Extractability and mobility of mercury from agricultural soils surrounding industrial and mining contaminated areas

This study focussed on a comparison of the extractability of mercury in soils with two different contamination sources (a chlor-alkali plant and mining activities) and on the evaluation of the influence of specific soil properties on the behaviour of the contaminant. The method applied here did not target the identification of individual species, but instead provided information concerning the mobility of mercury species in soil. Mercury fractions were classified as mobile, semi-mobile and non-mobile. The fractionation study revealed that in all samples mercury was mainly present in the semi-mobile phase (between 63% and 97%). The highest mercury mobility (2.7 mg kg(-1)) was found in soils from the industrial area. Mining soils exhibited higher percentage of non-mobile mercury, up to 35%, due to their elevated sulfur content. Results of factor analysis indicate that the presence of mercury in the mobile phase could be related to manganese and aluminium soil contents. A positive relation between mercury in the semi-mobile fraction and the aluminium content was also observed. By contrary, organic matter and sulfur contents contributed to mercury retention in the soil matrix reducing the mobility of the metal. Despite known limitations of sequential extraction procedures, the methodology applied in this study for the fractionation of mercury in contaminated soil samples provided relevant information on mercury's relative mobility.     

Characteristics of mercury exchange flux between soil and air in the heavily air-polluted area,eastern Guizhou,China

To investigate the characteristics of mercury exchange between soil and air in the heavily air-polluted area, total gaseous mercury (TGM) concentration in air and Hg exchange flux were measured in Wanshan Hg mining area (WMMA) in November, 2002 and July–August, 2004. The results showed that the average TGM concentrations in the ambient air (17.8–1101.8 ng m⁻³), average Hg emission flux (162–27827 ng m⁻² h⁻¹) and average Hg dry deposition flux (0–9434 ng m⁻² h⁻¹) in WMMA were 1–4 orders of magnitude higher than those in the background area. It is said that mercury-enriched soil is a significant Hg source of the atmosphere in WMMA. It was also found that widely distributed roasted cinnabar banks are net Hg sources of the atmosphere in WMMA. Relationships between mercury exchange flux and environmental parameters were investigated. The results indicated that the rate of mercury emission from soil could be accelerated by high total soil mercury concentration and solar irradiation. Whereas, highly elevated TGM concentrations in the ambient air can restrain Hg emission from soil and even lead to strongly atmospheric Hg deposition to soil surface. A great amount of gaseous mercury in the heavily polluted atmosphere may cycle between soil and air quickly and locally. Vegetation can inhibit mercury emission from soil and are important sinks of atmospheric mercury in heavily air-polluted area.     

Impact of mercury emissions from historic gold and silver mining: Global modeling

We compare a global model of mercury to sediment core records to constrain mercury emissions from the 19th century North American gold and silver mining. We use information on gold and silver production, the ratio of mercury lost to precious metal produced, and the fraction of mercury lost to the atmosphere to calculate an a priory mining inventory for the 1870s, when the historical gold rush was at its highest. The resulting global mining emissions are 1630 Mg yr^?1, consistent with previously published studies. Using this a priori estimate, we find that our 1880 simulation over-predicts the mercury deposition enhancements archived in lake sediment records. Reducing the mining emissions to 820 Mg yr^?1 improves agreement with observations, and leads to a 30% enhancement in global deposition in 1880 compared to the pre-industrial period. For North America, where 83% of the mining emissions are located, deposition increases by 60%. While our lower emissions of atmospheric mercury leads to a smaller impact of the North American gold rush on global mercury deposition than previously estimated, it also implies that a larger fraction of the mercury used in extracting precious metals could have been directly lost to local soils and watersheds.     

Arsenic Background Concentrations in Florida,U.S.A. Surface Soils: Determination and Interpretation

