W4 AM Environmental Fate of Mercury|
Wednesday, 16 November 2005: 8:00 AM - 11:40 AM in Ballroom 4
430 (AAA-1113-333544) Gross photo-reduction kinetics of mercury in temperate freshwater lakes and rivers: Development of a general model for DGM dynamics.
Start time: 8:00 AM
O'Driscoll, N1, Siciliano, S2, Lean, DR3, Amyot, M1, 1 University of Montreal, Montreal, Quebec, Canada2 University of Saskatchewan, Saskatoon, Saskatchewan, Canada3 University of Ottawa, Ottawa, Ontario, Canada
Previous published methods to quantify mercury photo-reduction only provide data for net-photo-reduction, since photo-oxidation processes occur simultaneously. In this research we combine continuous dissolved-gaseous mercury (DGM) analysis with a LUZCHEM ICH-2 photo-reactor and quartz sparger. Using this novel technique, DGM gross photo-reduction kinetics for constant UVB and UVA irradiations were measured every 5 minutes over a period of 23 hours for sterile freshwater from diverse environments. Gross photo-reduction proceeded for the initial 200 minutes after which total mercury was depleted in the sample and photo-reduction decreased to negligible amounts. Photo-reduction was not linked to a loss of DOC fluorescence, with substantial losses in DOC fluorescence observed during the incubations for UVA radiation but not for UVB. Pseudo first order reaction kinetics fit the data very well (r2 > 0.87 for all samples) and rate constants were derived by curve fitting. Rate constants were 10 times lower for lakes (mean kUVB = 6.91 x 10-5 s-1; SE = 1.20 x 10-6 and mean kUVA = 6.09 x 10-5 s-1; SE = 3.97 x 10-7) compared to rivers (mean kUVB = 2.46 x 10-4; SE = 3.91 x 10-6 and mean kUVA = 2.23 x 10-4 s-1; SE = 8.19 x 10-6). Here we propose a generalized model for mercury photo-redox dynamics for temperate lake and river systems using a reversible first order reaction model. The lake model was validated using principal axis analysis to compare observed and predicted DGM data (n=279) from a variety of lake sites in Nova Scotia and Central Quebec. Principal axis analysis found a linear fit (correlation = 0.80; slope = 2.04) between predicted and observed environmental DGM values when log normalized. Error on the predicted values was attributed to estimates of available reducible mercury and the effect of DGM volatilization on observed data.
431 (ECK-1117-680942) Mercury pollution dynamics in urban areas: the influence of the built environment on surface and air fluxes.
Start time: 8:20 AM
Eckley, C1, Branfireun, B1, 1 University of Toronto Mississauga, Mississauga, ON, Canada
Multiple studies have shown that urban areas contain elevated concentrations of mercury when compared to rural areas. The objective of our research is to determine how built urban surfaces (such as windows and pavement) influence the flux of mercury between urban environmental compartments. Understanding the fluxes of mercury between compartments (air, surface, water) is important to understanding how to manage/reduce urban environmental mercury concentrations. This research focuses specifically on the flux of mercury from the atmosphere to urban surfaces and the flux from surfaces back to the atmosphere. Accumulation of mercury on windows in Toronto, Canada was monitored monthly for 1 year. Windows were sampled with variations in exposure to precipitation, aspect, and angle. The results showed that mercury concentrations on sheltered windows (average: 56 ng/m2) were an order of magnitude higher than windows exposed to precipitation washoff (average: 4 ng/m2), suggesting that mercury deposited to impervious urban surfaces can be readily removed. Mercury accumulation on windows was also found to vary with surface aspect and angle. Similar to windows, accumulation on paved surfaces varied with exposure to precipitation. The surface concentration of mercury on paved surfaces was observed to change by over an order of magnitude between wet and dry periods. Size separation of street dust revealed that fine particles had significantly higher mercury concentrations than coarse material at all the sites studied. Overall, the average mercury concentration on paved surfaces (610 ng/m2) was much higher than observed on windows. The surface-to-air flux of mercury from windows and paved locations was determined using a dynamic flux chamber. The magnitude of the surface-to-air flux was dependent on ambient conditions and was not strictly related to surface mercury concentrations.
432 (BAN-1117-832183) Exploring links between mercury cycling and hypoxia in the Gulf of Mexico.
