Air Hg Concentrations Research Articles

Insights into seasonal variations in mercury isotope composition of lichens

Lichens are commonly used to assess mercury (Hg) concentrations in air because of their cost-effectiveness. However, recent research has revealed temporal variations in the isotopic composition of Hg. Previous work on this topic leaves open questions about the repeatability of data over multiple seasons, different types of sampling (transplantation or in-situ collection), and diverse locations. This study aims to address these issues by conducting a high-frequency sampling campaign of in-situ and transplanted lichens and atmospheric particulate matter (APM). Sampling sites included a range of areas, from pristine to Hg-contaminated sites. Isotopic analysis showed that the isotopic composition of Hg in lichens undergoes mass-dependent fractionation and changes with time. The heaviest isotopic composition was observed in summer and the lightest in winter. These trends were consistent across polluted and unpolluted environments, as well as in both in-situ and transplanted lichens and in APM. The results further indicated towards a correlation between changes in Hg concentrations and isotopic composition in lichens and environmental factors. All of these variables seem to be changing at the same frequency and may have not just correlation but also causation relationship. Environmental factors seem to be influencing the Hg concentrations and isotopic composition. The summer high temperatures might be influencing the heavier isotopic fingerprint observed in lichens during the same season. Similarities with APM-bound Hg suggest a common underlying mechanism. This study highlights the importance of considering temporal and seasonal trends, as well as the method of lichen sampling, when interpreting results. Researchers using lichens as proxies for atmospheric Hg concentrations or isotope ratios should consider these findings when designing their studies.

Atmospheric mercury speciation and concentration at the urban and industrial sites in Taiwan over a three-year period

Mercury (Hg) is a toxic metal known to be detrimental to human health and wildlife survival due to its serious toxicity to the central nervous system. In this study, measurements of atmospheric mercury in Taiwan over three years suggested significantly higher total Hg concentrations (p < 0.001) during the dry season compared with the wet season for both urban and industrial sites, indicating that precipitation played a role through scavenging Hg. Total gaseous mercury (TGM) was the main component in air accounting for >90% of the total Hg, which included particulate mercury (Hgp). Furthermore, extreme Hg concentrations were observed at sites near cement works (TGM: 18 ng m−3; Hgp: 913 pg m−3) and iron-steel plants (TGM: 24.3 ng m−3; Hgp: 871 pg m−3), indicating a strong role for these two stationary emission sources to Hg concentrations in ambient air. This study contributes to improved understanding of atmospheric mercury speciation and concentrations near iron-steel plants and cement works.

Investigation of the biochemical controls on mercury uptake and mobility in trees

Atmospheric elemental mercury (Hg(0)) enters plant stomata, becomes oxidized, and is then transferred to annual growth rings providing an archive of air Hg(0) concentrations. To better understand the processes of Hg accumulation and translocation, the foliage of quaking aspen and Austrian pine were exposed to Hg(0), and methylmercury (MeHg) or Me198Hg via roots, in controlled exposures during the summer. Isotopic measurements demonstrated, in a laboratory setting, that the natural mass-dependent fractionation observed was the same as that measured in field studies, with the lighter isotopes being preferentially taken up by the leaves. Hg was measured in plant tissues across seasons. Aspen trees moved Hg into new growth immediately after exposure, resorbed Hg in the fall, and then distributed Hg to new growth tissues in the spring. Austrian pine did not reallocate Hg. Mercury measured in aspen leaf fractions of trees exposed to Hg(0) demonstrated that 85 % of Hg was in the cell wall. It was also found that redox-active molecules, such as H2O2, could potentiate the release of cell wall-bound Hg from aspen leaves, providing a potential mechanism for remobilization. Regardless of the mechanism, the ability of aspen to reallocate Hg to new tissues indicates that Hg distribution in tree rings from aspen do not provide a reliable record of yearly changes in atmospheric Hg(0).

Increased allergic and asthmatic risks in children residing in industrial areas by surveying the pre-inflammatory (IgE, IL-4 and IL-13) biomarkers.

