Some local environmental effects on mercury emission and absorption at a soil surface

Labile carbon inputs boost microbial contribution to legacy mercury reduction and emissions from industry-polluted soils

Soils is a crucial reservoir influencing mercury (Hg) emissions and soil-air exchange dynamics, partially modulated by microbial reducers aiding Hg reduction. Yet, the extent to which microbial engagements contribute to soil Hg volatilization remains largely unknown. Here, we characterized Hg-reducing bacterial communities in natural and anthropogenically perturbed soil environments and quantified their contribution to soil Hg(0) volatilization. Our results revealed distinct Hg-reducing bacterial compositions alongside elevated mercuric reductase (merA) gene abundance and diversity in soils adjacent to chemical factories compared to less-impacted ecosystems. Notably, solely industry-impacted soils exhibited increased merA gene abundance along Hg gradients, indicating microbial adaption to Hg selective pressure through quantitative changes in Hg reductase and genetic diversity. Microcosm studies demonstrated that glucose inputs boosted microbial involvement and induced 2-8 fold increments in cumulative Hg(0) volatilization in industry-impacted soils. Microbially-mediated Hg reduction contributed to 41.6% of soil Hg(0) volatilization in industry-impacted soils under 25% water-holding capacity and glucose input conditions over a 21-day incubation period. Alcaligenaceae, Moraxellaceae, Nitrosomonadaceae and Shewanellaceae were identified as potential contributors to Hg(0) volatilization in the soil. Collectively, our study provides novel insights into microbially-mediated Hg reduction and soil-air exchange processes, with important implications for risk assessment and management of industrial Hg-contaminated soils.

Gaseous Elemental Mercury Exchange Fluxes over Air-Soil Interfaces in the Degraded Grasslands of Northeastern China

Mercury (Hg) is a global pollutant that may potentially have serious impacts on human health and ecologies. The gaseous elemental mercury (GEM) exchanges between terrestrial surfaces and the atmosphere play important roles in the global Hg cycle. This study investigated GEM exchange fluxes over two land cover types (including Artemisia anethifolia coverage and removal and bare soil) using a dynamic flux chamber attached to the LumexR RA915+ Hg analyzer during the growing season from May to September of 2018, in which the interactive effects of plant coverage and meteorological conditions were highlighted. The daily mean ambient levels of GEM and the total mercury concentrations of the soil (TSM) were determined to be 12.4 ± 3.6 to 16.4 ± 5.6 ng·m-3 and 32.8 to 36.2 ng·g-1, respectively, for all the measurements from May to September. The GEM exchange fluxes (ng·m-2·h-1) during the five-month period for the three treatments included the net emissions from the soil to the atmosphere (mean 5.4 to 7.1; range of -27.0 to 47.3), which varied diurnally, with releases occurring during the daytime hours and depositions occurring during the nighttime hours. Significant differences were observed in the fluxes between the vegetation coverage and removal during the growing months (p < 0.05). In addition, it was determined that the Hg fluxes were positively correlated with the solar radiation and air/soil temperature levels and negatively correlated with the air relative humidity and soil moisture under all the conditions (p < 0.05). Overall, the results obtained in this study demonstrated that the grassland soil served as both a source and a sink for atmospheric Hg, depending on the season and meteorological factors. Furthermore, the plants played an important inhibiting role in the Hg exchanges between the soil and the atmosphere.

Temporal trends of urinary mercury in Chinese people from 1970s to 2010s: A review

Mercury (Hg) is one of the most toxic heavy metals. It can migrate around the globe and magnify through the food chain, ultimately harming human health. Urinary Hg reflects recent exposure of Hg, which reflects the status of environmental contamination by Hg. This review summarized the levels and presented temporal trends of urinary Hg in Chinese people (both the general public and the occupationally exposed people) reported from 1970s to 2010s. It was found that urinary Hg levels in 92.3% of the reported population were less than the reference value (10.0 µg/L) recommended by Chinese health authority, while 76.9% were less than the reference value (4.0 µg/L) recommended by World Health Organization (WHO) in the general public in China. For the temporal trend from 1970s to 2010s, the urinary Hg levels in the general public in China were found to decrease gradually. In the occupationally exposed people, the urinary Hg levels generally exceeded the reference value (10.0 µg/L) for the general public, and about half of them were higher than the occupational exposure limit (35.0 µg/g creatinine) set by Chinese Occupational Health Standard (WS/T 265 - 2006). From 1970s to 2010s, the urinary Hg levels in occupationally exposed population increased first and then decreased slowly. Hg miners in Guizhou were found to have the highest urinary Hg levels, while workers in Anhui, Chongqing, Qinghai and Shanxi also had high levels of urinary Hg. In all, the urinary Hg levels in both the general public and the occupationally exposed people decreased from 1970s to 2010s, especially in recent decades. Attention should be paid to occupationally exposed people since high levels of urinary Hg were found in them. The message provided in this review can help better understand the situation of Hg burden in Chinese people and lay a basis for the coming effectiveness evaluation on the implementation of Minamata Convention on Mercury. Capsule abstract: The urinary Hg levels in both the general public and the occupationally exposed people in China are decreasing.

Vegetation Mediated Mercury Flux and Atmospheric Mercury in the Alpine Permafrost Region of the Central Tibetan Plateau

Measurements of land-air mercury (Hg) exchanges over vegetated surfaces are needed to further constrain Hg fluxes over vegetated terrestrial surfaces. Yet, knowledge of land-air Hg dynamics in alpine grasslands remains poor. Hg fluxes over an alpine meadow were measured throughout a full vegetation period in the central Tibetan Plateau (TP). This TP grassland served as a small source of atmospheric total gaseous Hg (TGM) during vegetation period (0.92 μg m^-2). Hg fluxes decreased logarithmically during plant growing season, resulting from the influence of vegetation by light shading and plant Hg uptake, although the latter might be minor due to low biomass at this site. Temporal patterns of TGM indicated the importance of land-air dynamics in regulating TGM levels. During the plant emergence, diel pattern of TGM covaried with Hg emission fluxes resulting in lower concentrations at night and higher concentrations in afternoon. During all other vegetation stages, TGM showed minima before dawn and "morning peak" shortly after sunrise, in conjunction with corresponding Hg fluxes showing sink before dawn and source after sunrise. Moreover, TGM concentrations showed a decreasing trend with plant growing, further indicating the role of vegetation in driving seasonal TGM variations by regulating land-air Hg dynamics.