Background concentrations of soil arsenic have been used as an alternative soil cleanup criterion in many states in the U.S. This research addresses issues related to the interpretation of background concentrations of arsenic in near pristine soils in Florida. Total arsenic was measured in 448 taxonomic and geographic representative surface soil samples using USEPA Method 3052 (HCl-HNO₃-HF, microwave digestion) and graphite furnace atomic absorption spectrophotometry analysis procedure. Values were log-normally distributed, with geometric mean and baseline concentration (defined as 95% of the expected range of background concentrations) providing the most satisfactory statistical results. An upper baseline concentration of 6.21 mg As/kg was estimated for undisturbed soils (n = 267) compared to 7.63 mg As/kg for disturbed soils (n = 181). Temporal trend of total soil arsenic concentrations from 1967 to 1989 paralleled decreased usage of arsenic in U.S. agriculture. Soil arsenic background concentrations were generally higher in south Florida than in north and central Florida, and associated with wet soils. Individual high arsenic sites were scattered throughout the state, but the most highly concentrated of these occurred in the Leon-Lee belt along the Ocala uplift district extending to the southwestern flatwoods district. Extrapolation of the data using a single arsenic value regardless of the taxonomic and geographical differences in soil arsenic distribution would underestimate potential arsenic contamination in upland soils.     

Biotransformation of atrazine and metolachlor within soil profile and changes in microbial communities

Biotransformation studies of atrazine, metolachlor and evolution of their metabolites were carried out in soils and subsoils of Northern Greece. Trace atrazine, its metabolites and metolachlor residues were detected in field soil samples 1 year after their application. The biotransformation rates of atrazine were higher in soils and subsoils of field previously exposed to atrazine (maize field sites) than in respective layers of the field margin. The DT₅₀ values of atrazine ranged from 5 to 18 d in the surface layers of the adapted soils. DT₅₀ values of atrazine increased as the soil depth increased reaching the value of 43 d in the 80–110 cm depth layer of adapted soils. Metolachlor degraded at slower rates than atrazine in surface soils, subsoils of field and field margins with the respective DT₅₀ values ranging from 56 to 72 d in surface soils and from 165 to 186 d in subsoils. Hydroxyatrazine was the most frequently detected metabolite of atrazine. The maximum concentrations of metolachlor-OXA and metolachlor-ESA were detected in the soil layers of 20–40 cm depth after 90 d of incubation. Principal Component Analysis (PCA) of soil Phospholipid Fatty Acids (PLFAs), fungal/bacterial and Gram-negative/Gram-positive ratios of the PLFA profiles revealed that the higher biotransformation rates of atrazine were simultaneously observed with the abundance of Gram-negative bacteria while the respective rates of metolachlor were observed in soil samples with abundance of fungi.     

Biogenic nitric oxide emissions from cropland soils

Emissions of nitric oxide (NO) were determined during late spring and summer 1995 and the spring of 1996 from four agricultural soils on which four different crops were grown. These agricultural soils were located at four different sites throughout North Carolina. Emission rates were calculated using a dynamic flow-through chamber system coupled to a mobile laboratory for in-situ analysis. Average NO fluxes during late spring 1995 were: 50.9±47.7 ng N m⁻² s⁻¹ from soil planted with corn in the lower coastal plain. Average NO fluxes during summer 1995 were: 6.4±4.6 and 20.2±19.0 ng N m⁻² s⁻¹, respectively, from soils planted with corn and soybean in the coastal region; 4.2±1.7 ng N m⁻² s⁻¹ from soils planted with tobacco in the piedmont region; and 8.5±4.9 ng N m⁻² s⁻¹ from soils planted with corn in the upper piedmont region. Average NO fluxes for spring 1996 were: 66.7±60.7 ng N m⁻² s⁻¹ from soils planted with wheat in the lower coastal plain; 9.5±2.9 ng N m⁻² s⁻¹ from soils planted with wheat in the coastal plain; 2.7±3.4 ng N m⁻² s⁻¹ from soils planted with wheat in the piedmont region; and 56.1±53.7 ng N m⁻² s⁻¹ from soils planted with corn in the upper piedmont region. An apparent increase in NO flux with soil temperature was present at all of the locations. The composite data from all the research sites revealed a general positive trend of increasing NO flux with soil water content. In general, increases in total extractable nitrogen (TEN) appeared to be related to increased NO emissions within each site, however a consistent trend was not evident across all sites.     

