Mercury speciation in the Scheldt Estuary

Surface waters of the Scheldt Estuary were sampled on various occasions between 1991 and 1994. Longitudinal particulate Hg (PM) concentrations ranged from 0.4 – 1.7 μgHg/g and are essentially controlled by physical mixing of polluted fluvial particulates with relatively unpolluted marine particulates. Total dissolved mercury (TDM)concentrations ranged from 0.5 to 5.2 ng/L and are strongly influenced by removal and mobilization processes in the upper estuary, while in the lower estuary mixing processes cause a progressive decrease in TDM towards the mouth. Speciation studies showed that dissolved Hg is predominantly bound to strong complexing ligands (organic substances) in the upper estuary, but this fraction decreases with increasing salinity. In June 1993, however, the reactive mercury fraction was also high in the upper estuary. Model calculations showed that a conditional stability constant for Hg- humic acid interactions of 10¹⁹ was a good estimate for the Scheldt estuary. Dissolved methylmercury was analyzed on three occasions. Significant seasonal variations were observed with concentrations ranging from 11 to 120 pg/L in the winter and 80 to 400 pg/L in summer. Supersaturation of Hg° is observed throughout the whole estuary resulting in an estimated evasion flux of 140–1400 ng/m² day.     

Modeling the elemental mercury cycle in Pallette Lake,Wisconsin, USA

The spatial and temporal distribution of elemental Hg (Hg°) and reactive Hg (Hg_R) has been studied on Pallette Lake, Wisconsin during May – August, 1993 and May, 1994. In general, Hg° concentrations near the lake surface greatly exceeded saturation with respect to atmospheric Hg° indicating a flux out (?) of the lake. Evasional losses were estimated using a thin film model and averaged ?101 pmol m^?2 d^?1 during July and August, 1993. A large portion of atmospherically deposited Hg is re-emitted. Thus, in-lake Hg° production' and evasion to the atmosphere will significantly reduce the amount of Hg which is transported to the sediments, the principal site of methylation. Laboratory experiments were conducted to ascertain the rate of Hg° formation from Hg(II). Reduction was significantly lower in heat sterilized lakewater suggesting Hg° production was biologically mediated. The temporal distribution of epilimnetic Hg°, as measured at the lake center, was influenced by Hg° evasion, Hg° production and advective transport of water parcels of differing Hg content. Spatial gradients in Hg° and Hg_R were identified and a transport model was employed to estimate the advective flux of Hg°. The importance of atmospheric deposition and sediment-water interaction as sources of Hg_R to epilimnetic waters were examined. Porewater concentrations of Hg° and Hg_R were determined on several occasions. During May, 1994, the depletion of lakewater Hg_R following a input pulse due to rain was observed and the estimated removal rate (16–20% d^?1) agrees well with reduction rates obtained in the laboratory (23% d^?1).     

Atmospheric concentrations and deposition of Hg to A deciduous forest atwalker branch watershed,Tennessee, USA

Aerosol and total vapor-phase Hg concentrations in air have been measured at Walker Branch Watershed, Tennessee for ≈ 2 yr. Airborne Hg at this site is dominated by vapor forms which exhibit a strong seasonal cycle, with summer maxima that correspond to elevated air temperature. Concentrations in this forest are near background levels; however, concentrations at a site within 3 km are significantly elevated due to emissions from Hg-contaminated soils. The concentration data have been combined with a recently modified dry deposition model to estimate dry deposition fluxes to the deciduous forest at Walker Branch. Weekly mean modeled V_d values for Hg° ranged from <0.01 (winter) to > 0.1 (summer) cm s¹. Weekly dry deposition fluxes ranged from <0.1 μg m⁻² during winter to > 1.0 μgg m⁻² in the summer. Our dry deposition estimates plus limited measurements of wet deposition in this area indicate that dry deposition may be the dominant input process in this forest, at least during the summer.     