Start time: 8:40 AM
Bank, M1, Shine, J1, Chesney, E2, Rabalais, N2, Jay, J3, Lincoln, R1, Senn, D1, 1 Harvard School of Public Health, Department of Environmental Health, Boston, MA, USA2 Louisiana Universities Marine Consortium, Chauvin, LA, USA3 Department of Civil and Environmental Engineering, Los Angeles, CA, USA
Mercury (Hg) pollution is a widespread and chronic environmental problem that has recently gained considerable attention from policymakers, public health officials, and natural resource managers. Methylmercury is the highly toxic form of Hg that readily bioaccumulates in fish and other biota. Humans are exposed to methylmercury primarily (> 60%) through consumption of fish from coastal marine environments. Coastal eutrophication is another global phenomenon that has garnered substantial attention over the last decade. Increased nutrient fluxes to coastal waters cause enhanced primary production, and, during seasonal stratification, can result in low-oxygen (hypoxic) bottom waters due to aerobic respiration of settling organic matter. Because mercury is primarily methylated by sulfate reducing bacteria (SRB) found in anaerobic sediments, it is reasonable to hypothesize that coastal eutrophication may influence mercury methylation rates in coastal sediments, although the relationship is complex. Up to a certain point, increased organic carbon flux to sediments should enhance mercury methylation in the sediments by stimulating sulfate reduction. However, elevated levels of organic carbon or sulfide can slow methylation rates by making Hg unavailable for uptake by SRB. In this study, we explore links between methylmercury and hypoxia in the Gulf of Mexico, which regularly experiences large-scale seasonal hypoxia. Sediment cores, porewater and gray snapper (Lutjanus griseus) and red snapper (Lutjanus campechanus) tissue samples were collected across a gradient of hypoxia frequency off the Louisiana coast to determine: 1) the spatial distribution of mercury levels and mercury speciation; and 2) if coastal eutrophication and hypoxia exert influences over mercury biomagnification and bioaccumulation in marine ecosystems. The potential cumulative and synergistic effects of mercury pollution, coastal eutrophication, and hypoxia on environmental health are also summarized.
433 (BER-1117-656429) The impact of sediment resuspension and clam density on the cycling and bioaccumulation of methylmercury.
Start time: 9:00 AM
Bergeron, C1, Mason, R1, Porter, E1, 1 University of Maryland Center for Environmental Science Chesapeake Biological Laboratory, Solomons, MD, USA
Sediment is an important repository for mercury (Hg) and the dominant site for Hg methylation in estuarine environments. Benthic organisms in contact with contaminated sediment have the opportunity to accumulate high levels of Hg, especially methylmercury (MeHg) from porewater, overlying water and food. Resuspension provides a potential mechanism for transferring Hg and MeHg from the sediment to the pelagic food chain and filter feeding organisms and has been found to enhance Hg methylation. The objective of this study was to determine the effect of sediment resuspension and clam density (M. mercenaria) on Hg cycling and bioaccumulation of Hg and MeHg into benthic organisms and zooplankton. Clam density potentially impacts methylation since clams initially destablize the sediments and enhance resupension. Clam feeding can also impact the density and growth of phytoplankton and potentially their Hg concentration. Tidal resuspension was simulated in mesocosm tanks that had realistic bottom shear stress and water column turbulence. In a further effort to examine the complex trophic dynamics in the systems, a Hg stable isotope was added as a tracer to examine of the rate of Hg transfer from the water to sediments, its subsequent in situ methylation, and the resultant cycling and bioaccumulation of the isotope through the system. The added isotope rapidly partitioned to particles so that little Hg remained dissolved after 24 hours. Furthermore, there was sufficient evidence to suggest that this Hg was methylated and bioaccumulated over the four-week experiment. Overall, the results suggest that Hg cycling is affected more by resuspension than clam density, and that Hg added to the system is initially more bioavailable for methylation and becomes increasing less bioavailable with time.
Start time: 9:20 AM
434 (LEA-1116-298353) Mercury Cycling in a Wetland Dominated Ecosystem: A Multidisciplinary Study of Kejimkujik Park Nova Scotia.
