Atmospheric Mercury Deposition Research Articles

Atmospheric Deposition and Re-Emission of Mercury Estimated in a Prescribed Forest-Fire Experiment in Florida, USA

Prescribed fires are likely to re-emit atmospherically deposited mercury (Hg), and comparison of soil Hg storage in areas affected by prescribed fire to that in similar unburned areas may provide cross-validating estimates of atmospheric Hg deposition. Prescribed fires are common in the southeastern United States (US), a region of relatively high Hg deposition compared to the rest of the US, and are thus a potentially significant source of re-emitted atmospheric Hg. Accordingly, Hg was determined in soil layers of a prescribed fire experiment in a Florida longleaf pine forest. The Hg deficit in the annually burned forest floor relative to the forest floor unburned for 46 years (0.180 g ha−1 yr−1) agreed to within 5% of an independent estimate of Hg deposition for this site based on a regional monitoring network and computer model (0.171 g ha−1 yr−1). Consideration of other potential inputs and outputs of Hg suggested that atmospheric deposition was the primary input of Hg to the site. If extrapolated, these results suggest that prescribed fires in the southeastern US mainly re-emit atmospherically deposited Hg and that this re-emission is less than 1% of total US anthropogenic emissions. However, emissions at other sites may vary due to the possible presence of Hg in underlying geological strata and differences in fire regime and levels of atmospheric Hg deposition.

Modeling Atmospheric Mercury Deposition in the Vicinity of Power Plants

Two mathematical models of the atmospheric fate and transport of mercury (Hg), an Eulerian grid–based model and a Gaussian plume model, are used to calculate the atmospheric deposition of Hg in the vicinity (i.e., within 50 km) of five coal–fired power plants. The former is applied using two different horizontal resolutions: coarse (84 km) and fine (16.7 km). More than 96% of the power plant Hg emissions are calculated with the plume model to be transported beyond 50 km from the plants. The grid–based model predicts a lower fraction to be transported beyond 50 km: >91% with a coarse resolution and >95% with a fine resolution. The contribution of the power plant emissions to total Hg deposition within a radius of 50 km from the plants is calculated to be <8% with the plume model, <14% with the Eulerian model with a coarse resolution, and <10% with the Eulerian model with a fine resolution. The Eulerian grid–based model predicts greater local impacts than the plume model because of artificially enhanced vertical dispersion; the former predicts about twice as much Hg deposition as the latter when the area considered is commensurate with the resolution of the grid–based model. If one compares the local impacts for an area that is significantly less than the grid–based model resolution, then the grid–based model may predict lower local deposition than the plume model, because two compensating errors affect the results obtained with the grid–based model: initial dilution of the power plant emissions within one or more grid cells and enhanced vertical mixing to the ground.

Predicting mercury wet deposition in Florida: A simple approach

Atmospheric mercury deposition is currently simulated using complex models that incorporate known transport and transformation processes. Though comprehensive, significant errors still exist between simulated and measured Mercury Deposition Network (MDN) data. The goal of this work was to develop a simpler approach to predict mercury deposition. Weekly precipitation sampling in Orlando, FL was conducted from September 2003 and presently continues. Rainfall and mercury deposition data were gathered from this site and 7 others located in and around Florida, to investigate spatial and seasonal patterns. Approximately 80% of Florida's rainfall and mercury deposition occur during the wet season. Regional wet and dry season equations were developed to predict mercury deposition from rainfall depth. A positive linear relationship was observed between rainfall depth and mercury deposition ( R 2 = 0.80 ). Model results were validated with MDN measurements at the Orlando site. This tool can be applied to predict mercury deposition at any location in Florida using local rainfall data.