Toxic metal(loid)s can lead to high damages on human. This work was conducted to investigate the levels of metal(loid)s in PM2.5 and a total of 123 male children's (aged 6-9years) blood chosen from different areas in Ahvaz and their association with the pre-inflammatory (Immunoglobulin E and cytokines: IgE, IL-4 and IL-13) responses in serum cells. Six metal(loid)s (arsenic, cadmium, chromium, mercury, nickel and lead) in three regions including industrial (Padad), vehicle traffic (Golestan) and reference (Kianpars) areas were studied. Results showed the concentrations of As, Cr, Cd, Ni and Hg in the ambient air of industrial area (Padad) (P < 0.001), and Pb in vehicle traffic area (Golestan) were higher (p < 0.001). Moreover, the mean levels of IgE (mean = 146.44pg/200landa, P < 0.003), IL-4 (mean = 548.23pg/200landa, P < 0.001) and IL-13 (mean = 53.21pg/200landa, P < 0.001) in Padad were higher than Golestan and Kianpars. Our results suggest that living in industrial areas leads to accelerated synthesis of IgE, IL-4 and IL-13 in blood. The spatial distribution of children's serum IgE, IL-4 and IL-13 concentrations showed an abnormal increase of 240 to 400pg/200landa for IgE, 950 to 1400pg/200landa for IL-4 and 90 to 128pg/200landa for IL-13. Our results indicate children in the industrial area are prone to asthma, allergy, miRNA mutation, and other chronic diseases.

Mercury pollution in Peru: geographic distribution, health hazards, and sustainable removal technologies.

Peru is one of the great gold producers worldwide. However, a significant portion of the gold produced in Peru derives from artisanal small-scale gold mining (ASGM) in the Andes and Amazon. In ASGM, gold amalgamation with mercury (Hg) is a critical procedure to refine gold through the formation of Au-Hg alloys. Due to the rudimentary and improvised techniques conducted by small-scale and informal miners, Hg contamination has become of great concern and is strictly associated with ASGM. Multiple studies have evidenced notably high concentrations of Hg in consumable fish species, rivers, sediments, and air in locations where ASGM is one of the main sources of income to local communities and is carried out aggressively. In the present review, we have conducted a systematic search for national and international literature reporting the concentration and distribution of Hg pollution across environmental compartments, biota, and human samples in Peru. The results and data retrieved from the articles were quantitatively and qualitatively analyzed, and the distribution of Hg across environmental compartments was visualized through a geographic information system. Additionally, we reviewed the use of adsorption techniques as alternatives to treat Hg0 vapor from the gold shop and smelter flues, one of the main sources of hazardous levels of Hg exposure.

Reconstructing atmospheric Hg levels near the oldest chemical factory in central Europe using a tree ring archive

The Chemical Factory in Marktredwitz (CFM) is known as the oldest chemical factory in Germany (1778–1985), and from the beginning of the 20th century focused primarily on the production of mercury (Hg) compounds. Due to extensive pollution, together with employee health issues, the CFM was shut in 1985 by a government order and remediation works proceeded from 1986 to 1993. In this study, tree ring archives of European Larch (Larix decidua Mill.) were used to reconstruct changes of air Hg levels near the CFM. Mercury concentrations in larch boles decreased from 80.6 μg kg−1 at a distance of 0.34 km–3.4 μg kg−1 at a distance of 16 km. The temporal trend of atmospheric Hg emissions from the CFM reconstructed from the tree ring archives showed two main peaks. The first was in the 1920s, with a maximum tree ring Hg concentration 249.1 ± 43.9 μg kg−1 coinciding with when the factory had a worldwide monopoly on the production of Hg-based seed dressing fungicide. The second peak in the 1970s, with a maximum tree ring Hg concentration of 116.4 ± 6.3 μg kg−1, was associated with a peak in the general usage and production of Hg chemicals and goods. We used the tree ring record to reconstruct past atmospheric Hg levels using a simple model of Hg distribution between the larch tree rings and atmosphere. The precision of the tree ring model was checked against the results of air Hg measurements during the CFM remediation 30 years ago. According to the tree ring archives, the highest air Hg concentrations in the 1920s in Marktredwitz were over 70 ng m−3. Current air Hg levels of 1.18 ng m−3, assessed in the city of Marktredwitz, indicate the lowest air Hg in the past 150 years, underscoring the effective remediation of the CFM premises 30 years ago.

Chemistry of surface water, precipitation, throughfall, leaves, sediment, soil, and air near a gold mining region in Peru.