Foliar exchange of mercury vapor: Evidence for a compensation point

Historical studies for crop and weed species documented elemental Hg vapor (Hg°) deposition to foliage, but they used Hg° concentrations that were orders of magnitude higher than levels now known to occur under background conditions, possibly creating artificially high gradients between the atmosphere and landscape surfaces. Measurements of Hg° exchange with white oak (Quercus alba L.), red maple (Acer rubrum L.), Norway spruce (Picea abies L.), and yellow-poplar (Liriodendron tulipifera L.) foliage were conducted in an open gas exchange system that allows for simultaneous measurements of CO₂, H₂O and Hg° exchange under controlled environmental conditions. When Hg° concentrations were held at 0.5 to 1.5 ng m^?3, red maple (Acer rubrum L.), Norway spruce (Picea abies L.), yellow-poplar (Liriodendron tulipifera L.), and white oak (Quercus alba L.) foliage exhibited mean Hg° emissions of 5.5, 1.7, 2.7, and 5.3 ng m^?2 h^?1, respectively. At Hg° concentrations between 9 and 20 ng m^?3 little net exchange of Hg° was observed. However at concentrations between 50 and 70 ng m^?3 the Hg° was deposited to foliage at rates between 22 and 38 ng m^?2 h^?1. These data suggest that dry foliar surfaces in terrestrial forest landscapes may be a dynamic exchange surface that can function as a source or sink dependent on the magnitude of current Hg° concentrations. These data provide evidence of species-specific compensation concentrations (or compensation points) for Hg° deposition to seedling foliage in the 10–25 ng m^?3 range.     

Weekly Measurements over One Year of Ammonia Concentrations and Surface Exchange Fluxes at a Danish Heathland with Passive Wind-Vane Flux Samplers in an Aerodynamic Gradient Configuration

The present study aims to establish the annual NH₃ deposition to an inland heathland in Denmark using a micro-meterological approach with passive wind-vane flux samplers. The integrating samplers were replaced at weekly intervals from May 1995 to May 1996. The average concentration, 2.05 μg m^-3 at the heathland is at a moderate level when compared to heathlands in other parts of Europe. The average deposition velocity was 0.83 cm s^-1 which is within the range of depositon velocities found for other heathlands in Europe. The average canopy resistance was found to be relatively high, 61 s ^-1. The measurements yielded a total NH₃-N deposition of 2.4 (± 0.9) kg ha^-1 yr^-1 with a data coverage of 71% for 1995/1996. In 40% of this time the flux is regarded as zero because the flux is not significant different from zero. In 60% of this time the significant fluxes varied from –0.052 μg m^-2 s^-1 (deposition equal 16.4 kg N ha^-1 yr^-1) to 0.089 μg m^-2 s^-1 (emission equal 28.2 kg N ha^-1 yr^-1). The method is only able to direct measure significant fluxes down to the equivalence of 0.010 μg m^-2 s^-1 (approximately 3.2 kg ha^-1 yr^-1). Therefore the exact deposition cannot be determined by the applied method at very low deposition sites such as a coastal heathland in Denmark. In a high-deposition area as in the central Netherlands the method gave significant fluxes with a 100% data coverage for a two month period.     

Historical deposition rates of mercury in scandinavia estimated by dating and measurement of mercury in cores of peat bogs

Historical deposition rates of Hg were determined in 7 ombrotrophic bogs located far from direct sources in Sweden and Norway. The peat bog cores were dated using ²¹⁰Pb. Based on the dating result 10 to 12 slices from each core were analyzed for Hg. In Southwestern Scandinavia (Rörvik) the deposition rate has increased from about 10 to about 30 μg Hg m^?2 yr^?1 since the beginning of this century. In Northwestern Norway (Överbygd) the deposition rate has increased from about 10 to about 35 μg Hg m^?2 yr^?1 since the 1960's. In Southeast Sweden (Aspvreten) the deposition rate decreased since the beginning of this century. There are no significant trends in the historical deposition rates at the two other stations in middle Scandinavia. A comparison between recent Hg deposition rates measured by peat bog analysis, wet precipitation and mosses shows good agreement at all stations except those in Northern Norway were local dry deposition of Hg may be an important source of Hg.     