Atmospheric mercury in Norway: Contributions from different sources

The environmental loadings of national Norwegian mercury emissions compared to the loadings of atmospheric long range transported mercury have been estimated using national emission data and EMEP model data. The results indicate that atmospheric long-range transport to Norway is somewhat larger than the national Norwegian emissions of mercury. Atmospheric deposition of mercury has been studied using data from Norwegian monitoring programs on mercury in precipitation, mosses, natural surface soils, and lake sediments. Precipitation data show no significant time trend during 1990–2002, whereas moss samples show similar concentrations from 1985 to 1995, but a 30% decrease from 1995 to 2000. Concentrations of mercury in peat cores and reference sediments indicate that the current mercury levels measured in surface sediments, surface soils and mosses at background sites in Norway are substantially affected by long-range atmospheric transport.

Evaluation of mercury pollution in cultivated and wild plants from two small communities of the Tapajós gold mining reserve, Pará State, Brazil

This study examines the total Hg contamination in soil and sediments, and the correlation between the total Hg concentration in soil and vegetables in two small scale gold mining areas, São Chico and Creporizinho, in the State of Para, Brazilian Amazon. Total Hg values for soil samples for both study areas are higher than region background values (ca. 0.15 mg/kg). At São Chico, mean values in soils samples are higher than at Creporizinho, but without significant differences at α < 0.05 level. São Chico's aboveground produce samples possess significantly higher values for total Hg levels than samples from Creporizinho. Creporizinho's soil–root produce regression model were significant, and the slope negative. Creporizinho's soil-aboveground and root wild plants regression models were also significant, and the slopes positives. Although, aboveground : root ratios were > 1 in all of São Chico's produce samples, soil–plant parts regression were not significant, and Hg uptake probably occurs through stomata by atmospheric mercury deposition. Wild plants aboveground : root ratios were < 1 at both study areas, and soil–plant parts regressions were significant in samples of Creporizinho, suggesting that they function as an excluder. The average total contents of Hg in edible parts of produces were close to FAO/WHO/JECFA PTWI values in São Chico area, and much lower in Creporizinho. However, Hg inorganic small gastrointestinal absorption reduces its adverse health effects.

Impact of mercury atmospheric deposition on soils and streams in a mountainous catchment (Vosges, France) polluted by chlor-alkali industrial activity: The important trapping role of the organic matter

Total atmospheric Hg contamination in a French mountainous catchment upstream from a chlor-alkali industrial site was assessed using Hg concentrations in the deepest soil horizon, in the stream bottom sediments, in river waters and in bryophytes. The natural background level of Hg content deriving from rock weathering was estimated to 32 ng g − 1 in the deepest soil layers. The soils appear to be Hg contaminated in two stages: atmospheric deposition and leaching through the soil profiles of Hg-organic matter complexes. The Hg enrichment factor (EF Hg Sc) which could be calculated by normalization to a conservative element like Sc, allows to estimate the major contribution (63% to 95%) of the atmospheric inputs, even in the upper part of the basin. This contribution may be attributed to diffuse regional atmospheric deposition of Hg and is mainly due to the geographic location of the chlor-alkali plant. This study shows for the first time that the mercury enrichment is proportional to the carbon content indicating that most of the atmospheric mercury deposition is trapped by the organic matter contained in the soils and in the stream sediments. The Hg stock in the soils of the upper catchment and the soil erosion contribution to the riverine Hg fluxes are estimated for the first time and allow to assess the Hg residence time. It indicates that Hg is trapped in the soils of such a polluted catchment for probably several thousand years.

Methylmercury in Mosquitoes Related to Atmospheric Mercury Deposition and Contamination

