A Quantitative Method to Measure the Kinetics of Elemental Mercury Emissions From Black Shale (Nova Scotia, Canada)

A controlled chamber method using continuous gold trap atomic fluorescence spectroscopy (AFS) (Tekran 2537X) for the analysis of Hg(0) emissions from moderate mass rock samples was developed and tested. A series of black shale and other bedrock samples from Nova Scotia, Canada, were used to test the method and its reproducibility. Hg(0) emissions at 170°C were measured to quantify both free surficial Hg(0) and Hg(0) that had penetrated the rock structure. High volumes of chamber air (45 L) were sampled using 30 min collection times to achieve detectable elemental mercury (Hg(0)) emissions. We found higher percentage masses of Hg(0) were released (1.1%-4.1% of total Hg mass present) in black shale samples as compared to granite and basalt samples from the same region (0.0%-0.3% released) over 350 h of continuous analysis time. The pseudo first order emission rate constants ranged from 0.015-0.245 h-1 (mean 0.063 h-1, standard deviation (SD) 0.102) for the black shale samples analyzed and was 0.004 h-1 for the granite sample. The 24-h zero-order emission rate constants ranged between 0.41 and 3.54 ng h-1 (mean 1.4 ng h-1, SD 1.3) for the black shale samples analyzed and were ~ 0.01 ng h-1 for the granite and basalt samples. This technique has useful implications for examining rock properties and Hg(0) emission rates.

A synthesis of mercury research in the Southern Hemisphere, part 1: Natural processes

Recent studies demonstrate a short 3-6-month atmospheric lifetime for mercury (Hg). This implies Hg emissions are predominantly deposited within the same hemisphere in which they are emitted, thus placing increasing importance on considering Hg sources, sinks and impacts from a hemispheric perspective. In the absence of comprehensive Hg data from the Southern Hemisphere (SH), estimates and inventories for the SH have been drawn from data collected in the NH, with the assumption that the NH data are broadly applicable. In this paper, we centre the uniqueness of the SH in the context of natural biogeochemical Hg cycling, with focus on the midlatitudes and tropics. Due to its uniqueness, Antarctica warrants an exclusive review of its contribution to the biogeochemical cycling of Hg and is therefore excluded from this review. We identify and describe five key natural differences between the hemispheres that affect the biogeochemical cycling of Hg: biome heterogeneity, vegetation type, ocean area, methylation hotspot zones and occurence of volcanic activities. We review the current state of knowledge of SH Hg cycling within the context of each difference, as well as the key gaps that impede our understanding of natural Hg cycling in the SH. The differences demonstrate the limitations in using NH data to infer Hg processes and emissions in the SH.

Migration and transformation of soil mercury in a karst region of southwest China: Implications for groundwater contamination

Guizhou Province is located in the heart of a karst zone in southwest China, which is one of the largest karst areas in the world. Given the fragile surface ecosystem and highly developed underground karst structure, the migration and transformation of soil Hg may impact groundwater quality in karst environments with high Hg background concentrations. This study examines the vertical migration and transformation of soil mercury (Hg) in two karst catchments, Huilong and Chenqi, with the former containing high Hg contents associated with mineralization and the latter representing regional background Hg. The results show that the soil Hg pool in the Huilong catchment was as high as 44.4 ± 4.2 g m^-2, whereas in the Chenqi catchment was only 0.17±0.02 g m^-2. Compared with farmland soil, forest soil showed a significant loss of Hg. The results of L₃ X-ray absorption near edge structure of Hg indicated that α-HgS, the primary mineral of Hg ore, gradually changed to other mineral types during soil formation. In Huilong catchment, the proportion of organic bound Hg(SR)₂ out of total Hg decreased from 44.0% to 20.3% when soil depth increased from 10 cm to 160 cm in farmland soil profile and from 39.3% to 34.5% in forest soil profile, while the proportion of ionic Hg increased with soil depth, from 4.2% to 10.7% in the farmland soil profile and from 6.7% to 11.6% in the forestland soil profile. Results from the triple-mixing isotope model show that soil Hg accounts for more than 80% Hg in groundwater in the two catchments. Results from this study indicate potential risks of soil Hg entering into groundwater in this karst area.

Measuring volatile emissions from biosolids: A critical review on sampling methods

As a by-product of wastewater treatment, biosolids are a source of volatile emissions which can lead to community complaints due to odours and other pollution risks. Sampling methods play a significant role in collecting gas emissions from biosolids-related sources (i.e., pure biosolids, landfilling, land application and composting of biosolids). Though a range of different sampling techniques (flux hood, wind tunnel, static chamber, headspace devices) have been explored in many published papers, the management and best practice for sampling emissions from biosolids is unclear. This paper presents a comprehensive review of sampling methods for collecting gaseous emissions from biosolids. To account for the inconsistent terminologies used to describe sampling devices, a standard nomenclature by grouping sampling devices into five categories was proposed. Literature investigating emission sampling from biosolids-related sources was reviewed. Subsequently a critical analysis of sampling methods in terms of design, advantages, and disadvantages were compiled based on literature findings and assumed mechanistic understanding of operation. Key operational factors such as the presence of fans, purge gas flow rates, insertion depth, and incubation conditions were identified and their level of influence on the measurement of emissions were evaluated. From the review, there are still knowledge gaps regarding sampling methods used to collect gases from biosolids-related sources. Therefore, a framework for the management of emission sampling methodologies based on common sampling purposes was proposed. This critical review is expected to improve the understanding of sampling methodologies used in biosolids-related sources, by demonstrating the potential implications and impacts due to different choices in sampling methods.

Mantle Hg isotopic heterogeneity and evidence of oceanic Hg recycling into the mantle

The geochemical cycle of mercury in Earth's surface environment (atmosphere, hydrosphere, biosphere) has been extensively studied; however, the deep geological cycling of this element is less well known. Here we document distinct mass-independent mercury isotope fractionation (expressed as Δ¹⁹⁹Hg) in island arc basalts and mid-ocean ridge basalts. Both rock groups show positive Δ¹⁹⁹Hg values up to 0.34‰ and 0.22‰, respectively, which deviate from recent estimates of the primitive mantle (Δ¹⁹⁹Hg: 0.00 ± 0.10‰, 2 SD)¹. The positive Δ¹⁹⁹Hg values indicate recycling of marine Hg into the asthenospheric mantle. Such a crustal Hg isotope signature was not observed in our samples of ocean island basalts and continental flood basalts, but has recently been identified in canonical end-member samples of the deep mantle¹, therefore demonstrating that recycling of mercury can affect both the upper and lower mantle. Our study reveals large-scale translithospheric Hg recycling via plate tectonics.

Total mercury and methylmercury (MeHg) in braised and crude Boletus edulis carpophores during various developmental stages

We collected and processed Boletus edulis (King Bolete) carpophores grouped in four batches based on their developmental stage (button stage, young-white, large-white, and large-yellow). The study aimed, for the first time, to examine the B. edulis content and effect of braising and to estimate the intake of total mercury (THg) and methylmercury (MeHg) from a single meal based on whole (wet) weight (ww) and dry weight (dw). In braised carpophores, THg concentrations ranged from 0.2668 ± 0.0090 to 0.5434 ± 0.0071 mg kg-1 ww at different developmental stages, whereas crude products concentrations ranged from 0.1880 ± 0.0247 to 0.2929 ± 0.0030 mg kg-1 ww. The button stage crude carpophores were more highly contaminated with THg than at later stages of maturity, but MeHg levels were lower (p < 0.0001). On the other hand, braised button stage carpophores showed more MeHg than at later maturity stages. MeHg contributed at 1.9 ± 0.7% in THg in crude mushrooms and at 1.4 ± 0.3% in braised meals. The effect of braising was to increase the average THg and MeHg contents in fresh mushroom meals by 52 ± 31% and 53 ± 122% respectively, but a reduction of 40 ±14% and 40 ± 49% respectively was seen on a dw basis. The potential intakes of THg and MeHg from braised meals of B. edulis studied were small and considered safe.