Start time: 10:00 AM
Lean, D.R.1, O'Driscoll, N.2, Rencz, A.3, 1 University of Ottawa, Ottawa, Ontario, Canada2 University of Montreal, Montreal, Quebec, Canada3 Geological Survery of Canada, Ottawa, Ontario, Canada
The motivation for this project was the alarming levels of mercury in biota in Kejimkujik Park, Nova Scotia, Canada. Specifically, the high levels of mercury in both fish tissue and loon blood. This project was a unique opportunity to bring together researchers to investigate this multidisciplinary environmental problem. The multidisciplinary research approach clearly identifies several major findings related to Hg cycling: (i) potential mercury inputs to the lakes (wet deposition and geology) are similar to other areas in Canada; (ii) high percentages of wetlands in these lakes contribute to high DOC and as a result of low buffering capacity the pH is low in the associated lake water; (iii) high DOC and low pH are the driving factors behind the levels of Hg in fish; (iv) lithology may have an indirect effect on the Hg cycle through changes to hydrology, wetland formation, and DOC export. Ultimately, we would like to know if levels of Hg in biota would be less if emissions to the atmosphere were reduced. From our work we know that similar levels of deposition will have profoundly different effects in different regions. When Hg(II) falls on sites with the right conditions for efficient methyl mercury formation, contaminated food chains will result. This talk will provide an overview of our research and highlight the main findings of the multidisciplinary group.
435 (HOP-1116-866405) A Mass Balance Model for Mercury in the Willamette Basin, Oregon, USA.
Start time: 10:20 AM
Hope, B1, 1 Oregon Department of Environmental Quality, Portland, OR, USA
In the Willamette River Basin (Basin), methylmercury levels in fish triggered health advisories and required development of a mercury Total Maximum Daily Load (TMDL) for the Willamette River. A seasonally-responsive dynamic systems model is used to identify the principal sources of natural and anthropogenic mercury, the relative contributions of these sources to the river, the impact of hypothetical reductions in specific natural and anthropogenic sources on mercury levels in surface water, sediment, and fish tissue, and the degree to which any such changes would be clearly discernible to environmental managers and Basin stakeholders. Two scenarios are modeled. One considered all currently known natural and anthropogenic mercury sources and another which (hypothetically) eliminated all local, but not global, anthropogenic sources and greatly lowered native soil erosion rates. Elimination of local air emissions is estimated to reduce runoff of air-deposited mercury by 34% and advection from the Basin by 12%. Lowering erosion rates is estimated to reduce particulate runoff by 57%, deposition from the water column to surficial sediment by 33%, and fluvial load by 24%; for a net reduction of 26% in the total mercury load to the river. Such hypothetical reductions bring methylmercury concentrations in higher trophic level fish to levels that would allow restoration of fish consumption as a beneficial use. However, several factors, primarily technical feasibility and global sources, may impede attempts to attain this beneficial use. Because local anthropogenic emissions make relatively smaller contributions to the Basin than do persistent global sources (sources over which there is little, if any, possibility of local control), localized environmental management actions alone may not be adequate to address mercury impacts within the Basin.
436 (POI-1117-752994) An Integrated Study of Mercury Dynamics in Sediment-Water-Air Interfaces in the Upper St. Lawrence River.
Start time: 10:40 AM
Poissant, L1, 2, O’Driscoll, N2, Canário, J3, Ridal, J4, Delongchamp, T2, Pilote, M1, Constant, P1, Blais, J2, Lean, D2, 1 Atmospheric Toxic Processes, Meteorological Service of Canada, Montréal, Québec, Canada2 Biology Department, University of Ottawa, Ottawa, Ontario, Canada3 INIAP/IPIMAR, Dep. Aquatic Environment, Lisbon, Portugal4 St. Lawrence River Institute of Environmental Sciences, Cornwall, Ontario, Canada
Mercury species present in freshwater as well as in sediments may be reduced biotically and abiotically to Hg0 which may eventually volatilize to the atmosphere thereby reducing the available mercury in a freshwater system. An intensive study of mercury speciation and flux dynamics in surface water and near-sediment water was completed during May 24-26, 2005 in the Upper St. Lawrence River near Cornwall, Ontario. Preliminary results indicated a very dynamic river ecosystem in respect to mercury and its related chemistry. We found the following: (i) A mean mercury air-water flux of 0.44 ng/m2/h (n=588) was measured over 48 hours. Significant correlations (p<0.01) were calculated between mercury flux and solar radiation (R2=0.36); wind speed (R2=0.26) and air temperature (R2=0.29) but not with water temperature (R2=0.03); (ii) Ultra Violet (UV) radiation penetrated to a significant water depth with 74% of the UVB intensity and 48% of the UVA intensity attenuated at a depth of 30 cm. At 1 meter depth there was 96% attenuation of UVB and 78% attenuation of UVA intensity; (iii) Dissolved gaseous mercury (DGM) levels near the sediments did not seem increase with solar radiation as it did in the surface water in the morning. For surface water, Hg(0) levels were generally less than 10 pg/L during the night then raised to 30-60 pg/L during the day (n=781). Near the sediment DGM values remained less than 10 pg/L after sunrise; (iv) During the day/night period, pH ranged from 7.1 to 8.0 and EH from 50 to 100 mV in surface sediments. Both parameters were higher in the daily period. These results may be explained by the consumption/production of oxygen by phytobenthos and/or early diagenetic reactions taking place near the sediment-water interface. This paper will expand on these results and their relevance to mercury cycling in river ecosystems. This work highlights the importance of integrated fieldwork in mercury research.