A connection between loadings of inorganic Hg, especially from the atmosphere, and accumulation of methylmercury (MeHg) in aquatic biota has not been firmly established. Mosquitoes (Diptera: Culicidae) may be a useful indictor of Hg contamination or MeHg accumulation in aquatic ecosystems because they have aquatic life stages, and their ubiquitous distribution permits sampling across wide ranges of climate, biological productivity, and atmospheric Hg deposition. We examined MeHg in adult mosquitoes from subtropical (Florida), maritime (California), continental (Michigan), and arctic (Alaska) regions of North America that span a range in wet atmospheric Hg deposition (1.5-15 microg m(-2) y(-1)). More than 90% of the Hg in mosquitoes was MeHg, and concentrations varied among locations. Levels of MeHg differed among mosquito species at six sites in northwest Florida (Ochlerotatus atlanticus < Culex nigripalpus < Anopheles crucians); this may be related to differences in biogeochemical characteristics of the aquatic habitat that affect dietary accumulation of MeHg during the larval stage. Mosquito MeHg was related positively to wet atmospheric Hg deposition among locations where atmospheric deposition is the principal source of Hg, and it was greatly enhanced in Hg-polluted environs near the Sulphur Bank Mine in Lake County, California. These results suggest that MeHg in mosquitoes may be a useful and sensitive indicator of Hg loadings to aquatic systems, including that derived from atmospheric deposition.

Patterns of Hg Bioaccumulation and Transfer in Aquatic Food Webs Across Multi-lake Studies in the Northeast US

The northeastern USA receives some of the highest levels of atmospheric mercury deposition of any region in North America. Moreover, fish from many lakes in this region carry Hg burdens that present health risks to both human and wildlife consumers. The overarching goal of this study was to identify the attributes of lakes in this region that are most likely associated with high Hg burdens in fish. To accomplish this, we compared data collected in four separate multi-lake studies. Correlations among Hg in fish (4 studies) or in zooplankton and fish (2 studies) and numerous chemical, physical, land use, and ecological variables were compared across more than 150 lakes. The analysis produced three general findings. First, the most important predictors of Hg burdens in fish were similar among datasets. As found in past studies, key chemical covariates (e.g., pH, acid neutralizing capacity, and SO4) were negatively correlated with Hg bioaccumulation in the biota. However, negative correlations with several parameters that have not been previously identified (e.g., human land use variables and zooplankton density) were also found to be equally important predictors. Second, certain predictors were unique to individual datasets and differences in lake population characteristics, sampling protocols, and fish species in each study likely explained some of the contrasting results that we found in the analyses. Third, lakes with high rates of Hg bioaccumulation and trophic transfer have low pH and low productivity with relatively undisturbed watersheds suggesting that atmospheric deposition of Hg is the dominant or sole source of input. This study highlights several fundamental complexities when comparing datasets over different environmental conditions but also underscores the utility of such comparisons for revealing key drivers of Hg trophic transfer among different types of lakes.

Mercury in lakes and lake fishes on a conservation-industry gradient in Brazil

Mercury contamination in freshwater food webs can be severe and persistent, and freshwater fish are a major source of mercury contamination in humans. Northern hemisphere studies suggest that the primary pathway by which freshwater fish accumulate mercury is the food web, and that atmospheric deposition is the primary route by which mercury enters freshwater systems. Levels of atmospheric deposition are closely linked to proximity to sources of mercury emissions. These propositions have not been tested in the southern hemisphere. In this study, we measured mercury levels at three lakes in southern Brazil and assessed relationships between mercury in precipitation, lake water, sediment and fish tissues at sites close to (industrial and suburban areas) and distant from (protected conservation area) sources of mercury emissions. We also assessed relationships between mercury in fish species and their trophic habits. Mercury concentrations in sediment and lake water did not vary among lakes. In contrast, mercury in precipitation at the study lakes increased with proximity to industrial sources. Mercury in fish tissue generally increased along the same gradient, but also varied with trophic level and preferred depth zone. Atmospheric mercury deposition to these closed lakes may be directly linked to concentrations in fish, with surface-feeding piscivorous species attaining the highest concentrations.