Accumulation and leaching potential of some pharmaceuticals and potential endocrine disruptors in soils irrigated with wastewater in the Tula Valley,Mexico

The reuse of wastewater for irrigation of agricultural land is a well established practice but introduces many contaminants into the terrestrial environment including pharmaceuticals and personal care products. This study reports the persistence and leaching potential of a group of acidic pharmaceuticals, carbamazepine, and three endocrine disruptors in soils from the Tula Valley in Mexico, one of the largest irrigation districts in the world that uses untreated wastewater. After irrigation of soil columns with fortified wastewater over the equivalent of one crop cycle, between 0% and 7% of the total added amounts of ibuprofen, naproxen, and diclofenac and between 0% and 25% of 4-nonylphenol, triclosan, and bisphenol-A were recovered from the soil profiles. Carbamazepine was more persistent, between 55% and 107% being recovered. Amounts in leachates suggested that movement through the soil was possible for all of the analytes, particularly in profiles of low organic matter and clay content. Analysis of soil samples from the Tula Valley confirmed the general lack of accumulation of the acidic pharmaceuticals (concentrations from below the limit of detection to 0.61 μg kg⁻¹) and endocrine disruptors (concentrations from below the limit of detection to 109 μg kg⁻¹) despite continual addition through regular irrigation with untreated wastewater; there was little evidence of movement through the soil profiles. In contrast, carbamazepine was present in horizon A of the soil at concentrations equivalent to several years of additions by irrigation (2.6–7.5 μg kg⁻¹) and was also present in the deeper horizons. The persistence and mobility of carbamazepine suggested a potential to contaminate groundwater.     

Measurements of GEM fluxes and atmospheric mercury concentrations (GEM,RGM and Hgp) from an agricultural field amended with biosolids in Southern Ont., Canada (October 2004–November 2004)

Five weeks of gaseous elemental mercury (GEM), reactive gaseous mercury (RGM) and particle bound mercury (Hg^p) concentrations as well as fluxes of GEM were measured at Maryhill, Ontario, Canada above a biosolids amended field. The study occurred during the autumn of 2004 (October–November) to capture the effects of cool weather conditions on the behaviour of mercury in the atmosphere. The initial concentration of total mercury (Hg) in the amended soil was relatively low (0.4 μg g⁻¹±10%).A micrometeorological approach was used to infer the flux of GEM using a continuous two-level sampling system with inlets at 0.40 and 1.25 m above the soil surface to measure the GEM concentration gradient. The required turbulent transfer coefficients were derived from meteorological parameters measured on site. The average GEM flux over the study was 0.1±0.2 ng m⁻² h⁻¹(±one standard deviation). The highest averaged hourly GEM fluxes occurred when the averaged net radiation was highest, although the slight diurnal patterns observed were not statistically significant for the complete flux data series. GEM emission fluxes responded to various local events including the passage of a cold front when the flux increased to 2 ng m⁻² h⁻¹ and during a biosolids application event at an adjacent field when depositional fluxes peaked at −3 ng m⁻² h⁻¹. Three substantial rain events during the study kept the surface soil moisture near field capacity and only slightly increased the GEM flux. Average concentrations of RGM (2.3±3.0 pg m⁻³), Hg^p (3.0±6.2 pg m⁻³) and GEM (1.8±0.2 ng m⁻³) remained relatively constant throughout the study except when specific local events resulted in elevated concentrations. The application of biosolids to an adjacent field produced large increases in Hg^p (25.8 pg m⁻³) and RGM (21.7 pg m⁻³) concentrations only when the wind aligned to impact the experimental equipment. Harvest events (corn) in adjacent fields also corresponded to higher concentrations of GEM and Hg^p but with no elevated peaks in RGM concentrations. Diurnal patterns were not statistically significant for RGM and Hg^p at Maryhill.     

Quantifying natural source mercury emissions from the Ivanhoe Mining District,north-central Nevada,USA

In order to assess the importance of mercury emissions from naturally enriched sources relative to anthropogenic point sources, data must be collected that characterizes mercury emissions from representative areas and quantifies the influence of various environmental parameters that control emissions. With this information, we will be able to scale up natural source emissions to regional areas. In this study in situ mercury emission measurements were used, along with data from laboratory studies and statistical analysis, to scale up mercury emissions for the naturally enriched Ivanhoe Mining District, Nevada. Results from stepwise multi-variate regression analysis indicated that lithology, soil mercury concentration, and distance from the nearest fault were the most important factors controlling mercury flux. Field and lab experiments demonstrated that light and precipitation enhanced mercury emissions from alluvium with background mercury concentrations. Diel mercury emissions followed a Gaussian distribution. The Gaussian distribution was used to calculate an average daily emission for each lithologic unit, which were then used to calculate an average flux for the entire area of 17.1 ng Hg m⁻² h⁻¹. An annual emission of ∼8.7×10⁴ g of mercury to the atmosphere was calculated for the 586 km² area. The bulk of the Hg released into the atmosphere from the district (∼89%) is from naturally enriched non-point sources and ∼11% is emitted from areas of anthropogenic disturbance where mercury was mined. Mercury emissions from this area exceed the natural emission factor applied to mercury rich belts of the world (1.5 ng m⁻² h⁻¹) by an order of magnitude.     