Influence of soil redox state on mercury sorption and reduction capacity

We investigated the mechanisms of interactions between divalent aqueous Hg and rock samples originating from an outcropping rock formation, the Albian Tégulines Clay (France, Aube). Two solid samples collected at two different depths (7.7 and 21.2 m depth) in the rock formation were selected since, in situ, they had and were still experiencing contrasting redox conditions, and thus had different mineralogy with regards to the minerals containing redox-sensitive elements, in particular iron. The sample that was the closer to the surface was under oxidizing conditions and contained goethite and siderite, while the deeper one was under reducing conditions and had more siderite, together with pyrite and magnetite. The redox state of the samples was preserved throughout the present study by careful conditioning, preparation, and use them under O₂-free conditions. The two samples had similar affinity for Hg, with a retention coefficient (R_D) ranging between 10² and 10⁶ mol·kg^-1 when the aqueous Hg concentration ranged between 4.4 and 10⁷ ng·L^-1 with the lowest concentration for the highest R_D. However, the mechanisms of interaction differed. In the oxidized sample, no change in Hg redox state was observed, and the retention was due to reversible adsorption on the mineral phases (including organic matter). In contrast, upon interaction with the deeper and reduced sample, Hg was not only adsorbed on the mineral phases, but part of it was also reduced to dissolve elemental Hg. This reduction was attributed to magnetite and siderite and highlights the influence of mineralogy on the geochemical cycle of Hg.

Newly deposited atmospheric mercury in a simulated rice ecosystem in an active mercury mining region: High loading, accumulation, and availability

Mercury (Hg) mining activities are an important anthropogenic source of atmospheric Hg. The Xunyang Hg mine located in Shaanxi Province is the largest active Hg producing centre in China. To understand the biogeochemical processes of atmospheric Hg through Hg mining activities, six groups of experimental pots were carefully designed to investigate the effect of Hg mining activities on Hg contamination from atmospheric deposition in the local surface soils. Based on the variations of Hg in the soil from the experimental pots, the deposition flux and loading of Hg in the Xunyang Hg mining district were investigated. The results showed that the average concentration of total gaseous mercury (TGM) as high as 193 ± 122 ng m^-3 was observed in the ambient air, which was orders of magnitude higher than that in remote areas. The average deposition flux and annual loading of atmospheric Hg were 72 mg m^-2 y^-1 and 10 t y^-1, respectively. The dominant atmospheric Hg deposition is within a distance range of 6.0-12 km from the Hg retorting facility, accounting for approximately 85% of the total Hg loading. After 14 months of exposure, total mercury (THg) concentrations in the soil from the experimental pots increased 0.35-9.5 times, and the highest concentrations of methylmercury (MeHg) (3.7 ± 2.9 μg kg^-1) in soil were observed in February. Concentrations as high as 643 μg kg^-1 THg and 13 μg kg^-1 MeHg in rice were observed in the second experimental year. Elevated concentrations of both THg and MeHg in rice indicated that the newly deposited atmospheric Hg was bioavailable, readily methylated, and taken up by rice, suggesting that the ongoing Hg mining activities cause serious Hg contamination in the soil-rice ecosystem and posed a threat to local residents in the Xunyang Hg mining area.

Temporal changes in the content of labile and stabile mercury forms in soil and their inflow to the southern Baltic Sea

Rivers represent the main source of mercury (Hg) in the Southern Baltic. Nevertheless, the concentration and proportion of individual Hg forms in rivers depend on the management of the river basin, as well as on the intensity of meteorological phenomena. Hence the aim of the present study was to determine the influence of drought and rains/intense rains on the content of labile and stable Hg forms in the soil of river catchments with various types of land management, and on the inflow of bioavailable mercury to the coastal zone of the sea. Soil and sediment samples were taken from two rivers flowing into Puck Bay (Southern Baltic): the Reda and Gizdepka. In order to determine Hg concentration and the proportions of its particular forms in the collected material, the thermo-desorption method was used. Five periods were identified during which the soil was enriched with various Hg forms. The obtained results showed that in periods of intensive development of vegetation, the soil becomes enriched with absorbed mercury (Hg_abs). On the other hand, as a result of Hg emissions during the heating of buildings, mercury associated with halides (Hg_ads1) is deposited on land, as was primarily recorded in catchments where individual household furnaces were found. Both mild and intense rainfalls intensified the surface run-off, which contributed to soil erosion, causing the transport of both Hg_abs and Hg_ads1 to the river bed. However, the soil was more enriched with labile mercury in anthropogenic catchments, as they are only slightly overgrown with vegetation, the presence of which limits soil erosion. During periods of snow melting, there was intensive leaching and transportation of Hg_ads1, which had been deposited on the land surface during the intensive combustion of fossil fuels. In each of the designated periods, stable mercury sulphide was formed in the soil. However, the highest proportion of HgS was found during a period of drought, when organic matter decomposed and there was inflow of sulphur compounds from farms. Taking into consideration the anomalous study periods, the largest load of mercury introduced along with the bed sediment of the Gizdepka into the sea was recorded during downpour/flood. Nevertheless, the most bioavailable Hg-enriched load was introduced during snow melting period.

An experimental study of the impacts of solar radiation and temperature on mercury emission from different natural soils across China

Mercury (Hg) emission from natural soil is one of the most important contributors to global Hg cycles. Research on Hg emission from soil to air has been carried out in China. Currently, most of the research focuses on contaminated sites in China, while research in other regions is rare. To provide more accurate information on Hg emissions from soil to air in China and obtain additional laboratory data to verify the role of solar radiation and temperature in this process, we sampled and measured Hg emission fluxes from various natural soils (range, 48-240 ng/g) across mainland China under different solar radiation (0-900 W·m^-2) and temperature (15-45 °C) conditions in a laboratory. We found that in different places in China, Hg emissions from natural soils occurred more easily when the soil Hg concentration, temperature, and solar radiation were high, but the impacts were different among the regions due to different soil types. Hg emissions from natural soils (0.071-24 ng·m²·h^-1) were typically lower than those from contaminated sites, suggesting that additional measurements in natural soils are desirable. The results of this study could provide more accurate information on Hg emission from natural soil to air and help establish a nationwide natural soil Hg emission inventory in China.