Formation and evasion of dissolved gaseous mercury in large enclosures amended with 200HgCl2

The mercury experiment to assess atmospheric loading in Canada and the United States (METAALICUS) aims at establishing the link between atmospheric deposition of mercury (Hg) and Hg concentrations in fish. As part of this initiative, we conducted an enclosure experiment in Lake 239 (ON, Canada). Our goal was to follow over time dissolved gaseous mercury (DGM) concentrations, after the addition of 200HgCl2, to assess post-depositional Hg dynamics. DGM concentrations reached very high levels in surface waters (up to 6 ng l−1) during the days following the spike. This increase in DGM levels coincided with a decrease in total Hg in the enclosure. Photoreduction rates of Hg were high after spiking (1 ng l−1 h−1) and decreased by two orders of magnitude during the summer, with low rates observed in August (0.01 ng l−1 h−1). These low rates may be caused by photobleaching of dissolved organic carbon. Water-to-air Hg fluxes (evasion) were measured with a flux chamber and modelled using DGM; both methods yielded similar fluxes when using time-averaged DGM values. Together, these results indicate that, under certain conditions, large amounts of newly deposited Hg(II) may be converted to DGM by photochemical processes and lost by evasion across the air/water interface.

Atmospheric mercury speciation and deposition in the Bay St. François wetlands

Atmospheric mercury speciation and deposition are critical to understanding the fate of mercury in the environment. The importance of atmospheric mercury speciation and deposition was investigated during an intensive field campaign in the Bay St. François wetlands in late summer 2002. Measured gaseous elemental mercury (GEM), reactive gaseous mercury (RGM), and particulate mercury (PM: 0.1–2.5 μm) concentrations were 0.85–2.16 ng/m3 (average 1.38 ng/m3), 0–22 pg/m3 (average 3.63 pg/m3), and 0.5–18 pg/m3 (average 6.44 pg/m3), respectively. PM and RGM represented &lt;1% of the total mercury. We reported the first synchronized automated high‐time‐resolution mercury species fluxes. The average GEM flux was 32.1 ng/m2/h (positive sign means volatilization, and negative sign indicates deposition) with a maximum deposition value of 110 ng/m2/h and a maximum volatilization value of 278 ng/m2/h. The average RGM flux was −2.6 ng/m2/h with a maximum deposition value of 25.6 ng/m2/h and a maximum evasion value of 0.6 ng/m2/h. The average PM flux was −0.4 ng/m2/h with a maximum deposition value of 8.7 ng/m2/h and a maximum resuspension value of 32.7 ng/m2/h. RGM contributed over 90% to the total dry deposition of mercury (GEM, RGM, and PM). GEM evasion exceeded deposition of GEM, RGM, and PM, thus suggesting other sources of mercury to the mercury budget such as wet deposition through precipitation or soil. The median dry deposition velocities calculated from flux and concentration measurements were 0.19 cm/s (GEM) &lt; 2.1 cm/s (PM) &lt; 7.6 cm/s (RGM). The dry deposition velocity of PM is large and should be viewed as upper limits only. Although RGM should be rapidly depositing species, as predicted by its solubility, little RGM flux was observed at night. Time series of canopy wetness and RGM fluxes suggested that RGM fluxes are not driven by RGM solubility (in water) since the canopy was dry when larger RGM deposition periods were observed during daytime. It is suggested that the vegetation might directly uptake RGM and release elemental gaseous mercury during daytime. Our experimental data showed that photochemically reactive air masses could produce RGM, which is rapidly removed by dry deposition to the surfaces. Lifetime of RGM over vegetation canopy is on the order of a few hours.

14C-AMS as a tool for the investigation of mercury deposition at a remote Amazon location

We present results of the atmospheric mercury deposition rate in the Amazon region during the last 43000 years. Lake sediment samples were collected from the Lagoa da Pata, a small and remote lake in northern Brazilian Amazon. The samples were divided in sub-samples, for C, Hg, N and 14C-AMS analyses. Three main paleoclimatic events could be identified. The mercury accumulation rates were found to be larger during the periods of the Holocene and Pleistocene associated with high temperatures and frequency of forest fires.

14C-AMS as a tool for the investigation of mercury deposition at a remote Amazon location

We present results of the atmospheric mercury deposition rate in the Amazon region during the last 43 000 years. Lake sediment samples were collected from the Lagoa da Pata, a small and remote lake in northern Brazilian Amazon. The samples were divided in sub-samples, for C, Hg, N and 14 C-AMS analyses. Three main paleoclimatic events could be identified. The mercury accumulation rates were found to be larger during the periods of the Holocene and Pleistocene associated with high temperatures and frequency of forest fires.