Influence of mature compost amendment on total and bioavailable polycyclic aromatic hydrocarbons in contaminated soils

A laboratory microcosm study was carried out to assess the influence of compost amendment on the degradation and bioavailability of PAHs in contaminated soils. Three soils, contaminated with diesel, coal ash and coal tar, respectively, were amended with two composts made from contrasting feedstock (green waste and predominantly meat waste) at two different rates (250 and 750 t ha^?1) and incubated for 8 months. During this period the treatments were sampled for PAH analysis after 0, 3, 6 and 8 months. Total and bioavailable fractions were obtained by sequential ultrasonic solvent extraction and hydroxypropyl-β-cyclodextrin extraction, respectively, and PAHs were identified and quantified by GC–MS. Bioavailability decrease due to sorption was only observed at the first 3 months in the diesel spiked soil. After 8 months, compost addition resulted in over 90% loss of total PAHs irrespective of soil types. Desorption and degradation contributed to 30% and 70%, respectively, of the PAH loss in the spiked soil, while PAH loss in the other two soils resulted from 40% enhanced desorption and 60% enhanced degradation. Compost type and application rates had little influence on PAH bioavailability, but higher PAH removal was observed at higher initial concentration during the early stage of incubation. The bioavailable fraction of PAH was inversely correlated to the number of benzene rings and the octanol–water partition coefficient. Further degradation was not likely after 8-month although over 30% of the residual PAHs were bioavailable, which highlighted the application of bioavailability concept during remediation activities.     

Effects of sewage sludge biochar on plant metal availability after application to a Mediterranean soil

Pyrolytic conversion of sewage sludge into biochar could be a sustainable management option for Mediterranean agricultural soils. The aim of this work is to evaluate the effects of biochar from sewage sludge pyrolysis on soil properties; heavy metals solubility and bioavailability in a Mediterranean agricultural soil and compared with those of raw sewage sludge. Biochar (B) was prepared by pyrolysis of selected sewage sludge (SL) at 500 °C. The pyrolysis process decreased the plant-available of Cu, Ni, Zn and Pb, the mobile forms of Cu, Ni, Zn, Cd and Pb and also the risk of leaching of Cu, Ni, Zn and Cd. A selected Mediterranean soil was amended with SL and B at two different rates in mass: 4% and 8%. The incubation experiment (200 d) was conducted in order to study carbon mineralization and trace metal solubility and bioavailability of these treatments. Both types of amendments increased soil respiration with respect to the control soil. The increase was lower in the case of B than when SL was directly added. Metals mobility was studied in soil after the incubation and it can be established that the risk of leaching of Cu, Ni and Zn were lower in the soil treated with biochar that in sewage sludge treatment. Biochar amended samples also reduced plant availability of Ni, Zn, Cd and Pb when compared to sewage sludge amended samples.     

Sorption of sulfadiazine on Brazilian soils

Antimicrobials, among them sulfonamides are widely used in veterinary medicine and can contaminate the environment. The degree to which antimicrobials adsorb onto soil particles varies widely, as does the mobility of these drugs. Sulfadiazine (SDZ) was used to study the adsorption–desorption in Brazilian soil–water systems, using batch equilibrium experiments. Sorption of SDZ was carried out using four types of soils. Adsorption and desorption data were well fitted with Freundlich isotherms in log form (r > 0.999) and (0.984 < r < 0.999), respectively. An adsorption–desorption hysteresis phenomenon was apparent in all soils ranging from 0.517 to 0.827. The experimental results indicate that the Freundlich sorption coefficient (K_F) values for SDZ ranged from 0.45 to 2.6 μg^1?1/n (cm³)^1/n g^?1.     