Heavy Metal-Resistant Filamentous Fungi as Potential Mercury Bioremediators

Filamentous fungi native to heavy metals (HMs) contaminated sites have great potential for bioremediation, yet are still often underexploited. This research aimed to assess the HMs resistance and Hg remediation capacity of fungi isolated from the rhizosphere of plants resident on highly Hg-contaminated substrate. Analysis of Hg, Pb, Cu, Zn, and Cd concentrations by X-ray spectrometry generated the ecological risk of the rhizosphere soil. A total of 32 HM-resistant fungal isolates were molecularly identified. Their resistance spectrum for the investigated elements was characterized by tolerance indices (TIs) and minimum inhibitory concentrations (MICs). Clustering analysis of TIs was coupled with isolates’ phylogeny to evaluate HMs resistance patterns. The bioremediation potential of five isolates’ live biomasses, in 100 mg/L Hg²⁺ aqueous solution over 48 h at 120 r/min, was quantified by atomic absorption spectrometry. New species or genera that were previously unrelated to Hg-contaminated substrates were identified. Ascomycota representatives were common, diverse, and exhibited varied HMs resistance spectra, especially towards the elements with ecological risk, in contrast to Mucoromycota-recovered isolates. HMs resistance patterns were similar within phylogenetically related clades, although isolate specific resistance occurred. Cladosporium sp., Didymella glomerata, Fusarium oxysporum, Phoma costaricensis, and Sarocladium kiliense isolates displayed very high MIC (mg/L) for Hg (140–200), in addition to Pb (1568), Cu (381), Zn (2092–2353), or Cd (337). The Hg biosorption capacity of these highly Hg-resistant species ranged from 33.8 to 54.9 mg/g dry weight, with a removal capacity from 47% to 97%. Thus, the fungi identified herein showed great potential as bioremediators for highly Hg-contaminated aqueous substrates.

Planular-vertical distribution and pollution characteristics of cropland soil Hg and the estimated soil-air exchange fluxes of gaseous Hg over croplands in northern China

As an important reservoir of mercury (Hg), cropland play an important role in the Hg cycle, but it was poorly understood in northern China. The major objectives of this study are to ascertain the distribution characteristics of soil Hg and then assess its pollution level and potential risk, and further evaluate the role of cropland in northern China in the global soil-air exchange of Hg based on the simulation experiments and regional survey. The average Hg concentration in surface soils of the 30 sites in northern China was 116.1 ± 135.8 ng g^-1, which was significantly higher than background values. The surface soils show a significant spatial heterogeneity in Hg concentration, and the Hg levels near provincial capitals were higher than those at corresponding prefecture-level cities, revealing that the soil Hg levels were closely associated with the local industrial and economic development. Profile data shows that topsoil Hg concentration was significantly higher than those in deeper layers at most of sites, indicating the more serious pollution situation in recent years. Generally, the higher the surface soil Hg concentration, the more obvious this top-bottom decreasing trend. The planular-vertical distribution patterns of TOM share similar trends as those of soil Hg concentration, indicating Hg concentration was closely associated with TOM content. Statistical results show that the mean CF, E_rⁱ, and I_geo values were 4.0 ± 5.0, 161 ± 198, 0.76 ± 1.34, respectively, and more than two thirds of sampling sites were moderately and considerably polluted. The mean annual accumulative flux of Hg in the northern China was 20.9 ± 43.8 μg m^-2 yr^-1, and the total net emission fluxes of Hg from the croplands in six provinces were 8.37 ton yr^-1. This indicates that although the cropland occasionally acts as a sink, it represents an important natural source of atmospheric Hg as a whole.

Fifty years of volcanic mercury emission research: Knowledge gaps and future directions

Volcanism is a potentially important natural source of mercury (Hg) to the environment. However, its impact on the global Hg cycle remains poorly understood despite advances over the last five decades. This represents a major uncertainty in our understanding of the relative contributions of natural and anthropogenic Hg sources to the global atmosphere. This uncertainty, in turn, impacts evaluation of the effectiveness of policies to mitigate the impact of anthropogenic Hg on the environment. Here we critically review recent progress in volcanic Hg emission research, including advances in sampling methods and understanding of the post-emission behavior of Hg in the atmosphere. Our statistical analysis of the limited available data shows that the plumes of non-arc volcanoes exhibit significantly higher Hg concentrations than arc volcanoes, yet the latter emit 3-fold higher Hg fluxes on average. Arc volcanism also dominates volcanic gas emissions globally, indicating that arc volcanoes should be a priority for future Hg emission research. We explore several methodological challenges that continue to hinder progress in quantifying global volcanic Hg emissions, and discuss the importance of longer time-frame data collection to capture temporal variations in emissions. Recommendations are proposed for working toward a more accurate assessment of the global volcanic Hg flux. A detailed summary of all published volcanic Hg emissions data worldwide is also presented as a reference tool for future work.

Onshore mud volcanoes as a geological source of mercury: Case study from the Kerch Peninsula, Caucasus continental collision zone

Three mud volcanoes (MVs) in the Kerch Peninsula were studied as a geological source of mercury. The study focused on total mercury (THg) concentrations in MV waters, mud masses and plants colonizing MV areas; gaseous elemental mercury (GEM) in the atmosphere above MVs; and sulfide mercury (HgS) and HgCl₂ species in representative samples of mud masses. THg concentrations in the illite-smectite mud masses ranged from 38 to 920 ng/g. They contained up to 70% of total mercury in sulfide form (in pyrite and cinnabar), but lacked HgCl₂. THg values in MV waters of HCO₃-Cl/Na- and/or Cl-HCO₃/Na-types with рН = 7.4-9.5 mostly fell in a range of 79-440 ng/L, but rarely exceeded 600 ng/L, being comparable with those for geothermal systems. Another issue of interest was the distribution of THg in below- and above-ground parts of halophyte plant Limonium caspium. THg was incorporated into the plant roots, leaves and flowers; the roots exhibited higher concentrations of THg relative to the other organs. The Hg bioaccumulation factor ranged from 0.06 to 0.76. GEM concentrations measured over large bubbling MV pools and newly formed cracks showed values (50 to 520 ng·m^-3) higher than background values (≤3 ng·m^-3) associated with pristine test sites and background values measured within three MV areas of the Kerch peninsula that is slightly higher than background concentration for the Northern Hemisphere. Maximum GEM contents were comparable with the values found in geothermal and magmatic volcanic provinces.

Status and environmental management of soil mercury pollution in China: A review

The harm from mercury pollution to human health and the environment has long been known. In recent years, the combination of industrial activities and long-term atmospheric transport has resulted in a sustained increase in mercury concentrations in soils. However, soil remediation and mercury-contaminated soil management in China are still in its infancy, and there is ample space for the development of related research. We systematically reviewed several pertinent topics and found that soil mercury pollution around mines and industrial soil in China is the most serious. The highest mercury content is found in the soil around the Tongren mercury mine in Guizhou Province and the thermometer factories. The average content of soil mercury is similar to that of atmospheric mercury emission in China. Mercury content in soil gradually decreases from the southeast to the northwest. In order to repair the mercury-contaminated soil, solidification and stabilization technology have been developed in China and applied in the engineering of restoration. In the future, we will study more effective stabilizer materials and select plants highly rich in mercury, to develop low-cost and high-repair-rate remediation technology. China has also developed a series of policies, regulations, and regulatory documents to manage mercury pollution, such as the Agricultural Land Standard and the Construction Land Standard. Compared with other countries, the screening values for soil mercury in China are relatively low. China has also established control standards for methylmercury in soils of residential and industrial land. In addition, China has issued emission standards and control notices related to the mercury industry. However, there are still shortcomings in soil remediation technology and environmental management systems for mercury pollution in China. In the future, China will formulate standards according to local conditions and improve the responsibility mechanism, financial mechanism, and level of public participation.

