga Shield lakes have continued to increase since the peak atmospheric deposition period due to on-going catchment transport, and may reflect recent climate change favoring late-fall and early-winter precipitation as rain rather than snow. The divergent trends in metal accumulation rates between ecoregions and environmental archives demonstrate that interactions of climate and catchment characteristics will be key to future contamination trajectories for subarctic lakes following reductions of anthropogenic metal emissions in North America.

Spatial distribution of mercury accumulation in the surface soil of Japanese forests

ABSTRACT Mercury (Hg) is a pollutant that can affect human and ecosystem health. The transport and fate of Hg in the environment are dynamic and complex, but our understanding remains unclear for Japanese forest ecosystems. Here, we report the first country-wide survey of Hg concentrations in litter and surface mineral soil layers in 42 forest stands across Japan. The median concentrations of Hg in the litter layer and 0–10 cm of mineral soils were 99 (range: 56.7–297) and 145 (range: 22.8–294) μg kg−1, respectively, and tended to decrease down to 50 cm. There was a positive relationship between the Hg and total organic carbon concentrations in soil, suggesting that organic carbon strongly binds with Hg in soil. There was a significant positive correlation between the Hg and lead concentrations in the litter layer. Partial least square regression analysis indicated that the soil and litter properties as well as the atmospheric and geological Hg concentrations and some soil characteristics such as soil pH, organic matter properties and soil physical factors were effective explanatory variables of the country-wide spatial patterns of Hg concentrations in litter and mineral soil. In addition, we found the influence of atmospheric Hg is stronger in litter layer, whereas the influences of geological and soil factors are stronger in mineral soil. These results suggest that air pollution partly affects the spatial patterns of Hg concentrations in litter and soil of Japanese forests under the given geological and soil conditions at the country scale.

China's retrofitting measures in coal-fired power plants bring significant mercury-related health benefits

Summary China has implemented retrofitting measures in coal-fired power plants (CFPPs) to reduce air pollution through small unit shutdown, the installation of air pollution control devices (APCDs), and power generation efficiency improvement. The reductions in highly toxic Hg emissions and their related health impacts by these measures remain poorly understood. Here, we evaluated the health benefits of reduced Hg emissions via retrofitting measures during China's 12th Five-Year Plan (2011–2015) by combining plant-level Hg emission inventories with the China Hg Risk-Source-Tracking Model. We found that the measures reduced Hg emissions by 23.5 tons (approximately 1/5 of that from CFPPs in 2010), preventing 30,484.77 total points of intelligence quotient decrement and 114 deaths between 2011 and 2015. These benefits were dominated by CFPP shutdowns and APCD installations, and nearly 50% of provincial health benefits were attributable to Hg reductions in other regions. We suggest that Hg control strategies should consider various factors, such as CFPP location, population density, and trade-offs between reductions in total Hg and in Hg2+.

A synthesis of patterns of environmental mercury inputs, exposure and effects in New York State

Mercury (Hg) pollution is an environmental problem that adversely affects human and ecosystem health at local, regional, and global scales—including within New York State. More than two-thirds of the Hg currently released to the environment originates, either directly or indirectly, from human activities. Since the early 1800s, global atmospheric Hg concentrations have increased by three- to eight-fold over natural levels. In the U.S., atmospheric emissions and point-source releases to waterways increased following industrialization into the mid-1980s. Since then, water discharges have largely been curtailed. As a result, Hg emissions, atmospheric concentrations, and deposition over the past few decades have declined across the eastern U.S. Despite these decreases, Hg pollution persists. To inform policy efforts and to advance public understanding, the New York State Energy Research and Development Authority (NYSERDA) sponsored a scientific synthesis of information on Hg in New York State. This effort includes 23 papers focused on Hg in atmospheric deposition, water, fish, and wildlife published in Ecotoxicology. New York State experiences Hg contamination largely due to atmospheric deposition. Some landscapes are inherently sensitive to Hg inputs driven by the transport of inorganic Hg to zones of methylation, the conversion of inorganic Hg to methylmercury, and the bioaccumulation and biomagnification along food webs. Mercury concentrations exceed human and ecological risk thresholds in many areas of New York State, particularly the Adirondacks, Catskills, and parts of Long Island. Mercury concentrations in some biota have declined in the Eastern Great Lakes Lowlands and the Northeastern Highlands over the last four decades, concurrent with decreases in water releases and air emissions from regional and U.S. sources. However, widespread changes have not occurred in other ecoregions of New York State. While the timing and magnitude of the response of Hg levels in biota varies, policies expected to further diminish Hg emissions should continue to decrease Hg concentrations in food webs, yielding benefits to the fish, wildlife, and people of New York State. Anticipated improvements in the Hg status of aquatic ecosystems are likely to be greatest for inland surface waters and should be roughly proportional to declines in atmospheric Hg deposition. Efforts that advance recovery from Hg pollution in recent years have yielded significant progress, but Hg remains a pollutant of concern. Indeed, due to this extensive compilation of Hg observations in biota, it appears that the extent and intensity of the contamination on the New York landscape and waterscape is greater than previously recognized. Understanding the extent of Hg contamination and recovery following decreases in atmospheric Hg deposition will require further study, underscoring the need to continue existing monitoring efforts.