Mercury fallout in Hawaii

Mercury fallout was measured 10 m from the selected emission site, the Sulfur Banks fumarole area, Hawaii Volcanoes National Park; at stations on Maui and Oahu, respectively 200 km and 380 km distant from the Sulfur Banks; and at the Hawaii Geothermal Project drill site, only 40 km from source. Sulfur Banks and Oahu measurements were carried out on six occasions between 1972 and 1976, each time within the same 24 h period. Gold foil was used for collection of elemental mercury (Hg°) and copper foil for both oxidized (Hg_ox) and elemental forms. The rate of deposition at the Sulfur Banks was high ? 800 μm m^?2 day^?1, or 300 kgkm^?2 annually. The same figure applied to the relatively nearby geothermal project site. At both remote stations the fallout rate was approximately 10 fold lower. At four measurement times out of six the ratio Hg^O/Hg_ox ranged from 0.195 to 0.463 at the Sulfur Banks source and from 1.80 to 5.15 at the remote stations. On two occasions, heavy rains selectively reduced Hg_ox at the emission site. Model calculations compared Sulfur Banks fallout with rates of re-emission of Hg by vegetation, and the importance of the biotic factor in determination of mass balances and fluxes was emphasized. Aspects of the geochemistry and toxicology of Hg were considered briefly in relation to emission and deposition, and to the occurrence of Hg°.     

Cadmium and lead contamination of soils near plastic stabilizing materials producing plants in Northern Taiwan

Atmospheric mobilization and exchange at the air-water interface are significant features of biogeochemical cycling of Hg at the Earth's surface. Our marine studies of Hg have been extended to terrestrial aquatic systems, where we are investigating the tropospheric cycling, deposition and air-water exchange of Hg in the mid-continental lacustrine environs of northcentral Wisconsin. This program is part of a multidisciplinary examination into the processes regulating the aquatic biogeochemistry of Hg in temperate regions. Trace-metal-free methodologies are employed to determine Hg and alkylated Hg species at the picomolar level in air, water and precipitation. We have found Hg concentrations and atmospheric fluxes in these fresh water systems to be similar to open ocean regions of the Northern Hemisphere. A well constrained mass balance for Hg has been developed for one of the lakes, Little Rock Lake, which is an extensively studied clear water seepage lake that has been divided with a sea curtain into two basins, one of which is untreated (reference pH: 6.1) while the other is being experimentally acidified (current pH: 4.7). This budget shows that the measured total atmospheric Hg deposition (ca. 10 μg m⁻² yr⁻¹) readily accounts for the total mass of Hg in fish, water and accumulating in the sediments of Little Rock Lake. This analysis demonstrates the importance of atmospheric Hg depositional fluxes to the geochemical cycling and bioaccumulation of Hg in temperate lakes. It further suggests that modest increases in atmospheric Hg loading could lead directly to enhanced levels of Hg in biota. Analogous modeling for monomethylmercury (MMHg) is as yet limited. Nevertheless, preliminary data for the atmospheric deposition of MMHg indicate that this flux is insufficient. to account for the amounts of MMHg observed in biota. An in-lake synthesis of MMHg is implicated. The importance of volatile Hg which is principally in the elemental form, and its evasion to the atmosphere is also illustrated. We suggest that the in-lake production of Hg° can reduce the Hg (II) substrate used in the in-lake microbiological synthesis of MMHg.     

Quantitative Evaluation of Atmospheric Deposition Flux of Mercury in Sediments within the City of Juarez,Mexico

The city of Juarez is located in the northernpart of Mexico at the border with the United States. This reportinvestigates the mercury (Hg) contribution from atmosphericsources and its accumulation in the Juarez area estimated bymeasuring the concentration of total Hg in sediments of a smallartificial pond located within the urban area of the Juarez-ElPaso metroplex. The pond is intermittently fed by Hg-free(concentration below detection levels) groundwater from a privatewell, with sporadic input of storm overflow from a nearby watertreatment facility. Total Hg concentrations in the sedimentsvaried between 20 (detection level value) and 454 μg kg^-1 dry wt, with an average value of 202.8±153.9 μg kg^-1. Physicalcharacteristics of the sediments varied among samples, althoughnot as drastically as their Hg content did. Among the sedimentparameters, the organic matter content correlated best with theHg content. A simplified balance of total mercury supply in theaquatic system revealed a sediment Hg flux of 336.0 μg m^-2 yr^-1 and a maximum Hg atmospheric flux of 119 mg m^-2 yr^-1.Our unexpected finding of significant concentrations of Hg in thetreated wastewater and in the water column stresses the need ofcareful consideration of all possible sources in determiningmercury atmospheric deposition flux.     