Mercury in traditionally foraged species of fungi (macromycetes) from the karst area across Yunnan province in China

The objective of this study is to better quantify the occurrence, intake, and potential risk from Hg in fungi traditionally foraged in SW China. The concentrations and intakes of Hg were measured from 42 species including a "hard" flesh type polypore fungi and a" soft" flesh type edible species that are used in traditional herbal medicine, collected during the period 2011-2017. Three profiles of forest topsoil from the Zhenyuan site in 2015 and Changning and Dulong sites in 2016 were also investigated. The concentrations of Hg in composite samples of polypore fungi were usually below 0.1 mg kg-1 dry weight (dw) but higher levels, 0.11 ± 0.01 and 0.24 ± 0.00 mg kg-1 dw, were noted in Ganoderma applanatum and Amauroderma niger respectively, both from the Nujiang site near the town of Lanping in NW Yunnan. Hg concentrations in Boletaceae species were usually well above 1.0 mg kg-1 dw and as high as 10 mg kg-1 dw. The quality of the mushrooms in this study in view of contamination with Hg showed a complex picture. The "worst case" estimations showed probable intake of Hg from 0.006 μg kg-1 body mass (bm) ("hard" type flesh) to 0.25 μg kg-1 bm ("soft" flesh) on a daily basis for capsulated products, from 17 to 83 μg kg-1 bm ("soft" flesh) in a meal ("hard" type flesh mushrooms are not cooked while used in traditional herbal medicine after processing), and from 0.042 to 1.7 and 120 to 580 μg kg-1 bm on a weekly basis, respectively. KEY POINTS: • Polypore species were slightly contaminated with Hg. • Hg maximal content in the polypore was < 0.25 mg kg-1 dry weight. • Many species from Boletaceae family in Yunnan showed elevated Hg. • Locals who often eat Boletus may take Hg at a dose above the daily reference dose.

Recent advances in understanding and measurement of Hg in the environment: Surface-atmosphere exchange of gaseous elemental mercury (Hg0)

The atmosphere is the major transport pathway for distribution of mercury (Hg) globally. Gaseous elemental mercury (GEM, hereafter Hg⁰) is the predominant form in both anthropogenic and natural emissions. Evaluation of the efficacy of reductions in emissions set by the UN's Minamata Convention (UN-MC) is critically dependent on the knowledge of the dynamics of the global Hg cycle. Of these dynamics including e.g. red-ox reactions, methylation-demethylation and dry-wet deposition, poorly constrained atmosphere-surface Hg⁰ fluxes especially limit predictability of the timescales of its global biogeochemical cycle. This review focuses on Hg⁰ flux field observational studies, namely the theory, applications, strengths, and limitations of the various experimental methodologies applied to gauge the exchange flux and decipher active sub-processes. We present an in-depth review, a comprehensive literature synthesis, and methodological and instrumentation advances for terrestrial and marine Hg⁰ flux studies in recent years. In particular, we outline the theory of a wide range of measurement techniques and detail the operational protocols. Today, the most frequently used measurement techniques to determine the net Hg⁰ flux (>95% of the published flux data) are dynamic flux chambers for small-scale and micrometeorological approaches for large-scale measurements. Furthermore, top-down approaches based on Hg⁰ concentration measurements have been applied as tools to better constrain Hg emissions as an independent way to e.g. challenge emission inventories. This review is an up-dated, thoroughly revised edition of Sommar et al. 2013 (DOI: 10.1080/10643389.2012.671733). To the tabulation of >100 cited flux studies 1988-2009 given in the former publication, we have here listed corresponding studies published during the last decade with a few exceptions (2008-2019). During that decade, Hg stable isotope ratios of samples involved in atmosphere-terrestrial interaction is at hand and provide in combination with concentration and/or flux measurements novel constraints to quantitatively and qualitatively assess the bi-directional Hg⁰ flux. Recent efforts in the development of relaxed eddy accumulation and eddy covariance Hg⁰ flux methods bear the potential to facilitate long-term, ecosystem-scale flux measurements to reduce the prevailing large uncertainties in Hg⁰ flux estimates. Standardization of methods for Hg⁰ flux measurements is crucial to investigate how land-use change and how climate warming impact ecosystem-specific Hg⁰ sink-source characteristics and to validate frequently applied model parameterizations describing the regional and global scale Hg cycle.

Mercury bioaccumulation in zooplankton and its relationship with eutrophication in the waters in the karst region of Guizhou Province, Southwest China

Zooplankton play an important role in the transfer of mercury (Hg) from the lower to upper trophic positions in the food chain. In this study, total mercury (THg) and methylmercury (MeHg) levels were measured in three size fractions of zooplankton collected from three reservoirs (Hongfeng, Baihua, and Aha Reservoir) and one wetland in karst areas to understand mercury accumulation in zooplankton from alkaline environments. The results showed that the alkaline waters had lower zooplankton MeHg levels (0.1 to 66.8 ng g^-1) than most of the acidic waters reported. However, the zooplankton THg levels (6.3 to 494.9 ng g^-1) were comparable. The macro-zooplankton (> 500 μm) had significantly higher THg and MeHg levels than meso-zooplankton (116 to 500 μm) in the three reservoirs at all seasons, which showed biomagnification of mercury in the food chain. The correlation between Hg in water and zooplankton and Hg in zooplankton of different sizes indicated that THg bioaccumulation in zooplankton was related to the THg levels in water; however, MeHg bioaccumulation in zooplankton was controlled by many other factors, such as their feeding and living habits. In the three reservoirs, the THg and MeHg concentrations in zooplankton decreased with increasing eutrophication. However, compared with the three reservoirs, Caohai Wetland, with large amounts of aquatic plants, had a much lower trophic level and higher MeHg content in water but much lower zooplankton MeHg levels and bioaccumulation factors (BAFs). The large amounts of plant residue might dilute mercury in the food chain, revealing that high primary production could result in lower Hg bioaccumulation, rather than only being influenced by nutrient levels.

Bio-concentration potential and associations of heavy metals in Amanita muscaria (L.) Lam. from northern regions of Poland

Fruiting bodies of Amanita muscaria and topsoil beneath from six background areas in northern regions of Poland were investigated for the concentration levels of Ag, Al, Ba, Ca, Cd, Co, Cu, Fe, Hg, K, Mg, Mn, Na, Rb, Sr, and Zn. In addition, the bioconcentration factors (BCF values) were studied for each of these metallic elements. Similar to studies from other basidiomycetes, A. muscaria showed species-specific affinities to some elements, resulting in their bioconcentration in mycelium and fruiting bodies. This mushroom growing in soils with different levels of the geogenic metallic elements (Ag, Al, Ba, Ca, Co, Cu, Fe, Hg, K, Mg, Mn, Na, Rb, Sr, and Zn) showed signs of homeostatic accumulation in fruiting bodies of several of these elements, while Cd appeared to be accumulated at a rate dependent of the concentration level in the soil substrate. This species is an efficient bio-concentrator of K, Mg, Cd, Cu, Hg, Rb, and Zn and hence also contributes to the natural cycling of these metallic elements in forest ecosystems.

Mercury evasion from a boreal peatland shortens the timeline for recovery from legacy pollution

Peatlands are a major source of methylmercury that contaminates downstream aquatic food webs. The large store of mercury (Hg) in peatlands could be a source of Hg for over a century even if deposition is dramatically reduced. However, the reliability of Hg mass balances can be questioned due to missing long-term land-atmosphere flux measurements. We used a novel micrometeorological system for continuous measurement of Hg peatland-atmosphere exchange to derive the first annual Hg budget for a peatland. The evasion of Hg (9.4 µg m⁻² yr⁻¹) over the course of a year was seven times greater than stream Hg export, and over two times greater than wet bulk deposition to the boreal peatland. Measurements of dissolved gaseous Hg in the peat pore water also indicate Hg evasion. The net efflux may result from recent declines in atmospheric Hg concentrations that have turned the peatland from a net sink into a source of atmospheric Hg. This net Hg loss suggests that open boreal peatlands and downstream ecosystems can recover more rapidly from past atmospheric Hg deposition than previously assumed. This has important implications for future levels of methylmercury in boreal freshwater fish and the estimation of historical Hg accumulation rates from peat profiles.

