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Atmospheric mercury - An overview
Abstract
This paper presents a broad overview and synthesis of current knowledge and understanding pertaining to all major aspects of mercury in the atmosphere. The significant physical, chemical, and toxicological properties of this element and its environmentally relebant species encountered in the atmosphere are examined. Atmospheric pathways and processes considered herein include anthropogenic as well as natural sources of Hg emissions to the atmosphere, aerial transport and dispersion (including spatial and temporal variability), atmospheric transformations (both physical and chemical types), wet and dry removal/deposition processes to Earth's surface. In addition, inter-compartmental (air-water/soil/vegetation) transfer and biogeochemical cycling of mercury are considered and discussed. The section on numerical modelling deals with atmospheric transport models as well as process-oriented models. Important gaps in our current knowledge of mercury in the atmospheric environment are identified, and suggestions for future areas of research are offered.
... Notably, comparing magnitudes across the dataset, 58% of marine-Hg fluxes and 66% of ice- and western regions of the United States, alongside the increasing [53] or slowing decreasing 258 trends [10] in the central region depending on targeted periods. Overall, the general statistically 259 insignificant decreasing trends of lake-Hg and peat-Hg fluxes in North America are a contrast 260 to the significant reductions in Europe. ...
... The GEOS-Chem simulation of Hg consisted of wet and dry deposition [10]. Wet deposition exists in 114 ...
Global ecosystems face mercury contamination, yet long-term data is scarce, hindering understanding of ecosystem responses to atmospheric Hg input changes and policy evaluation. To address this gap, this study compiled a global mercury accumulation flux database using 221 cores from peat, lake, ice, and marine deposits. From 1700 to 2012, global averaged fluxes in peat, lake, ice, and marine deposits increased five-fold, six-fold, six-fold, and eight-fold, respectively. Notably, lake and peat mercury fluxes generally mirrored trends in total atmospheric mercury deposition modelled by GEOS-Chem and thus can reflect policy effects. For instance, the decreases of lake and peat mercury fluxes post-1950 in Europe evidenced effective environmental policies, while rises in East Asia-Oceania highlighted coal-use impacts, inter alia. Conversely, mercury fluxes in marine sediments and high-altitude natural deposits did not correspond well with atmospheric deposition, emphasising natural influences over anthropogenic impacts. Our study underscores these key regions and ecosystems for future mercury management.
... Among gaseous species, GEM is the most volatile and the predominant atmospheric form (typically >95% [13]), characterized by high stability and an elevated (6 months to 1 year) residence time in the atmosphere [14] due to its comparative chemical inertness. Thanks to these features, GEM can be transported up to thousands of kilometers from the source [15]. RGM mainly refers to divalent inorganic species (HgCl 2 , HgO, HgSO 4 ) and to methylated forms (methyl-and dimethyl-Hg). ...
... Mercury sources are both natural and anthropogenic. Mercury is naturally emitted in the atmosphere by geothermal activity, weathering of superficial rocks and soil, volcanic activity, but is also re-emitted from vegetation surface, from ocean and water bodies, or through wildfires [15,21]. Anthropogenic Hg sources are mainly linked to fossil fuel combustion, waste incineration, industrial processes like cement and building production, metal smelting, refining, and manufacturing [3,22]. ...
Mercury (Hg) is a toxic and persistent element, easily bio-accumulable in the food chain with several dangerous effects on people’s health. Among Hg airborne species, gaseous elemental mercury (GEM) is dominant, more persistent in the atmosphere, and highly absorbable by humans. The issue of atmospheric Hg pollution is largely discussed by several environmental agencies, giving rise to a number of remarkably different threshold values beyond which exposure to Hg in its different species is deemed dangerous. The present paper presents a comprehensive compilation of the threshold limit values (TLVs) suggested/recommended by environmental health agencies regarding the exposition to airborne Hg. The work tries to clarify the applicability of the threshold concentrations, their terminology, and the methods by which they were calculated. The most critical key-points in Hg TLVs derivation and use are stressed. The literature revision identifies about 20 TLVs: among these, only four are legally transposed into environmental laws, while the majority are just recommendations. There is a high variability of suggested values for gaseous Hg TLVs, mostly resulting from the different methodologies applied for their calculation. This difference is the consequence of a considerable independence among agencies that suggest or enforce Hg limit values. However, in the past years, a generalized substantial lowering of the Hg TLVs, both for chronic and occupational exposure, has been observed. This tendency reflects a revision trend towards a more protective approach for people’s health.
... Volcanic eruptions can release large amounts of gaseous Hg 0 , which can remain in the atmosphere for ~0.5-1 years (Witt et al., 2008) significantly longer than other volcanic materials emitted as aerosols and particles (Jaenicke, 1980;Witt et al., 2008). Thus, Hg has a greater potential for global distribution than other volcanic trace metals and can readily achieve hemispheric exchange (Schroeder and Munthe, 1998). Gaseous Hg 0 released into the atmosphere can be taken up directly by leaves in the tree canopy on land and buried after plant death (Fleck et al., 1999;Frescholtz et al., 2003;Ericksen et al., 2003). ...
... Gaseous Hg 0 released into the atmosphere can be taken up directly by leaves in the tree canopy on land and buried after plant death (Fleck et al., 1999;Frescholtz et al., 2003;Ericksen et al., 2003). On the other hand, gaseous Hg 0 released by volcanoes is oxidized in the atmosphere to reactive gaseous mercury (Hg 2+ ), which exists as oxidized mercury compounds such as HgCl 2 , HgBr 2 and Hg(OH) 2 (Schroeder and Munthe, 1998). Hg 2+ is chemically more active, has a lower concentration in the atmosphere, is soluble in water, and can be adsorbed on the surface of atmospheric particles and transformed into particulate mercury Hg (p) , thus having a shorter atmospheric residence time (Selin, 2009). ...
Several mass extinction events and major paleoenvironmental perturbations during the Phanerozoic have been linked to massive volcanic eruptions, especially those associated with large igneous province (LIP) emplacement. Because magmatism during LIPs can be accompanied by the release and widespread dispersal of mercury (Hg), Hg concentration in sedimentary rocks has proven to be a useful proxy for paleovolcanism. Organic matter is often the primary host of Hg in sedimentary rocks, so total organic carbon (TOC) is commonly used to normalize Hg and thus robustly assess anomalies. Nevertheless, the singular use of anomalies in Hg/TOC to assess volcanic activity is questionable. Sulfides or clay minerals also act as hosts for Hg, with sulfides in particular having a strong affinity for Hg in reducing environments. At the same time, the source of organic matter has a potentially very strong influence on Hg abundance because the Hg binding potential of different organic matter types varies. Here, we investigate the influence of organic matter content and type on Hg concentrations and investigate how
Hg is hosted in shallow marine and nearshore sedimentary rocks of the Lower Jurassic Precipice Sandstone and Evergreen Formation from the Surat Basin, Australia. Our results demonstrate that sulfides were likely the main host of Hg in these rocks, despite the general absence of reducing conditions in these rocks and the significant variability in organic matter sources. Our results suggest that researchers should routinely collect sulfide or at least total sulfur concentration data when testing for volcanic Hg enrichment in ancient sedimentary rocks.
... Atmospheric mercury (Hg) measurements and underlying biases have long been a topic of discussion in the scientific community. Hg is actively emitted into the atmosphere from both natural and anthropogenic sources [1,2], where the atmosphere functions as a transient reservoir, a medium of transport mechanisms, and a facilitator of complex Hg-redox reactions [3,4] that lead to wet and dry deposition of different Hg species back to terrestrial and aquatic environments [5,6]. Hg in the aquatic environment is methylated and bioaccumulates in the food chain, thereby exposing humans to toxic methyl mercury (MeHg) through the consumption of larger predatory fish [7]. ...
... Hg in the aquatic environment is methylated and bioaccumulates in the food chain, thereby exposing humans to toxic methyl mercury (MeHg) through the consumption of larger predatory fish [7]. Though atmospheric Hg exists in oxidation states of 0, +1, and +2 [2], it is measured and operationally defined as gaseous elemental Hg (GEM), gaseous oxidized Hg (GOM), and particulate-bound Hg (PBM) [8][9][10][11][12][13]. The exact composition of GOM is poorly understood due to the lack of adequate measurement methods for continuous monitoring of different GOM species in the ambient air. ...
Background: The current speciation methods for mercury (Hg) measurements are fraught with considerable uncertainty, from sample collection to calibration. High reactivity of gaseous oxidized Hg (GOM) species and their ultra-trace level presence makes them difficult to sample and calibrate. Given that improper calibration may lead to measurement biases, reliable and metrologically traceable calibration methods are required for accurately quantifying GOM in air. In the present study, we applied the recently developed calibration method based on non-thermal plasma oxidation of elemental Hg, to a commercially available Hg air speciation system for actual environmental measurements of GOM for the first time.
Results: Hg species such as HgO, HgCl2, and HgBr2 were produced with trace amounts of reactant gases (oxygen and electrolytically produced chlorine and bromine) and the production was driven by plasma-assisted oxidation. The plasma oxidation efficiency of elemental Hg with oxygen was 98.5 ± 7.5 % (k = 2), while that for chlorine and bromine was 96.8 ± 6.9 % (k = 2) and 97.4 ± 9.6 % (k = 2), respectively. The calibration method was tested against the internal permeation (Hg0) source of the Tekran 2537B Hg analyzer on-field by loading HgO to different KCl-coated denuders using the plasma. GOM concentrations were measured using the Tekran speciation system. With internal calibration, concentrations were up to 9.1 % lower than those in plasma calibration, thereby emphasizing the importance of the calibration strategy. Measurement uncertainty (k = 2) further emphasizes this distinction. Internal calibration measurement uncertainty was 36.8 %, while plasma calibration boasted lower uncertainty at 13.8 %.
Significance: The non-thermal plasma calibration strategy, as a unique and discrete calibration method traceable to the NIST SRM 3133 for ambient air GOM measurements, provide a higher level of confidence in the accuracy of GOM measurements with several advantages over other methods. Calibrations at extreme low concentrations (<100 pg) are possible with this method relevant to ambient air GOM concentrations.
... Mercury (Hg) is a pollutant of global concern due to its persistence, neurotoxicity, and bioaccumulation. 1 Gaseous elemental mercury [Hg(0)] is the most abundant form of Hg in the atmosphere and can be transported regionally and globally due to its extended atmospheric residence time (>0.5 years). 2,3 Atmospheric Hg(0) is released via both anthropogenic (e.g., mining and fossil fuel combustion) and natural sources (e.g., hydrothermal and volcanic activities, biomass burning). 4 Recent estimates of Hg emissions from anthropogenic sources are reasonably accurate, whereas those from natural sources still have large uncertainties 5,6 due to a limited understanding of the air-surface Hg(0) exchange processes over different land uses. ...
... Generally, atmospheric mercury exists as gaseous elemental Hg (Hg o , GEM), reactive gaseous Hg (RGM), and particlebound Hg (Hg(P)). Hg o is the predominant form in the atmosphere (>95%) and the rest accounts for RGM (≈3%) and Hg(P) (≈1%) [1]. The analysis of atmospheric mercury is not straightforward task due to its low existing concentrations and high risk of contamination. ...