Artisanal and small-scale gold mining (ASGM) is the primary global source of anthropogenic mercury (Hg) emissions and a large source of landscape change. ASGM occurs throughout the world, including in the Peruvian Amazon. This data set contains measurements of surface water, precipitation, throughfall, leaves, sediment, soil, and air samples from across the Madre de Dios region of Peru, in locations near and remote from ASGM. These data were collected to determine the fate and transport of Hg across the landscape. Samples were collected in 2018 and 2019. Data predominantly included total Hg and methyl Hg concentrations in surface water, precipitation, throughfall, leaves, sediment, soil, and air. Additional water and soil parameters were also measured to better characterize their chemistry. There are no copyright restrictions; please cite this data paper when the data are used in publication.

Mercury pollution in China: implications on the implementation of the Minamata Convention.

Mercury (Hg) is a toxic metal released into the environment through human activities and natural processes. Human activities have profoundly increased the amount of Hg in the atmosphere and altered its global cycling since the Industrial Revolution. Gaseous elemental Hg is the predominant form of Hg in the atmosphere, which can undergo long-range transport and atmospheric deposition into the aquatic systems. Hg deposition elevates the methylmercury (MeHg) level in fish through bioaccumulation and biomagnification, which poses a serious human health risk. Acute poisoning of MeHg can result in Minamata disease, while low-level long-term exposure in pregnant women can reduce the intelligence quotient of infants. After five sessions of intergovernmental negotiation, the Minamata Convention on mercury entered into force in August 2017 to protect human health and the environment from Hg pollution. Currently China contributes the largest quantity of Hg production, consumption, and emission globally. However, the status of Hg pollution in the environment in China and its associated health risk remains relatively unknown, which hinders the development of implementation plans of the Minamata Convention. In this paper, we provide a comprehensive review on the atmospheric release of Hg, distribution of air Hg concentration, human exposure to MeHg and health impacts caused by Hg pollution in China. Ongoing improvement of air pollution control measures is expected to further decrease anthropogenic Hg emissions in China. Air Hg concentrations in China are higher than the background values in the Northern Hemisphere, with spatial distribution largely influenced by anthropogenic emissions. Long-term observations of GEM in China show a decline in recent years. The net Hg transport outflow from China in 2013 is estimated to be 511 t year-1, and ∼60% of such outflow is caused by natural surface Hg emissions. Hg concentrations in fish and rice in China are relatively low and therefore the associated risks of human Hg exposure are low. Future research needs and recommendations for the implementation of the Minamata Convention are also discussed in this paper.

Ambient air particulates and Hg(p) concentrations and dry depositions estimations, distributions for various particles sizes ranges

Ambient air TSP concentrations, dry deposition fluxes and particulate-bound mercury (Hg(p)) concentrations were measured and analyzed at a complex (traffic, residential and commercial) site. Zhang and He’s model[ 1 ] was used to predict the dry deposition fluxes of ambient air particulates and Hg(p) at this complex site. The results revealed that October had the highest mean particulate concentration and lowest Hp(p) concentration and dry deposition flux. The mean calculated dry deposition fluxes of PM2.5 and PM2.5-10 accounted for 1%–2% and 0.06%–5% of the average total calculated dry deposition particle flux, respectively. The average calculated particle dry depositions flux of PM10+, accounted for 93%–99% of the average total calculated dry depositions particle flux. Finally, the model of Zhang and He underestimated the ambient air dry depositions fluxes of both particulates and Hg(p) for all particles sizes (PM2.5, PM2.5-10, PM10 +) at the mixed site in this study. Better results concerning the dry deposition fluxes of pollutants were obtained as the particles size increased.

Air Concentrations of Gaseous Elemental Mercury and Vegetation–Air Fluxes within Saltmarshes of the Tagus Estuary, Portugal