Accumulation and distribution of metallic elements and metalloids in edible Amanita fulva mushrooms

Baseline concentrations of Ag, Al, As, Ba, Ca, Cd, Co, Cu, Cr, Fe, K, Mg, Mn, Na, Ni, P, Pb, Rb, Sr, Tl, V, U and Zn were presented in Amanita fulva collected from unpolluted areas in Poland. There is no previous data published on the bio-element constituents of A. fulva. A very narrow range of values was determined by ICP-DRC-MS and ICP-AES for the trace elements Ag, Co, Cu, Cr, Ni, Rb, Sr, Tl and Zn in caps and of Ag, Co, Cu, Mn, Ni, Sr, U and Zn in stipes and also for the macro elements K, P, Na and Mg. The fruitbodies of A. fulva from the northern (Baltic Sea coastal forests) and southwestern (Lower Silesia forests) sites differed substantially in cadmium, lead and uranium, and those from the Lower Silesia region showed them in greater concentrations. This observation may imply that A. fulva under typical geochemical site conditions is able to regulate the accumulation of many of the elements mentioned in fruiting bodies.

Mercury in forest mushrooms and topsoil from the Yunnan highlands and the subalpine region of the Minya Konka summit in the Eastern Tibetan Plateau

This study aimed to investigate and discuss the occurrence and accumulation of mercury in the fruiting bodies of wild-growing fungi (Macromycetes) collected from montane forests in two regions of southwestern China with differences in soil geochemistry, climate and geographical conditions. Fungal mycelia in soils of the subalpine region of the Minya Konka (Gongga Mountain) in Sichuan and in the highlands of Yunnan efficiently accumulated mercury in fruiting bodies (mushrooms). The examined sites in Yunnan with highly mineralized red and yellow soils showed Hg contents ranging from 0.066 to 0.28 mg kg^-1 dry biomass (db) which is roughly similar to the results obtained for samples collected from sites with dark soils relatively rich in organic matter from a remote, the subalpine region of Minya Konka. Due to the remoteness of the subalpine section of Minya Konka, as well as its elevation and climate, airborne mercury from long-range transport could be deposited preferentially on the topsoil and the Hg levels determined in soil samples taken beneath the fruiting bodies were up to 0.48 mg kg^-1 dry matter. In Yunnan, with polymetallic soils (Circum-Pacific Mercuriferous Belt), Amanita mushrooms showed mercury in caps of fruiting bodies of up to 7.3 mg kg^-1 dry biomass. Geogenic Hg from the mercuriferous belt seems to be the overriding source of mercury accumulated in mushrooms foraged in the regions of Yunnan, while long-range atmospheric transport and subsequent deposition are the mercury sources for specimens foraged in the region of Minya Konka.

High mercury accumulation in two subtropical evergreen forests in South China and potential determinants

Forests play an important role in global mercury (Hg) cycling. To explain the high Hg accumulation in subtropical forest ecosystems, we studied temporal dynamics of Hg, carbon (C), nitrogen (N), and sulfur (S) in forest soil profiles, as well as litterfall flux and precipitation, in an old-growth moist evergreen broadleaf (EB) forest and a mossy coppice (MC) forest from South China over seven years. The mean soil Hg concentration was 257 ± 14 ng g^-1 in the O-horizon and 248 ± 15 ng g^-1 in the A-horizon for the EB forest, and 94 ± 27 ng g^-1 in the O-horizon and 70 ± 11 ng g^-1 in the A-horizon for the MC forest. Annual variations in Hg concentration were suggested to be associated with variations in precipitation and litterfall biomass. Significant vertical Hg transport was only observed in the MC forest, which was attributed to its lower organic matter content. Correlation and stoichiometry analyses further suggested that the dynamics in Hg concentration in the forest floor was also closely linked to the variation in S concentration. Additionally, the difference in the soil Hg pool between these two forests was attributed to different litterfall biomass fluxes.

Surface-air mercury fluxes across Western North America: A synthesis of spatial trends and controlling variables

Mercury (Hg) emission and deposition can occur to and from soils, and are an important component of the global atmospheric Hg budget. This paper focuses on synthesizing existing surface-air Hg flux data collected throughout the Western North American region and is part of a series of geographically focused Hg synthesis projects. A database of existing Hg flux data collected using the dynamic flux chamber (DFC) approach from almost a thousand locations was created for the Western North America region. Statistical analysis was performed on the data to identify the important variables controlling Hg fluxes and to allow spatiotemporal scaling. The results indicated that most of the variability in soil-air Hg fluxes could be explained by variations in soil-Hg concentrations, solar radiation, and soil moisture. This analysis also identified that variations in DFC methodological approaches were detectable among the field studies, with the chamber material and sampling flushing flow rate influencing the magnitude of calculated emissions. The spatiotemporal scaling of soil-air Hg fluxes identified that the largest emissions occurred from irrigated agricultural landscapes in California. Vegetation was shown to have a large impact on surface-air Hg fluxes due to both a reduction in solar radiation reaching the soil as well as from direct uptake of Hg in foliage. Despite high soil Hg emissions from some forested and other heavily vegetated regions, the net ecosystem flux (soil flux+vegetation uptake) was low. Conversely, sparsely vegetated regions showed larger net ecosystem emissions, which were similar in magnitude to atmospheric Hg deposition (except for the Mediterranean California region where soil emissions were higher). The net ecosystem flux results highlight the important role of landscape characteristics in effecting the balance between Hg sequestration and (re-)emission to the atmosphere.

Environmental impact of CO2, Rn, Hg degassing from the rupture zones produced by Wenchuan M s 8.0 earthquake in western Sichuan, China

The concentrations and flux of CO2, (222)Radon (Rn), and gaseous elemental mercury (Hg) in soil gas were investigated based on the field measurements in June 2010 at ten sites along the seismic rupture zones produced by the May 12, 2008, Wenchuan M s 8.0 earthquake in order to assess the environmental impact of degassing of CO2, Rn and Hg. Soil gas concentrations of 344 sampling points were obtained. Seventy measurements of CO2, Rn and Hg flux by the static accumulation chamber method were performed. The results of risk assessment of CO2, Rn and Hg concentration in soil gas showed that (1) the concentration of CO2 in the epicenter of Wenchuan M s 8.0 earthquake and north end of seismic ruptures had low risk of asphyxia; (2) the concentrations of Rn in the north segment of seismic ruptures had high levels of radon, Maximum was up to level 4, according to Chinese code (GB 50325-2001); (3) the average geoaccumulation index I geo of soil Hg denoted the lack of soil contamination, and maximum values classified the soil gas as moderately to strongly polluted in the epicenter. The investigation of soil gas CO2, Rn and Hg degassing rate indicated that (1) the CO2 in soil gas was characterized by a mean [Formula: see text] of -20.4 ‰ and by a mean CO2 flux of 88.1 g m(-2) day(-1), which were in the range of the typical values for biologic CO2 degassing. The maximum of soil CO2 flux reached values of 399 g m(-2) day(-1) in the epicenter; (2) the soil Rn had higher exhalation in the north segment of seismic ruptures, the maximum reached value of 1976 m Bq m(-2) s(-1); (3) the soil Hg flux was lower, ranging from -2.5 to 18.7 n g m(-2) h(-1) and increased from south to north. The mean flux over the all profiles was 4.2 n g m(-2) h(-1). The total output of CO2 and Hg degassing estimated along seismic ruptures for a survey area of 18.17 km(2) were approximately 0.57 Mt year(-1) and 688.19 g year(-1). It is recommended that land-use planners should incorporate soil gas and/or gas flux measurements in the environmental assessment of areas of possible risk. A survey of all houses along seismic ruptures is advised as structural measures to prevent the ingress of soil gases, including CO2 and Rn, were needed in some houses.