Gold-coated sand for amalgamation was synthesized and applied for the determination of mercury in ambient air using a home-made dual gold trap unit coupled to atomic absorption spectrometer. Gold-coated sand is prepared by chemical reduction of Au(III) solution with hydroxylamine depositing elemental gold on acid-etched sand. A home-made dual gold trap unit which focused time-resolved mercury trapped from the sampling/first trap provided an increase in sensitivity and reliability for the analysis of ultra-trace mercury in air was designed and tested. Instrumental detection and quantitation limits (IDL and IQL) of system were 3.9 and 13pg Hg, respectively. Method detection and quantitation limits (MLOD and MLOQ) of system were 0.04 and 0.13ngHg.m-3 for sampling flow rate of 200mL.min-1 and sampling time of 8 hours. Sampling system for gaseous elemental mercury was set up and cooperated with home-made desorption system were preliminarily applied for analysis of atmospheric mercury in samples collected at Hochiminh city University of Science. The atmospheric mercury concentrations were in range of 2.7 – 8.1ng Hg. m-3 which were comparable to Hg concentration found in other cities in the world.
... Mercury (Hg) is liquid at room temperature, volatile, and highly toxic to biota [1]. Mercury in the environment can bio-accumulate through the food chain and is classified by the United States Environmental Protection Agency (USEPA) as a persistent bio-accumulative toxic (PBT) chemical [2,3]. ...
Particulate-bound mercury (PBM) has a large dry-deposition rate and removal coefficient, both of which import mercury into terrestrial and marine ecosystems, causing global environmental problems. In order to illustrate the concentration characteristics, main sources, and health risk of PBM in the atmospheric environment during the spring dust storm period in Xi’an in 2022, PM2.5 samples were collected in Xi’an in March 2022. The concentration of PBM and the PM2.5 composition, including water-soluble ions and elements, were analyzed. The input of dust caused a significant increase in the concentration of PBM, Ca2+, Na+, Mg2+, SO42−, and metal elements in the aerosol. The research results revealed that the dust had a strong enrichment influence on the atmospheric PBM in Xi’an. Anthropogenic mercury emissions and long-distance migration in the sand source area promote the rise in PBM concentration and should be included in the mercury inventory. The values of the risk index for a certain metal (Eri) (572.78–1653.33) and the geo-accumulation index (Igeo) (2.47–4.78) are calculated during this study, showing that atmospheric PBM has a strong pollution level with respect to the ecological environment and that Hg mainly comes from anthropogenic mercury emissions. The non-carcinogenic health risk of atmospheric PBM in children (8.48 × 10−2) is greater than that in adults (1.01 × 10−2). The results show that we need to pay more attention to children’s health in the process of atmospheric mercury pollution control. This study discusses the distribution characteristics of PBM during spring sandstorms and the effects of atmospheric mercury on residents’ health, providing a basis for studying the sustainable development of environmental health and formulating effective strategies for mercury emission control.
... Mercury is naturally present in the Earth's crust, and processes such as rock weathering and volcanic activity facilitate its release into the environment [2]. The emission of gasses from soil, plants, and the sea surface is also recognized as a significant natural source [3]. Furthermore, apart from natural sources, anthropogenic activities contribute to the release of mercury. ...
... Once oxidized, it becomes reactive gaseous mercury (Hg 2+ ) and can become bound to fine particles (Hg p ). Both Hg 2+ and Hg p are deposited via rainfall and/or particle fallout 38 . The speciation of Hg in terrestrial and marine reservoirs strongly affects its mobility and toxicity, and, therefore, its effects on the biosphere. ...
... Once oxidized, it becomes reactive gaseous mercury (Hg 2+ ) and can become bound to fine particles (Hg p ). Both Hg 2+ and Hg p are deposited via rainfall and/or particle fallout 38 . The speciation of Hg in terrestrial and marine reservoirs strongly affects its mobility and toxicity, and, therefore, its effects on the biosphere. ...
The long-term effects of the Central Atlantic Magmatic Province, a large igneous province connected to the end-Triassic mass-extinction (201.5 Ma), remain largely elusive. Here, we document the persistence of volcanic-induced mercury (Hg) pollution and its effects on the biosphere for ~1.3 million years after the extinction event. In sediments recovered in Germany (Schandelah-1 core), we record not only high abundances of malformed fern spores at the Triassic-Jurassic boundary, but also during the lower Jurassic Hettangian, indicating repeated vegetation disturbance and stress that was eccentricity-forced. Crucially, these abundances correspond to increases in sedimentary Hg-concentrations. Hg-isotope ratios (δ²⁰²Hg, Δ¹⁹⁹Hg) suggest a volcanic source of Hg-enrichment at the Triassic-Jurassic boundary but a terrestrial source for the early Jurassic peaks. We conclude that volcanically injected Hg across the extinction was repeatedly remobilized from coastal wetlands and hinterland areas during eccentricity-forced phases of severe hydrological upheaval and erosion, focusing Hg-pollution in the Central European Basin.
... Among them, Hg 0 is the main species to be emitted from soils to the atmosphere (Kentisbeer et al. 2014). Hg volatilization rates are broad, ranging from 1 ng/(m 2 ·h) in background soils (Schroeder and Munthes 1998) to 100,000 ng/(m 2 ·h) in highly contaminated sites (Zhang and Lindberg 1999). ...
The dynamic change of redox conditions is a key factor in emission of elemental mercury (Hg⁰) from riparian soils. The objective of this study was to elucidate the influences of redox conditions on Hg⁰ emission from riparian soils. Soil suspension experiments were conducted to measure Hg⁰ emission from five Hg-contaminated soil samples in two redox conditions (i.e., treated with air or with N2). In four of the five samples, Hg⁰ emission was higher in air treatment than on N2 treatment. Remaining one soil, which has higher organic matter than other soils, showed no distinct difference in Hg⁰ production between air and N2 treatment. In soil suspensions subject to N2 treatment, the dissolved organic carbon (DOC) and Fe²⁺ concentrations were 3.38- to 1.34-fold and 1.44- to 2.28-fold higher than those in air treatment, respectively. Positive correlations were also found between the DOC and Fe²⁺ (r = 0.911, p < 0.01) and Hg²⁺ (r = 0.815, p < 0.01) concentrations in soil solutions, suggesting Fe²⁺ formation led to the release of DOC, which bound to Hg²⁺ in the soil and, in turn, limited the availability of Hg²⁺ for reduction to Hg⁰ in N2 treatment. On the other hand, for remaining one soil, more Hg²⁺ might be adsorbed onto the DOM in the air treatment, resulted in the inhibition of Hg⁰ production in air treatment. These results imply that the organic matter is important to prevent Hg⁰ production by changing redox condition. Further study is needed to prove the role of organic matter in the production of Hg⁰.
... The Hg chemistry in the atmosphere is quite complex and the subject of current scientific research. Excellent overviews of possible mercury oxidation pathways in the atmosphere are, for example, Schroeder and Munthe (1998), Holmes et al. (2010), Shah et al. (2016), Obrist et al. (2018), andLyman et al. (2020). They summarize the possible role of OH, O 3 , bromine, photochemistry, and aqueous-phase reduction. ...
Aerosol particles with diameters larger than 40 nm were collected during the flight campaign StratoClim 2017 within the Asian tropopause aerosol layer (ATAL) of the 2017 monsoon anticyclone above the Indian subcontinent. A multi-impactor system was installed on board the aircraft M-55 Geophysica, which was operated from Kathmandu, Nepal. The size and chemical composition of more than 5000 refractory particles/inclusions of 17 selected particle samples from seven different flights were analyzed by use of scanning electron microscopy (SEM) and transmission electron microscopy (TEM) combined with energy dispersive X-ray (EDX) microanalysis. Based on chemical composition and morphology, the refractory particles were assigned to the following particle groups: extraterrestrial, silicates, Fe-rich, Al-rich, Hg-rich, other metals, C-rich, soot, Cl-rich, and Ca-rich. Most abundant particle groups within the refractory particles are silicates and C-rich (non-volatile organics). In samples taken above the tropopause, extraterrestrial particles are becoming increasingly important with rising altitude. The most frequent particle sources for the small (maximum in size distribution DP-max=120 nm) refractory particles carried into the ATAL are combustion processes at the ground (burning of fossil fuels/biomass burning) and the agitation of soil material. The refractory particles in the ATAL represent only a very small fraction (< 2 % by number for particles > 40 nm) of the total aerosol particles, which are dominated by species like ammonium, sulfate, nitrate, and volatile organics. During one flight, a large number of very small (DP-max=25 nm) cinnabar particles (HgS) were detected, which are supposed to originate from a ground source such as coal combustion or underground coal fires.
... Gaseous elemental Hg(0) is readily uptaken by vegetation, therefore negative Δ 199 Hg values are observed in vegetation (see Section 5.2.1). (0) is also oxidized by atmospheric oxidants (e.g., O 3 and halogens, Schroeder and Munthe, 1998) to form gaseous Hg(II) species that are easily scavenged by cloud droplets (Gratz et al., 2020). Subsequent photoreduction of Hg(II) in cloud droplets then results in opposing Δ 199 Hg signals between GEM and oxidized Hg(II) species (Gratz et al., 2020). ...
... It is a highly volatile element with a long half-life in the atmosphere. As a result of these physical properties, it is ubiquitous in the environment and exposure is not an isolated problem but rather a global threat to human health [24]. In recent years, research has revealed that even chronic exposure to very low exposure concentrations has the ability to cause long-term neurological and renal damage [25]. ...
Heavy metal pollution in aquaculture farms through the food chain has a significant impact on the ecosystem and human health, which may be dangerous as a result of improper management, improper waste management, and excessive use of artificial feed to increase performance and increase profits. Optimum fish production strongly depends on the physical, chemical and biological properties of water. Therefore, successful fishpond management requires a deep understanding of water quality. This study was conducted to assess heavy metal contamination in water samples of five selected aquaculture ponds located in and around Upputeru Reserve Forest in Bhimavaram mandal of West Godavari District. The ten heavy metals analyzed are cadmium (Cd), mercury (Hg), lead (Pb), arsenic (As), manganese (Mn), chromium (Cr), nickel (Ni), copper (Cu), zinc (Zn) and iron (iron). Atomic absorption spectroscopy (AAS) was adopted for the analysis of heavy metals. Most of these values were well below the standards given for drinking (BIS, WHO, EU, US EPA) and pond aquaculture purposes. Although metal levels did not exceed the threshold limit, appropriate measures and continuous monitoring are recommended to reduce heavy metal contamination in farms and prevent deterioration of water qualityupputeru reserve forest
... Atmospheric Hg is operationally defined as gaseous elemental mercury (GEM; Hg(0) in reactions), gaseous oxidized mercury (GOM), and PBM. GEM, with a lifetime of 0.5-1 year, can be oxidized to gaseous oxidized mercury (GOM), which can further be transformed into PBM via gas-particle partitioning (GPP) with relatively short lifetimes ranging from hours to weeks (Schroeder & Munthe, 1998). Reactive mercury (=GOM + PBM) can be removed from the atmosphere through wet and dry deposition, which is one major input for Hg in the oceanic and terrestrial ecosystems. ...
Mercury (Hg) is a global pollutant whose atmospheric deposition is a major input to the terrestrial and oceanic ecosystems. Gas‐particle partitioning (GPP) of gaseous oxidized mercury (GOM) redistributes speciated Hg between gas and particulate phase and can subsequently alter Hg deposition flux. Most 3‐dimensional chemical transport models either neglected the Hg GPP process or parameterized it with measurement data limited in time and space. In this study, CMAQ‐newHg‐Br (Ye et al., 2018, https://doi.org/10.1002/2017ms001161) was updated to CMAQ‐newHg‐Br v2 by implementing a new GPP scheme and the most up‐to‐date Hg redox chemistry and was run for the northeastern United States over January‐November 2010. CMAQ‐newHg‐Br v2 reproduced the measured spatiotemporal distributions of gaseous elemental mercury (GEM) and particulate bound mercury (PBM) concentrations and Hg wet deposition flux within reasonable ranges and simulated dry deposition flux in agreement with previous studies. The GPP scheme improved the simulation of PBM via increasing winter‐, spring‐ and fall‐time PBM concentrations by threefold. It also improved simulated Hg wet deposition flux with an increase of 2.1 ± 0.7 μgm² in the 11‐month accumulated amount, offsetting half of the decreasing effect of the updated chemistry (−4.2 ± 1.8 μgm²). Further, the GPP scheme captured the observed Kp‐T relationship as reported in previous studies without using measurement data and showed advantages at night and in rural/remote areas where existing empirical parameterizations failed. Our study demonstrated CMAQ‐newHg‐Br v2 a promising assessment tool to quantify impacts of climate change and emission reduction policy on Hg cycling.