437 (MIL-1117-641743) Interaction of mercury with dissolved organic matter under sulfidic conditions.
Start time: 11:00 AM
Miller, C1, Mason, R1, Gilmour, C2, 1 University of Maryland Center of Environmental Science, Chesapeake Biological Laboratory, Solomons, MD, USA2 Smithsonian Environmental Research Center, Edgewater, MD, USA
In most environments, thermodyamic models predict mercury (Hg) is complexed with dissolved organic matter (DOM) but under sulfidic conditions, inorganic Hg-sulfide complexes dominate the Hg speciation. The complexation of Hg with sulfide has been correlated with the bacterial formation of methylmercury (MeHg), the form of Hg with bioaccumalates in organisms. The diffusive uptake of neutrally charged Hg-sulfide complexes by sulfate reducing bacteria, a group of bacteria that have been linked to Hg methylation, is proposed to be a controlling factor in Hg methylation. While the importance of Hg-sulfide complexation to Hg methylation has been demonstrated, the abundance of these complexes has only been predicted using thermodynamic models. Using octanol-water partitioning, it was determined that thermodynamic models overestimate the abundance of neutrally charged Hg-sulfide complexes in sulfidic porewater samples. Subsequent laboratory studies, using octanol-water partitioning and ultrafiltration, indicated that the presence of DOM reduced the formation of inorganic Hg-sulfide complexes, likely due to the formation of complexes between the Hg, sulfide and DOM. Such complexes are not included in current thermodynamic models. Thioglycolate and EDTA were used as model DOM ligands to elucidate the interaction occurring between Hg, sulfide and organic compounds. The complexation of Hg with DOM under oxic conditions has been shown to be controlled by thiol groups on DOM, but it does not appear that thiol functional groups are the only functional groups on organic molecules which can facilitate the formation of Hg, sulfide and DOM complexes. This demonstrated interaction of Hg with DOM under sulfidic conditions changes the current understanding of Hg speciation. Since Hg-sulfide speciation can control Hg methylation, the interaction of Hg with DOM in sulfidic environments could impact the formation of MeHg and could account for the differences found in the degree of Hg methylation across ecosystems.
438 (MUR-1117-814822) TRIM.FaTE and 3MRA Model Comparison of Multimedia Mercury Fate and Transport.
Start time: 11:20 AM
Murphy, R1, Jones, B1, Laniak, G2, Murphy, D3, 1 ICF Consulting, Research Triangle Park, NC2 USEPA/ORD, Athens, GA3 USEPA/OAQPS, Research Triangle Park, NC
TRIM.FaTE, the Fate, Transport, and Ecological Exposure module of USEPA's Total Risk Integrated Methodology, is a mass-balanced, multimedia compartmental model designed to support EPA's needs in assessing non-air impacts of air pollutants. In this model comparison exercise, the results from a TRIM.FaTE case study in which mercury was emitted into the air from a single facility were compared to results derived from a customized application of another EPA multimedia fate and transport modeling system, 3MRA (Multimedia, Multi-pathway, Multi-receptor Exposure and Risk Assessment). 3MRA was developed originally for analysis of hazardous waste management policies and consists of multiple linked models (including several EPA legacy models, such as ISCST3 and EXAMS) to simulate the transport of pollutant from source to receptor. The two models were applied to the same site, using the same emissions data for a 30-year time period, but the majority of the input parameters were set independently by the two model teams in order to create a robust comparison of the two model applications. Estimated concentrations and deposition rates of various forms of mercury were compared for the 30-year period across a broad set of media (biotic and abiotic) in multiple locations, with focus on media and locations of particular interest (such as upper trophic-level fish in a nearby pond). Reasons for differences in various results were identified and ranged from different methods for simulating mercury fate in air and other media, to different spatial approaches underlying the two models, to differences in input values. Overall, the model comparison enhanced the confidence in both models, improved understanding of the impact of particular inputs or process models within the context of both models, helped to identify areas where further evaluation would be informative, and provided information to assist scientists with regard to future applications of these models.