Investigating sources of seasonal variation in mercury exported from an upland-peatland ecosystem in northern Minnesota using mercury stable isotopes (original) (raw)
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Environmental Science & Technology, 2008
The purpose of the METAALICUS experiment was to examine the timing and magnitude of the response of fish Hg concentrations to changes in atmospheric Hg loading. Enriched stable Hg isotopes were applied as HgNO 3 to the lake (202 Hg), wetland (198 Hg) and upland (200 Hg) compartments of the L658 watershed at ~22 ug m-2 yr-1 since 2001 (1, 2). However, the present study focused on deposition of ambient Hg, not the experimentally-applied isotopic Hg. Analytical Methods Precipitation and throughfall samples collected between 1992 and 2000 were analysed for total Hg (THg; all forms of Hg in a sample) using EPA Method 1631 (3) by Flett Research Ltd. (Winnipeg, MB). Briefly, all Hg in samples was oxidized to Hg(II) by the addition of BrCl, reduced to Hg(0) using SnCl 2 , purged onto gold traps, thermally desorbed and analyzed by cold vapour atomic fluorescence spectrometry (CVAFS). Samples collected in the METAALICUS watershed between 2001 and 2006 were analysed using inductively coupled plasma mass spectrometry (ICP-MS, 4, 5). Because ICP-MS quantifies concentrations of individual Hg isotopes, it was possible to distinguish concentrations of ambient Hg from the experimentally loaded enriched Hg isotopes. To calculate concentrations of ambient Hg, an isotope that was not experimentally applied to the watershed was used as an ambient Hg surrogate (199 Hg). Samples collected in 2001-2004 were analyzed at the Trent University Worsfold Water Quality Center (Peterborough, ON). Samples were continuously mixed in-line with SnCl 2 using peristaltic pumps, and the reduced gaseous Hg(0) formed was separated in a custom-made gas/liquid separator and swept into the plasma of a Finnigan Element 2 ICP-MS (6). For samples collected between 2005 and 2006, analysis was completed at the University of Alberta Biogeochemical Laboratory (Edmonton, AB). In this laboratory, reduction of Hg and gas/liquid separation was accomplished using an automated Tekran 2600 total Hg analyzer interfaced with a PerkinElmer Elan DRC-e ICP-MS for detection. Precipitation and throughfall samples collected for methylmercury (MeHg) analyses prior to 2001 were distilled, ethylated by additions of sodium tetra-ethyl-borate (NaBEt 4), and volatile Hg species were purged and trapped using either carbo or tenax traps. Samples were thermally desorbed and separated by gas chromatography before quantification by CVAFS (7, 8). Samples collected in the METAALICUS watershed were analyzed for MeHg as described above, except that
Spanish Journal of Agricultural Research, 2009
The sources of mercury (Hg) variability in agricultural soils have been evaluated using 624 soil samples that were taken in the northeast of Spain. The Hg concentration ranges were 1-717 µg kg -1 . This was a wide range, although 90% of the values for Hg contents were estimated between 2.5 and 70 µg kg -1 . Other soil parameters (the pH, organic matter, carbonates and particle size) showed little correlation with the Hg content. The anthropogenic influence was linked to specific practises, in particular the application of slurries. Maps of the spatial distribution indicated various areas with high concentration levels that are attributed to anthropogenic influences. Evidence of human activity can be seen in the Ebro delta, which reflects the accumulation of metals in the basin over many years, and on the Ebro headwaters, characterized by intense mining and smelting activities in the past. A significant portion of the increased Hg content in the Ebro valley probably comes from the deposition of anthropogenic atmospheric Hg due to emissions from industrial activities.
Mercury as a Global Pollutant: Sources, Pathways, and Effects
Mercury (Hg) is a global pollutant that affects human and ecosystem health. We synthesize understanding of sources, atmosphere-landocean Hg dynamics and health effects, and consider the implications of Hgcontrol policies. Primary anthropogenic Hg emissions greatly exceed natural geogenic sources, resulting in increases in Hg reservoirs and subsequent secondary Hg emissions that facilitate its global distribution. The ultimate fate of emitted Hg is primarily recalcitrant soil pools and deep ocean waters and sediments. Transfers of Hg emissions to largely unavailable reservoirs occur over the time scale of centuries, and are primarily mediated through atmospheric exchanges of wet/dry deposition and evasion from vegetation, soil organic matter and ocean surfaces. A key link between inorganic Hg inputs and exposure of humans and wildlife is the net production of methylmercury, which occurs mainly in reducing zones in freshwater, terrestrial, and coastal environments, and the subsurface ocean. Elevated human exposure to methylmercury primarily results from consumption of estuarine and marine fish. Developing fetuses are most at risk from this neurotoxin but health effects of highly exposed populations and wildlife are also a concern. Integration of Hg science with national and international policy efforts is needed to target efforts and evaluate efficacy.
Mercury and Methylmercury Dynamics in a Coastal Plain Watershed, New Jersey, USA
Water, Air, & Soil Pollution, 2010
The upper Great Egg Harbor River watershed in New Jersey's Coastal Plain is urbanized but extensive freshwater wetlands are present downstream. In 2006downstream. In -2007 to assess levels of total mercury (THg) found concentrations in unfiltered streamwater to range as high as 187 ng/L in urbanized areas. THg concentrations were <20 ng/L in streamwater in forested/wetlands areas where both THg and dissolved organic carbon concentrations tended to increase while pH and concentrations of dissolved oxygen and nitrate decreased with flushing of soils after rain. Most of the river's flow comes from groundwater seepage; unfiltered groundwater samples contained up to 177 ng/L of THg in urban areas where there is a history of well water with THg that exceeds the drinking water standard (2,000 ng/L). THg concentrations were lower (<25 ng/L) in unfiltered groundwater from downstream wetland areas. In addition to higher THg concentrations (mostly particulate), concentrations of chloride were higher in streamwater and groundwater from urban areas than in those from downstream wetland areas. Methylmercury (MeHg) concentrations in unfiltered streamwater ranged from 0.17 ng/L at a forest/wetlands site to 2.94 ng/L at an urban site. The percentage of THg present as MeHg increased as the percentage of forest + wetlands increased, but also was high in some urban areas. MeHg was detected only in groundwater <1 m below the water/sediment interface. Atmospheric deposition is presumed to be the main source of Hg to the wetlands and also may be a source to groundwater, where wastewater inputs in urban areas are hypothesized to mobilize Hg deposited to soils.