... For decades, thermal desorption has been commercially used to recover Hg from Hg-containing waste due to its low boiling point (367 ℃) compared to other metals, which means that it starts to vaporize, and transform into its natural state (Hg 0 ) phase at this temperature. However, the decomposition temperature of (Hg 0 ) into other forms of mercury is much higher, around 600-800 ℃ [36,37]. Under the heat, Hg is evaporated, and extracted from waste, then condensed to liquid form. ...
... While redox conditions and organic matter (OM) availability and composition are key determinants in the mobility of Hg in aquatic/saturated-subsurface environments, pH (Andersson, 1979;Gu et al., 2011;Manceau and Nagy, 2019), chloride concentration (Cl − ; Schuster, 1991), and speciation of Hg inputs (particularly for polluted systems; McLagan et al., 2022) also play important roles. Solubilities of Hg species vary widely from practically insoluble cinnabar species (≈ 2 × 10 −24 g L −1 ) via low-solubility elemental Hg (Hg(0): ≈ 5 × 10 −5 g L −1 ) to highly soluble mercury(II) chloride (HgCl 2 : 66 g L −1 ) (Sanemasa, 1975;Schroeder and Munthe, 1998;Skyllberg et al., 2012). In systems that are OM limited, clay minerals and oxides; hydroxides; and oxyhydroxides of Fe, Mn, and Al become increasingly important sorbents for Hg species (Lockwood and Chen, 1973;Schuster, 1991;Kim et al., 2004). ...
Sorption of mercury (Hg) in soils is suggested to be predominantly associated with organic matter (OM). However, there is a growing collection of research that suggests that clay minerals and Fe/Mn oxides are also important solid phases for the sorption of soluble Hg in soil–groundwater systems. We use a series of (60 mL syringe based) column experiments to examine sorption and subsequent desorption of HgCl2 solutions (experiment 1 (EXP1): 46.1 ± 1.1 mg L−1; experiment 2 (EXP2): 144 ± 6 mg L−1) in low-OM (0.16 ± 0.02 %) solid-phase aquifer materials. Analyses of total Hg concentrations, Hg speciation (i.e. pyrolytic thermal desorption (PTD)), and Hg stable isotopes are performed on both solid- and liquid-phase samples across sorption and desorption phases of the experiments. The sorption breakthrough curve best fitted a Freundlich model. Despite the very low-OM content, the Hg equilibrium sorptive capacity in these columns is very high: 1510 ± 100 and 2320 ± 60 mg kg−1 for EXP1 and EXP2, respectively, and it is similar to those determined for high-OM soils. Data from the experiments on mass-dependent Hg stable isotope fractionation data from these experiments (described by δ202Hg) support preferential sorption of lighter isotopes to the solid-phase materials with results indicating an isotopically heavier liquid phase and an isotopically lighter solid phase. Desorption fits exponential decay models, and 46 ± 6 % and 58 ± 10 % of the sorbed Hg is removed from the solid-phase materials at the termination of desorption in EXP1 and EXP2, respectively. The divergence of δ202Hg values between liquid and solid phases also continues into desorption. This desorption profile is linked to the initial release of easily exchangeable Hg(II) species physically sorbed to Fe/Mn oxides and clay mineral surfaces (liquid phase enriched in heavy isotopes) and then slower release of Hg(II) species that have undergone secondary reaction to more stable/less-soluble Hg(II) species and/or diffusion/transport into the mineral matrices (processes favouring lighter isotopes; solid phase enriched in lighter isotopes). The secondary production of Hg(0) within the columns is confirmed by PTD analyses that indicate distinct Hg(0) release peaks in solid-phase samples at <175 ∘C, which again agrees with field observations. Retardation (RD) and distribution (KD) coefficients are 77.9 ± 5.5 and 26.1 ± 3.0 mL g−1 in EXP1, respectively, and 38.4 ± 2.7 and 12.4 ± 0.6 mL g−1 in EXP2, respectively. These values are similar to values derived from column experiments on high-OM soil and provide the basis for future Hg fate and transport modelling in soil–groundwater systems.
... Some suspended particles and volatile HMs can reach the atmosphere through coal mining dust. Indeed, atmospheric Hg might enter river sediments from discharge sources through dry and wet depositions more than ten kilometers away, then adsorbed on the surface of clay particles and organic matter in sediments, resulting in Hg accumulation in sediments (Schroeder et al., 1998;Pirrone et al., 2010;Wang et al., 2012). The coefficient of variation (CV) of the eight HM elements ranged from 0.364 to 0.730, indicating uneven spatial distributions of the HM contents in the study area (CV > 0.36). ...
Identifying the sources of heavy metals (HMs) in river sediments is crucial to effectively mitigate sediment HM pollution and control its associated ecological risks in coal-mining areas. In this study, ecological risks resulting from different pollution sources were evaluated using an integrated method combining the positive matrix factorization (PMF) and the potential ecological risk index (RI) model. A total of 59 sediment samples were collected from the Kuye River and analyzed for eight HMs (Zn, Cr, Ni, Cu, Pb, As, Cd, and Hg). The obtained results showed that the sediment HM contents were higher than the corresponding soil background values in Shaanxi Province. The average sediment Hg content was 3.42 times higher than the corresponding background value. The PMF results indicated that HMs in the sediments were mainly derived from industrial, traffic, agricultural, and coal-mining sources. The RI values ranged from 26.15 to 483.70. Hg was the major contributor (75%) to the ecological risk in the vicinity of the Yanjiata Industrial Park. According to the PMF-based RI model, coal-mining activities exhibited the strongest impact on the river ecosystem (48.79%), followed, respectively, by traffic (34.41%), industrial (12.70%), and agricultural (4.10%) activities. These results indicated that the major anthropogenic sources contributing to the HM contents in the sediments are not necessarily those posing the greatest ecological risks. The proposed integrated approach in this study was useful in evaluating the ecological risks associated with different anthropogenic sources in the Kuye River, providing valuable suggestions for reducing sediment HM pollution and effectively protecting river ecosystems.
... A small (1-2 meter) temporal offset between Hg-I/Hg-II and CIE-I/CIE-II results from the different pathways by which Hg and carbon isotopes travel though the system. Hg particles settle at the surface in less than two years after their volcanic release (Schroeder and Munthe, 1998), whereas carbon isotopes have a much longer residence time. Because of slow incorporation into organic matter and low settling rates, it takes several thousands of years for the excursion to be fully expressed in the geological record. ...
The arid climate of the Late Triassic was interrupted by a particularly humid episode known as the Carnian Pluvial Episode (CPE; ca. 234–232 million years ago). The CPE is often linked to eruptions in the Wrangellia Large Igneous Province (LIP), and is assumed to have led to global warming, enhanced weathering, water deoxygenation, and biotic changes. However, direct evidence for a temporal link between volcanic activity and chemical weathering has not yet been established due to the lack of comprehensive records across the CPE. In this study, geochemical and mineralogical analyses are applied to a lacustrine stratigraphic succession of the Jiyuan Basin (North China) that captures the CPE in high resolution. We identify four distinct pulses of enhanced continental chemical weathering characterized by elevated Chemical Index of Alteration values and kaolinite contents. These peaks in continental weathering coincide with Hg/TOC enrichments and negative organic carbon isotope excursions that mark four short (∼400 kyr) but intense pulses of Wrangellia LIP volcanism. In combination with signs of increased humidity, our findings provide direct and independent evidence that Wrangellia LIP eruptions significantly altered CPE chemical weathering rates in response to global warming and wetting. The lake experienced eutrophication and water deoxygenation after each volcanic pulse but the swift recovery of carbon isotopes suggests that the system rapidly returned to conditions prior to the volcanic perturbation. Organic carbon burial facilitated by widespread dysoxic and anoxic waters, and CO2 consumption via enhanced weathering likely played crucial roles in the rapid climatic recovery after each volcanic pulse.
... The sorbent is in a diffusive Radiello® barrier protected by a polyethylene shield. The mercury passive sampler primarily samples GEM, which makes up the majority (>95%) of total gaseous Hg at background sites (Schroeder and Munthe 1998). After exposure, the Hg passive samplers were returned to Tekran for Hg desorption and determination. ...
Large amounts of mercury (Hg) were consumed and emitted into the atmosphere during the process of amalgam electrolysis used to produce chlorine and caustic soda since the 19th century. In Europe, amalgam electrolysis has been gradually replaced by advanced Hg-free technologies. In this work, we described changes in atmospheric Hg and bulk Hg wet deposition during the phasing out of an amalgam electrolytic line of a chlor-alkali plant in Neratovice, Czech Republic, central Europe. Bulk wet deposition Hg near the chlor-alkali plant was low at 3.6 ± 0.8 µg m-2 yr-1 due to low annual precipitation amounts (486 ± 97 mm) in the period 2015-2021. Nevertheless, it was elevated with respect to a nearby reference site both before and after the decommissioning of the electrolytic line. Switching off the amalgam electrolytic line did not notably affect bulk wet deposition Hg near the chlor-alkali plant. Levels of gaseous elemental Hg (GEM) and particle-bound Hg (PBM) monitored seasonally four times per year in a 24-hour measurement indicated rapid declines in four nearby settlements set in cardinal directions from the Hg emission source. Mean atmospheric GEM and PBM concentrations decreased rapidly from 9.0 ± 2.1 ng m-3 and 243 ± 255 pg m-3 in the period 2013-2017 when amalgam electrolysis was operating, to 3.3 ± 0.4 ng m-3 and 32 ± 6 pg m-3 in the period 2018-2021 after its decommissioning in November 2017. Seasonal changes of GEM were determined primarily by the changes in temperature with the highest concentrations in summer, while PBM air levels were lowest in summer due to the highest seasonal precipitation amount. GEM concentrations at the four monitored settlements at Neratovice remained elevated with respect to regional background, but PBM levels decreased to background levels.
... Once oxidized it becomes reactive gaseous mercury (Hg 2+ ) and can become ne particle-bound Hg (Hg p ). These particles are deposited via rainfall and/or particle fallout 33 . ...
The long-term effects of the Central Atlantic Magmatic Province (CAMP), a large igneous province connected to the end-Triassic mass-extinction (201.5 Ma), remain largely elusive. Here, we document the persistence of volcanic-induced mercury pollution and its effects on the biosphere for 2 million years after the extinction event. In sediments recovered in Germany (Schandelah-1 core), we record not only high abundances of malformed fern spores at the Triassic-Jurassic boundary, but also during the Hettangian, indicating repeated vegetation disturbance and environmental stress that was eccentricity forced. Crucially, these abundances correspond to spikes in sedimentary Hg concentrations. Hg-isotope ratios (δ ²⁰² Hg, Δ ¹⁹⁹ Hg) indicate a volcanic source at the Triassic-Jurassic boundary but a terrestrial source for the early Jurassic peaks. We conclude that Hg injected by CAMP across the extinction was repeatedly remobilized from coastal wetlands and hinterland areas during eccentricity-forced phases of severe hydrological upheaval and erosion, focusing Hg-pollution in shallow marine basins.