Status of mercury accumulation in agricultural soil across China: Spatial distribution, temporal trend, influencing factor and risk assessment

Given its wide distribution in the natural environment and global transport potential, mercury (Hg) is regarded as a ubiquitous pollutant. In this study, we carried out nation-wide sampling campaigns across China to investigate the distribution of Hg in agricultural soils. Concentrations of Hg in the soils collected in 2011 and 2016 ranged from 0.04 to 0.69 and 0.06-0.78 mg kg^-1, respectively. Based on the data from 2016, the reserve of Hg in the surface arable soils (0-20 cm) in China was 4.1 × 10⁴ metric tons and Chinese cultivated soils accounted for 63.4-364 metric tons of Hg released to the global atmosphere. The soil Hg concentrations were significantly higher than the reference background level, highlighting the impacts of anthropogenic activities. The vertical distribution pattern showed a clear enrichment at the surface and a decrease with depth of the soils. Comparison of calculated geo-accumulation indexes among individual provinces showed that Northwest China had higher levels of Hg contamination than other regions of China, likely due to long-term energy related combustions in the area. Soil Hg level showed strong positive correlations with organic matter contents of soil, as well as the mean annual precipitation and temperature of the sampling locations. The non-carcinogenic human health risks of soil Hg were below the threshold level, but the general risk to the ecosystem was considerable. The increases in Hg accumulation from 2011 to 2016 at provincial level were found to relate to coal combustion, power generation and per capita GDP. This examination of energy consumption and socioeconomic drivers for China's soil Hg reserve increase is critical for direct Hg control by guiding policy-making and targets of technology development in era of rapid economic growth.

Soil surface Hg emission flux in coalfield in Wuda, Inner Mongolia, China

Hg emission flux from various land covers, such as forests, wetlands, and urban areas, have been investigated. China has the largest area of coalfield in the world, but data of Hg flux of coalfields, especially, those with coal fires, are seriously limited. In this study, Hg fluxes of a coalfield were measured using the dynamic flux chamber (DFC) method, coupled with a Lumex multifunctional Hg analyzer RA-915+ (Lumex Ltd., Russia). The results show that the Hg flux in Wuda coalfield ranged from 4 to 318 ng m^-2 h^-1, and the average value for different areas varied, e.g., coal-fire area 99 and 177 ng m^-2 h^-1; no coal-fire area 19 and 32 ng m^-2 h^-1; and backfilling area 53 ng m^-2 h^-1. Hg continued to be emitted from an underground coal seam, even if there were no phenomena, such as vents, cracks, and smog, of coal fire on the soil surface. This phenomenon occurred in all area types, i.e., coal-fire area, no coal-fire area, and backfilling area, which is universal in Wuda coalfield. Considering that many coalfields in northern China are similar to Wuda coalfield, they may be large sources of atmospheric Hg. The correlations of Hg emission flux with influence factors, such as sunlight intensity, soil surface temperature, and atmospheric Hg content, were also investigated for Wuda coalfield. Graphical abstract ᅟ.

Exchange pattern of gaseous elemental mercury in landfill: mercury deposition under vegetation coverage and interactive effects of multiple meteorological conditions

Landfill is known as a potential source of atmospheric Hg and an important component of the local or regional atmospheric Hg budget. This study investigated the gaseous elemental Hg surface-air fluxes under differing conditions at a typical municipal solid waste landfill site, highlighting the interactive effects of plant coverage and meteorological conditions. The results indicated that Hg fluxes exhibited a feature represented by diel variation. In particular, Hg deposition was observed under a condition of Kochia sieversiana coverage, whereas emission that occurred after K. sieversiana was removed. Hg emission was the dominant mode under conditions of Setaria viridis coverage and its removal; however, the average Hg emission flux with the S. viridis coverage was nearly four times lower than after its removal. These findings verified that the plant coverage should be a key factor influencing the Hg emission from landfills. In addition, Hg fluxes were correlated positively with solar radiation and air/soil temperature and correlated inversely with relative humidity under all conditions, except K. sieversiana coverage. This suggested that the interactive effects of meteorological conditions and plant coverage played a jointly significant role in the Hg emission from landfills. It was established that K. sieversiana can inhibit Hg emission efficiently, and therefore, it could potentially be suitable for use as a plant-based method to control Hg pollution from landfills.

Remediation of mercury-polluted soils using artificial wetlands

Mexico's mercury mining industry is important for economic development, but has unfortunately contaminated soils due to open-air disposal. This case was seen at two sites in the municipality of Pinal de Amoles, State of Queretaro, Mexico. This paper presents an evaluation of mercury dynamics and biogeochemistry in two soils (mining waste soil) using ex-situ wetlands over 36 weeks. In soils sampled in two former mines of Pinal de Amoles, initial mercury concentrations were 424 ± 29 and 433 ± 12 mg kg^-1 in La Lorena and San Jose, former mines, respectively. Typha latifolia and Phragmites australis were used and 20 reactors were constructed (with and without plants). The reactors were weekly amended with a nutrient solution (NPK), for each plant, at a pH of 5.0. For remediation using soils from San Jose 70-78% of mercury was removed in T. latifolia reactors and 76-82% in P. australis reactors, and for remediation of soils from La Lorena, mercury content was reduced by 55-71% using T. latifolia and 58-66% in P. australis reactors. Mercury emissions into the atmosphere were estimated to be 2-4 mg m^-2 h^-1 for both soils.