Polluted precipitation and the geochronology of mercury deposition in lake sediment of northern Minnesota

Elevated Hg levels in game fish from wilderness lakes in northern Minnesota led to the present study of sediment cores from two lakes to ascertain the source and history of Hg deposition. Natural background levels of Hg were found to range from 0.03 to 0.06 μg g^?1, with cultural levels as high as 0.16 μg g^?1. Reconstructed geochronologies reveal a dramatic two-fold increase in Hg flux, from 0.008 to 0.017 μg cm^?2 yr^?1, occuring after the year 1880, suggesting an anthropogenic influence. No industrial or geologic source of Hg is found in the study watersheds. The entire historical increase in Hg flux can be accounted for by atmospheric loading provided that 1/5 of all the Hg presently supplied to the watershed via precipitation is ultimately deposited in lake sediment. Hg levels in fish are not correlated with Hg levels in lake sediment, although there is a link to acid-sensitivity of lake water, amount of acid-neutralizing geologic material exposed in the watershed, and watershed area/lake volume ratio. Thermal stratification of lake water and a complexation-adsorption mechanism are proposed to account for variations in Hg levels observed in sediment collected from different sites.     

Mercury Accumulation in Foliage over Time in Two Northern Mixed-Hardwood Forests

Concentrations of mercury (Hg) in live foliage increased ten-fold from spring bud break (mean ± std. dev. from bothsites: 3.5±1.3 ng g^-1) to autumn litterfall(36±8 ng g^-1). Mercury in foliage did not behavesimilarly to eight other elements with known soil or aerosolsources (Aluminum (Al), Vanadium (V), Strontium (Sr), Rubidium(Rb), Copper (Cu), Zinc (Zn), Barium (Ba), and lead (Pb)),suggesting that Hg originated from a distinct pathway. Based onmeasured and modeled data, uptake of only 25% of the availableambient dry deposited Hg⁰ could explain all of the Hgmeasured in foliage throughout the growing season. Estimates ofgaseous elemental Hg (Hg⁰) uptake from soil water accountedfor 3–14%% of the Hg in litterfall. Mercury deposition toforested sites in the Lake Champlain and Lake Huron basins washighest in litterfall (40%), followed by total throughfall(33%), and precipitation (27%). The Hg flux in litterfall was15.8±1.9~μg m^-2 yr^-1 to the Lake ChamplainWatershed in 1995 and was 11.4±2.8~μg m^-2 yr^-1 to the Lake Huron Watershed in 1996. In comparison, the Hg fluxes in precipitation and total throughfall were 9.0±0.6 and 11.6±0.7~μg m^-2 yr^-1in the Lake Champlain Watershed (1995), and 8.7±0.5 and 10.5±1.0~μg m^-2 yr^-1 in the Lake Huron Watershed (1996).     

Pre-industrial atmospheric deposition of mercury: Uncertain rates from lake sediment and peat cores

Lacustrine sediment cores from depositional areas have frequently been used to estimate pre-industrial rates of atmospheric Hg deposition. However, this approach tends to result in overestimates, partly because of Hg inputs from the catchment, partly because of a horizontal redistribution of sediments within lakes. Peat core studies may suffer from a vertical migration of Hg due to water table fluctuations. A natural Hg deposition rate around 2 μg m^?2 y^?1 is suggested to be more realistic than values of 3 to 12 μg m^?2 y^?1 reported from recent studies. The anthropogenic impact on the present Hg deposition may have been underestimated accordingly.     

Total sulfur content in the humus layer of urban polluted forest soils

Total S content of the humus layer was determined from Scots pine forests in the surroundings of Oulu, an industrialized city in northern Finland. The S content nearest the city center and emission sources (zone IV; bar x=3870 μg g^?1 on an organic matter basis) was about twice as high as in three background areas (80 to 170 km from the city) and about 40% higher than at the sites which were ca 20 km from the main emission sources (zone I). The estimated accumulation of S in humus layer was, on average, 0.4 to 0.6 g m^?2 yr^?1 in the most polluted study sites and 0.1 to 0.2, 0.2 to 0.3 and 0.4 to 0.5 g m^?2 yr^?1 in zones I, II, and III, respectively.     