... As a result, this form of mercury is poorly deposited in the atmosphere and can stay in it for up to a year. This makes Hg 0 a long-range pollutant, which can be transported with air masses for long distances into polar regions (Schroeder and Munthe, 1998;Selin et al., 2007;Gustin and Jaffe, 2010). Hg 0 can be transformed into Hg 2+ due to oxidation, and after oxidation most of the mercury can be deposited. ...
The Antarctic is the most isolated region in the world; nevertheless, it has not avoided the negative impact of human activity, including the inflow of toxic mercury (Hg). Hg deposited in the Antarctic marine environment can be bioavailable and accumulate in the food web, reaching elevated concentrations in high-trophic-level biota, especially if methylated. Zooplankton, together with phytoplankton, are critical for the transport of pollutants, including Hg to higher trophic levels. For the Southern Ocean ecosystem, one of the key zooplankton components is the Antarctic krill Euphausia superba, the smaller euphausiid Thysanoessa macrura, and the amphipod Themisto gaudichaudii – a crucial food source for most predatory fish, birds, and mammals. The main goal of this study was to determine the Hg burden, as well as the distribution of different Hg forms, in these dominant Antarctic planktonic crustaceans. The results showed that the highest concentrations of Hg were found in T. gaudichaudii, a typically predatory taxon. Most of the Hg in the tested crustaceans was labile and potentially bioavailable for planktivorous organisms, with the most dangerous methylmercury (MeHg) accounting for an average of 16 % of the total mercury. Elevated Hg concentrations were observed close to the land, which is influenced by the proximity to penguin and pinniped colonies. In areas near the shore, volcanic activity might be a possible cause of the increase in mercury sulfide (HgS) content. The total Hg concentration increased with the trophic position and ontogenetic stage of predation, specific to adult organisms. In contrast, the proportion of MeHg decreased with age, indicating more efficient demethylation or elimination. The Hg magnification kinetics in the study area were relatively high, which may be related to climate-change induced alterations of the Antarctic ecosystem: additional food sources and reshaped trophic structure.
... The preconcentration methods used for comparisons are sampling and analysing all mercury species in the atmosphere. Along 355 with GEM, GOM and particle-bound mercury (PBM) are also present in the atmosphere (Schroeder and Munthe, 1998). During the thermal desorption of mercury from gold traps, GOM and PBM are reduced, in the end being analysed as GEM as well. ...
The monitoring of low gaseous elemental mercury (GEM) concentrations in the atmosphere requires continuous high-resolution measurements and corresponding calibration capabilities. Currently, continuous calibration for GEM is still an issue at ambient concentrations (1–2 ng m−3). This paper presents a continuous flow calibration for GEM, traceable to NIST 3133 Standard Reference Material (SRM). This calibration approach was tested using a direct mercury analyser based on atomic absorption spectrometry with Zeeman background correction (Zeeman AAS). The produced continuous flow of GEM standard was obtained through reduction of Hg2+ from liquid SRM NIST 3133 and used for traceable calibration of Zeeman AAS. Measurements of atmospheric GEM using the calibrated Zeeman AAS were compared with two methods: manual gold amalgamation atomic fluorescence spectrometry (AFS) calibrated with the chemical reduction of NIST 3133 and automated gold amalgamation AFS calibrated using the mercury bell-jar syringe technique. The comparisons showed that factory-calibrated Zeeman AAS underestimates concentrations under 10 ng m−3 by up to 35 % relative to the two other methods of determination. However, when a calibration based on SRM NIST 3133 was used to perform a traceable calibration of Zeeman AAS, the results were more comparable with other methods. The expanded relative combined uncertainty for Zeeman AAS ranged from 8 % for measurements at the 40 ng m−3 level to 91.6 % for concentrations under 5 ng m−3 using the newly developed calibration system. High uncertainty for measurements performed under 5 ng m−3 was due mainly to instrument noise and concentration variation in the samples.
Vegetative leaves have long been considered a significant receiver of gaseous Hg in the atmosphere, offering the potential to passively monitor palaeo-atmospheric Hg concentrations; however, few constraints on this exist. In this study, we conduct Hg measurements on three Ginkgo leaf collections: i) modern leaves from ten sampling sites across China, ii) modern leaves collected monthly across one growing season in Nanjing (China), iii) fossil ginkgoaleans leaves from the Middle Jurassic (China). The results from this study reveal that the foliar Hg concentrations (with an average concentration of 61 ng·g-1, N = 272) were higher than those observed in Ginkgo leaf samples previously studied from Ireland and the USA. Additionally, the leaf age and atmospheric Hg concentrations represent two primary factors impacting foliar Hg contents in Ginkgo. Hg concentrations in fossil cuticular samples (with an average concentration of 585.5 ng·g-1) were observed notably higher than those in modern Ginkgo leaves (avg. 61 ng·g-1) and sediments from the same layers (avg. 113 ng·g-1). Considering possible Hg migration during fossilization, we suggested that the elevated Hg concentrations in fossil cuticles were attributed to both the retention of Hg in leaves and the loss of leaf content during fossilization. Based on 23 fossil ginkgoalean samples from 6 beds of the Dameigou section (spanning from the Early to the Middle Jurassic), Qaidam Basin, China, we detected a Hg anomaly through Hg concentrations in fossil cuticles during the presumed palaeo-volcanic event (the Karoo-Ferrar Large Igneous Province (LIP)). This preliminary test supports the notion that variations in Hg concentrations in fossil cuticle may potentially reflect the gaseous Hg changes in the Jurassic palaeo-atmosphere, triggered by LIP volcanism at this time. This finding highlights the possibility of using fossil plant cuticle as a Hg proxy of palaeo-atmospheric Hg loading.
Mercury (Hg) enrichments in ancient sediments have been used as a proxy of volcanism, especially large igneous province (LIP) eruptions. However, considering the existence of other potential Hg sources besides volcanoes and the diverse factors (e.g., organic matters, clay minerals, sulfide minerals and Fe oxides) that can affect Hg sequestration, there are considerable uncertainties to simply regard sedimentary Hg anomalies as signatures of volcanic activities. Mercury stable isotopes, a promising tool for tracing the origins and transformations of Hg, have been increasingly used for determining the causes of Hg spikes and understanding the geochemical behavior of Hg in the geologic record. To date, lots of researches have applied Hg concentrations and Hg isotopes to identify LIP volcanisms linking with significant geological events such as mass extinctions, ocean anoxic events and other environmental perturbations that mainly occurred in the Phanerozoic. However, the results in previous studies clearly show that not all Hg enrichments are derived from volcanic inputs, which emphasize the need for more caution in using Hg as a fingerprint of volcanism. With a better understanding of Hg isotopes in the future, there will be important implications for Hg isotopes to reconstruct volcanic activities in the rock records and their impacts on biological evolution.
Atmospheric heavy metal (HMs) pollution that impacts the environment and human health is one of the increasingly concerning problems in developing countries. Southeast Asia (SEA) is now described as a dynamic and rapidly developing region and is facing problems of air pollution, including HMs in the atmosphere. According to the International Cancer Research Institute (IARC), some metals (e.g., Pb, As, Ni, Cd, Hg, Cd, Cr) are particularly harmful to human health. In this chapter, we focus on the knowledge of atmospheric HMs in the SEA region over the last 15 years, in which, the potential sources and spatio temporal distribution of atmospheric HMs in SEA were discussed in detail. Research on atmospheric HMs is unevenly distributed in the SEA region and most of the studies concentrated in countries such as Thailand, Malaysia, and Vietnam. By employing multivariable models, including PCA and PMF, studies show that both anthropogenic sources (e.g., transportation, biomass burning, and industrial processes) and natural sources (e.g., volcanic eruption and dust storms) can contribute to elevated atmospheric HMs. HMs concentrations in industrial areas are often higher than in urban/background locations. On a seasonal basis, HMs concentrations in the dry season are often higher than in the rainy season. Certain knowledge gaps pertaining to atmospheric HMs in the SEA region necessitate comprehensive investigation. Specifically, there is a need for rigorous research focused on elucidating the deposition of atmospheric HMs as well as research regarding atmospheric mercury (Hg). This chapter presents scientific information on atmospheric HMs pollution in SEA from both regulatory and research perspectives. It aims to enhance the understanding of HMs contaminations in the SEA region by providing updated and rigorous scientific analysis.
Knowledge gaps of mercury (Hg) biogeochemical processes in the tropical rainforest limit our understanding of the global Hg mass budget. In this study, we applied Hg stable isotope tracing techniques to quantitatively understand the Hg fate and transport during the waterflows in a tropical rainforest including open-field precipitation, throughfall, and runoff. Hg concentrations in throughfall are 1.5–2 times of the levels in open-field rainfall. However, Hg deposition contributed by throughfall and open-field rainfall is comparable due to the water interception by vegetative biomasses. Runoff from the forest shows nearly one order of magnitude lower Hg concentration than those in throughfall. In contrast to the positive Δ199Hg and Δ200Hg signatures in open-field rainfall, throughfall water exhibits nearly zero signals of Δ199Hg and Δ200Hg, while runoff shows negative Δ199Hg and Δ200Hg signals. Using a binary mixing model, Hg in throughfall and runoff is primarily derived from atmospheric Hg0 inputs, with average contributions of 65 ± 18 and 91 ± 6%, respectively. The combination of flux and isotopic modeling suggests that two-thirds of atmospheric Hg2+ input is intercepted by vegetative biomass, with the remaining atmospheric Hg2+ input captured by the forest floor. Overall, these findings shed light on simulation of Hg cycle in tropical forests.
The monitoring of low gaseous elemental mercury (GEM) concentrations in the atmosphere requires continuous high-resolution measurements and corresponding calibration capabilities. Currently, continuous calibration for GEM is still an issue at ambient concentrations (1–2 ng m−3). This paper presents a continuous flow calibration for GEM, traceable to NIST 3133 Standard Reference Material (SRM). This calibration approach was tested using a direct mercury analyser based on atomic absorption spectrometry with Zeeman background correction (Zeeman AAS). The produced continuous flow of GEM standard was obtained via the reduction of Hg2+ from liquid NIST 3133 SRM and used for the traceable calibration of the Zeeman AAS device. Measurements of atmospheric GEM using the calibrated Zeeman AAS were compared with two methods: (1) manual gold amalgamation atomic fluorescence spectrometry (AFS) calibrated with the chemical reduction of NIST 3133 and (2) automated gold amalgamation AFS calibrated using the mercury bell-jar syringe technique. The comparisons showed that a factory-calibrated Zeeman AAS device underestimates concentrations under 10 ng m−3 by up to 35 % relative to the two other methods of determination. However, when a calibration based on NIST 3133 SRM was used to perform a traceable calibration of the Zeeman AAS, the results were more comparable with other methods. The expanded relative combined uncertainty for the Zeeman AAS ranged from 8 % for measurements at the 40 ng m−3 level to 91.6 % for concentrations under 5 ng m−3 using the newly developed calibration system. High uncertainty for measurements performed under 5 ng m−3 was mainly due to instrument noise and concentration variation in the samples.