Enhancement of surface flow constructed wetlands performance at low temperature through seasonal plant collocation

In the present study, a novel seasonal plant collocation system (SPCS), specifically the Potamogeton crispus and Phragmites australis series system, was investigated to enhance the performance of surface flow constructed wetlands (SFCWs) at low temperature. Results of a year-round experiment showed that SPCS conquered the adverse effect of low temperature and achieved sustainable nutrients removal. In addition, during winter, removal efficiencies of NH₄-N, TP, COD, and TN in SPCS were 18.1%, 17.6%, 10.1% and 5.2% higher than that in the control, respectively. P. crispus and P. australis complemented each other in terms of plant growth and plant uptake during the experiment period. Furthermore, it emerged that P. crispus could increase the quantity of ammonia oxidizing bacteria by 10.2%, due to its high oxygen enrichment ability. It is suggested that seasonal plant collocation has a promising future in SFCWs of areas being affected by climate change, e.g. northern China.

Mercury pollution in the lake sediments and catchment soils of anthropogenically-disturbed sites across England

Sediment cores and soil samples were taken from nine lakes and their catchments across England with varying degrees of direct human disturbance. Mercury (Hg) analysis demonstrated a range of impacts, many from local sources, resulting from differing historical and contemporary site usage and management. Lakes located in industrially important areas showed clear evidence for early Hg pollution with concentrations in sediments reaching 400-1600 ng g^-1 prior to the mid-19th century. Control of inputs resulting from local management practices and a greater than 90% reduction in UK Hg emissions since 1970 were reflected by reduced Hg pollution in some lakes. However, having been a sink for Hg deposition for centuries, polluted catchment soils are now the major Hg source for most lakes and consequently recovery from reduced Hg deposition is being delayed.

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.

Volatilization of elemental mercury from fresh blast furnace sludge mixed with basic oxygen furnace sludge under different temperatures

Blast furnace sludge (BFS) is a waste with elevated mercury (Hg) content due to enrichment during the production process of pig iron. To investigate the volatilization potential of Hg, fresh samples of BFS mixed with basic oxygen furnace sludge (BOFS; a residue of gas purification from steel making, processed simultaneously in the cleaning devices of BFS and hence mixed with BFS) were studied in sealed column experiments at different temperatures (15, 25, and 35 °C) for four weeks (total Hg: 0.178 mg kg(-1)). The systems were regularly flushed with ambient air (every 24 h for the first 100 h, followed by every 72 h) for 20 min at a flow rate of 0.25 ± 0.03 L min(-1) and elemental Hg vapor was trapped on gold coated sand. Volatilization was 0.276 ± 0.065 ng (x m: 0.284 ng) at 15 °C, 5.55 ± 2.83 ng (x m: 5.09 ng) at 25 °C, and 2.37 ± 0.514 ng (x m: 2.34 ng) at 35 °C. Surprisingly, Hg fluxes were lower at 35 than 25 °C. For all temperature variants, an elevated Hg flux was observed within the first 100 h followed by a decrease of volatilization thereafter. However, the background level of ambient air was not achieved at the end of the experiments indicating that BFS mixed with BOFS still possessed Hg volatilization potential.

Inhibition of mercury release from forest soil by high atmospheric deposition of Ca²⁺ and SO₄²⁻

As one of the most important natural mercury (Hg) sources, soil release (emission to the atmosphere or leaching to soil water) depends on various factors, some of which can be affected by atmospheric deposition. We studied the effect of flue gas desulfurization gypsum (FGDG) addition on soil Hg release in a Masson pine (Pinus massoniana) forest in southwestern China. FGDG addition simulated atmospheric deposition of Ca(2+), SO4(2-) and Hg, which are commonly high in China. Results showed that Hg concentration in soil water decreased with the gypsum treatment, suggesting that the mobility of Hg in mineral soil was reduced. Moreover, the application of gypsum also seems to have decreased Hg emission from the soil, shown by the lower Hg contents in leaf tissues of ground vegetation in the treated plots than in the reference. Both Hg mobility in the soil and Hg emission to the atmosphere were decreased despite the additional Hg input from FGDG. The decreased DOC concentration in soil water and the elevated organic sulfur content in the soil Oe & Oa horizons were speculated to result in an enhanced capacity of surface soil to bind Hg, and thus to reduce Hg release from the soil. However, with the increasingly stringent control of particulate matter (PM) and sulfur dioxide (SO2) emissions in China, the deposition of Ca(2+) and SO4(2-) is expected to decrease, and their ability to inhibit soil Hg release is likely to decline in the future.

Spatial distribution of mercury in the surface soils of the urban areas, Arak, Iran

This study assessed the baseline concentrations and spatial distribution of total mercury (Hg) in urban soils of the city of Arak, Iran. Concentrations of Hg were determined in soil collected from urban areas, and the spatial distribution was analyzed using the semivariogram approach in geostatistical technology. Mercury in soil ranged from 66.3 to 581 µg/kg. The experimental variogram of soil mercury concentrations was best-fitted by a spherical model. A spatial distribution map revealed that Hg concentration showed decreasing trends from south to north, west to east and center to suburb. Overall, the results showed that Hg concentrations in urban soils of Arak may be considered medium or low.

Quantifying the effects of soil temperature, moisture and sterilization on elemental mercury formation in boreal soils

Soils are a source of elemental mercury (Hg(0)) to the atmosphere, however the effects of soil temperature and moisture on Hg(0) formation is not well defined. This research quantifies the effect of varying soil temperature (278-303 K), moisture (15-80% water filled pore space (WFPS)) and sterilization on the kinetics of Hg(0) formation in forested soils of Nova Scotia, Canada. Both, the logarithm of cumulative mass of Hg(0) formed in soils and the reduction rate constants (k values) increased with temperature and moisture respectively. Sterilizing soils significantly (p < 0.05, n = 10) decreased the percent of total Hg reduced to Hg(0). We describe the fundamentals of Hg(0) formation in soils and our results highlight two key processes: (i) a fast abiotic process that peaks at 45% WFPS and depletes a small pool of Hg(0) and; (ii) a slower, rate limiting biotic process that generates a large pool of reducible Hg(II).