Characterization of size-fractionated particulate mercury in Shanghai ambient air

The size-fractionated particulate mercury in ambient air was collected at the top of a university campus building in Shanghai from March 2002 to September 2003. Wet digestion followed by cold vapor atom adsorption spectroscopy (CVAAS) was employed to analyze total particulate mercury concentration. Two-step extraction was performed to differentiate volatile particle-phase mercury (VPM), reactive particle-phase mercury (RPM) and inert particle-phase mercury (IPM). The average concentrations of mercury in PM_1.6, PM₈ and total suspended particle (TSP) were 0.058–0.252, 0.148–0.398 and 0.233–0.529 ng m⁻³, respectively. About 50%–60% of mercury in PM₈ was in PM_1.6, and about 60%–70% of mercury in TSP was in PM₈. Particulate mercury was mainly concentrated on fine particles. The mercury fraction in fine particulate matters (<1.6 μm) was over 4 μg g⁻¹ while 1–2 μg g⁻¹ in TSP. Both were much higher than background values, suggesting that anthropogenic sources are the predominant emission contributors. Seasonal variation indicated that the mercury in TSP in spring was higher than that in summer; however, the mercury in fine particles (<1.6 μm) varied little. The fact that fine particulate mercury (<1.6 μm) was well correlated with sulfate and elemental carbon, but not with fluoride, chloride, nitrate and organic carbon, demonstrates that fine particulate mercury is closely associated with stationary sources and gas–particle transformation. Speciation analysis of mercury showed that VPM fraction decreased with the decrease of particle size, while IPM fraction increased and occupied over 50% in particle <1.6 μm. The detailed species in VPM, RPM and IPM were discussed. Coal burning was estimated to contribute approximately 80% of total atmospheric mercury.     

Modelling atmospheric mercury transport and deposition across Europe and the UK

There are inadequate measurements of surface ambient concentrations of mercury species and their deposition rates for the UK deposition budget to be characterized. In order to estimate the overall mercury flux budget for the UK, a simple long-term 1D Lagrangian trajectory model was constructed that treats emissions (1998), atmospheric transformation and deposition across Europe. The model was used to simulate surface concentrations of mercury and deposition across Europe at a resolution of 50 km×50 km and across the UK at 20 km×20 km. The model appeared to perform adequately when compared with the few available measurements, reproducing mean concentrations of elemental gaseous mercury at particular locations and the magnitude of regional gradients. The model showed that 68% of the UK's mercury emissions are exported and 32% deposited within the UK. Of deposition to the UK, 25% originates from the Northern Hemisphere/global background, 41% from UK sources and 33% from other European countries. The total mercury deposition to the UK is in good agreement with other modelling, 9.9 tonne yr⁻¹ cf. 9.0 tonne yr⁻¹, for 1998. However, the attribution differs greatly from the results of other coarser-scale modelling, which allocates 55% of the deposition to the UK from UK sources, 4% from other European countries and 60% from the global background atmosphere. The model was found to be sensitive to the speciation of emissions and the dry deposition velocity of elemental gaseous mercury. The uncertainties and deficiencies are discussed in terms of model parameterization and input data, and measurement data with which models can be validated. There is an urgent requirement for measurements of removal terms, concentrations, and deposition with which models can be parameterized and validated.     

Polycyclic aromatic hydrocarbons in Costa Rican air and soil: A tropical/temperate comparison

Surface soil and passive air samples from a network of 23 sampling sites across Costa Rica were analyzed for polycyclic aromatic hydrocarbons (PAHs), allowing for an evaluation of absolute levels, spatial distribution patterns, air/soil concentration (A/S) ratios and relative composition. Annual mean concentrations of four-ring PAHs in air were low (median of approximately 40 pg m⁻³), except in Costa Rica's densely populated central valley (approximately 650 pg m⁻³). PAH concentrations in soil were also low (median of 5 ng g⁻¹ dry weight) and comparable to those reported for other tropical regions. These low soil concentrations result in A/S ratios of four-ring PAHs in Costa Rica that are higher than the equilibrium air–soil partitioning coefficients and also higher than A/S ratios reported for temperate locations. A series of model calculations of increasing complexity were used to seek an explanation for variable A/S ratios of PAHs under tropical and temperate conditions. Temperature-driven changes in air–soil partitioning and differences in PAH degradability under temperate and tropical conditions are insufficient to explain the higher soil concentrations and lower A/S ratios in temperate regions. However, these can be explained by atmospheric deposition of PAHs during historical periods of much higher emissions and air concentrations and by persistence of PAHs in soils on the order of decades. Low PAH concentrations in tropical soils were found to be consistent with constant or increasing emissions, and in particular, do not require that degradation rates in soil are much faster than in temperate areas. In comparison to temperate soils, soils from Costa Rica and other tropical regions have a higher relative abundance of the lighter PAHs. This likely reflects a higher source contribution from biomass burning in the tropics, as well as the preferential loss of lighter PAHs from temperate soils that experienced high PAH deposition in the past.     