Mercury (Hg) is a toxic metal that is easily released into the atmosphere as a gas or a particulate. Since Hg has serious health impacts based on human exposure, it is a major concern where it accumulates. Southern Florida is a region of high Hg deposition in the United States. It has entered the southern Florida environment for over 56 MY. For the past 3000 to 8000 years, Hg has accumulated in the Everglades peatlands, where approximately 42.3 metric tons of Hg was deposited. The pre-industrial source of mercury that was deposited into the Everglades was from the atmosphere, consisting of combined Saharan dust and marine evasion. Drainage and the development of the Everglades for agriculture, and other mixed land uses have caused a 65.7% reduction in the quantity of peat, therefore releasing approximately 28 metric tons of Hg into the southern Florida environment over a period of approximately 133 years. Both natural and man-made fires have facilitated the Hg release. The current range in mercury release into the southern Florida environment lies between 994.9 and 1249 kg/yr. The largest source of Hg currently entering the Florida environment is from combined atmospheric sources, including Saharan dust, aerosols, sea spray, and ocean flux/evasion at 257.1–514.2 kg/yr. The remobilization of Hg from the Everglades peatlands and fires is approximately 215 kg/yr. Other large contributors include waste to energy incinerators (204.1 kg/yr), medical waste and crematory incinerators (159.7+ kg/yr), and cement plant stack discharge (150.6 kg/yr). Minor emissions include fuel emissions from motorized vehicles, gas emissions from landfills, asphalt plants, and possible others. No data are available on controlled fires in the Everglades in sugar farming, which is lumped with the overall peatland loss of Hg to the environment. Hg has impacted wildlife in southern Florida with recorded excess concentrations in fish, birds, and apex predators. This bioaccumulation of Hg in animals led to the adoption of regulations (total maximum loads) to reduce the impacts on wildlife and warnings were given to consumers to avoid the consumption of fish that are considered to be contaminated. The deposition of atmospheric Hg in southern Florida has not been studied sufficiently to ascertain where it has had the greatest impacts. Hg has been found to accumulate on willow tree leaves in a natural environment in one recent study. No significant studies of the potential impacts on human health have been conducted in southern Florida, which should be started based on the high rates of Hg fallout in rainfall and known recycling for organic sediments containing high concentrations of Hg.
The Cretaceous Period was marked by the formation of numerous Large Igneous Provinces (LIPs), several of which were associated with geologically rapid climate, environmental, and biosphere perturbations, including the early Aptian and latest Cenomanian Oceanic Anoxic Events (OAEs 1a and 2, respectively). In most cases, magmatic CO 2 emissions are thought to have been the major driver of climate and biosphere degradation. This work summarises the relationships between Cretaceous LIPs and environmental perturbations, focussing on how volcanism caused climate warming during OAE 1a using osmium-isotope and mercury concentration data. The new results support magmatic CO 2 output from submarine LIP activity as the primary trigger of climate warming and biosphere stress before/during OAE 1a. This submarine volcanic trigger of OAE 1a (and OAE 2), two of the most climatically/biotically severe Cretaceous events, highlights the capacity of oceanic LIPs to impact Earth's environment as profoundly as many continental provinces. Cretaceous magmatism (and likely output of CO 2 and trace-metal micronutrients) was apparently most intense during those OAEs; further studies are needed to better constrain eruption histories of those oceanic plateaus. Another open question is why the Cretaceous Period overall featured a higher rate of magmatic activity and LIP formation compared to before and afterwards.
Supplementary material at https://doi.org/10.6084/m9.figshare.c.7026011
Mercury is a global pollutant that poses significant risks to human health and the environment. Natural sources of mercury include volcanic eruptions, while anthropogenic sources include industrial processes, artisanal and small-scale gold mining, and fossil fuel combustion. Contamination can arise through various pathways, such as atmospheric deposition, water and soil contamination, bioaccumulation, and biomagnification in food chains. Various remediation strategies, including phytoremediation, bioremediation, chemical oxidation/reduction, and adsorption, have been developed to address mercury pollution, including physical, chemical, and biological approaches. The effectiveness of remediation techniques depends on the nature and extent of contamination and site-specific conditions. This review discusses the challenges associated with mercury pollution and remediation, including the need for effective monitoring and management strategies. Overall, this review offers a comprehensive understanding of mercury contamination and the range of remediation techniques available to mitigate its adverse impacts.
Graphical Abstract
1 is the first mitochondrion-targeted fluorescent probe based on ESIPT phthalimide for the detection of Hg ²⁺ with large Stokes shift, rapid response, and high sensitivity and selectivity.
Many atmospheric chemicals occur in the gas phase as well as in liquid cloud droplets and aerosol particles. Therefore, it is necessary to understand their distribution between the phases. According to Henry’s law, the equilibrium ratio between the abundances in the gas phase and in the aqueous phase is constant for a dilute solution. Henry’s law constants of trace gases of potential importance in environmental chemistry have been collected and converted into a uniform format. The compilation contains 46 434 values of Henry’s law constants for 10 173 species, collected from 995 references. It is also available on the internet at https://www.henrys-law.org (last access: October 2023). This article is a living review that supersedes the now obsolete publication by Sander (2015).
Stable mercury (Hg) isotope ratios are an emerging tracer for biogeochemical transformations in environmental systems, but their application requires knowledge of isotopic enrichment factors for individual processes. We investigated Hg isotope fractionation during dark, abiotic reduction of Hg(II) by dissolved iron(Fe)(II), magnetite, and Fe(II) sorbed to boehmite or goethite by analyzing both the reactants and products of laboratory experiments. For homogeneous reduction of Hg(II) by dissolved Fe(II) in continuously purged reactors, the results followed a Rayleigh distillation model with enrichment factors of −2.20 ± 0.16‰ (ε202Hg) and 0.21 ± 0.02‰ (E199Hg). In closed system experiments, allowing reequilibration, the initial kinetic fractionation was overprinted by isotope exchange and followed a linear equilibrium model with −2.44 ± 0.17‰ (ε202Hg) and 0.34 ± 0.02‰ (E199Hg). Heterogeneous Hg(II) reduction by magnetite caused a smaller isotopic fractionation (−1.38 ± 0.07 and 0.13 ± 0.01‰), whereas the extent of isotopic fractionation of the sorbed Fe(II) experiments was similar to the kinetic homogeneous case. Small mass-independent fractionation of even-mass Hg isotopes with 0.02 ± 0.003‰ (E200Hg) and ≈ −0.02 ± 0.01‰ (E204Hg) was consistent with theoretical predictions for the nuclear volume effect. This study contributes significantly to the database of Hg isotope enrichment factors for specific processes. Our findings show that Hg(II) reduction by dissolved Fe(II) in open systems results in a kinetic MDF with a larger ε compared to other abiotic reduction pathways, and combining MDF with the observed MIF allows the distinction from photochemical or microbial Hg(II) reduction pathways.
We have modified recently published dry deposition models to estimate deposition velocities (Vd) for Hg in both fine aerosol and vapor form to forest canopy surfaces. Aerosol and total vapor phase Hg concentrations in air previously measured at Walker Branch Watershed in Tennessee have been used with model results to estimate dry deposition to a deciduous forest. The concentration data confirm that airborne Hg is dominated by vapor forms at this site and exhibits concentrations moderately above continental background levels. The modeled Vd values reflect published data which suggest that dry deposition of Hg vapor is strongly controlled by surface transport processes, notably stomatal and mesophyll resistances, the latter dominating. Weekly mean Vd values ranged from 0.006 (winter) to 0.12 (summer) cm s-1. We have also measured concentration gradients of Hg vapor in air above this forest to estimate air-surface exchange during short-term experiments. While the model results indicate that the canopy is a sink for Hg vapor, the concentration profiles suggest that the forest soils are a source during some periods, the combined effect of which is net Hg fluxes in the upward direction. Application of a detailed canopy turbulence model yielded soil emission rates of the order of 50 ng Hg m-2 h-1, ~10% of which is deposited in the canopy. Our modeled dry deposition estimates plus limited measurements of wet deposition in this area suggest that dry and wet deposition may be comparable in magnitude.
Plant biomass plays a significant role in the global environmental partitioning phenomena and plants are good indicators of tropospheric contamination levels by chlorinated hydrocarbons. In the present research 300 samples of plants were collected in 265 areas distributed worldwide and analyzed for HCB (hexachlorobenzene), α-HCH (hexachlorocyclohexane), γ-HCH, p,pâ²-DDT,o,pâ²-DDT, and p,pâ²-DDE (degradation product of DDT). Global HCB distribution is strongly dependent on the temperature, the HCB being present mainly in samples from cold areas. The sum of DDTs show higher concentrations in samples from topical areas, while the sum of HCHs is higher in the plants from the Northern Hemisphere. These results are discussed, taking into account the role of physicochemical properties in determining the global distribution as well as the air age of the contamination.
This article describes the use of a two-layer model to estimate the flux of various gases across the air-sea interface.
Surface soils collected near the Almaden, Spain, mercury mine reflected increasing concentrations of mercury (Hg) with proximity to the mine due to weathered mineral deposits and to atmospheric deposition of Hg from the smelter. Extractions with NaHCO3 or NH4OAc removed small amounts of Hg from both control (20 km from the mine; total Hg = 2.3 μg/g) and mine site soils (1 km; total Hg = 97 μg/g). Density gradient centrifugation indicated a significant fraction of the Hg to be associated with a high-density mineral fraction, presumably cinnabar. Accumulation of Hg by alfalfa suggested a dual mechanism of uptake; roots accumulated Hg in proportion to the soil levels, while serial plant material absorbed Hg vapor directly from the atmosphere. Soil fertilization with and without liming significantly increased total Hg uptake, largely due to plant growth stimulation. Liming itself had no significant effect. The rate of volatilization of elemental Hg from both soils (~0.13 and 0.33 μg/m2 per hour at 25°C, for control and mine site, respectively) exceeded reported background emission rates by factors of 4 to 10, increasing with surface temperature and Hg content and decreasing with increased plant cover.
This chapter is not intended to be a comprehensive review of the biogeochemical cycle of atmospheric Hg. Rather, the approach in organizing this discussion has been to highlight three separate but related research projects dealing with the sources and fate of atmospheric mercury vapor. These projects, completed in 1980, involved research on three of the most important industrial sources of Hg vapor to the atmosphere, the chloralkali, mercury mining, and electric power generation industries. In summarizing these case studies, these findings are updated as appropriate in light of recently published information.
Atmospheric sources are recognized to be significant in the cycling of Hg in the biosphere, yet there are few reliable data on air/surface exchange rates of Hg in forests. We have developed a tower-based micrometeorological method for measuring gas-phase Hg fluxes over environmental surfaces, and have used this approach to measure Hg° fluxes over soils, vegetation, and water surfaces. These fluxes have been combined with modeling results based on measurements of atmospheric Hg concentrations and speciation to quantify the overall flux of Hg between the atmosphere and the ground. These results are compared with a study of the biogeochemical cycle of Hg in the temperate deciduous forest at Walker Branch Watershed in the southeastern United States. Our preliminary results suggest that the largest Hg fluxes in forests involve gas exchange at the air/vegetation interface. Given the magnitude of these fluxes and their level of uncertainty, this forest could act as a net source or sink for atmospheric Hg, indicating the importance of better understanding the role of Hg exchange at the vegetation surface.
Looking at emission quantities of chemicals is useful for an initial comparison of sources, but such a comparison does not relate linearly to health risk to human and non-human populations, but is a key input for risk assessment. Accurate emissions data are just now becoming available in the US for the trace element, mercury (Hg). We can use these emissions estimates to constrain risk assessments, to bound emissions for countries which lack data, and to further constrain the global cycle. Two parts of the equation remain highly uncertain: the amount of emitted Hg that participates in the global cycle and the quantification of natural sources; the latter is our greatest research need.
It is well known that mercury and many of its compounds are volatile, and readily cycled at the earth’s surface. Moreover, the major transfer of Hg from terrestrial sources to the oceans occurs by exchange at the sea surface. Thus, the atmospheric cycle of Hg over the oceans and the processes affecting Hg exchange between the air and the sea are a predominant feature of the global Hg cycle. Our understanding of the behavior and fate of Hg in the marine environment is improving. Elucidation of the current state of knowledge regarding the cycling of Hg between the atmosphere and oceans makes a very fine case study. There are sufficient reliable data and geochemically consistent results to provide a working framework. There also appears to be much room to question current dogma and for speculation.