Study on the reduction of atmospheric mercury emissions from mine waste enriched soils through native grass cover in the Mt. Amiata region of Italy

Atmospheric mercury emissions from mine-waste enriched soils were measured in order to compare the mercury fluxes of bare soils with those from other soils covered by native grasses. Our research was conducted near Mt. Amiata in central Italy, an area that was one of the largest and most productive mining centers in Europe up into the 1980s. To determine in situ mercury emissions, we used a Plexiglas flux chamber connected to a portable mercury analyzer (Lumex RA-915+). This allowed us to detect, in real time, the mercury vapor in the air, and to correlate this with the meteorological parameters that we examined (solar radiation, soil temperature, and humidity). The highest mercury flux values (8000ngm(-2)h(-1)) were observed on bare soils during the hours of maximum insulation, while lower values (250ngm(-2)h(-1)) were observed on soils covered by native grasses. Our results indicate that two main environmental variables affect mercury emission: solar radiation intensity and soil temperature. The presence of native vegetation, which can shield soil surfaces from incident light, reduced mercury emissions, a result that we attribute to a drop in the efficiency of mercury photoreduction processes rather than to decreases in soil temperature. This finding is consistent with decreases in mercury flux values down to 3500ngm(-2)h(-1), which occurred under cloudy conditions despite high soil temperatures. Moreover, when the soil temperature was 28°C and the vegetation was removed from the experimental site, mercury emissions increased almost four-fold. This increase occurred almost immediately after the grasses were cut, and was approximately eight-fold after 20h. Thus, this study demonstrates that enhancing wild vegetation cover could be an inexpensive and effective approach in fostering a natural, self-renewing reduction of mercury emissions from mercury-contaminated soils.

Investigation of factors affecting gaseous mercury concentrations in soils

The purpose of this study was to determine the effects of soil temperature, soil moisture, redox potential (Eh) and soil organic matter (SOM) on the total gaseous mercury (TGM) concentrations in background soils. Our measurements were made in a grass field and deciduous forest at the Piney Reservoir Ambient Air Monitoring Station (PRAAMS) in Garrett County, Maryland. Three plots in each area were sampled every third week from July 2009 to June 2010 at the Oe-A soil horizon interface, the A-E soil horizon interface, and 5 and 10 cm into the E soil horizon. The mean soil TGM concentration for all depths in the forest (2.3 ± 2.2 ng m(-3)) was significantly higher than the mean soil TGM concentration in the grass field (1.5 ± 1.9 ng m(-3)). Soil TGM at all depths was most strongly and consistently correlated to soil temperature. The soil TGM concentrations were highest and most variable at the forest Oe-A soil horizon interface (4.1 ± 2.0 ng m(-3)), ranging from 1.5 to 8.4 ng m(-3). This soil horizon interface had 11 to 26% more SOM and the soil Eh was 100 to 400 mV lower than the other soil depths. Our results suggest that soil temperature, soil Eh and SOM are significant factors affecting TGM concentrations in forest soils. Future studies of TGM dynamics in background soils may benefit from closely monitoring the organic soil horizon.

Measurement instability and temporal bias in chemical soil monitoring: sources and control measures

Concern that human impacts on the environment may be harmful to natural resources such as soils as well as to living conditions is the major motivation for long-term environmental monitoring. However, the evidence that measurement bias is not constant through time affects time series as an artifact; this also holds true for chemical soil monitoring. Measurement instabilities occur along the whole measurement chain, from soil sampling to the expression of results. The first step in controlling measurement instability is to identify its relevant sources, and the second is to control it by stabilizing, minimizing, or quantifying measurement instability. For all five steps in the measurement process, from soil sampling to the expression of the analytical results, sources of measurement instability are identified and measures of control discussed, leading to the main conclusion concerning the requirement to continuously control the relevant environmental and measurement boundary conditions that may affect measurement instability. The innovative aspect of this paper consists in explicitly addressing measurement instability in chemical soil monitoring and tracking it along the whole measurement chain. The paper is also a plea for a change of paradigm in long-term environmental monitoring, namely to consider temporal measurements as unstable unless their degree of stability is traceably demonstrated, adequately quantified, and included in interpretation.

Mercury in urban soils with various types of land use in Beijing, China

Mercury (Hg) concentration was investigated for 127 urban soil samples collected from business area (BA), classical garden (CG), culture and education area (CEA), public green space (PGS), residential area (RA) and roadside area (RSA) in Beijing. The median of Hg concentration in Beijing was 0.26 mg/kg. The value in CG was much higher than the other 5 types of land use, which was due to the historical use of Hg. More than 87% of the samples were not contaminated according to the guideline values of China, UK, Canada, and USEPA. Spatial distribution map revealed that Hg concentration showed a decreasing trend from the center to the suburb, it increased with the age of the urban area. Hg contamination in urban area of Beijing is marked by features of non-point sources associated with human activities, and it is most likely to be the common characteristics of Hg contamination in cities.

Dynamics of mercury fluxes and their controlling factors in large Hg-polluted floodplain areas

Environmental pollution by mercury (Hg) is a considerable environmental problem world-wide. Due to the occurrence of Hg volatilization from their soils, floodplains can function as an important source of volatile Hg. Soil temperature and soil water content related to flood dynamics are considered as important factors affecting seasonal dynamics of total gaseous mercury (TGM) fluxes. We quantified seasonal variations of TGM fluxes and conducted a laboratory microcosm experiment to assess the effect of temperature and moisture on TGM fluxes in heavily polluted floodplain soils. Observed TGM emissions ranged from 10 to 850 ng m(-2) h(-1) and extremely exceeded the emissions of non-polluted sites. TGM emissions increased exponentially with raised air and soil temperatures in both field (R(2): 0.49-0.70) and laboratory (R(2): 0.99) experiments. Wet soil material showed higher TGM fluxes, whereas the role of soil water content was affected by sampling time during the microcosm experiments.