Conditional sampling for measuring mercury vapor fluxes

Surface–atmosphere mercury fluxes are difficult to measure accurately. Current techniques include dynamic flux chambers and micrometeorological gradient and aerodynamic approaches, all of which have a number of intrinsic problems associated with them. We have adapted conditional sampling (relaxed eddy accumulation), a micrometeorological technique commonly used to measure other trace gas fluxes, to measure surface–air mercury fluxes. Our initial flux measurement campaign over an agricultural soil consisted of two 1-week measurement periods, and was longer in duration than previously reported mercury flux measurement periods. Fluxes during both measurement periods ranged between 190.5 (evolution) and –91.7 ng m⁻² h⁻¹ (deposition) with an average evolution of 9.67 ng m⁻² h⁻¹. The data showed significant diurnal trends, weakly correlated with shallow soil temperatures and solar radiation. This initial trial run indicates that conditional sampling has much promise for the accurate quantification of both short and long-term mercury fluxes.     

Comparing the desorption and biodegradation of low concentrations of phenanthrene sorbed to activated carbon,biochar and compost

Carbonaceous soil amendments are applied to contaminated soils and sediments to strongly sorb hydrophobic organic contaminants (HOCs) and reduce their freely dissolved concentrations. This limits biouptake and toxicity, but also biodegradation. To investigate whether HOCs sorbed to such amendments can be degraded at all, the desorption and biodegradation of low concentrations of ¹⁴C-labelled phenanthrene (?5 μg L^?1) freshly sorbed to suspensions of the pure soil amendments activated carbon (AC), biochar (charcoal) and compost were compared. Firstly, the maximum abiotic desorption of phenanthrene from soil amendment suspensions in water, minimal salts medium (MSM) or tryptic soy broth (TSB) into a dominating silicone sink were measured. Highest fractions remained sorbed to AC (84 ± 2.3%, 87 ± 4.1%, and 53 ± 1.2% for water, MSM and TSB, respectively), followed by charcoal (35 ± 2.2%, 32 ± 1.7%, and 12 ± 0.3%, respectively) and compost (1.3 ± 0.21%, similar for all media). Secondly, the mineralization of phenanthrene sorbed to AC, charcoal and compost by Sphingomonas sp. 10-1 (DSM 12247) was determined. In contrast to the amounts desorbed, phenanthrene mineralization was similar for all the soil amendments at about 56 ± 11% of the initially applied radioactivity. Furthermore, HPLC analyses showed only minor amounts (<5%) of residual phenanthrene remaining in the suspensions, indicating almost complete biodegradation. Fitting the data to a coupled desorption and biodegradation model revealed that desorption did not limit biodegradation for any of the amendments, and that degradation could proceed due to the high numbers of bacteria and/or the production of biosurfactants or biofilms. Therefore, reduced desorption of phenanthrene from AC or charcoal did not inhibit its biodegradation, which implies that under the experimental conditions these amendments can reduce freely dissolved concentration without hindering biodegradation. In contrast, phenanthrene sorbed to compost was fully desorbed and biodegraded.     

Atmospheric mercury in the Great Smoky Mountains compared to regional and global levels