Translocation and distribution of mercury in biomasses from subtropical forest ecosystems: evidence from stable mercury isotopes

To understand its source, distribution, storage, and translocation in the subtropical forest ecosystems, mercury (Hg) concentrations and stable isotopes in forest biomass tissues (foliage, branch, bark, and trunk) were investigated at Ailao Mountain National Nature Reserve, Southwest China. The total Hg (THg) concentrations in the samples show the following trend: mature foliage (57 ± 19 ng g−1) > bark (11 ± 4.0 ng g−1) > branch (5.4 ± 2.5 ng g−1) > trunk (1.6 ± 0.7 ng g−1). Using the measured THg concentrations and the quantity of respective biomasses, the Hg pools in the forest are: wood (60 ± 26 μg m−2) > bark (51 ± 18 μg m−2) > foliage (41 ± 11 μg m−2) > branch (26 ± 8.3 μg m−2). The tree biomasses displayed negative δ202Hg (− 1.83‰ to − 3.84‰) and ∆199Hg (− 0.18‰ to − 0.62‰). The observed ∆200Hg (− 0.08‰ to 0.04‰) is not significantly from zero. A ∆199Hg/∆201Hg ratio of 1.05 was found in tree biomasses, suggesting that mercury has undergone Hg(II) photoreduction processes. A Hg-isotope based binary mixing model suggests that Hg in the tree biomasses mainly originated from foliage uptake of atmospheric Hg0, constituting 67%, 80%, and 77% of Hg in wood, branch, and bark, respectively. Our study sheds new light on the transportation and sources of Hg in the subtropical forest ecosystems.

Desert dust as a significant carrier of atmospheric mercury

The atmospheric circulation plays a critical role in the global transport and deposition of atmospheric pollutants such as mercury (Hg). Desert dust emissions contribute to nearly 60–95% of the global dust budget and thus, desert dust may facilitate atmospheric Hg transport and deposition to the downwind regions worldwide. The role of desert dust in biogeochemical cycling of Hg, however, has not been well recognized by the Hg research community. In this study, we measured the concentration of particulate bound Hg (HgP) in total suspended particulate (TSP) collected from China’s largest desert, Taklimakan Desert, between 2013 and 2017. The results show that HgP concentrations over the Taklimakan Desert atmosphere are remarkably higher than those observed from background sites in China and are even comparable to those measured in most of the Chinese metropolitan cities. Moreover, HgP concentrations in the Taklimakan Desert exhibit a distinct seasonal pattern peaking during dust storm outbreak periods in spring and summer (March to August). A preliminary estimation demonstrates that export of total Hg associated with atmospheric dust from the Taklimakan Desert could be 59.7 ± 60.3 (1SD) Mg yr−1. The unexpectedly high HgP concentrations during duststorms, together with consistent seasonal pattern of Hg revealed from the snow/ice, clearly demonstrate that Asian desert dust could act as a significant carrier of atmospheric Hg to the cryosphere of Western China and even can have further global reach.

Binding of Hg to preformed ferrihydrite-humic acid composites synthesized via co-precipitation and adsorption with different morphologies

Iron (hydr)oxide-natural organic matter (NOM) colloids, the dominant components of soil, usually occur in varied circumstances and may affect Hg transport and fate in soil. This study aims to reveal the Hg binding to preformed composites rather than only focusing on Hg retention by iron (hydr)oxides in the presence of NOM. Ferrihydrite-humic acid (FH-HA) is chosen as a representative composite, and the effect of the complexation method and FH morphology on Hg binding to various composites is evaluated. Three types of composites are developed: a dense coprecipitated composite (p-d-f), a gel-like adsorbed composite (a-g-f) and a dense adsorbed (a-d-f) composite. Batch sorption and stirred-flow kinetic tests together with surface property analysis and modern spectral analyses are carried out to explore the binding behavior of Hg to the three composites and clarify the interactions in the ternary systems of FH-HA-Hg. The results show that the Hg sorption isotherms all fit well with the Langmuir model, and the maximum sorption capacities follow the order a-g-f> a-d-f > p-d-f, implying that the adsorbed composite is more favorable than the coprecipitated composite for Hg binding and a gel morphology is more beneficial than a dense morphology. The stirred-flow experiments show that the adsorbed composite has a small advantage in Hg sorption compared to the coprecipitated composite and that the gel-like composite can adsorb more Hg at a faster rate than the dense composite. Both FH and HA participate in Hg sorption, and FH-HA-Hg complexes are speculated to form. These findings are helpful to better understand the mobility and fate of Hg in soils, as well as the associated dynamic model for predicting Hg behavior in the environment where the iron (hydr) oxide-NOM composites are pre-existed.