Mercury in soils and plants in an abandoned cinnabar mining area (SW Spain)

An abandoned cinnabar mining area located in the South-West of Spain has been studied with the aim of assessing its mercury pollution level and enhancing the knowledge about the Hg soil/plant relationship. To do so, soils and plants were sampled near an inactive smelter and around two mining sites present in this area. Critical total Hg concentrations were found in the close environs of pollutant sources. These also show high levels of elemental Hg (up to 8 mg kg(-1)), but quite low exchangeable Hg contents (0.008-0.038 mg kg(-1)). Most plant specimens display in their aboveground tissues Hg concentrations comprised in the range 0.1-10 mg kg(-1), with a great proportion (50%) showing critical levels. Greater Hg contents were found in plant specimens growing in soils with higher elemental Hg concentrations. The plant species displaying the greatest Hg levels are either perennial species of small-medium size and/or showing medium-highly corrugated leaves, or annual plants of small size. Marrubium vulgare L., Bromus madritensis L. and Trifolium angustifolium L. are the plant species with the highest Hg contents (37.6, 12.7 and 9.0 mg kg(-1), respectively). Leaf specific surface seems an important feature in the atmospheric Hg uptake by plants.

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.

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).

Distribution characteristics of total mercury and methylmercury in the topsoil and dust of Xiamen, China

The levels and distribution of mercury (Hg) species, including total mercury (THg) and methylmercury (MeHg) in the topsoil and dust collected from twenty sampling stations located in different land function areas of Xiamen, China, were investigated. The THg concentrations in topsoil ranged from 0.071 to 1.2 mg/kg, and in dust ranged from of 0.034 to 1.4 mg/kg. For stations where the THg of dust was less than 0.31 mg/kg, THg concentrations in the topsoil were significantly correlated to those in the corresponding dust (r = 0.597, n = 16, P = 0.014). The MeHg concentrations in topsoil were varied between 0.14 and 5.7 microg/kg. The ratios of MeHg/THg in the topsoil ranged from 0.069% to 0.74%. The range of MeHg concentration in the dust were 0.092-2.3 microg/kg. The ratios of MeHg/THg in the dust were at the same level as those in the topsoil. The MeHg concentrations in both topsoil and dust were linked to corresponding THg concentrations and soil organic matter. Neither THg nor MeHg concentration in the topsoil and dust was obviously linked to the land function.

A note on elevated total gaseous mercury concentrations downwind from an agriculture field during tilling

Elevated mercury concentrations were measured at the University of Connecticut's mercury forest flux tower during spring agricultural field operations on an adjacent corn field. Concentrations at the tower were elevated, a peak of 7.03 ng m(-3) over the background concentration of 1.74+/-0.26 ng m(-3), during times when the prevailing wind was from the direction of the corn field and during periods when the soil was disturbed by tilling. Strong deposition to the forest was recorded at the point of measurement when atmospheric mercury concentrations were elevated. The strongest deposition rate was a 1 hour maximum of -4011 ng m(-2) h(-1) following the initial peak in atmospheric concentrations, Analyses of the meteorological conditions and mercury content in agricultural soil, manure and the diesel consumed in the tilling operation indicate that the source of the mercury was from the agricultural tilling operations and it was advected over the tower enriching the atmospheric concentrations above the forest canopy leading to deposition. These results indicate that agriculture operations resulting in a disturbed soil surface may be a source of atmospheric mercury originating from the pool of mercury bound in the soil. This represents a previously undocumented source of mercury emissions resulting from anthropogenic activities.

Effects of pH, organic acids, and competitive cations on mercury desorption in soils

The effects of pH, organic acids, and competitive cations on Hg(2+) desorption were studied. Three representative soils for rice production in China, locally referred to as a yellowish red soil (YRS), purplish clayey soil (PCS), and silty loam soil (SLS) and classified as Gleyi-Stagnic Anthrosols in FAO/UNESCO nomenclature, were, respectively, collected from Jiaxin County, Deqing County, and Xiasha District of Hangzhou City, Zhejiang Province. Most of the added Hg(2+) was adsorbed at low initial concentrations (<2 mg l(-1)). Desorption of the adsorbed Hg(2+) in 0.01M KCl (simulating soil solution) was minimal, but was significantly enhanced by the change of pH, and the presence of organic acids or competitive cations. The desorption of Hg(2+) in the soils decreased with pH from 3.0 to 5.0, leveled off at pH 5.0-8.0, but increased with pH from 7.0 to 9.0. The presence of organic ligands enhanced Hg(2+) desorption in the soils except for YRS, in which the addition of tartaric, malic, or oxalic acid reduced Hg(2+) desorption at low concentrations (<10(-4)M), but Hg(2+) desorption generally increased with organic acid concentration. Citric acid was most effective in increasing Hg(2+) desorption, followed by tartaric acid and malic acid; and oxalic acid was the least effective. Desorption of adsorbed Hg(2+) increased with increasing concentrations of added Cu(2+) or Zn(2+). Applied Cu(2+) increased Hg(2+) desorption more than Zn(2+) at the same loading rate.

CAPSULE

The effects of organic acids and competitive cations on Hg desorption in soil-water system are related to their concentrations, basic chemical properties, and soil properties.

Effect of organic matter and pH on mercury release from soils

An investigation was conducted on the effect of organic matter (OM) and pH on mercury (Hg) release from soils. Hg release flux was measured using the dynamic flux chamber (DFC) combined with the Lumex multifunctional mercury analyzer in both laboratory experiment and field monitoring. The results showed that Hg emission from the OM-added soils was apparently low because of the high affinity of OM to Hg, resulting in the reverse order as the amount of OM addition. Meanwhile, Hg release flux from different pH value soils exhibited the same trend for both Hg(2+) and Hg2(2+) treatment, increasing the Hg flux with pH value of soils increasing. The trend of Hg release in the pH dependence experiment has been well in agreement with that from the field test. In addition, Hg release seemed to be related to its species in the soil, the flux from Hg(2+)-added soil was obviously higher than that of Hg22z-added soil by the laboratory experiment.