Gaseous and aerosol products formed in the Cl-atom initiated reaction of CH3HgCH3 were studied by the FT IR method in the photolysis of Cl2-CH3HgCH3 mixtures in the presence and absence of O2 at ∼300 K. The results are consistent with the predominant occurrence of the displacement reaction Cl + CH3HgCH3 → CH3HgCl + CH3 as the primary process. The relative rate constant for the Cl-atom reactions of CH3HgCH3 and n-C4H10 was determined to be k(Cl+CH3HgCH3)/k(Cl+n-C4H10) = 1-25 ± 0.06 (σ) by the competitive decay method. This value combined with the literature value of k(Cl+n-C4H10) = (2.20 ± 0.13) × 10-10 cm3 molecule-1 s-1 gives k(Cl+CH3HgCH3) = (2.75 ± 0.30) × 10-10 cm3 molecule-1 s-1.
The behavior of a mercurous-mercuric chloride fungicide (Caloclor) added to turfgrass and bare soil was investigated. From 44 to 56% of the total Hg added to a turfgrass surface was lost in 57 days. Plant uptake and removal upon cutting did not account for these losses which were attributed to volatilization of metallic Hg formed in the turfgrass-soil system. Where additions were made in the turfgrass root zone, loss was reduced and redistribution of Hg in the soil followed a pattern in qualitative agreement with metallic Hg formation and redistribution. Verification of volatilization from bare soil surfaces was made.
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A chemical scheme based upon current knowledge of physicochemical forms and transformation reactions of atmospheric mercury has been implemented into a regional pollutant dispersion model for Europe. Existing databases for anthropogenic mercury emissions in Europe have been updated for 1987 and 1988 using new information on source data from eastern European countries including the former German Democratic Republic. Concentrations of total gaseous and particle associated mercury in air and mercury in precipitation calculated by the model are compared with observed values at Roervik in southwestern Sweden, Aspvreten, south of Stockholm and other locations of the Nordic network, on a daily basis. The results show that the model is capable of simulating long-range transport of mercury from Central Europe to Scandinavia including discrete events with peak concentrations in air and precipitation in the range of 10 ng m−3 and 100 ng −1, respectively. Coinciding observed and calculated peak concentrations indicate that exceptionally high mercury emissions, most probably from chlor-alkali industry and lignite coal combustion in East Germany and Czechoslovakia, must have occurred in 1987 and 1988.
As part of an ongoing study of the atmospheric deposition of Hg in the Lake Champlain watershed, event throughfall, event precipitation, ambient, green foliage, and litterfall samples were collected and analyzed for Hg from a mixed hardwood forest in Underhill Center, VT, for six weeks during the months of August and September 1994. During this time period, the volume-weighted mean Hg concentration in throughfall (12.0 ± 8.5 ng ℓ−1) was higher than in precipitation (6.5 ± 2.8 ng ℓ−1). In August and September 1994, the total deposition of Hg in throughfall was estimated to be 3.1 μgm−2 (1.9 μg m−2 in precipitation) to the deciduous hardwood forests in the Lake Champlain basin. The mean Hg concentration in litterfall (53.2± 11.4 ng g−1) was significantly greater than the mean concentration in green foliage (34.2 +7.2 ng g−1), suggesting uptake of Hg from the atmosphere by foliage. Estimated annual litterfall deposition to the Lake Champlain basin was 13 μg m−2. This study suggests that throughfall and litterfall play a significant role in the cycling and deposition of Hg in the Lake Champlain watershed.
We used the modified Bowen ratio method to estimate the fluxes of vapor-phase elemental Hg (Hg0) over background forest soils during the summer and fall of 1993. Fluxes were derived from the concentration gradients of total gaseous Hg between sampling heights of 25 and 165 cm and the concurrently determined turbulent diffusion coefficients of reference trace gases (i.e. H2O or CO2). The concentration and gradient data of Hg0 measured during the campaigns generally fell in relatively narrow ranges of 1.52–3.68 and −0.16 to 0.32 ng m−3 (over 140 cm), respectively: means ( ± 1 S.D.) for the corresponding; emission and deposition fluxes were found to be 7.5 ± 7.0 (n= 30) and −2.2 ± 2.4 ng m−2 h−1 (n=9), respectively. From the data collected during a series of sequential measurements, reproducible patterns of diurnal exchange emerged: (1) small bidirectional fluxes of Hg0 in the morning, (2) peak emissions near midafternoon, and (3) generally insignificant exchange during the nighttime. The fluxes of Hg over soil surfaces appear to be driven by a combined effect of several meteorological factors, including wind speed, vertical mixing, and soil temperature. Comparison of environmental conditions for both emission and deposition events showed that the direction of fluxes may be strongly influenced by the stability conditions of the boundary layer. The overall results of our emission and dry-deposition measurements in concern-with recent studies of wet-deposition rates in the forest ecosystem suggest that source strengths of this forest soil system may be of the same order of magnitude as sink strengths.
Rate coefficients for the reaction of the nitrate radical with dimethyl mercury (DMHg) have been determined. The absolute rate was measured at temperatures from 258 to 358 K in the pressure range between 2.7 and 5.0 hPa using the fast-flow-discharge technique. The Arrhenius expression is 3.2 × 10−11 exp[−(1760 ± 400)/T] cm3 molecule−1 s−1, corresponding to a rate coefficient of 8.7 × 10−14 cm3 molecule−1 s−1 at 298 K and an activation energy of 14.6 ± 3.3 kJ mol−1. The atmospheric lifetime of DMHg with respect to NO3 radicals is 4 h at a radical concentration of 1 × 109 molecules cm−3. Elemental mercury was identified as a minor reaction product.
The Regional Lagrangian Model of Air Pollution (RELMAP) is used to simulate the emission, transport and diffusion, chemical transformation, and wet and dry deposition of elemental mercury gas, divalent mercury gas and particulate mercury. Based on recent modeling advances in Europe, the RELMAP has been modified to simulate a reduction-oxidation (redox) balance for mercury dissolved in cloud and rain water. This redox balance is used in the estimation of a variable precipitation scavenging ratio for elemental mercury. The results of the simulation are used to estimate the quantity of mercury emitted to the air annually over the United States and the amount that is subsequently deposited back to U.S. soils and water bodies. An analysis of the modeling results also provides some information about the areas of the country thought to have the most significant exposure from all air emissions of mercury.
In an effort to identify the effect of municipal sewage sludge application on mercury (Hg) concentrations in soil, we studied the contamination of sludge-amended soil with inorganic and methyl Hg and the emission of these contaminants to the atmosphere using a Teflon dynamic flux chamber. The routine application of municipal sewage sludge to cropland significantly increased both total and methyl Hg in surface soil from 80 to 6100 μg kg-1 and 0.3 to 8.3 μg kg-1, respectively. Both inorganic and methyl Hg were transported from the sludge/soil matrix to the environment by emission to the atmosphere, however, there was no indication of Hg transport in limited soil water lysimeter experiments. Our data from soil amended with municipal sewage sludge represent the first quantitatively measured terrestrial source of methyl mercury (MeHg) to the atmosphere. Sludge- amended soil emitted an average of 12 to 24 pg m-2 h-1 of monomethyl Hg and ~100 ng m-2 h-1 of inorganic Hg to the atmosphere. A simple dispersion model suggests that sludge-amended soil may increase regional atmospheric MeHg concentrations by ~5%. These data highlight the need for further research to quantify the transport of Hg from sludge-amended soil and identify the sources of MeHg in the atmosphere.
Surface soils collected near the Almadén, Spain, mercury mine reflected increasing concentrations of mercury (Hg) with proximity to the mine due to weathered mineral deposits and to atmospheric deposition of Hg from the smelter. Extractions with NaHCO3 or NH4OAc removed small amounts of Hg from both control (20 km from the mine; total Hg = 2.3 µg/g) and mine site soils (1 km; total Hg = 97 µg/g). Density gradient centrifugation indicated a significant fraction of the Hg to be associated with a high-density mineral fraction, presumably cinnabar. Accumulation of Hg by alfalfa suggested a dual mechanism of uptake; roots accumulated Hg in proportion to the soil levels, while aerial plant material absorbed Hg vapor directly from the atmosphere. Soil fertilization with and without liming significantly increased total Hg uptake, largely due to plant growth stimulation. Liming itself had no significant effect. The rate of volatilization of elemental Hg from both soils (∼0.13 and 0.33 µg/m² per hour at 25°C, for control and mine site, respectively) exceeded reported background emission rates by factors of 4 to 10, increasing with surface temperature and Hg content and decreasing with increased plant cover.
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In the covered catchment at Lake Gårdsjön, the reversibility of acidification and the effects on Hg output of a decreased deposition of Hg and MeHg have been investigated since 1991. A first indication of a decreased from the covered catchment, caused by the artificial removal of Hg and MeHg input, has been observed. This has occurred in parallel with an overall decrease in Hg deposition fluxes in SW Sweden during 1990 to 1993. In the sediments of two acidified lakes, Lake Gårdsjön (limed) and Lake Härsevatten (acid), Hg concentrations decrease by 60% in the top cm, from the maximum around 1000 ng g-1 at 5 cm depth indicating a decreasing deposition during the last 10 years. This decrease has occurred in parallel with decreasing atmospheric S-levels and is most likely caused by decreasing European Hg emissions. Decreasing trends of MeHg in run-off from two catchments has also been observed while the Hg output has remained somewhat more stable.
Using a newly developed technique, methylmercury species have been quantified in several precipitation and lake water samples. Mercury species are determined by aqueous-phase ethylation to the volatile dialkyl analogs, followed by cryogenic gas chromatographic (GC) separation. Mercury-specific detection by cold vapour atomic fluorescence spectrometry permits detection limits of about 0.1 pg as Hg. Snow samples collected from north-central Wisconsin contained monomethylmercury levels of about 0.25 pM (0.05 ng l−1 Hg) and total mercury concentrations of 20 pM (4 ng l−1 Hg). A time series of rain samples collected during a storm passing over the North Olympic Peninsula in western Washington State showed average monomethylmercury levels of 0.75 pM (0.15 ng l−1 Hg), with total mercury concentrations from 10 to 25 pM (2–5 ng l−1 Hg). Total mercury showed a strong washout effect over the course of the storm, while methylmercury appeared to show a diurnal pattern, with elevated levels during the daylight hours. No dimethylmercury was observed in any precipitation sample. Methylmercury was observed in most lakes studied, with a high of 3.1 pM (0.64 ng l−1 Hg) in Onadaga Lake, New York, and a low of < 0.015 pM in Lake Crescent, located in the Olympic Mountains of Washington State.
A number of actions have been undertaken within the National Atmospheric Deposition Program (NADP) to implement a regional mercury deposition network. This paper describes a field test designed to evaluate a collector design and protocol for implementation within a new Hg network. The collector chosen for evaluation is a “dual-orifice” collector, designed to sample precipitation for mercury and other metals simultaneously. The method chosen for Hg analysis was cold vapour atomic fluorescence spectroscopy (CVAFS). The weekly precipitation Hg concentrations range between 4.29 and 17.88 ng ℓ−1, with a volume-weighted mean of 10 ng ℓ−1 comparable to those reported in other ongoing studies in North America and Europe. Calculated deposition flux ranges from 43 to 358 ng m−2 week−1, with a mean of 186 ng m−2 week−1.