Accumulation and distribution of mercury in fruiting bodies by fungus Suillus luteus foraged in Poland, Belarus and Sweden

Presented in this paper is result of the study of the bioconcentration potential of mercury (Hg) by Suillus luteus mushroom collected from regions within Central, Eastern, and Northern regions of Europe. As determined by cold-vapor atomic absorption spectroscopy, the Hg content varied from 0.13 ± 0.05 to 0.33 ± 0.13 mg kg(-1) dry matter for caps and from 0.038 ± 0.014 to 0.095 ± 0.038 mg kg(-1) dry matter in stems. The Hg content of the soil substratum (0-10 cm layer) underneath the fruiting bodies showed generally low Hg concentrations that varied widely ranging from 0.0030 to 0.15 mg kg(-1) dry matter with mean values varying from 0.0078 ± 0.0035 to 0.053 ± 0.025 mg kg(-1) dry matter, which is below typical content in the Earth crust. The caps were observed to be on the richer in Hg than the stems at ratio between 1.8 ± 0.4 and 5.3 ± 2.6. The S. luteus mushroom showed moderate ability to accumulate Hg with bioconcentration factor (BCF) values ranging from 3.6 ± 1.3 to 42 ± 18. The consumption of fresh S. luteus mushroom in quantities up to 300 g week(-1) (assuming no Hg ingestion from other foods) from background areas in the Central, Eastern, and Northern part of Europe will not result in the intake of Hg exceeds the provisional weekly tolerance limit (PTWI) of 0.004 mg kg(-1) body mass.

New Constraints on Terrestrial Surface-Atmosphere Fluxes of Gaseous Elemental Mercury Using a Global Database

Despite 30 years of study, gaseous elemental mercury (Hg(0)) exchange magnitude and controls between terrestrial surfaces and the atmosphere still remain uncertain. We compiled data from 132 studies, including 1290 reported fluxes from more than 200,000 individual measurements, into a database to statistically examine flux magnitudes and controls. We found that fluxes were unevenly distributed, both spatially and temporally, with strong biases toward Hg-enriched sites, daytime and summertime measurements. Fluxes at Hg-enriched sites were positively correlated with substrate concentrations, but this was absent at background sites. Median fluxes over litter- and snow-covered soils were lower than over bare soils, and chamber measurements showed higher emission compared to micrometeorological measurements. Due to low spatial extent, estimated emissions from Hg-enriched areas (217 Mg·a(-1)) were lower than previous estimates. Globally, areas with enhanced atmospheric Hg(0) levels (particularly East Asia) showed an emerging importance of Hg(0) emissions accounting for half of the total global emissions estimated at 607 Mg·a(-1), although with a large uncertainty range (-513 to 1353 Mg·a(-1) [range of 37.5th and 62.5th percentiles]). The largest uncertainties in Hg(0) fluxes stem from forests (-513 to 1353 Mg·a(-1) [range of 37.5th and 62.5th percentiles]), largely driven by a shortage of whole-ecosystem fluxes and uncertain contributions of leaf-atmosphere exchanges, questioning to what degree ecosystems are net sinks or sources of atmospheric Hg(0).

Evaluation of the mercury contamination in mushrooms of genus Leccinum from two different regions of the world: Accumulation, distribution and probable dietary intake

This study focused on investigation of the accumulation and distribution of mercury (Hg) in mushrooms of the genus Leccinum that emerged on soils of totally different geochemical bedrock composition. Hg in 6 species from geographically diverse regions of the mercuriferous belt areas in Yunnan of SW China, and 8 species from the non-mercuriferous regions of Poland in Europe was measured. Also assessed was the probable dietary intake of Hg from consumption of Leccinum spp., which are traditional organic food items in SW China and Poland. The results showed that L. chromapes, L. extremiorientale, L. griseum and L. rugosicepes are good accumulators of Hg and the sequestered Hg in caps were up to 4.8, 3.5, 3.6 and 4.7 mg Hg kg(-1) dry matter respectively. Leccinum mushrooms from Poland also efficiently accumulated Hg with their average Hg content being an order of magnitude lower due to low concentrations of Hg in forest topsoil of Poland compared to the elevated contents in Yunnan. Consumption of Leccinum mushrooms with elevated Hg contents in Yunnan at rates of up to 300 g fresh product per week during the foraging season would not result in Hg intake that exceeds the provisional weekly tolerance limit of 0.004 mg kg(-1) body mass, assuming no Hg ingestion from other foods.

Evaluation of Mercury Contamination in Fungi Boletus Species from Latosols, Lateritic Red Earths, and Red and Yellow Earths in the Circum-Pacific Mercuriferous Belt of Southwestern China

For the first time, highly elevated levels of mercury (Hg) have been documented for several species of the edible Fungi genus Boletus growing in latosols, lateritic red earths, and red and yellow earths from the Yunnan province of China. Analysis of Hg concentrations in the genus suggests that geogenic Hg is the dominant source of Hg in the fungi, whereas anthropogenic sources accumulate largely in the organic layer of the forest soil horizon. Among the 21 species studied from 32 locations across Yunnan and 2 places in Sichuan Province, the Hg was found at elevated level in all samples from Yunnan but not in the samples from Sichuan, which is located outside the mercuriferous belt. Particularly abundant in Hg were the caps of fruiting bodies of Boletus aereus (up to 13 mg kg-1 dry matter), Boletus bicolor (up to 5.5 mg kg-1 dry matter), Boletus edulis (up to 22 mg kg-1 dry matter), Boletus luridus (up to 11 mg kg-1 dry matter), Boletus magnificus (up to 13 mg kg-1 dry matter), Boletus obscureumbrinus (up to 9.4 mg kg-1 dry matter), Boletus purpureus (up to 16 mg kg-1 dry matter), Boletus sinicus (up to 6.8 mg kg-1 dry matter), Boletus speciosus (up to 4.9mg kg-1 dry matter), Boletus tomentipes (up to 13 mg kg-1 dry matter), and Boletus umbriniporus (up to 4.9 mg kg-1 dry matter). Soil samples of the 0-10 cm topsoil layer from the widely distributed locations had mercury levels ranging between 0.034 to 3.4 mg kg-1 dry matter. In Yunnan, both the soil parent rock and fruiting bodies of Boletus spp. were enriched in Hg, whereas the same species from Sichuan, located outside the mercuriferous belt, had low Hg concentrations, suggesting that the Hg in the Yunnan samples is mainly from geogenic sources rather than anthropogenic sources. However, the contribution of anthropogenically-derived Hg sequestered within soils of Yunnan has not been quantified, so more future research is required. Our results suggest that high rates of consumption of Boletus spp. from Yunnan can deliver relatively high doses of Hg to consumers, but that rates can differ widely because of large variability in mercury concentrations between species and locations.

Eddy covariance flux measurements of gaseous elemental mercury using cavity ring-down spectroscopy

A newly developed pulsed cavity ring-down spectroscopy (CRDS) system for measuring atmospheric gaseous elemental mercury (GEM) concentrations at high temporal resolution (25 Hz) was used to successfully conduct the first eddy covariance (EC) flux measurements of GEM. GEM is the main gaseous atmospheric form, and quantification of bidirectional exchange between the Earth's surface and the atmosphere is important because gas exchange is important on a global scale. For example, surface GEM emissions from natural sources, legacy emissions, and re-emission of previously deposited anthropogenic pollution may exceed direct primary anthropogenic emissions. Using the EC technique for flux measurements requires subsecond measurements, which so far has not been feasible because of the slow time response of available instrumentation. The CRDS system measured GEM fluxes, which were compared to fluxes measured with the modified Bowen ratio (MBR) and a dynamic flux chamber (DFC). Measurements took place near Reno, NV, in September and October 2012 encompassing natural, low-mercury (Hg) background soils and Hg-enriched soils. During nine days of measurements with deployment of Hg-enriched soil in boxes within 60 m upwind of the EC tower, the covariance of GEM concentration and vertical wind speed was measured, showing that EC fluxes over an Hg-enriched area were detectable. During three separate days of flux measurements over background soils (without Hg-enriched soils), no covariance was detected, indicating fluxes below the detection limit. When fluxes were measurable, they strongly correlated with wind direction; the highest fluxes occurred when winds originated from the Hg-enriched area. Comparisons among the three methods showed good agreement in direction (e.g., emission or deposition) and magnitude, especially when measured fluxes originated within the Hg-enriched soil area. EC fluxes averaged 849 ng m(-2) h(-1), compared to DFC fluxes of 1105 ng m(-2) h(-1) and MBR fluxes of 1309 ng m(-2) h(-1). This study demonstrated that a CRDS system can be used to measure GEM fluxes over Hg-enriched areas, with a conservative detection limit estimate of 32 ng m(-2) h(-1).