Improvements in measurement technology are permitting development of a more detailed scientific understanding of the cycling of mercury in the global atmospheric environment. Critical to advancing the state of knowledge is the acquisition of accurate measurement of speciated mercury (gaseous and particulate) at ground research stations in a variety of settings located around the globe. This paper describes one such research effort conducted at TVA's Look Rock air quality monitoring site in Tennessee—a mountain top site (813 m elevation) just west of the Great Smoky Mountains National Park. The Great Smoky Mountains National Park is the largest National Park in the eastern US and it receives environmental protection under a variety of US statutes. Gaseous and particle mercury species along with some additional trace gases were measured at Look Rock during two field studies totaling 84 days in the spring and summer of 2004. Average results for the entire sampling period are: gaseous elemental mercury Hg(0): 1.65 ng m⁻³, reactive gaseous mercury RGM: 0.005 ng m⁻³, particulate mercury Hg(p): 0.007 ng m⁻³. Literature review indicates that these levels are within the range found for other rural/remote sites in North America and worldwide. Reactive and particulate mercury comprised together less than 1%, on average, of total airborne mercury at Look Rock. When compared to the global background mercury literature, the Look Rock measurements demonstrate that the atmospheric mercury levels in the vicinity of the Great Smoky Mountains National Park are clearly dominated by the global atmospheric pool, not by local or regional sources.     

The dry-deposition of speciated mercury to the Florida Everglades: Measurements and modeling

The Florida Everglades Dry-Deposition Study (FEDDS) was designed to test the viability of using new and existing measurement techniques in the estimation of the dry-depositional loading of speciated mercury (elemental gaseous, reactive gaseous and particulate) to a mixed sawgrass (Cladium jamaicense) and cattail (Typha domingensis) stand within the Florida Everglades. Measurement intensives were performed during 24 February–04 March 1999 and 05–21 June 2000, which corresponded to the climatological dry and wet seasons in South Florida, respectively. During these intensives, direct measurements of mercury dry-deposition were made using a newly developed surrogate water surface technique. These direct measurements were compared with modeled estimates of mercury dry-deposition to the site that were obtained through the use of an inferential or “bigleaf” model that was modified for use with speciated mercury. On-site measurements of ambient speciated mercury concentrations and numerous micrometeorological variables were used as input to the model.The average mercury dry-deposition measured during the 1999 FEDDS measurement intensive was 13.3±4.0 ng m⁻² day⁻¹, while the modeled deposition for this period was 3.4±2.3 ng m⁻² day⁻¹. The average mercury dry-deposition measured during the 2000 FEDDS measurement intensive was lower, 5.9±2.8 ng m⁻² day⁻¹, while the average modeled deposition for this period was 1.8±0.6 ng m⁻² day⁻¹. A least-squares linear regression suggests that the model was able to explain 74% and 73% of the variability in the datasets for the 1999 and 2000 FEDDS intensives, respectively. While reported reductions in total mercury emissions across South Florida between study periods could explain the reductions in both the measured and predicted mercury dry-deposition estimates, the increased presence of cumulus convection during the summer-intensive could have also resulted in a removal of reactive and particulate mercury species within the atmosphere of South Florida.     

Speciated mercury in size-fractionated particles in Shanghai ambient air

Size-fractionated particles were collected at two sites from July 2004 to April 2006 in Shanghai. The mercury in particles was extracted and divided operationally into four species: exchangeable particulate mercury (EXPM), HCl-soluble particulate mercury (HPM), elemental particulate mercury (EPM) and residual particulate mercury. The total particulate Hg concentration during the study period ranged from 0.07 ng m^?3 to 1.45 ng m^?3 with the average 0.56 ± 0.22 ng m^?3 at site 1, while 0.20 ng m^?3–0.47 ng m^?3 with the average 0.33 ± 0.09 ng m^?3 at site 2, which is far higher than some foreign cities and comparable to some cities with heavy air pollution in China. The Hg mass content also displayed evident size distribution, with higher value in PM_1.6–3.7, somewhat higher or lower than the source profile. EXAM was only found in the summer, HPM have higher percentage in summer and fall rather than in winter and spring. The different mercury species showed different correlation to temperature, relative humidity, wind speed. HPM positively depends on temperature at both sites which implies the importance of mercury transformation on particles. In foggy days TPM increased greatly, but HPM didn't vary greatly as anticipated. Instead, RPM gained a distinguished increase. It demonstrated that aqueous reaction and complex heterogenic reactions in droplet might happen in acidic environment. The correlation of mercury with other pollutants including SO₂, NO₂, CO and PM₁₀ varies with the different mercury forms. Hybrid single-particle lagrangian integrated trajectories (HYSPLIT) model was used to back trace air mass at different representative days and results indicated that transportation from Huabei Plain will increase mercury concentration in winter and fall to some extent. The possible existing compounds and their atmospheric behavior of HPM, EPM and RPM were calculated and the compared to analyze its implication on atmospheric mercury cycle.