Relative consumptions of aqueous Hg0 and S(IV) due to reactions with O3 have been used to estimate the rate constant for the reaction of Hg0 and O3. Ratios ranging from <0.1 to >10 were measured in the pH range 4.5–9.5. The results were interpreted in terms of a second-order reaction of Hg0 and O3 with a rate constant k = (4.7±2.2) × 107 M−1s−1 which is independent of pH and temperature. Steady-state concentrations of dissolved inorganic mercury in atmospheric waters (rain and clouds) have been estimated using the rate constant determined in this work and previously reported rate constants for the reduction of Hg2+ by S(IV). At gas-phase concentrations of SO2>0.5 ppb, concentrations of dissolved inorganic mercury in the range 1–25 pM (0.2–5 ngℓ−1) are predicted at different pH and gas-phase concentrations of O3, which agrees reasonably well with measured concentrations. At lower SO2 concentration, the calculated values are unreasonably high, which indicates that other reducing processes may be of importance under these conditions.
Mercury evaporation from soil columns of an iron humus podzol treated with various amounts of HgCl2 and CH3HgCl was measured over 3500 h. The effects of rain acidity, rain duration, and rain intensity were investigated. Hg evaporation from CH3HgCl‐treated soil columns seems to be a biologically determined process. Hg evaporation from HgO2‐treated soil probably is mainly an abiotic process, following a pseudo first‐order reaction with rapidly decreasing evaporation rate due to a decreasing amount of available Hg. The added Hg compounds were transformed to highly volatile Hg and/or (CH3)2Hg. The Hg evaporation rate decreased with increasing rain acidity, which may cause accumulation of Hg in the soil. No effects of rain duration and rain intensity were found.
During the last decade a new pattern of Hg pollution has been discerned, mostly in Scandinavia and North America. Fish from low productive lakes, even in remote areas, have been found to have a high Hg content. This pollution problem cannot be connected to single Hg discharges but is due to more widespread air pollution and long-range transport of pollutants. A large number of waters are affected and the problem is of a regional character. The national limits for Hg in fish are exceeded in a large number of lakes. In Sweden alone, it has been estimated that the total number of lakes exceeding the blacklisting limit of 1 mg Hg kg-1 in 1-kg pike is about 10 000.
Annual emissions of anthropogenic Hg to the atmosphere in different regions of the world during the last decade show an interesting dichotomy: the emissions in the developed countries increased at the rate of about 4.5–5.5% yr−1 up to 1989 and have since remained nearly constant, while in developing countries the emissions continue to rise steadily at the rate of 2.7–4.5% yr−1. On a global basis, however, the total anthropogenic emissions of Hg increased by about 4% yr−1 during the 1980s, peaked in 1989 at about 2290 t and are currently decreasing at the rate of about 1.3% yr−1. Solid waste disposal through incineration processes is the dominant source of atmospheric mercury in North America (∼ 40%), Central and South America (∼34%), western Europe (∼28%) and Africa (∼30%), whereas coal combustion remains the dominant source in Asia (∼42%) and eastern Europe and the former USSR (∼40%). Mining and smelting of Zn and Pb represent the major industrial source of Hg in Oceania (∼35%).
Field studies were performed in Canada (at Eagle Lake in north-western Ontario) during July 1986 and subsequently at four oligotrophic forest lakes in south-western Sweden during 1988 and 1989 to determine the extent of mercury volatilization. The Canadian investigations involved simultaneous measurements of total vapour-phase mercury concentrations in air sampled immediately above the water surface and over land nearby. A diurnal cycle was observed for mercury emissions from Eagle Lake, with day-time volatilization rates significantly larger than night-time rates. The Swedish field measurements employed a flux chamber. This device was used to determine the rates at which volatile mercury species were emitted from the lakes. Volatilization occurred from each of the Swedish forest lakes during the warmer seasons of the year (with near-surface water temperatures in the 13–23°C range). For day-time measurements, volatilization rates were generally 3–10 ng Hg m−2 h−1. Daytime fluxes were, on average, about 2.5-times larger than night-time fluxes. Experiments conducted during the winter season (with water temperatures just above the freezing point) indicated very little, if any, emission of volatile mercury species from the lake surface.
Several dry deposition methods for Mercury (Hg) are being developed and tested in our laboratory. These include big-leaf and multilayer resistance models, micrometeorological methods such as Bowen ratio gradient approaches, laboratory controlled plant chambers, and throughfall. We have previously described our initial results using modeling and gradient methods. Throughfall may be used to estimate Hg dry deposition if some simplifying assumptions are met. We describe here the application and initial results of throughfull studies at the Walker Branch Watershed forest, and discuss the influence of certain assumptions on interpretation of the data. Throughfall appears useful in that it can place a lower bound to dry deposition under field conditions. Our preliminary throughfall data indicate net dry deposition rates to a pine canopy which increase significantly from winter to summer, as previously predicted by our resistance model. Atmospheric data suggest that rainfall washoff of fine aerosol dry deposition at this site is not sufficient to account for all of the Hg in net throughfall. Potential additional sources include dry deposited gas-phase compounds, soil-derived coarse aerosols, and oxidation reactions at the leaf surface.
Due to a considerable increase of anthropogenic mercury emissions, the mercury load of many soils has risen significantly, for instance in northern Europe. Understanding the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological concern. This paper presents a method for obtaining qualitative and quantitative information about mercury translocation in and evaporation from soil. Soil lysimeters were treated with Hg‐labeled HgCl2 and CH3HgCl and irrigated with artificial rain. It was demonstrated that the leaching of Hg can be detected by measuring the relative y‐activity throughout the soil profile by means of Na(TI)I detectors. Furthermore, the set‐up was designed to allow detection of Hg volatilization from soil by using traps of iodized charcoal, followed by a potassium peroxodisulfate solution and measuring the γ‐activity. The amount of radioactive Hg in soil leachate was measured by a Na(Tl)I well‐type detector after upconcentration. The determination of monomethyl Hg was been performed by extraction procedures that isolate the methyl mercury compounds. The amount of Hg retained in the soil profile and the real depth of leaching were determined by stratifying the soil profile at the end of the experiment and measuring the y‐activity. With control of all pathways of Hg, the experimental design allows performance of a mass balance analysis.
Mercury evaporation from undisturbed iron‐humus podzol lysimeters was measured over 3 months after treatment with HgCl2 spiked with radioactive Hg. The relative evaporation rate from HgCl2 treated soils followed the sum of two exponential functions. Because evaporation asymptotically approaches zero with time, the integral of the fit curve represents the evaporative loss in percent of atmospheric deposition. For the soil investigated, about 5% of atmospheric Hg deposition was reemitted into the atmosphere. It is hypothesized that mercury evaporation can decrease the leaching of mercury in and from soil significantly; this effect is probably increasing with decreasing rain acidity or soil acidity. Mercury deposited as soluble salt remains susceptible to reemission to air for 300 d after incorporation into the soil matrix. Indications are found that Hg evaporation from soils in geological background areas predominantly derives from recent atmospheric Hg deposition and not from geological sources.
This study was conducted to determine if mercury is being released to the atmosphere from an inland waterway (the Wabigoon River system of N.W. Ontario, Canada) known to be contaminated with this metal from industrial wastewater discharges. Chemical and meteorological data were collected at three sites over a 3‐week, period during the summer of 1986. At each site, simultaneous measurements were performed of total vapour‐phase Hg over water and over an adjacent land surface. A sparger device was used to probe for the presence of volatile forms of mercury dissolved in the water. The paper describes innovative sampling and analytical techniques and presents new environmental data.
A PROPER inventory of atmospheric emissions from natural sources is basic to our understanding of the atmospheric cycle of the trace metals (and metalloids), and is also needed for assessing the extent of regional and global pollution by toxic metals1. It is generally presumed that the principal natural sources of trace metals in the atmosphere are wind-borne soil particles, volcanoes, seasalt spray and wild forest fires2–6. Recent studies have shown, however, that particulate organic matter is the dominant component of atmospheric aerosols in non-urban areas7–10 and that over 60% of the airborne trace metals in forested regions can be attributed to aerosols of biogenic origin11,12. Here I estimate that biogenic sources can account for 30–50% of the global baseline emissions of trace metals. For most of the toxic metals, the natural fluxes are small compared with emissions from industrial activities, implying that mankind has become the key agent in the global atmospheric cycle of trace metals and metalloids.
Several actions have been undertaken within the National Atmospheric Deposition Program (NADP) to implement a regional mercury deposition network. This paper reports on the general findings of a National Atmospheric Deposition Program workshop on sampling mercury in precipitation, which has led to several conclusions important to the design of a regional sampling network for mercury.
Observations of lead ratios and trace element concentrations in atmospheric aerosols at a rural location in Ontario, Canada confirm results of a previous study of urban aerosols that showed there are significant differences in the isotopic composition of lead from Canadian autos, Canadian smelters and eastern American sources. Lead measurements in fall 1984 and spring 1986 were apportioned to the respective sources as follows: for 1984 (55, 2, 43%) and for 1986 (69, 7, 24%). Lead isotopic and meteorological information point to In as the best elemental tracer of emissions from selected northern Canadian smelters.
Gaseous and aerosol products formed in the HO-radical initiated reaction of CH3HgCH3 were studied by the long-path FT IR method in the photolysis of CH3HgCH3-C2H5ONO-NO mixtures typically at 10, 10, and 20 ppm each in 700 torr of air at ∼300 K. The results were consistent with the predominant occurrence of the displacement reaction of HO + CH3HgCH3 → CH3HgOH + CH3 as the primary process. The relative rate constant for the HO-radical reactions of CH3HgCH3 and C2H4 was determined to be k(C2H4)/k(CH3HgCH3) = 0.43 ± 0.03 (σ). This value combined with the literature value of k(C2H4) = (8.48 ± 0.39) × 10-12 cm3 molecule-1 s-1 gives k(CH3HgCH3) = (1.97 ± 0.23) × 10-11 cm3 molecule-1 s-1.
This paper documents the atmospheric mercury concentrations above anthropogenically contaminated and naturally enriched sites in central western Nevada. Atmospheric mercury concentrations were measured at five representative regional sites (1.2−7.5 ng/m3) and two anthropogenically contaminated areas (13−866 ng/m3) in the Carson River Superfund Site. The highest regional concentrations were measured at the Steamboat Geothermal area, where mercury mineralization occurs naturally. Concurrent with atmospheric sampling, environmental conditions were monitored to assess their covariance with mercury concentrations. Atmospheric mercury concentrations were influenced by multiple factors with dominance exerted by substrate mercury concentration, site surface characteristics, and local and synoptic scale air masses. A mercury flux of 5−125 (±50%) μg of mercury m-2 h-1 was estimated via modified K-theory for a contaminated location. This flux was scaled up to estimate the contribution of atmospheric mercury from mine wastes within the Carson River Superfund Site. The estimated annual flux (150−400 kg/yr) is comparable to that from a 1000 MW coal-fired power plant (300 kg/yr). The projected longevity of this diffuse source exceeds 104 years, so the cumulative contribution over time from this region far exceeds the corresponding contribution of a coal-fired power plant whose life time is measured in decades.
Data on the accumulation and release kinetics on azalea leaves exposed to constant vapor levels of trifluralin, hexachlorobenzene, mirex, thionazin, and sulfotep are reported. Leaf/air bioconcentration factors from these and other similar experiments were used to develop a correlation with air/water and 1-octanol/water partition coefficients.