In situ air concentrations of gaseous elemental mercury (Hg(0)) and vegetation–atmosphere fluxes were quantified in both high (Cala Norte, CN) and low-to-moderate (Alcochete, ALC) Hg-contaminated saltmarsh areas of the Tagus estuary colonized by plant species Halimione portulacoides (Hp) and Sarcocornia fruticosa (Sf). Atmospheric Hg(0) ranged between 1.08–18.15 ng m−3 in CN and 1.18–3.53 ng m−3 in ALC. In CN, most of the high Hg(0) levels occurred during nighttime, while the opposite was observed at ALC, suggesting that photoreduction was not driving the air Hg(0) concentrations at the contaminated site. Vegetation–air Hg(0) fluxes were low in ALC and ranged from −0.76 to 1.52 ng m−2 (leaf area) h−1 for Hp and from −0.40 to 1.28 ng m−2 (leaf area) h−1 for Sf. In CN, higher Hg fluxes were observed for both plants, ranging from −9.90 to 15.45 ng m−2 (leaf area) h−1 for Hp and from −8.93 to 12.58 ng m−2 (leaf area) h−1 for Sf. Mercury flux results at CN were considered less reliable due to large and fast variations in the ambient air concentrations of Hg(0), which may have been influenced by emissions from the nearby chlor-alkali plant, or historical contamination. Improved experimental setup, the influence of high local Hg concentrations and the seasonal activity of the plants must be considered when assessing vegetation–air Hg(0) fluxes in Hg-contaminated areas.

Black pine (Pinus nigra) barks: A critical evaluation of some sampling and analysis parameters for mercury biomonitoring purposes

Abstract Tree barks are increasingly used as biomonitors of airborne pollutants. However, many authors stress the poor comparability of the results achieved in different studies. This drawback is mainly caused by a poor understanding of the critical sampling parameters to be considered. To minimize the biases that could be introduced during sampling, in this study the barks of Pinus nigra J.F. Arnold from thirteen sites were investigated in the abandoned Mt. Amiata mercury (Hg) mining district (Southern Tuscany, Italy) and surroundings. The influence of some sampling and analyzing parameters on Hg content was critically assessed. At each site, a total of eight bark samples were taken from a single tree at two heights (70 cm and 150 cm from soil) and at four different sides of the trunk, corresponding to the four cardinal directions; a composite soil sample was also collected. Mercury contents in barks range from 0.1 to 28.8 mg/kg, and are correlated with soil Hg contents (1–480 mg/kg), indicating that barks record both gaseous Hg concentrations in air, and wind-transported Hg-bearing particulate. For each tree, samples at 70 cm and 150 cm show Hg contents of the same order of magnitude, even if values for 150 cm are slightly less dispersed, possibly because barks at 70 cm are more influenced by random soil particles. There is no statistically significant dependence of Hg content on direction and tree age. Simulated rain events cause a negligible loss of Hg from barks. Results suggest that a convenient sampling practice for Pinus nigra is to collect a bark slice (typically 1–2 mm) within the outermost 1.5 cm layer.

Mercury emission from underground coal fires in the mining goaf of the Wuda Coalfield, China

The Wuda Coalfield, Inner Mongolia suffers from serious coal fires for more than half a century. Fire-extinguishing projects have been carried out to suppress the coal fires since the last decade, but sporadic surface fires still occur and underground fires are more prevailing. Here, we used a real-time RA-915M Mercury Analyzer with modified inlet to monitor gaseous Hg concentrations in fumes emitted from boreholes that were designed to detect and control the underground coal fires. Meanwhile, offline methods were used to collect the fumes and analyze the contents of the gases including CO, CO2, CH4, C2H6, C2H4 and C2H2. The results showed that gaseous Hg concentrations in fumes from boreholes ranged from 6.42 ± 0.73 to 123.53 ± 34.66 ng m−3, with an average value of 49 ± 44 ng m−3. We suggest that the amounts of coal left for burning or smoldering mainly accounted for the large variation in fume Hg concentrations of underground coal fires. The gaseous Hg concentrations in near-surface air surrounding boreholes varied from 2.38 ± 0.28 to 13.10 ± 0.97 ng m−3, with a mean value of 6.68 ± 3.09 ng m−3. They were higher than the ambient air Hg concentrations measured at a background site near the Yellow River (<2 ng m−3), suggesting underground coal fires were one significant Hg pollution source. Importantly, we found that gaseous Hg concentrations in the boreholes had significantly positive correlations with temperatures and CO (a traditional coal-fire index gas) contents, implying that Hg has the potential to serve as an index gas to monitor the occurrences of underground coal fires in mining goafs.

Assessment of air pollution by mercury in South African provinces using lichens Parmelia caperata as bioindicators.