Atmospheric mercury emissions from polluted gold mining areas (Venezuela)

Soil, waste rock and mud from mercury-gold amalgamation mining areas of El Callao (Venezuela) are highly enriched in Hg (0.5-500 microg g(-1)) relative to natural background concentrations (<0.1 microg g(-1)). Mercury fluxes to the atmosphere from twelve polluted sites of this area were measured in situ (6 a.m. to 8 p.m.) using a Plexiglas flux chamber connected to a portable mercury analyzer (model RA-915+; Lumex, St. Petersburg, Russia). Mercury fluxes ranged between 0.65 and 420.1 microg m(-2) h(-1), and the average flux range during the diurnal hours was 9.1-239.2 microg m(-2) h(-1). These flux values are five orders of magnitude higher than both reported world background Hg fluxes (1-69 ng m(-2) h(-1)) and the regional values, which are in the range 2-10 ng m(-2) h(-1). The flux results obtained in this study are, however, similar to those measured at Hg polluted sites such as chloro-alkali plants or polymetallic ore mining districts (>100,000 ng m(-2) h(-1)). The results from this study also show that Hg emissions from the soil are influenced by solar radiation, soil temperature and soil Hg concentration. Our data suggest that solar radiation may be the dominant factor affecting Hg degrees emission since the major species of mercury in polluted soil is Hg degrees (85-97% of total Hg). The simple release of Hg degrees vapor is probably the dominant process occurring with incident light in the field. The apparent activation energy for mercury emission indicates that the volatilization of mercury mainly occurred as a result of the vaporization of elemental mercury in soil. The degree of Hg emission differed significantly among the soil sites studied, which may be due to variations in soil texture, organic matter content and soil compaction.

Airborne total gaseous mercury and exposure in a Venezuelan mining area

This paper presents a short-term monitoring study of total gaseous mercury (TGM) in air, and exposure to airborne mercury. The evaluation was carried out in polluted mining sites (El Callao, Venezuela), where for decades mercury has been used in diverse stages of gold mining activities. The contamination is mainly due to emission of Hg0 during gold amalgamation and burning, which can cause direct human health risks. Total gaseous mercury (TGM) in air was analysed in mill, jewellery and indoor house sites, and at different heights (height profiles near the surface) at polluted and not polluted sites. Mercury concentration in air was measured with a portable mercury analyser (Lumex Ra-915+). Time weighted average mercury (TWA) was calculated for the evaluation of mercury exposure. TWA values ranged between 0.28 microg m(-3) and >100 microg m(-3). These measurements were done during sunny and dry days. In the case of mills and gold workshops, the values were over the limit recommended by the World Health Organization to exposure (25 microg m(-3)) and NIOSH limit (50 microg m(-3)). Indoors in a house, the air Hg average value was 2.58 microg m(-3) exceeding EPA (0.3 microg m(-3)) and ATSDR (1 microg m(-3)) guidelines. The mercury concentration at different height profiles, varied between 1766 microg m(-3) and 0.014 microg m(-3). Mercury height profiles were described by a power function model of the form c(Hg) = ah(-b), where a parameter describes the magnitude of Hg emission. For polluted sites there was a significant correlation between a and Hg in soil or Hg emission from soil to air, while b is only significantly correlated with air temperature. An air and soil mercury measurement transect was carried out at a mill site up to a distance of 1000 m, and it was observed that the air mercury concentration decreases with increasing distance from the mill site, and inversely to Hg soil content.

Development and application of a laboratory flux measurement system (LFMS) for the investigation of the kinetics of mercury emissions from soils

Recent measurements at different locations suggest that the emission of mercury from soils may play a more pronounced role in the global mercury cycle as suggested by global emission inventories and global mercury cycling models. For up scaling and modelling of mercury emissions from soils a comprehensive assessment of the processes controlling the emission of mercury from soils is imperative. We have developed a laboratory flux measurement system (LFMS) to study the effect of major environmental variables on the emission of mercury under controlled conditions. We have investigated the effects of turbulent mixing, soil temperature and solar radiation on the emission of mercury from soils. The emission of mercury from soils is constant over time under constant experimental conditions. The response of the mercury emission flux to variations of the atmospheric transfer parameters such as turbulence requires a rapid adjustment of the equilibrium that controls the Hg(o) concentration in the soil air. It has been shown that the light-induced flux is independent of the soil temperature and shows a strong spectral response to UV-B.

Mercury in the topsoil and dust of Beijing City

Research on mercury concentration in the dust and topsoil of Beijing City reveals the following conclusions: mercury concentration in Beijing topsoil and dust is middle compared to other mercury concentration studies and varies greatly in different sampling spots. Mercury concentration in the topsoil is between 0.019mg.kg(-1) and 0.966mg.kg(-1), it is about 2.11 times and 12.08 times of mercury concentration background in Beijing soil respectively. Mercury concentration in Beijing dust has a range of 0.053 to 1.378mg.kg(-1); the maximum mercury concentration in the Beijing dust in 2003 is about 2.2 times of that in 1992. These results show that mercury pollution in Beijing topsoil and dust are serious, and mercury tends to enrich in the dust compared to the adjacent topsoil. Mercury in topsoil and dust of Beijing City has obvious regional differentiation characteristics, which is highest in the center of Beijing City and lower away from the center to the suburbs. In detail, mercury concentration in the topsoil samples and dust samples are highest in Dongsi area and lowest in the blank spot. Mercury in Beijing's topsoil belonging to point pollution is mainly from local area; mercury in the dust belongs to non-point source pollution because the source of mercury in the dust is very complex. Natural factors and anthropological factors have certain effect on mercury concentration in the topsoil and dust, and anthropological factors have more effect. The results are very important to protect and enhance our environmental quality.

Mercury in urban soils: a comparison of local spatial variability in six European cities

The objective of this study was to quantify and assess for the first time the variability of total mercury in urban soils at a European level, using a systematic sampling strategy and a common methodology. We report results from a comparison between soil samples from Aveiro (Portugal), Glasgow (Scotland), Ljubljana (Slovenia), Sevilla (Spain), Torino (Italy) and Uppsala (Sweden). At least 25 sampling points (in about 4-5 ha) from a park in each city were sampled at two depths (0-10 and 10-20 cm). Total mercury was determined by pyrolysis atomic absorption spectrometry with gold amalgamation. The quality of results was monitored using certified reference materials (BCR 142R and BCR 141R). Measured total mercury contents varied from 0.015 to 6.3 mg kg(-1). The lowest median values were found in Aveiro, for both surface (0-10 cm) and sub-surface (10-20 cm) samples (0.055 and 0.054 mg kg(-1), respectively). The highest median mercury contents in soil samples were found in samples from Glasgow (1.2 and 1.3 mg kg(-1), for surface and sub-surface samples, respectively). High variability of mercury concentrations was observed, both within each park and between cities. This variability reflecting contributions from natural background, previous anthropogenic activities and differences in the ages of cities and land use, local environmental conditions as well as the influence of their location within the urban area. Short-range variability of mercury concentrations was found to be up to an order of magnitude over the distance of only a few 10 m.