Mercury fluxes from volcanic and geothermal sources: an update

We review the state of knowledge on global volcanogenic Hg emissions to the atmosphere and present new data from seven active volcanoes (Poás, Rincón de la Vieja, Turrialba, Aso, Mutnovsky, Gorely and Etna) and two geothermal fields (Las Pailas and Las Hornillas). The variability of Hg contents (c. 4–125 ng m−3) measured in gaseous emissions reflects the dynamic nature of volcanic plumes, where the abundances of volatiles are determined by the physical nature of degassing and variable air dilution. Based on our dataset and previous work, we propose that an average Hg/SO2 plume mass ratio of c. 7.8×10−6 (±1.5×10−6; 1 SE, n=13) is best representative of open-conduit quiescent degassing. Taking into account the uncertainty in global SO2 emissions, we infer a global volcanic Hg flux from persistent degassing of c. 76±30 t a−1. Our data are derived from active volcanoes during non-eruptive periods and we do not have any direct constraint on the Hg flux during periods of elevated SO2 flux associated with large-scale effusive or explosive eruptions. This suggests that the time-averaged Hg flux from these volcanoes is even larger if the eruptive contribution is considered. Conversely, closed-conduit degassing and geothermal emissions contribute modest amounts of Hg.

Evidence for sites of methylmercury formation in a flowing water system: impact of anthropogenic barriers and water management

The Truckee River, California-Nevada, USA is impacted by mercury (Hg) contamination associated with legacy gold mining. In this work, we investigated the potential for hot-spots of methylmercury (MeHg) formation in the river. Mercury concentrations in multiple media were also used to assess the impacts of anthropogenic barriers, restoration, and water management in this flowing water ecosystem. Water samples were collected on a seasonal time step over 3 years, and analyzed for total Hg (THg) and MeHg concentrations, along with a variety of other water quality parameters. In addition, we measured THg and MeHg in sediments, THg in macroinvertebrates, and THg and δ(15)N and δ(13)C concentrations in fish. Differences in stable isotopes and Hg concentrations in fish were applied to understand the mobility of fish in the river. Mercury concentrations of specific macroinvertebrate species were used to identify sites of MeHg production. In general, loads of Hg and nutrients in the river reach above the Reno-Sparks metropolitan area were similar to that reported for pristine systems, while within and below the city, water quality impacts were observed. Fish isotope data showed that in the city reach food resources were different than those upriver and downriver. Based on Hg and isotope data, mobility of the fish in the river is impacted by anthropogenic obstructions and water manipulation. Below the city, particle bound Hg, derived from the legacy mining, continues to be input to the Truckee River. This Hg is deposited in riparian habitats and areas of river restoration, where it is methylated and becomes available to biota. During spring, when flows were highest, MeHg produced and stored in the sediments is mobilized and transported downriver. Fish and macroinvertebrate concentrations increased downriver indicating passive uptake from water. The information presented here could be useful for those doing river restoration and water manipulation in mercury contaminated environments.

Vertical profile measurements of soil air suggest immobilization of gaseous elemental mercury in mineral soil

Evasion of gaseous elemental Hg (Hg(0)g) from soil surfaces is an important source of atmospheric Hg, but the volatility and solid-gas phase partitioning of Hg(0) within soils is poorly understood. We developed a novel system to continuously measure Hg(0)g concentrations in soil pores at multiple depths and locations, and present a total of 297 days of measurements spanning 14 months in two forests in the Sierra Nevada mountains, California, U.S. Temporal patterns showed consistent pore Hg(0)g concentrations below levels measured in the atmosphere (termed Hg(0)g immobilization), ranging from 66 to 94% below atmospheric concentrations throughout multiple seasons. The lowest pore Hg(0)g concentrations were observed in the deepest soil layers (40 cm), but significant immobilization was already present in the top 7 cm. In the absence of sinks or sources, pore Hg(0)g levels would be in equilibrium with atmospheric concentrations due to the porous nature of the soil matrix and gas diffusion. Therefore, we explain decreases in pore Hg(0)g in mineral soils below atmospheric concentrations--or below levels found in upper soils as observed in previous studies--with the presence of an Hg(0)g sink in mineral soils possibly related to Hg(0)g oxidation or other processes such as sorption or dissolution in soil water. Surface chamber measurements showing daytime Hg(0)g emissions and nighttime Hg(0)g deposition indicate that near-surface layers likely dominate net atmospheric Hg(0)g exchange resulting in typical diurnal cycles due to photochemcial reduction at the surface and possibly Hg(0)g evasion from litter layers. In contrast, mineral soils seem to be decoupled from this surface exchange, showing consistent Hg(0)g uptake and downward redistribution--although our calculations indicate these fluxes to be minor compared to other mass fluxes. A major implication is that once Hg is incorporated into mineral soils, it may be unlikely subjected to renewed Hg(0)g re-emission from undisturbed, background soils emphasizing the important role of soils in sequestering past and current Hg pollution loads.

Accumulation of total mercury and methylmercury in rice plants collected from different mining areas in China

A total of 155 rice plants were collected from ten mining areas in three provinces of China (Hunan, Guizhou and Guangdong), where most of mercury (Hg) mining takes place in China. During the harvest season, whole rice plants were sampled and divided into root, stalk & leaf, husk and seed (brown rice), together with soil from root zone. Although the degree of Hg contamination varied significantly among different mining areas, rice seed showed the highest ability for methylmercury (MeHg) accumulation. Both concentrations of total mercury (THg) and MeHg in rice plants were significantly correlated with Hg levels in soil, indicating soil is still an important source for both inorganic mercury (IHg) and MeHg in rice plants. The obvious discrepancy between the distribution patterns of THg and MeHg reflected different pathways of IHg and MeHg accumulation. Water soluble Hg may play more important role in MeHg accumulation in rice plants.

Short-term impact of reservoir impoundment on the patterns of mercury distribution in a subtropical aquatic ecosystem, Wujiang River, southwest China

Surveys on pre- and post-impoundment total mercury concentrations in water, seston and fish were conducted during 2007-2008 in the Wujiang River, southwest China. Compared with the pre-impoundment, total mercury in the reservoir and downstream water rapidly increased by 164-303 % during the first half year of flooding, and then decreased by 61.7-62.2 % after 9 months of flooding. However, total mercury in seston from the reservoir and downstream generally declined. There was no significant difference in the total mercury between reservoir fish with different habitat preference and feeding habit. We find that fish tissue mercury concentration significantly increased threefold after flooding, and the increasing rate is lower than those in subarctic and temperate reservoirs. The pre- and post-impoundment fish samples exceeding the Chinese hygienic standard for tolerances of mercury in foods increased from 1.3 to 17.4 %. Long-term monitoring of fish mercury level in Wujiang River should be undertaken to ensure local food security.