Large-scale assessment of atmospheric air pollution by mercury (Hg) using lichen Parmelia caperata as biological indicator was undertaken using samples from five provinces of South Africa collected between 2013 and 2017. Analysis of lichens provides time-integrated data, which correspond to the mean Hg concentration in air at a specific location over a long time period. Determination of Hg in lichens was carried out by direct thermal decomposition of samples using a Zeeman-effect atomic absorption spectrometer, thereby requiring no chemical pretreatment. The lowest mercury concentration of 60 ± 8.0ngg-1 (n = 45) was measured in lichens from Limpopo province. This value was accepted as a background Hg concentration in SA lichens. The Hg in lichens from northern parts of Mpumalanga province varied from 72 ± 9.0 to 100 ± 17ngg-1 (n = 45), while in southern parts of the province, where 11 coal-fired electrical power stations are located, values ranged from 139 ± 7.0 to 183 ± 10ngg-1 (n = 28). The highest Hg concentration, 218 ± 21ngg-1 (n = 10), was found in lichens from Secunda, Mpumalanga province. It could be traced to the possible Hg emission during thermal treatment of coal at the largest SA industrial plant that transforms coal into liquid fuels. In Pretoria and Johannesburg, cities in Gauteng province, Hg in lichens was between 110 and 162ngg-1 (n = 48). Based on the results of measurements, the equation connecting Hg concentration in lichens with Hg concentration in air has been derived. It was used for the calculation of atmospheric Hg concentration in South African provinces. Calculated values (0.8-1.45ngm-3) were found to be within statistical summary of mean atmospheric Hg in remote places (1.70 ± 0.17ngm-3), and in other locations (1.5-3.0ngm-3) lower than in impacted areas of the world (5.20 ± 3.47ngm-3).

Mercury emission from industrially contaminated soils in relation to chemical, microbial, and meteorological factors

The Minamata Convention entered into force in 2017 with the aim to phase-out the use of mercury (Hg) in manufacturing processes such as the chlor-alkali or vinyl chloride monomer production. However, past industrial use of Hg had already resulted in extensive soil pollution, which poses a potential environmental threat. We investigated the emission of gaseous elemental mercury (Hg0) from Hg polluted soils in settlement areas in the canton of Valais, Switzerland, and its impact on local air Hg concentrations. Most soil Hg was found as soil matrix-bound divalent Hg (HgII). Elemental mercury (Hg0) was undetectable in soils, yet we observed substantial Hg0 emission (20–1392 ng m−2 h−1) from 27 soil plots contaminated with Hg (0.2–390 mg Hg kg−1). The emissions of Hg0 were calculated for 1274 parcels covering an area of 8.6 km2 of which 12% exceeded the Swiss soil remediation threshold of 2 mg Hg kg−1. The annual Hg0 emission from this area was approximately 6 kg a−1, which is almost 1% of the total atmospheric Hg emissions in Switzerland based on emission inventory estimates. Our results show a higher abundance of Hg resistance genes (merA) in soil microbial communities with increasing soil Hg concentrations, indicating that biotic reduction of HgII is likely an important pathway to form volatile Hg0 in these soils. The total soil Hg pool in the top 20 cm of the investigated area was 4288 kg; hence, if not remediated, these contaminated soils remain a long-term source of atmospheric Hg, which is prone to long-range atmospheric transport.

Multicompartment Mercury Contamination in Major Gold Mining Districts at the Department of Bolivar, Colombia.

Artisanal and small-scale gold mining is the main source of human exposure to mercury (Hg) in many countries. This study was designed to evaluate total Hg (T-Hg) concentrations in human hair, fish, soil, and air from two major gold-mining districts (GMDs) at the department of Bolivar, Colombia. Total Hg was analyzed using a direct Hg analyzer. The mean T-Hg concentration in hair samples was 3.07 ± 0.14μg/g (range 0.15-25.1μg/g; median 2.02μg/g). The highest Hg level was observed in Mojana GMD, specifically at Achi-La Raya (9.2 ± 0.6μg/g) and the lowest in Morales, at the Middle Magdalena GMD (1.50 ± 0.16μg/g). Hair T-Hg values exceeded the U.S. Environmental Protection Agency reference level of 1.0μg/g. Correlation between T-Hg in hair and stature was negative for the Mojana, but the opposite for Middle Magdalena, although for both GMDs hair T-Hg correlated positively with fish intake. The highest average T-Hg fish concentrations were observed in Caquetaia kraussii (0.37 ± 0.10μg/g), Sorubim cuspicaudus (0.32 ± 0.16μg/g), Plagioscion surinamensis (0.22 ± 0.02μg/g), Trachelyopterus insignis (0.20 ± 0.02μg/g), and Pseudoplatystoma magdaleniatum (0.20 ± 0.02μg/g). Human health risk assessment of Hg based on fish consumption suggested that, with the exception of P. magdalenae, all economically important fish species are potentially harmful for the communities. Soil Hg levels in amalgam burning facilities were extremely high, and Hg in the air around mines and gold-processing shops exceeded international guidelines. In short, Hg pollution in GMDs of Bolivar is extensive, and this situation requires special attention to reduce environmental and human health problems.