Spruce seedlings [Picea abies (L.) Karst.] were exposed in nutrient solutions to a range of concentrations of HgCl2 and CH3HgCl for 7 weeks. The mineral, chlorophyll and water contents of the needles, and dry weights of root and needles were then estimated. The rates of photosynthesis, transpiration and dark respiration of the intact plants were determined using a Li-cor portable photosynthesis-measuring system. CO2 uptake decreased as the supply of both forms of Hg increased. Rates of transpiration were significantly reduced only after exposure to CH3HgCl. Similar concentrations of Hg were found in needles independent of the form of Hg supplied. Decreased rates of CO2 uptake at 100 nM HgCl2 and 1 nM CH3HgCl could be explained by lower levels of chlorophyll, and by lower levels of chlorophyll and closed stomata at all other CH3HgCl concentrations. Only at 1000 nM HgCl2 were other photosynthetic parameters affected.
Decreased rates of transpiration and the lower chlorophyll levels in the needles did not appear to be due to the direct action of Hg, but rather to root damage that leads to a decrease in water supply and nutrient levels in the needles.
An attempt is made to assess present knowledge about atmospheric mercury: its occurrence in air and precipitation, chemical transformations taking place in the atmosphere, and mercury fluxes to and from the Earth's surface. Tentative budgets are estimated for mercury in the global atmosphere and in the atmosphere over Europe and Sweden.Major features revealed by this include the following:For the global atmosphere, current anthropogenic emissions are comparable to emissions by natural processes (pre-industrial). The present background fluxes are probably significantly augmented by anthropogenic emissions during the industrial era.A dominant fraction (≳80%) of the total mercury in the atmosphere consists of a volatile gaseous mercury form, presumably elemental mercury, Hg0. This mercury has an atmospheric residence time of at least a few months, maybe even one or two years, and is uniformly distributed throughout the troposphere (1–2 ng m−3).The volatile mercury vapour (Hg0) is oxidized in the atmosphere to unknown forms that are soluble and can be scavenged by precipitation or dry deposited at the surface. The oxidation process is not known but photochemical oxidants (including ozone) are likely to be important. The atmospheric residence time of the water soluble (non-volatile) mercury is in the range of a few days to a few weeks, corresponding to a characteristic transport distance of up to a few thousand kilometers.Even if a dominant fraction of the mercury emitted from an individual source, such as a chlor-alkali plant, is dispersed regionally or globally, a small fraction (<10%) is deposited locally. Increases by a factor of 10 to 100, above background deposition rates, have been measured within the nearest km of such plants. At a distance of 10–50 km, the deposition normally approaches the background value. Around a large Swedish smelter, mercury levels in lake sediments are significantly augmented even beyond 50 km from the plant.The contribution to current mercury deposition in Sweden from anthropogenic mercury emissions in other European countries is most likely larger than the contributions from current Swedish emissions.Measurements of mercury in lake sediments and peat bogs show that in southern Scandinavia, the rate of mercury deposition has increased by a factor of about 5 during the last hundred years. The increase in northern Scandinavia is significantly less, at most a factor of two. These increases are caused, most likely, by anthropogenic emissions into the atmosphere mainly within the European region.
ABSTRACTA flux chamber technique applied to volatile mercury species has been developed and evaluated. This technique can be used to measure the direction and magnitude of mercury transfer between the atmosphere and lake or soil surfaces. Measurements have been performed over four oligotrophic forest lakes in southwestern Sweden during 1988 and 1989. Net emission fluxes of mercury were measured from the lakes. The measured daytime fluxes during the warmer season (water temperatures 13–23 °C) were within the range 3–20 ng h−1 m−2 (average 7.9 ng h−1 m−2). The average night-time fluxes measured during the same season were 2 to 3 times smaller. Two sets of measurements, performed during the winter when water temperatures were ≤ 2 °C, gave flux values close to zero. Flux measurements were also performed over soil in a coniferous forest. Compared to the situation for the forest lakes, the fluxes of mercury over forest soil are much lower in magnitude, with values ranging from approximately − 2 to + 2 ng h−1 m−2 during different seasons. Emission was observed with an average of 0.3 ng h−1 m−2 when soil temperature was about 10 °C, while dry deposition was measured with an average of 0.9 ng h−1 m−2, when soil temperature was < 3 °C.
Deposition rates of Hg to forested land areas have been studied for 13 mo in two small forested catchments in south-western
Sweden. Monthly sampling of forest canopy throughfall water in a mature Norwegian spruce stand and precipitation to an open
field was carried out. Hg deposited to the catchments via litter fall was also considered. Integrated monthly samples of both
precipitation and throughfall water were collected by 6 and 45 separate collectors, respectively, designed for an unbiased
Hg sampling. The average Hg concentration in precipitation during this period was 13.0 ± 4.0 ng Hg L-1. The results show that
annual dry deposition of Hg to a spruce stand in throughfall water can be 50% of the wet deposition, 4 to 7 compared to 12
g Hg km−2 yr−1, respectively. A strong seasonal trend in Hg deposition via throughfall water is also present, with increased levels during
the growing season and with a monthly maximum in August. Further, the dry deposition measured in throughfall water seems to
be negligible during part of the winter.
Mercury is released into the atmosphere from natural and anthropogenic sources. Once in the air, Hg species will be dispersed,
chemically and physically transformed, and transported over varying distances (regional, continental and global scales) while
concurrently being subjected to removal processes. Modeling of the aerial transport and deposition of Hg to receptor sites
offers an attractive approach for integrating existing experimental data and represents an important tool for advancing our
understanding of environmental Hg pollution. Comprehensive modeling efforts of the atmospheric pathways and fate of this heavy
metal require knowledge of its atmospheric chemistry. To update and consolidate available information relevant to the atmospheric
chemistry of Hg, a computer-assisted search was undertaken of the primary scientific literature published during the last
ten years. Selected results from this literature survey are presented in this paper.
A seasonal variation of both particle and gaseous Hg concentrations in the atmosphere is present in south-western Sweden.
An average gaseous Hg level of 3.7 ng m−3 is found in winter, compared to 2.8 ng m−3 in summer. A weak decreasing south-north gradient for gaseous Hg in air over the Nordic countries is also present, with yearly
average values from 3.2 to 2.8 ng m−3. A gradient for particulate Hg is less clear. An air parcel trajectory sector classification of gaseous Hg levels in air,
and to some extent the particulate associated Hg, clearly demonstrates the increased concentrations in the southern sectors,
especially in south-western Sweden where the gaseous Hg increase is about I ng m−3. These observations are consistent with an influence from the European continent. The average concentrations of Hg in precipitation
at the various stations show a pronounced decreasing south-north gradient. A major portion of the total Hg present in precipitation
is associated with particles. For the southern stations, a strong correlation between Hg and sulfate, or pH, is present suggesting
a connection between Hg in precipitation and anthropogenic activities.
Aerosol and total vapor-phase Hg concentrations in air have been measured at Walker Branch Watershed, Tennessee for ≈ 2 yr.
Airborne Hg at this site is dominated by vapor forms which exhibit a strong seasonal cycle, with summer maxima that correspond
to elevated air temperature. Concentrations in this forest are near background levels; however, concentrations at a site within
3 km are significantly elevated due to emissions from Hg-contaminated soils. The concentration data have been combined with
a recently modified dry deposition model to estimate dry deposition fluxes to the deciduous forest at Walker Branch. Weekly
mean modeled Vd values for Hg° ranged from <0.01 (winter) to > 0.1 (summer) cm s1. Weekly dry deposition fluxes ranged from <0.1 µg m−2 during winter to > 1.0 µgg m−2 in the summer. Our dry deposition estimates plus limited measurements of wet deposition in this area indicate that dry deposition
may be the dominant input process in this forest, at least during the summer.
The gas phase reaction between elemental mercury (Hg0) and ozone (03) has been studied in sunlight, in darkness, at different temperatures, and different surface-to-volume (s/v) ratios. At 03 concentrations above 20 ppm, a loss of Hg0 and a simultaneous formation of oxidized mercury (Hg(II)) was observed. The results suggest a partly heterogeneous reaction, with a gas phase rate constant of 3210–20 cm3 molec.–1 s–1 at 20 C. This corresponds to an atmospheric Hg half-life of about one year at a mean global 03 concentration of 30 ppb.
As part of current efforts to understand the cycling of mercury (Hg) in the atmosphere, information is needed on its atmospheric speciation. Almost no data exists on water-soluble Hg(II) species in ambient air. A new technique for measuring gas phase water soluble Hg(II) species has been developed, utilizing a high-flow refluxing mist chamber. Extensive testing has been carried out, including attempts to rule out production of artifact Hg(II). Measurements at two locations (East-Central Tennessee and the Ohio-Indiana border) found approximately 0.05–0.15 ng/m3 of reactive Hg(II), representing ca. 3 to 5% of the total gaseous Hg. Limited tests of artifact Hg(II) production in the mist chamber by ozone oxidation and co-sampled aerosol Hg(II) suggest that the majority of the collected Hg(II) exists in ambient air in the gas phase.
The phenomena of cold condensation and fractionation of chemical contaminants on a global scale are discussed. The net result of these phenomena is that concentrations of certain atmospherically transported contaminants are higher than expected in the condensed, i.e. non gaseous media of water, soils, sediments and biota as a result of the temperature dependence of partitioning and transport phenomena. It is argued that the phenomena are best investigated by a combination of monitoring and modeling. This approach is illustrated in the form of a nine meridional segment model for hexachlorocyclohexane. It is suggested that this approach should be applied to Hg, but this is not presently possible because of the lack of data on Hg species properties and conversion rates. Available data have been used to test the hypothesis that lower temperatures cause enhanced partitioning from the atmosphere to a lake ecosystem at low temperatures by compiling a three species model of an atmosphere-water-sediment-fish system at 25 C and 0 C. Preliminary results show that the effect of this drop in temperature is to cause increases in concentrations throughout the aquatic ecosystem of factors of three to four, other factors being equal. Thus it is likely that a comprehensive global model will show that Hg is subject to the global fractionation phenomenon. It is recommended that attempts be made to develop such a model.
Atmospheric mobilization and exchange at the air-water interface are significant features of biogeochemical cycling of Hg
at the Earth's surface. Our marine studies of Hg have been extended to terrestrial aquatic systems, where we are investigating
the tropospheric cycling, deposition and air-water exchange of Hg in the mid-continental lacustrine environs of northcentral
Wisconsin. This program is part of a multidisciplinary examination into the processes regulating the aquatic biogeochemistry
of Hg in temperate regions. Trace-metal-free methodologies are employed to determine Hg and alkylated Hg species at the picomolar
level in air, water and precipitation. We have found Hg concentrations and atmospheric fluxes in these fresh water systems
to be similar to open ocean regions of the Northern Hemisphere. A well constrained mass balance for Hg has been developed
for one of the lakes, Little Rock Lake, which is an extensively studied clear water seepage lake that has been divided with
a sea curtain into two basins, one of which is untreated (reference pH: 6.1) while the other is being experimentally acidified
(current pH: 4.7). This budget shows that the measured total atmospheric Hg deposition (ca. 10 µg m−2 yr−1) readily accounts for the total mass of Hg in fish, water and accumulating in the sediments of Little Rock Lake. This analysis
demonstrates the importance of atmospheric Hg depositional fluxes to the geochemical cycling and bioaccumulation of Hg in
temperate lakes. It further suggests that modest increases in atmospheric Hg loading could lead directly to enhanced levels
of Hg in biota. Analogous modeling for monomethylmercury (MMHg) is as yet limited. Nevertheless, preliminary data for the
atmospheric deposition of MMHg indicate that this flux is insufficient. to account for the amounts of MMHg observed in biota.
An in-lake synthesis of MMHg is implicated. The importance of volatile Hg which is principally in the elemental form, and
its evasion to the atmosphere is also illustrated. We suggest that the in-lake production of Hg° can reduce the Hg (II) substrate
used in the in-lake microbiological synthesis of MMHg.