The cycling and sea-air exchange of mercury in the waters of the Eastern Mediterranean during the 2010 MED-OCEANOR cruise campaign

An oceanographic cruise campaign on-board the Italian research vessel Urania was carried out from the 26th of August to the 13th of September 2010 in the Eastern Mediterranean. The campaign sought to investigate the mercury cycle at coastal and offshore locations in different weather conditions. The experimental activity focused on measuring mercury speciation in both seawater and in air, and using meteorological parameters to estimate elemental mercury exchange at the sea-atmosphere interface. Dissolved gaseous mercury (DGM), unfiltered total mercury (UTHg) and filtered total mercury (FTHg) surface concentrations ranged from 16 to 114, 300 to 18,760, and 230 to 10,990pgL(-1), respectively. The highest DGM, UTHg and FTHg values were observed close to Augusta (Sicily), a highly industrialized area of the Mediterranean region, while the lowest values were recorded at offshore stations. DGM vertical profiles partially followed the distribution of sunlight, as a result of the photoinduced transformations of elemental mercury in the surface layers of the water column. However, at some stations, we observed higher DGM concentrations in samples taken from the bottom of the water column, suggesting biological mercury production processes or the presence of tectonic activity. Moreover, two days of continuous measurement at one location demonstrated that surface DGM concentration is affected by solar radiation and atmospheric turbulence intensity. Atmospheric measurements of gaseous elemental mercury (GEM) showed an average concentration (1.6ngm(-3)) close to the background level for the northern hemisphere. For the first time this study used a numerical scheme based on a two-thin film model with a specific parameterization for mercury to estimate elemental mercury flux. The calculated average mercury flux during the entire cruise was 2.2±1.5ngm(-2)h(-1). The analysis of flux data highlights the importance of the wind speed on the mercury evasion from sea surfaces.

Novel dynamic flux chamber for measuring air-surface exchange of Hg(o) from soils

Quantifying the air-surface exchange of Hg(o) from soils is critical to understanding the cycling of mercury in different environmental compartments. Dynamic flux chambers (DFCs) have been widely employed for Hg(o) flux measurement over soils. However, DFCs of different sizes, shapes, and sampling flow rates yield distinct measured fluxes for a soil substrate under identical environmental conditions. In this study, we performed an integrated modeling, laboratory and field study to design a DFC capable of producing a steady and uniform air flow over a flat surface. The new DFC was fabricated using polycarbonate sheets. The internal velocity field was experimentally verified against model predictions using both theoretical and computational fluid dynamics techniques, suggesting fully developed flow with velocity profiles in excellent agreement with model results. Laboratory flux measurements demonstrated that the new design improves data reproducibility as compared to a conventional DFC, and reproduces the model-predicted flux trend with increasing sampling flow. A mathematical relationship between the sampling flow rate and surface friction velocity, a variable commonly parametrized in atmospheric models, was developed for field application. For the first time, the internal shear property of a DFC can be precisely controlled using the sampling flow rate, and the flux under atmospheric condition can be inferred from the measured flux and surface shear property. The demonstrated methodology potentially bridges the gap in measured fluxes obtained by the DFC method and the micrometeorological methods.

A synthesis of rates and controls on elemental mercury evasion in the Great Lakes Basin

Rates of surface-air elemental mercury (Hg(0)) fluxes in the literature were synthesized for the Great Lakes Basin (GLB). For the majority of surfaces, fluxes were net positive (evasion). Digital land-cover data were combined with representative evasion rates and used to estimate annual Hg(0) evasion for the GLB (7.7 Mg/yr). This value is less than our estimate of total Hg deposition to the area (15.9 Mg/yr), suggesting the GLB is a net sink for atmospheric Hg. The greatest contributors to annual evasion for the basin are agricultural (∼55%) and forest (∼25%) land cover types, and the open water of the Great Lakes (∼15%). Areal evasion rates were similar across most land cover types (range: 7.0-21.0 μg/m(2)-yr), with higher rates associated with urban (12.6 μg/m(2)-yr) and agricultural (21.0 μg/m(2)-yr) lands. Uncertainty in these estimates could be partially remedied through a unified methodological approach to estimating Hg(0) fluxes.

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

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

Bioaccumulation of methylmercury versus inorganic mercury in rice (Oryza sativa L.) grain

Mercury (Hg) bioaccumulation in aquatic food webs has been much studied, motivated from high Hg levels found in many fish species important for human consumption. Hg bioaccumulation in terrestrial food chains have received little attention and assumed to be of minor importance. However, recent studies showed that rice can be an important pathway of methylmercury (MeHg) exposure to inhabitants in Hg mining areas in China. In this study, 59 sampling sites (including 32 sites from "heavily polluted area", 19 from "less-impacted area" and 8 from "control sites") were selected in a Hg mining area in China and both inorganic Hg (IHg) and MeHg were determined in rice grain (brown rice) and soil samples to evaluate Hg bioaccumulation in rice grain. Bio-Accumulation Factors (BAFs) for IHg ranged from 0.00014 to 0.51 and from 0.71 to 50 for MeHg. BAFs for MeHg were on average more than 800 times higher than those for IHg (maximum: 40,000 times). This study, for the first time, showed that rice grain is an intensive bioaccumulator of MeHg, but not of IHg, which may be trapped by the roots.

Gaseous mercury emissions from unsterilized and sterilized soils: the effect of temperature and UV radiation

Mercury (Hg) emissions from the soils taken from two different sites (deciduous and coniferous forests) in the Adirondacks were measured in outdoor and laboratory experiments. Some of the soil samples were irradiated to eliminate biological activity. The result from the outdoor measurements with different soils suggests the Hg emission from the soils is partly limited by fallen leaves covering the soils which helps maintain relatively high soil moisture and limits the amount of heat and solar radiation reaching the soil surface. In laboratory experiments exposure to UV-A (365 nm) had no significant effect on the Hg emissions while the Hg emissions increased dramatically during exposure to UV-B (302 nm) light suggesting UV-B directly reduced soil-associated Hg. Overall these results indicate that for these soils biotic processes have a relatively constant and smaller influence on the Hg emission from the soil than the more variable abiotic processes.

An elemental mercury diffusion coefficient for natural waters determined by molecular dynamics simulation

Mercury is a priority pollutant as its mobility between the hydrosphere and the atmosphere threatens the biosphere globally. The air-water gas transfer of elemental mercury (Hg0) is controlled by its diffusion through the water-side boundary layer and thus by its diffusion coefficient, D(Hg), the value of which, however, has not been established. Here, the diffusion of Hg0 in water was modeled by molecular dynamics (MD) simulation and the diffusion coefficient subsequently determined. Therefore the movement of either Hg(0) or xenon and 1000 model water molecules (TIP4P-Ew) were traced for time spans of 50 ns. The modeled D(Xe) of the monatomic noble gas agreed well with measured data; thus, MD simulation was assumed to be a reliable approach to determine D(Hg) for monatomic Hg(0) as well. Accordingly, Hg(0) diffusion was then simulated for freshwater and seawater, and the data were well-described by the equation of Eyring. The activation energies for the diffusion of Hg0 in freshwater was 17.0 kJ mol(-1) and in seawater 17.8 kJ mol(-1). The newly determined D(Hg) is clearly lower than the one previously used for an oceanic mercury budget. Thus, its incorporation into the model should lead to lower estimates of global ocean mercury emissions.

Sediment processes and mercury transport in a frozen freshwater fluvial lake (Lake St. Louis, QC, Canada)

An open-bottom and a closed-bottom mesocosm were developed to investigate the release of mercury from sediments to the water column in a frozen freshwater lake. The mesoscosms were deployed in a hole in the ice and particulate mercury (Hg(P)) and total dissolved mercury (TDHg) were measured in sediments and in water column vertical profiles. In addition, dissolved gaseous mercury (DGM) in water and mercury water/airflux were quantified. Concentrations of TDHg, DGM, and mercury flux were all higher in the open-bottom mesocosm than in the closed-bottom mesocosm. In this paper we focus on the molecular diffusion of mercury from the sediment in comparison with the TDHg accumulation in the water column. We conclude that the molecular diffusion and sediment resuspension play a minor role in mercury release from sediments suggesting that solute release during ebullition is an important transport process for mercury in the lake.