Results of a controlled field experiment to assess the use of tree tissue concentrations as bioindicators of air Hg

The utility of trees as bioindicators of atmospheric mercury (Hg) depends upon how accurately tree tissue concentrations reflect air-Hg concentrations at a given location and time. The relationship between air-Hg, and Hg concentration in tree tissues was investigated using potted Pinus nigra (Austrian pine) saplings 6 to 7 years in age moved from a tree farm in Oregon, USA, to three locations with different weather, two with different air total Hg (THg) concentrations, all with different predominant gaseous oxidized Hg chemistry, and one being impacted by the marine boundary layer. An aqueous Hg bromide root spike showed no significant effect on above ground tissue concentration. Over two growing seasons, needles, bark, and tree rings were sampled and analyzed for THg concentrations to compare with those collected when the trees originally arrived in Reno, NV (control) versus that measured in the new locations. Overall, foliar Hg concentrations increased significantly at all new locations relative to the control. Spring sample concentrations were lower than fall for foliage at two locations, indicating resorption of Hg along with nutrients. All trees had higher mean Hg concentrations in the outermost tree rings relative to the control, consistent with increased air total Hg concentrations and changing air chemistry. Higher concentrations were measured in the outer bark of trees where ambient GOM concentrations were highest. Higher inner bark concentrations were correlated with the more humid location where high methylmercury concentrations have been measured in fog. Results demonstrated that Pinus nigra tissues are effective biomonitors for air Hg exposures and that translocation from leaves to rings via the phloem is an important pathway for sequestration in plant tissue. We also show that plants are active assimilators of atmospheric Hg, and as such, local environmental conditions influence ring, bark, and foliage concentrations. The latter has important implications for understanding tissue Hg concentrations, and supports the use of tree ring Hg concentrations as archives.

Recent decrease trend of atmospheric mercury concentrations in East China: the influence of anthropogenic emissions

Abstract. Measurements of gaseous elemental mercury (GEM), other air pollutants, including SO2, NOx, O3, PM2.5, and CO, and meteorological conditions were carried out at Chongming Island in East China from 1 March 2014 to 31 December 2016. During the sampling period, GEM concentrations significantly decreased from 2.68 ± 1.07 ng m−3 in 2014 (March to December) to 1.60 ± 0.56 ng m−3 in 2016 (March to December). Monthly mean GEM concentration showed a significant decrease, at a rate of -0.60±0.08 ng m−3 yr−1 (R2=0.64, p &lt; 0.01 significance level). Combining the analysis of the potential source contribution function (PSCF), principle component analysis (PCA), and the emission inventory, we found that the Yangtze River Delta (YRD) region was the dominant source region of GEM in Chongming Island and the main source industries included coal-fired power plants, coal-fired industrial boilers, and cement clinker production. We further quantified the effect of emission change on the air Hg concentration variations at Chongming Island through a coupled method of trajectory clusters and air Hg concentrations. It was found that the reduction of domestic emissions was the main driver of GEM decline in Chongming Island, accounting for 70 % of the total decline. The results indicated that air pollution control policies targeting SO2, NOx, and particulate matter reductions had significant co-benefits on GEM.

Gaseous elemental mercury (GEM) fluxes over canopy of two typical subtropical forests in south China