Spatial distribution of total Hg in urban soils from an Atlantic coastal city (Aveiro, Portugal)

The aim of this study was to investigate the levels and the spatial distribution of total Hg concentrations in soils from the urban area of Aveiro (Portugal) in order to assess the impact of industrial activities and identified Hg emission sources in these urban soils. For this purpose, soils were collected in 25 sampling points (at two depths) within the urban perimeter and in places considered representative of the main green areas of the city. A median concentration of 0.091 mg kg(-1) (dry weight) was obtained, regardless the depth. Aveiro was considered a low polluted city in terms of total Hg and no direct effects of emissions of Hg from industrial activities nearby could be detected in these urban soils. Despite of the low values obtained, high variability (range of approximately 0.5 mg kg(-1)) was observed in the results. Such was considered to be related to characteristic features of soils in urban settings and to the behaviour of Hg in the urban environment.

A method of mercury removal from topsoil using low-thermal application

Mercury contamination in the environment is problematic due to the unusual physical properties and well-recognized toxicity of this common metal. The bioavailability of mercury depends strongly on its chemical speciation. Anthropogenic mercury and its compounds appear in soil as "hot spots" located close to industrial facilities that used or produced mercury. The nature of the chemical production process, transportation and disposal practices often determined the chemical composition and distribution of mercury in the surrounding soils. Current ex situ soil remediation methods are expensive, produce undesirable side effects to the environment and usually involve transportation of contaminated soil. In this project, sponsored by the U.S. Department of Energy, a low-cost, simple approach to removing mercury from soil was evaluated. The process uses low-temperature thermal desorption of volatile metallic mercury and its compounds, and subsequent vapor capture. The project consisted of laboratory and plot-scale experiments. The laboratory efforts evaluated theoretical calculations of mercury removal as a function of time and temperature. The plot-scale experiment was a practical application of the laboratory results. For both experiments, mercury-polluted soil was obtained from a chemical production facility located in southern Poland. In laboratory experiments, at temperature 373 K total mercury concentration decreased in soil by nearly 32%. In plot-scale experiments, at temperature 440 K, about 60-70% of total mercury was removed from the soil. At the end of the experiment, a test of soil biological activity was performed to check if the high temperature applied to the soil did not impair the soil growth properties. There was no negative effect of temperature found.

Principal biogeochemical factors affecting the speciation and transport of mercury through the terrestrial environment

It is increasingly becoming known that mercury transport and speciation in the terrestrial environment play major roles in methyl-mercury bioaccumulation potential in surface water. This review discusses the principal biogeochemical reactions affecting the transport and speciation of mercury in the terrestrial watershed. The issues presented are mercury-ligand formation, mercury adsorption/desorption, and elemental mercury reduction and volatilization. In terrestrial environments, OH-, Cl- and S- ions have the largest influence on ligand formation. Under oxidized surface soil conditions Hg(OH)2, HgCl2, HgOH+, HgS, and Hg0 are the predominant inorganic mercury forms. In reduced environments, common mercury forms are HgSH+, HgOHSH, and HgClSH. Many of these mercury forms are further bound to organic and inorganic ligands. Mercury adsorption to mineral and organic surfaces is mainly dictated by two factors: pH and dissolved ions. An increase in Cl- concentration and a decrease in pH can, together or separately, decrease mercury adsorption. Clay and organic soils have the highest capability of adsorbing mercury. Important parameters that increase abiotic inorganic mercury reduction are availability of electron donors, low redox potential, and sunlight intensity. Primary factors that increase volatilization are soil permeability and temperature. A decrease in mercury adsorption and an increase in soil moisture will also increase volatilization. The effect of climate on biogeochemical reactions in the terrestrial watershed indicates mercury speciation and transport to receiving water will vary on a regional basis.

Are mercury emissions from geologic sources significant? A status report

Geologic sources of atmospheric mercury include areas of fossil and current geothermal activity, recent volcanic activity, precious and base metal deposits, and organic rich sedimentary rocks. Early estimates of emissions from these sources were not based on measurements of mercury fluxes but implied based on the difference between emissions from anthropogenic point sources and wet/dry deposition estimates. In the past approximately 7 years significant progress has been made in development of methods for the measurement of mercury emissions, definition of those parameters most important in controlling emissions and scaling up emissions from natural source areas. This paper summarizes the work done on scaling of emissions from discrete areas of natural enrichment and from the State of Nevada, which is situated within a global belt of mercury enrichment. Preliminary data indicate that elemental mercury is the predominant (>95%) form of mercury being emitted from these sources. Scaling results suggest that the value used in early models to represent emissions from global mercuriferous belts is too low by at least three times.

Contribution of Spanish-American silver mines (1570-1820) to the present high mercury concentrations in the global environment: a review

In this review I evaluate the contribution of Spanish-American silver mines during the period 1570-1820 (a Spanish colonial period of 250 years) to the present high mercury concentrations in the global environment. The evaluation is based upon the following bibliographic information: (1) total amount of mercury consumed in Spanish-American silver mines between 1570 and 1820; (2) percentage of the total amount of mercury consumed in Spanish-American silver mines that may have been emitted to the atmosphere; (3) global natural input of mercury to the atmosphere; (4) worldwide anthropogenic emissions of mercury to the atmosphere; (5) residence time of mercury in the atmosphere; and (6) capacity of mercury to be deposited in the sediments of aquatic systems. From all this information, and owing to the relatively long time that has passed since Spanish-American silver mines were operational, I conclude that most of the mercury lost during the refining of silver via the patio amalgamation process is now sequestered into the sediments of aquatic systems, mainly in marine sediments. The high mercury concentrations now being reported in the global environment essentially are a consequence of the huge pollution caused by human activities during the past 20th century.