Gaseous mercury fluxes from the forest floor of the Adirondacks

The flux of gaseous elemental mercury (Hg(0)) from the forest floor of the Adirondack Mountains in New York (USA) was measured numerous times throughout 2005 and 2006 using a polycarbonate dynamic flux chamber (DFC). The Hg flux ranged between -2.5 and 27.2 ng m(-2) h(-1) and was positively correlated with temperature and solar radiation. The measured Hg emission flux was highest in spring, and summer, and lowest in winter. During leaf-off periods, the Hg emission flux was highly dependent on solar radiation and less dependent on temperature. During leaf-on periods, the Hg emission flux was fairly constant because the forest canopy was shading the forest floor. Two empirical models were developed to estimate yearly Hg(0) emissions, one for the leaf-off period and one for the leaf-on period. Using the U.S. EPA's CASTNET meteorological data, the cumulative estimated emission flux was approx. 7.0 microg Hg(0) m(-2) year(-1).

Feeding habits and habitats preferences affecting mercury bioaccumulation in 37 subtropical fish species from Wujiang River, China

The present study is the first to report the total mercury concentration of 37 fish species collected from Wujiang River, which is the largest branch on the southern bank of Yangtze River, China and proposed for hydropower development. Total mercury concentrations varied among the 37 subtropical species examined. We found higher mercury concentrations in carnivorous species demonstrating greater mercury bioaccumulation in species with more predatory feeding habits. There is no significant difference between fish grouped by habitat preference and feeding habit. However, carnivorous species preferring benthic positions had higher total mercury concentrations than others suggesting that mercury accumulation is related to the interaction of feeding habit and habitat preference. In our study, fish that are bottom living and feed on other fish or aquatic animals are more likely at high risk of mercury exposure. Additional mercury contamination and future impoundment may raise mercury concentration in fish in the Wujiang causing concern for human health and ecological impacts.

Mercury pollution in Guizhou, southwestern China - an overview

Mercury (Hg) is a global pollutant and poses a worldwide concern due to its high toxicity. Guizhou province is recognized as a heavily Hg-polluted area in China due to both the special geochemical background and human activities. Here an integrated overview of current knowledge on the behavior of Hg in environments, as well as human health risk with respect to Hg contaminations in Guizhou was presented. Two key anthropogenic Hg emission sources in Guizhou were coal combustion and metals smelting, which dominantly contributed to the high levels of Hg in local ecosystems and high fluxes of Hg deposition. The annual Hg emission from anthropogenic sources ranged between 22.6 and 55.5 t, which was about 6.3-10.3% of current total Hg emissions in China. Meanwhile, Hg Hg-enriched soil in the province serves an important natural Hg emission source to the ambient air. The local environment of Hg mining and zinc smelting areas are seriously contaminated with Hg. It is demonstrated that rice growing in Hg Hg-contaminated soil can accumulate methylmercury (MeHg) to a level to pose health threat to local inhabitants whose staple food is rice. Local inhabitants in Hg mining areas are exposed to Hg through inhalation of Hg vapor and consumption of rice with high level of MeHg. Rice intake is indeed the main MeHg exposure pathway to local inhabitants in Hg mining areas in Guizhou, which is contrary to the general point of view that fish and fish products are the main pathway of MeHg exposure to humans.

Dissolved gaseous mercury concentrations and mercury volatilization in a frozen freshwater fluvial lake

In situ mesocosm experiments were performed to examine dissolved gaseous mercury (DGM), mercury volatilization, and sediment interactions in a frozen freshwater fluvial lake (Lake St. Louis, Beauharnois, QC). Two large in situ mesocosm cylinders, one open-bottomed and one close-bottomed (no sediment diffusion), were used to isolate the water column and minimize advection. Mercury volatilization over the closed-bottom mesocosm did not display a diurnal pattern and was low (mean = -0.02 ng m(-2) h(-1), SD = 0.28, n=71). Mercury volatilization over the open-bottom mesocosm was also low (mean = 0.24 ng m(-2) h(-1), SD = 0.08, n=96) however a diurnal pattern was observed. Low and constant concentrations of DGM were observed in surface water in both the open-bottomed and close-bottomed mesocosms (combined mean = 27.6 pg L(-1), SD = 7.2, n=26). Mercury volatilization was significantly correlated with solar radiation in both the close-bottomed (Pearson correlation = 0.33, significance = 0.005) and open-bottomed (Pearson correlation = 0.52, significance = 0.001) mesocosms. However, DGM and mercury volatilization were not significantly correlated (at the 95% level) in either of the mesocosms (significance = 0.09 in the closed mesocosm and significance = 0.9 in the open mesocosm). DGM concentrations decreased with depth (from 62 to 30 pg L(-1)) in the close-bottomed mesocosm but increased with depth (from 30 to 70 pg L(-1)) in the open-bottomed mesocosm suggesting a sediment source. DGM concentrations were found to be high in samples of ice melt (mean 73.6 pg L(-1), SD = 18.9, n=6) and snowmelt (mean 368.2 pg L(-1), SD = 115.8, n=4). These results suggest that sediment diffusion of mercury and melting snow and ice are important to DGM dynamics in frozen Lake St. Louis. These processes may also explain the lack of significant correlations observed in the DGM and mercury volatilization data.

Distribution of mercury in surficial sediments from Todos Santos Bay, Baja California, México

During 2004 the spatial distribution of total Hg in sediments from Todos Santos Bay, Baja California, México was studied to evaluate the degree of environmental impact in this bay. The results showed low concentrations and no Hg enrichment at any site. These findings suggest natural levels of Hg in the water of Todos Santos Bay. The regional distribution of Hg/Fe shows lower values in the East and higher in the West of the bay. No significant correlations (p<0.05) were found between Hg and organic matter or particle size, suggesting that the distribution of Hg is not controlled by these variables.

Estimation of vegetative mercury emissions in China

Vegetative mercury emissions were estimated within the framework of Biogenic Emission Inventory System (BEIS3 V3.11). In this estimation, the 19 categories of U.S. Geological Survey landcover data were incorporated to generate the vegetation-specific mercury emissions in a 81-km Lambert Conformal model grid covering the total Chinese continent. The surface temperature and cloud-corrected solar radiation from a Mesoscale Meteorological model (MM5) were retrieved and used for calculating the diurnal variation. The implemented emission factors were either evaluated from the measured mercury flux data for forest, agriculture and water, or assumed for other land fields without available flux data. Annual simulations using the MM5 data were performed to investigate the seasonal emission variation. From the sensitivity analysis using two sets of emission factors, the vegetative mercury emissions in China domain were estimated to range from a lower limit of 79 x 10(3) kg/year to an upper limit of 177 x 10(3) kg/year. The modeled vegetative emissions were mainly generated from the eastern and southern China. Using the estimated data, it is shown that mercury emissions from vegetation are comparable to that from anthropogenic sources during summer. However, the vegetative emissions decrease greatly during winter, leaving anthropogenic sources as the major sources of emission.

Atmospheric monitoring at abandoned mercury mine sites in Asturias (NW Spain)

Mercury concentrations are usually significant in historic Hg mining districts all over the world, so the atmospheric environment is potentially affected. In Asturias, northern Spain, past mining operations have left a legacy of ruins and Hg-rich wastes, soils and sediments in abandoned sites. Total Hg concentrations in the ambient air of these abandoned mine sites have been investigated to evaluate the impact of the Hg emissions. This paper presents the synthesis of current knowledge about atmospheric Hg contents in the area of the abandoned Hg mining and smelting works at 'La Peña-El Terronal' and La Soterraña, located in Mieres and Pola de Lena districts, respectively, both within the Caudal River basin. It was found that average atmospheric Hg concentrations are higher than the background level in the area (0.1 microg Nm(-3)), reaching up to 203.7 microg Nm(-3) at 0.2 m above the ground level, close to the old smelting chimney at El Terronal mine site. Data suggest that past Hg mining activities have big influences on the increased Hg concentrations around abandoned sites and that atmospheric transfer is a major pathway for Hg cycling in these environments.