Evaluating the transport of Hg(II) in the presence of natural organic matter through a diffusive gradient in a thin-film passive sampler

The effects of a model natural organic matter (NOM) on the transport of Hg(II) into diffusive gradient in thin-film devices (DGTs) was evaluated in order to better understand their ability to measure colloidal Hg species in porewater. The presence of NOM significantly reduced the diffusivity of the Hg(II) species and the reduction was dependent upon NOM to Hg(II) ratio. This relationship was modeled by determining the Hg(II) partition coefficients (Kd) of size fractionated NOM obtained by ultrafiltration and estimating the Hg diffusivity through the DGT for the different NOM size fractions across a range of Hg-NOM ratios. The estimated diffusivities were consistent with experimental observations of uptake into the DGT. Overall, this study indicated that Hg(II) associated with NOM passes into a DGT, however the transport is slowed in accordance with the diffusivity of the NOM to which the Hg(II) is associated. Thus, the Hg—NOM association and complex diffusivities need to be considered when relating DGT uptake to Hg porewater concentration. The results also suggest that Hg(II) associated with colloidal or larger particles of negligible diffusivity are unlikely to contribute significantly to DGT measurements.

Terrestrial mercury transformation in the Tibetan Plateau: New evidence from stable isotopes in upland buzzards

Understanding the geochemical cycle of mercury (Hg) in the high-altitude Tibetan Plateau is of great value for studying the long-range transport of Hg. Herein, speciation and isotopic compositions of Hg in the muscle and feathers of upland buzzards (Buteo hemilasius) were studied to trace the terrestrial transformation of Hg in the Tibetan Plateau. Very low Hg content and relatively low δ202Hg values (feather: -0.77 ± 0.50‰, n = 9, muscle: -1.29 ± 0.29‰, n = 13, 1SD) were observed in upland buzzards. In contrast, the Δ199Hg values could be as high as 2.89‰ in collected samples. To our knowledge, this is the highest Δ199Hg value reported in avian tissues. Moreover, upland buzzards showed significantly different Δ199Hg values from fish collected from the same region, suggesting different generation and transformation processes of methylmercury (MeHg) in terrestrial and aquatic ecosystems. We speculated that different percentages of Hg undergoing photochemical reactions and contributions of atmospheric MeHg were possible reasons for observed differences. The results provide new clues for different circulation histories of Hg in terrestrial and aquatic ecosystems, which will be critical for further study of geochemical cycle and ecological risk of Hg in the environment.

Mercury sources in a subterranean spontaneous combustion area.

Mercury is a toxic, persistent, and mobile contaminant. Coal spontaneous combustion are widely distributed in the world and releases a great deal of Hg. Identifying the burning coal seam is crucial for quickly extinguishing a coalfield fire. Mercury isotopes can be effective for identifying burning coal seams and beneficial for combating coal spontaneous combustion. In this study, Hg isotopic ratios of coal, topsoil, dustfall, sand, coal fire sponges (CFS), and n-topsoil (topsoil near the CFS) from coal fire area No. 9 in the Wuda coalfield were determined using multiple-collector inductively coupled plasma mass spectrometry (MC-ICPMS). Analysis of the correlation coefficients between the δ202Hg and Hg concentrations and the low-temperature ashes indicate that the higher mineral concentration in coal seam No. 9 not only increases the Hg concentration but also leads to more positive δ202Hg values compared to those for coal seam No. 10. By analyzing the Hg isotope characterizations in coal seam No. 9 and No. 10, we determined that Hg isotope characterizations can be useful for discriminating different coal seam Hg values in a coalfield. Significant mass-dependent fractionation (MDF) occur in the coal burning. The fractionation effect of burning and absorption process can play a key role in the δ202Hg more negative of ground surface samples. If Hg isotopes is added, the effect of coal-fire monitoring may be better. In addition, these finding could be used to better understand the transport and cycling of Hg.