Modeling the atmospheric transport and deposition of mercury to the Great Lakes

A special version of the NOAA HYSPLIT_4 model has been developed and used to estimate the atmospheric fate and transport of mercury in a North American modeling domain. Spatial and chemical interpolation procedures were used to expand the modeling results and provide estimates of the contribution of each source in a 1996 anthropogenic US/Canadian emissions inventory to atmospheric mercury deposition to the Great Lakes. While there are uncertainties in the emissions inventories and ambient data suitable for model evaluation are scarce, model results were found to be reasonably consistent with wet deposition measurements in the Great Lakes region and with independent measurement-based estimates of deposition to Lake Michigan. Sources up to 2000 km from the Great Lakes contributed significant amounts of mercury through atmospheric transport and deposition. While there were significant contributions from incineration and metallurgical sources, coal combustion was generally found to be the largest contributor to atmospheric mercury deposition to the Great Lakes.

Annual time-series of total filterable atmospheric mercury concentrations in the Arctic

Total atmospheric mercury (TAM) is operationally defined as the sum of gaseous elemental mercury (GEM), gaseous oxidized inorganic mercury (GOIM), which is also called reactive gaseous mercury (RGM), and total filterable mercury (TFM). An annual weekly-integrated time-series of TFM concentrations in ambient air at Alert, Nunavut, Canada from March 1998 to March 1999 is reported in this paper. The observed TFM concentrations ranged from 0 to 0.37 ng m−3 with the highest value occurring in the spring after polar sunrise and the lowest in summer. The average values for the four seasons are 0.086 (March—May), 0.00085 (June—August), 0.0015 (September—November) and 0.013 ng m−3 (December 1998–February 1999) respectively. This pattern is anti-correlated to that of GEM concentration observed at the same location. The GOIM concentration, calculated using the equation [GOIM]=[TAM]−[GEM]−[TFM], is also anti-correlated with GEM concentration. The annual time-series of the TFM operational blank values shows the same temporal pattern as the TFM concentration, with values ranging from 0.00 to 0.011 ng m−3. These results confirm that, in the polar regions, GEM oxidation and atmospheric deposition of mercury occur mainly in the 3-month period after polar sunrise. Incisive laboratory and field experiments are needed to either confirm or rule out the springtime GEM oxidation/conversion mechanisms proposed in this paper.

Climatic and anthropogenic effects on atmospheric mercury accumulation rates in ombrotrophic bogs from Southern Ontario

To quantify the effects of human activities on atmospheric deposition of mercury in eastern Canada, an improved understanding of the natural variations of the concentrations, fluxes and sources of Hg over a long period of time is required. Peat cores from 3 sites in southern Ontario were used to reconstruct changes in atmospheric mercury accumulation rates for the past 10000 years. The net mercury accumulation rates and excess mercury (mainly anthropogenic) were calculated using the long-term average Hg/Br and Hg/Se. The average background mercury accumulation rate during the pre-anthropogenic period was 1.4±1.0 μg/m 2 .yr. An excess of Hg was observed only once during that period, probably reflecting a change in climate. Mercury contamination from anthropogenic sources began about AD 1475 at the Luther Bog, corresponding to extensive biomass burning for agricultural activities by Native North Americans. During the late 17 th and 18 th centuries, deposition of anthropogenic Hg was at least equal to that of Hg from natural sources. Hg pollution increased again at the beginning of the 19 th century. The maximum increase (up to 30 times) compared to background occurred during the 1950s, when the anthropogenic component represented up to 85% of the total atmospheric mercury deposition.