Abstract. Mercury (Hg) exchange between forests and the atmosphere plays an important role in global Hg cycling. The present estimate of global emission of Hg from natural source has large uncertainty, partly due to the lack of chronical and valid field data, particularly for terrestrial surfaces in China, the most important contributor to global atmospheric Hg. In this study, the micrometeorological method (MM) was used to continuously observe gaseous elemental mercury (GEM) fluxes over forest canopy at a mildly polluted site (Qianyanzhou, QYZ) and a moderately polluted site (Huitong, HT, near a large Hg mine) in subtropical south China for a full year from January to December in 2014. The GEM flux measurements over forest canopy in QYZ and HT showed net emission with annual average values of 6.67 and 0.30 ngm-2h-1, respectively. Daily variations of GEM fluxes showed an increasing emission with the increasing air temperature and solar radiation in the daytime to a peak at 13:00, and decreasing emission thereafter, even as a GEM sink or balance at night. High temperature and low air Hg concentration resulted in the high Hg emission in summer. Low temperature in winter and Hg absorption by plant in spring resulted in low Hg emission, or even adsorption in the two seasons. GEM fluxes were positively correlated with air temperature, soil temperature, wind speed, and solar radiation, while it is negatively correlated with air humidity and atmospheric GEM concentration. The lower emission fluxes of GEM at the moderately polluted site (HT) when compared with that in the mildly polluted site (QYZ) may result from a much higher adsorption fluxes at night in spite of a similar or higher emission fluxes during daytime. This shows that the higher atmospheric GEM concentration at HT restricted the forest GEM emission. Great attention should be paid to forests as a crucial increasing Hg emission source with the decreasing atmospheric GEM concentration in polluted areas because of Hg emission abatement in the future.

Mercury concentrations in environmental media at a hazardous solid waste landfill site and mercury emissions from the site

Mercury (Hg) concentrations in air, effluent water, landfill gas, leachate, groundwater, and soil at a hazardous solid waste landfill site in Korea were measured along with air–soil surface Hg exchange fluxes at the site. The concentrations and fluxes were considerably higher than have been found elsewhere in Korea. Gaseous Hg concentrations in the air peaked during the day, coinciding with Hg being released from the landfill surface. This suggests that air–soil exchange increased the Hg concentrations in the atmosphere. The air–soil exchange flux increased abruptly when solar radiation reached the soil surface. The Hg flux peaked about 3 h before the solar radiation peaked, possibly because reducible Hg was abundant at the soil surface. The Hg emission flux activation energy (E a) was low, indicating that the Hg species present and Hg–soil binding were probably not as important (because of the high Hg content of the soil) as in previous studies. The methylmercury to total Hg ratios in the discharged effluent, groundwater, and leachate was clearly higher than typically found in coastal water and freshwater, suggesting bacteria caused active methylation to occur under the reducing conditions in the anaerobic landfill. The results suggested that considerable amounts of Hg are probably transported from the landfill to nearby environmental media and that this will continue if waste with a high Hg content continues to be added to the landfill without being pretreated.

Air-sea exchange of gaseous mercury in the tropical coast (Luhuitou fringing reef) of the South China Sea, the Hainan Island, China.

The air-sea exchange of gaseous mercury (mainly Hg(0)) in the tropical ocean is an important part of the global Hg biogeochemical cycle, but the related investigations are limited. In this study, we simultaneously measured Hg(0) concentrations in surface waters and overlaying air in the tropical coast (Luhuitou fringing reef) of the South China Sea (SCS), Hainan Island, China, for 13days on January-February 2015. The purpose of this study was to explore the temporal variation of Hg(0) concentrations in air and surface waters, estimate the air-sea Hg(0) flux, and reveal their influencing factors in the tropical coastal environment. The mean concentrations (±SD) of Hg(0) in air and total Hg (THg) in waters were 2.34 ± 0.26ngm(-3) and 1.40 ± 0.48ngL(-1), respectively. Both Hg(0) concentrations in waters (53.7 ± 18.8pgL(-1)) and Hg(0)/THg ratios (3.8%) in this study were significantly higher than those of the open water of the SCS in winter. Hg(0) in waters usually exhibited a clear diurnal variation with increased concentrations in daytime and decreased concentrations in nighttime, especially in cloudless days with low wind speed. Linear regression analysis suggested that Hg(0) concentrations in waters were positively and significantly correlated to the photosynthetically active radiation (PAR) (R (2) = 0.42, p < 0.001). Surface waters were always supersaturated with Hg(0) compared to air (the degree of saturation, 2.46 to 13.87), indicating that the surface water was one of the atmospheric Hg(0) sources. The air-sea Hg(0) fluxes were estimated to be 1.73 ± 1.25ngm(-2)h(-1) with a large range between 0.01 and 6.06ngm(-2)h(-1). The high variation of Hg(0) fluxes was mainly attributed to the greatly temporal variation of wind speed.