Corrosion-Induced Release and Environmental Interaction of Chromium, Nickel and Iron from Stainless Steel

A cross-disciplinary research project has been implemented because of increased awareness of the potential environmental effects caused by dispersion of metals from external applications into the environment. The work comprises a 4-year (1998–2002) field exposure of grades 304 and 316 stainless steels, and a laboratory percolation study simulating 20–25 years of chromium and nickel containing runoff water interactions with soil. Total metal annual release rates varied between 0.2 and 0.7 mg m^?2 yr^?1 for Cr, between 0.1 and 0.8 mg m^?2 yr^?1 for Ni and between 10 and 200 mg m^?2 yr^?1 for Fe. Most Cr and Ni is present in an ionic form as a result of the limited presence of organic matter at the immediate release situation. Metal ion concentrations in the runoff water are far below reported ecotoxic concentrations. Studies of the environmental interaction between runoff water from stainless steel and soil show the majority of released Cr and Ni to be retained and their concentrations in percolation water to be very low (0.5–1 μg L^?1 and 1–5.5 μg L^?1 for Cr and Ni, respectively). Speciation calculations showed Cr to be primarily complexed to dissolved organic carbon while Ni also was present in an ionic form in the solution phase. Soil extractions showed Cr and Ni to be very strongly retained within the soil.     

The role of microorganisms in elemental mercury formation in natural waters

Gas evasion of elemental Hg (Hg°) from the open ocean plays a prominent role in the global mercury cycle. Elemental Hg is formed primarily by reduction of ionic Hg in the mixed layer of aquatic systems. By culturing phytoplankton in defined media, and by incubating natural seawater and freshwater samples, we have demonstrated that Hg° is produced by microorganisms, with formation rates (0.5 to 10% d^?1) similar to those estimated from mass balance studies. Our results also suggest that <3μm microorganisms are the primary Hg reducers in natural waters. Eucaryotic phytoplankton are capable of reducing ionic Hg to Hg° but the rate of reduction is insufficient to account for the observed reduction rates found in incubated field samples. Bacteria are thus the more likely Hg reducers. In seawater, cyanobacteria such asSynecococcus may account for much of the mercury reduction, while in the eutrophic, polluted Upper Mystic Lake north of Boston other procaryotic microorganisms are contributing to the overall Hg reductive capacity of the medium. By reducing ionic Hg, microorganisms play a pivotal role in the aquatic biogeochemistry of Hg, not only by enabling evasion to the atmosphere, but by directly decreasing the amount of ionic Hg available for methylation.     

Bulk deposition of metals in Tulsa,Oklahoma

Samples of bulk precipitation were collected at six sites adjacent to the Arkansas River in Tulsa, Oklahoma for a period of 11 mo (June 1980 to April 1981). Collected samples were analyzed by flameless atomic absorbtion spectrophotometry for Cd, Cr, Ni, Pb, and Zn. The data were reported as volume-weighted metal concentrations (μg L¹) and metal deposition (mg m^?2 yr^?1). Metal deposition was fairly constant from site to site and appeared to be proportional to the amount of precipitation collected. Zinc was by far the largest contributing metal, 497 mg m^?2 yr^?1 followed by Pb. Cr, Ni, and Cd with depositions of 25.5, 25.7, 7.02, and 0.95 mg m^?2 yr^?1 respectively. Concentration data varied greatly over the collection period. Compared to data previously reported in the literature, all of the metal concentrations obtained in this study fall within the ranges observed by other investigators with the exception of Zn which was slightly higher. The average volume-weighted concentrations in μg L^?1 were Cd-2.1, Cr-57.0, Ni-15.6, Pb-56.6, and Zn-1100.     

Atmospheric mercury concentrations above mercury contaminated mill tailings in the Carson River Drainage Basin,NV

During processing of the historic Comstock Ore, Virginia City, NV, an estimated 5.5 × 10⁹ g of metallic mercury (Hg) were released into the Carson River Drainage Basin. The Bessels Mill site is one of at least 75 locations where Hg was used to amalgamate the gold and silver from the ore. Although the mill is no longer standing, Hg contaminated tailings attest to its past location. Mercury concentrations in samples of tailings from the Bessels Mill site are as high as 1570 μg/g. Mercury concentrations vary spatially over the site. Total Hg concentrations in air measured directly over the site are well above regional background levels (1 to 7.1 ng/m³). The highest average atmospheric Hg concentration measured at the site was 240 ng/m³ for October 1993. The estimated range of Hg flux to the atmosphere from the site was 37 to 500 ng/m² hr. Atmospheric Hg concentrations varied seasonally, diurnally and spatially. Atmospheric Hg concentrations varied as a function of Hg concentration, soil and air temperature, wind speed and surface morphology.     