Retention of atmospheric Cu, Ni, Cd and Zn in an ombrotrophic peat profile near the Outokumpu Cu-Ni mine, SE-Finland

Peat cores taken from ombrotrophic bogs are widely used to reconstruct historical records of atmospheric lead and mercury deposition. In this study, the retention of copper, nickel, cadmium and zinc in peat bogs are studied by comparing high resolution, age dated concentration profiles with emissions from the main local source, the Outokumpu copper-nickel mine. An ombrotrophic peat core was taken from the vicinity of Outokumpu, E Finland. Copper and zinc concentrations of dry peat were measured by XRF, cadmium and nickel by GF-AAS, and sample ages by 210 Pb. Only copper and nickel show enhanced concentrations in layers covering the mining period, indicating a retention of these elements. However, the more detailed comparison of ore production rates and concentrations in age-dated samples show clearly that only copper is likely to be permanently fixed, while nickel doesn't reflect the mining activity. Even though copper is retained in the upper part of the profile, a possible redeposition of this element by secondary processes (e.g., water table fluctuations) can not be excluded. This question will be resolved by further investigations, e.g. by pore water profiles.

Contributions of global and regional sources to mercury deposition in New York State

A modeling system that includes a global chemical transport model (CTM) and a nested continental CTM (TEAM) was used to simulate the atmospheric transport, transformations and deposition of mercury (Hg). Three scenarios were used: (1) a nominal scenario, (2) a scenario conducive to local deposition and (3) a scenario conducive to long-range transport. Deposition fluxes of Hg were analyzed at three receptor locations in New York State. For the nominal scenario, the anthropogenic emission sources (including re-emission of deposited Hg) in New York State, the rest of the contiguous United States, Asia, Europe, and Canada contributed 11–21, 25–49, 13–19, 5–7, and 2–5%, respectively to total Hg deposition at these three receptors. Natural sources contributed 16–24%. The results from the local deposition and long-range transport scenarios varied only slightly from these results. However, there are still uncertainties in our understanding of the atmospheric chemistry of Hg that are likely to affect these estimates of local, regional and global contributions. Comparison of model simulation results with data from the Mercury Deposition Network suggests that local and regional contributions may currently be overestimated.

Accumulation and transformation of atmospheric mercury in soil

Field investigation and simulating experiments were carried out for understanding the accumulation and transformation of mercury in soil in relation to the deposition of atmospheric mercury. A positive correlation between the atmospheric mercury concentration and the content of mercury in soil was observed in the field investigation, with the correlation coefficient being 0.741** ( n=52). The mercury content in soil decreased with the increasing distance from the mercury emission source. Simulated experiment demonstrated that the higher the mercury content in air was, the higher was the amount of mercury accumulated in soil, which was in accordance with the results found from the field investigation. Transformation process occurred once mercury deposited into the soil. Analyses of soil samples exposed to air with mercury contents of 796.4±186.3 ng/m 3 for 2 months indicated that 24.58–26.86% of total mercury deposited into the soil existed in Hg 0 form, 0.10–0.12% in active form, 14.56–18.75% in HCl-dissoluble form, 0.86–5.84% in organic-bound form and 52.64–55.29% in residual form.

Role of volcanic dust in the atmospheric transport and deposition of polycyclic aromatic hydrocarbons and mercury.

The role of volcanic ash as scavenger of atmospheric pollutants, in their transport and final deposition to the ground is examined. Attention is focused on polycyclic aromatic hydrocarbons (PAHs) and on particulate mercury (Hgp). The ash-fall deposits studied belong to the 2001 and 2002 eruptive activity of Mount Etna, Southern Italy, and were investigated at three (2001) and four (2002) sites downwind of the major tephra dispersal pattern. The dry deposition of mercury and PAHs was determined, and, in particular, a downward flux to the ground of PAHs (approximately 7.29 microg m(-2) per day) and mercury (750 ng m(-2) per day) was estimated in Catania from October 26 to October 28, 2002. Finally, evidence on the anthropogenic origin of PAHs scavenged from the troposphere by volcanic ash is supported by the analysis of PAH compositions in granulometrically homogeneous fractions.