Gaseous Elemental Mercury Fluxes in New York City

As with many urban environments, a number of sources of airborne elemental mercury (Hg°) exist in New York City, yet little research has been conducted to examine the flux and sources of mercury in New York. In this study, we conducted ambient monitoring of Hg° at six locations in New York City. Airborne Hg° averaged 3.84±0.10 ng m^-3 and 3.70±0.08 ng m^-3 in the boroughs of Manhattan and Brooklyn respectively, yet only 2.69±0.03 ng m^-3 in a more residential neighborhood in Queens. Both precipitation and ambient temperature were significantly correlated with ambient Hg° levels in New York City, suggesting that the surface emission of mercury from urban surfaces plays a role in urban Hg° concentrations. Local sources were also seen to contribute to urban Hg° levels by leading to `spikes' of Hg° in which elevated concentrations were recorded for short periods of time.     

Atmospheric monitoring network operations and results in Canada

Atmospheric monitoring activities in Canada relevant to the long-range transport of atmospheric pollutants and the ‘acid rain’ problem are reviewed. Particular aspects examined are network objectives, station density and location, sampling protocol, and quality assurance. Results from a number of these networks are presented for the purpose of outlining the nature and extent of air and precipitation contamination by pollution released in eastern North America. Examples discussed include: the spatial distribution of acidic wet deposition, the temporal variation of acid-related substances in both air and precipitation, an episode of long-range transport, and the impact of acidic emissions on the Arctic atmosphere. Acidic wet deposition is greatest in Canada east of the Manitoba-Ontario border. In 1978, it ranged from 18 to 46 mmol H⁺ m^?2 yr^?1 in the southern half of eastern Canada, with maxima in southern Ontario (44 mmol H⁺ m^?2 yr^?1) and southwestern Quebec (46 mmol H⁺ m^?2 yr^?1). Western Canada receives less acidity in precipitation, but areas of some concern are the Pacific Coast (10 mmol H⁺ m^?2 yr^?1) and to a lesser extent northern Alberta and Saskatchewan (3 to 5 mmol H⁺ m^?2 yr^?1). Acidic emissions from mid-latitude sources which reach the Arctic in winter cause an increase in the acidity of snow from a pH of approximately 5.6 in the summer to values of 4.9 to 5.1 in January through March.     

Volatilization of demethylmercury and elemental mercury from river Elbe floodplain soils

It has been shown that an untreated mercury-polluted floodplain soil (containing 10 μg/g per dry weight (d.w.) total Hg and 12 ng/g (d.w.) monomethylmercury compounds (MMM)) of the river Elbe in Northern Germany contains both dimethylmercury (DMM) and elemental mercury (Hg°). This is the first time ever that DMM has been detected in unmodified soils. A novel purge- and-trap-technique involving a sequential thermodesorption-separation of the two species after trapping on a carbon molecular sieve (CMS) has been developed that allows the determination of the two species DMM and Hg° from aqueous solutions or soil samples by GC-CVAFS. The compounds' identities as Hg-species were confirmed by GC-ICP/MS. A DMM-concentration of 740 pg/g (d.w.) was determined in the soil; the Hg°-concentration was found to be at least four times larger, but could not yet be quantified. Since no precautions against losses via evapoartion were taken during sampling and storage, the original concentrations were probably much higher. Both DMM and Hg° are easily purged with N₂ from soils as well as from soil suspensions, indicating that the two species may readily evaporate from those soils under natural conditions. The amount of DMM determined in the soil suspension was significantly lower (80 pg/g (d.w.)) compared to that in the original soil sample, suggesting that DMM might not be stable under these conditions. Also, it was shown that in natural samples, MMM can be converted into DMM in the presence of sulfide, at S^2?-levels as low as 100 μg/g.